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Auto merge of #6824 - Y-Nak:refactor_loops_module, r=flip1995

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Refactor: organize loops file into loops module (Delegated)

`@flip1995` `@nahuakang`

closes #6693
r? `@flip1995`

 As we talked about in the PM of Zulip,  this PR is a delegated PR from `@nahuakang.`

Changes from the last commit of #6693:
1. Unify the name of the main entries of all modules to check, that was pointed out [here](https://github.com/rust-lang/rust-clippy/pull/6693#discussion_r582897713)
2. Simplify ` check_for_loop_arg`, that was pointed out [here](https://github.com/rust-lang/rust-clippy/pull/6693#discussion_r582914044) and [here](https://github.com/rust-lang/rust-clippy/pull/6693#discussion_r582929910)
3. Resolve conflicts

changelog: Refactor `loops.rs` file into `loops` module.
This commit is contained in:
bors 2021-03-03 10:34:22 +00:00
commit 43d19f63f7
21 changed files with 3386 additions and 3173 deletions
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3173
clippy_lints/src/loops.rs
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17
clippy_lints/src/loops/empty_loop.rs Normal file
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use super::EMPTY_LOOP;
use crate::utils::{is_in_panic_handler, is_no_std_crate, span_lint_and_help};
use rustc_hir::{Block, Expr};
use rustc_lint::LateContext;
pub(super) fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, loop_block: &'tcx Block<'_>) {
if loop_block.stmts.is_empty() && loop_block.expr.is_none() && !is_in_panic_handler(cx, expr) {
let msg = "empty `loop {}` wastes CPU cycles";
let help = if is_no_std_crate(cx.tcx.hir().krate()) {
"you should either use `panic!()` or add a call pausing or sleeping the thread to the loop body"
} else {
"you should either use `panic!()` or add `std::thread::sleep(..);` to the loop body"
};
span_lint_and_help(cx, EMPTY_LOOP, expr.span, msg, None, help);
}
}

58
clippy_lints/src/loops/explicit_counter_loop.rs Normal file
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use super::{
get_span_of_entire_for_loop, make_iterator_snippet, IncrementVisitor, InitializeVisitor, EXPLICIT_COUNTER_LOOP,
};
use crate::utils::{get_enclosing_block, is_integer_const, snippet_with_applicability, span_lint_and_sugg};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::intravisit::{walk_block, walk_expr};
use rustc_hir::{Expr, Pat};
use rustc_lint::LateContext;
// To trigger the EXPLICIT_COUNTER_LOOP lint, a variable must be
// incremented exactly once in the loop body, and initialized to zero
// at the start of the loop.
pub(super) fn check<'tcx>(
cx: &LateContext<'tcx>,
pat: &'tcx Pat<'_>,
arg: &'tcx Expr<'_>,
body: &'tcx Expr<'_>,
expr: &'tcx Expr<'_>,
) {
// Look for variables that are incremented once per loop iteration.
let mut increment_visitor = IncrementVisitor::new(cx);
walk_expr(&mut increment_visitor, body);
// For each candidate, check the parent block to see if
// it's initialized to zero at the start of the loop.
if let Some(block) = get_enclosing_block(&cx, expr.hir_id) {
for id in increment_visitor.into_results() {
let mut initialize_visitor = InitializeVisitor::new(cx, expr, id);
walk_block(&mut initialize_visitor, block);
if_chain! {
if let Some((name, initializer)) = initialize_visitor.get_result();
if is_integer_const(cx, initializer, 0);
then {
let mut applicability = Applicability::MachineApplicable;
let for_span = get_span_of_entire_for_loop(expr);
span_lint_and_sugg(
cx,
EXPLICIT_COUNTER_LOOP,
for_span.with_hi(arg.span.hi()),
&format!("the variable `{}` is used as a loop counter", name),
"consider using",
format!(
"for ({}, {}) in {}.enumerate()",
name,
snippet_with_applicability(cx, pat.span, "item", &mut applicability),
make_iterator_snippet(cx, arg, &mut applicability),
),
applicability,
);
}
}
}
}
}

27
clippy_lints/src/loops/explicit_into_iter_loop.rs Normal file
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use super::EXPLICIT_INTO_ITER_LOOP;
use crate::utils::{snippet_with_applicability, span_lint_and_sugg};
use rustc_errors::Applicability;
use rustc_hir::Expr;
use rustc_lint::LateContext;
use rustc_middle::ty::TyS;
pub(super) fn check(cx: &LateContext<'_>, args: &'hir [Expr<'hir>], arg: &Expr<'_>) {
let receiver_ty = cx.typeck_results().expr_ty(&args[0]);
let receiver_ty_adjusted = cx.typeck_results().expr_ty_adjusted(&args[0]);
if !TyS::same_type(receiver_ty, receiver_ty_adjusted) {
return;
}
let mut applicability = Applicability::MachineApplicable;
let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
span_lint_and_sugg(
cx,
EXPLICIT_INTO_ITER_LOOP,
arg.span,
"it is more concise to loop over containers instead of using explicit \
iteration methods",
"to write this more concisely, try",
object.to_string(),
applicability,
);
}

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clippy_lints/src/loops/explicit_iter_loop.rs Normal file
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use super::EXPLICIT_ITER_LOOP;
use crate::utils::{match_trait_method, snippet_with_applicability, span_lint_and_sugg};
use rustc_errors::Applicability;
use rustc_hir::{Expr, Mutability};
use rustc_lint::LateContext;
use rustc_middle::ty::{self, Ty, TyS};
use rustc_span::symbol::sym;
use crate::utils::{is_type_diagnostic_item, match_type, paths};
pub(super) fn check(cx: &LateContext<'_>, args: &[Expr<'_>], arg: &Expr<'_>, method_name: &str) {
let should_lint = match method_name {
"iter" | "iter_mut" => is_ref_iterable_type(cx, &args[0]),
"into_iter" if match_trait_method(cx, arg, &paths::INTO_ITERATOR) => {
let receiver_ty = cx.typeck_results().expr_ty(&args[0]);
let receiver_ty_adjusted = cx.typeck_results().expr_ty_adjusted(&args[0]);
let ref_receiver_ty = cx.tcx.mk_ref(
cx.tcx.lifetimes.re_erased,
ty::TypeAndMut {
ty: receiver_ty,
mutbl: Mutability::Not,
},
);
TyS::same_type(receiver_ty_adjusted, ref_receiver_ty)
},
_ => false,
};
if !should_lint {
return;
}
let mut applicability = Applicability::MachineApplicable;
let object = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
let muta = if method_name == "iter_mut" { "mut " } else { "" };
span_lint_and_sugg(
cx,
EXPLICIT_ITER_LOOP,
arg.span,
"it is more concise to loop over references to containers instead of using explicit \
iteration methods",
"to write this more concisely, try",
format!("&{}{}", muta, object),
applicability,
)
}
/// Returns `true` if the type of expr is one that provides `IntoIterator` impls
/// for `&T` and `&mut T`, such as `Vec`.
#[rustfmt::skip]
fn is_ref_iterable_type(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
// no walk_ptrs_ty: calling iter() on a reference can make sense because it
// will allow further borrows afterwards
let ty = cx.typeck_results().expr_ty(e);
is_iterable_array(ty, cx) ||
is_type_diagnostic_item(cx, ty, sym::vec_type) ||
match_type(cx, ty, &paths::LINKED_LIST) ||
is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) ||
is_type_diagnostic_item(cx, ty, sym!(hashset_type)) ||
is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
match_type(cx, ty, &paths::BINARY_HEAP) ||
match_type(cx, ty, &paths::BTREEMAP) ||
match_type(cx, ty, &paths::BTREESET)
}
fn is_iterable_array<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'tcx>) -> bool {
// IntoIterator is currently only implemented for array sizes <= 32 in rustc
match ty.kind() {
ty::Array(_, n) => n
.try_eval_usize(cx.tcx, cx.param_env)
.map_or(false, |val| (0..=32).contains(&val)),
_ => false,
}
}

70
clippy_lints/src/loops/for_kv_map.rs Normal file
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use super::FOR_KV_MAP;
use crate::utils::visitors::LocalUsedVisitor;
use crate::utils::{is_type_diagnostic_item, match_type, multispan_sugg, paths, snippet, span_lint_and_then, sugg};
use rustc_hir::{BorrowKind, Expr, ExprKind, Mutability, Pat, PatKind};
use rustc_lint::LateContext;
use rustc_middle::ty;
/// Checks for the `FOR_KV_MAP` lint.
pub(super) fn check<'tcx>(
cx: &LateContext<'tcx>,
pat: &'tcx Pat<'_>,
arg: &'tcx Expr<'_>,
body: &'tcx Expr<'_>,
expr: &'tcx Expr<'_>,
) {
let pat_span = pat.span;
if let PatKind::Tuple(ref pat, _) = pat.kind {
if pat.len() == 2 {
let arg_span = arg.span;
let (new_pat_span, kind, ty, mutbl) = match *cx.typeck_results().expr_ty(arg).kind() {
ty::Ref(_, ty, mutbl) => match (&pat[0].kind, &pat[1].kind) {
(key, _) if pat_is_wild(cx, key, body) => (pat[1].span, "value", ty, mutbl),
(_, value) if pat_is_wild(cx, value, body) => (pat[0].span, "key", ty, Mutability::Not),
_ => return,
},
_ => return,
};
let mutbl = match mutbl {
Mutability::Not => "",
Mutability::Mut => "_mut",
};
let arg = match arg.kind {
ExprKind::AddrOf(BorrowKind::Ref, _, ref expr) => &**expr,
_ => arg,
};
if is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) || match_type(cx, ty, &paths::BTREEMAP) {
span_lint_and_then(
cx,
FOR_KV_MAP,
expr.span,
&format!("you seem to want to iterate on a map's {}s", kind),
|diag| {
let map = sugg::Sugg::hir(cx, arg, "map");
multispan_sugg(
diag,
"use the corresponding method",
vec![
(pat_span, snippet(cx, new_pat_span, kind).into_owned()),
(arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
],
);
},
);
}
}
}
}
/// Returns `true` if the pattern is a `PatWild` or an ident prefixed with `_`.
fn pat_is_wild<'tcx>(cx: &LateContext<'tcx>, pat: &'tcx PatKind<'_>, body: &'tcx Expr<'_>) -> bool {
match *pat {
PatKind::Wild => true,
PatKind::Binding(_, id, ident, None) if ident.as_str().starts_with('_') => {
!LocalUsedVisitor::new(cx, id).check_expr(body)
},
_ => false,
}
}

45
clippy_lints/src/loops/for_loops_over_fallibles.rs Normal file
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use super::FOR_LOOPS_OVER_FALLIBLES;
use crate::utils::{is_type_diagnostic_item, snippet, span_lint_and_help};
use rustc_hir::{Expr, Pat};
use rustc_lint::LateContext;
use rustc_span::symbol::sym;
/// Checks for `for` loops over `Option`s and `Result`s.
pub(super) fn check(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>) {
let ty = cx.typeck_results().expr_ty(arg);
if is_type_diagnostic_item(cx, ty, sym::option_type) {
span_lint_and_help(
cx,
FOR_LOOPS_OVER_FALLIBLES,
arg.span,
&format!(
"for loop over `{0}`, which is an `Option`. This is more readably written as an \
`if let` statement",
snippet(cx, arg.span, "_")
),
None,
&format!(
"consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
snippet(cx, pat.span, "_"),
snippet(cx, arg.span, "_")
),
);
} else if is_type_diagnostic_item(cx, ty, sym::result_type) {
span_lint_and_help(
cx,
FOR_LOOPS_OVER_FALLIBLES,
arg.span,
&format!(
"for loop over `{0}`, which is a `Result`. This is more readably written as an \
`if let` statement",
snippet(cx, arg.span, "_")
),
None,
&format!(
"consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
snippet(cx, pat.span, "_"),
snippet(cx, arg.span, "_")
),
);
}
}

19
clippy_lints/src/loops/iter_next_loop.rs Normal file
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use super::ITER_NEXT_LOOP;
use crate::utils::{match_trait_method, paths, span_lint};
use rustc_hir::Expr;
use rustc_lint::LateContext;
pub(super) fn check(cx: &LateContext<'_>, arg: &Expr<'_>, expr: &Expr<'_>) -> bool {
if match_trait_method(cx, arg, &paths::ITERATOR) {
span_lint(
cx,
ITER_NEXT_LOOP,
expr.span,
"you are iterating over `Iterator::next()` which is an Option; this will compile but is \
probably not what you want",
);
true
} else {
false
}
}

79
clippy_lints/src/loops/manual_flatten.rs Normal file
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use super::utils::make_iterator_snippet;
use super::MANUAL_FLATTEN;
use crate::utils::{is_ok_ctor, is_some_ctor, path_to_local_id, span_lint_and_then};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::{Expr, ExprKind, MatchSource, Pat, PatKind, QPath, StmtKind};
use rustc_lint::LateContext;
use rustc_span::source_map::Span;
/// Check for unnecessary `if let` usage in a for loop where only the `Some` or `Ok` variant of the
/// iterator element is used.
pub(super) fn check<'tcx>(
cx: &LateContext<'tcx>,
pat: &'tcx Pat<'_>,
arg: &'tcx Expr<'_>,
body: &'tcx Expr<'_>,
span: Span,
) {
if let ExprKind::Block(ref block, _) = body.kind {
// Ensure the `if let` statement is the only expression or statement in the for-loop
let inner_expr = if block.stmts.len() == 1 && block.expr.is_none() {
let match_stmt = &block.stmts[0];
if let StmtKind::Semi(inner_expr) = match_stmt.kind {
Some(inner_expr)
} else {
None
}
} else if block.stmts.is_empty() {
block.expr
} else {
None
};
if_chain! {
if let Some(inner_expr) = inner_expr;
if let ExprKind::Match(
ref match_expr, ref match_arms, MatchSource::IfLetDesugar{ contains_else_clause: false }
) = inner_expr.kind;
// Ensure match_expr in `if let` statement is the same as the pat from the for-loop
if let PatKind::Binding(_, pat_hir_id, _, _) = pat.kind;
if path_to_local_id(match_expr, pat_hir_id);
// Ensure the `if let` statement is for the `Some` variant of `Option` or the `Ok` variant of `Result`
if let PatKind::TupleStruct(QPath::Resolved(None, path), _, _) = match_arms[0].pat.kind;
let some_ctor = is_some_ctor(cx, path.res);
let ok_ctor = is_ok_ctor(cx, path.res);
if some_ctor || ok_ctor;
let if_let_type = if some_ctor { "Some" } else { "Ok" };
then {
// Prepare the error message
let msg = format!("unnecessary `if let` since only the `{}` variant of the iterator element is used", if_let_type);
// Prepare the help message
let mut applicability = Applicability::MaybeIncorrect;
let arg_snippet = make_iterator_snippet(cx, arg, &mut applicability);
span_lint_and_then(
cx,
MANUAL_FLATTEN,
span,
&msg,
|diag| {
let sugg = format!("{}.flatten()", arg_snippet);
diag.span_suggestion(
arg.span,
"try",
sugg,
Applicability::MaybeIncorrect,
);
diag.span_help(
inner_expr.span,
"...and remove the `if let` statement in the for loop",
);
}
);
}
}
}
}

451
clippy_lints/src/loops/manual_memcpy.rs Normal file
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use super::{get_span_of_entire_for_loop, IncrementVisitor, InitializeVisitor, MANUAL_MEMCPY};
use crate::utils::sugg::Sugg;
use crate::utils::{
get_enclosing_block, higher, is_type_diagnostic_item, path_to_local, snippet, span_lint_and_sugg, sugg,
};
use if_chain::if_chain;
use rustc_ast::ast;
use rustc_errors::Applicability;
use rustc_hir::intravisit::walk_block;
use rustc_hir::{BinOpKind, Block, Expr, ExprKind, HirId, Pat, PatKind, StmtKind};
use rustc_lint::LateContext;
use rustc_middle::ty::{self, Ty};
use rustc_span::symbol::sym;
use std::iter::Iterator;
/// Checks for for loops that sequentially copy items from one slice-like
/// object to another.
pub(super) fn check<'tcx>(
cx: &LateContext<'tcx>,
pat: &'tcx Pat<'_>,
arg: &'tcx Expr<'_>,
body: &'tcx Expr<'_>,
expr: &'tcx Expr<'_>,
) -> bool {
if let Some(higher::Range {
start: Some(start),
end: Some(end),
limits,
}) = higher::range(arg)
{
// the var must be a single name
if let PatKind::Binding(_, canonical_id, _, _) = pat.kind {
let mut starts = vec![Start {
id: canonical_id,
kind: StartKind::Range,
}];
// This is one of few ways to return different iterators
// derived from: https://stackoverflow.com/questions/29760668/conditionally-iterate-over-one-of-several-possible-iterators/52064434#52064434
let mut iter_a = None;
let mut iter_b = None;
if let ExprKind::Block(block, _) = body.kind {
if let Some(loop_counters) = get_loop_counters(cx, block, expr) {
starts.extend(loop_counters);
}
iter_a = Some(get_assignments(block, &starts));
} else {
iter_b = Some(get_assignment(body));
}
let assignments = iter_a.into_iter().flatten().chain(iter_b.into_iter());
let big_sugg = assignments
// The only statements in the for loops can be indexed assignments from
// indexed retrievals (except increments of loop counters).
.map(|o| {
o.and_then(|(lhs, rhs)| {
let rhs = fetch_cloned_expr(rhs);
if_chain! {
if let ExprKind::Index(base_left, idx_left) = lhs.kind;
if let ExprKind::Index(base_right, idx_right) = rhs.kind;
if is_slice_like(cx, cx.typeck_results().expr_ty(base_left))
&& is_slice_like(cx, cx.typeck_results().expr_ty(base_right));
if let Some((start_left, offset_left)) = get_details_from_idx(cx, &idx_left, &starts);
if let Some((start_right, offset_right)) = get_details_from_idx(cx, &idx_right, &starts);
// Source and destination must be different
if path_to_local(base_left) != path_to_local(base_right);
then {
Some((IndexExpr { base: base_left, idx: start_left, idx_offset: offset_left },
IndexExpr { base: base_right, idx: start_right, idx_offset: offset_right }))
} else {
None
}
}
})
})
.map(|o| o.map(|(dst, src)| build_manual_memcpy_suggestion(cx, start, end, limits, &dst, &src)))
.collect::<Option<Vec<_>>>()
.filter(|v| !v.is_empty())
.map(|v| v.join("\n "));
if let Some(big_sugg) = big_sugg {
span_lint_and_sugg(
cx,
MANUAL_MEMCPY,
get_span_of_entire_for_loop(expr),
"it looks like you're manually copying between slices",
"try replacing the loop by",
big_sugg,
Applicability::Unspecified,
);
return true;
}
}
}
false
}
fn build_manual_memcpy_suggestion<'tcx>(
cx: &LateContext<'tcx>,
start: &Expr<'_>,
end: &Expr<'_>,
limits: ast::RangeLimits,
dst: &IndexExpr<'_>,
src: &IndexExpr<'_>,
) -> String {
fn print_offset(offset: MinifyingSugg<'static>) -> MinifyingSugg<'static> {
if offset.as_str() == "0" {
sugg::EMPTY.into()
} else {
offset
}
}
let print_limit = |end: &Expr<'_>, end_str: &str, base: &Expr<'_>, sugg: MinifyingSugg<'static>| {
if_chain! {
if let ExprKind::MethodCall(method, _, len_args, _) = end.kind;
if method.ident.name == sym!(len);
if len_args.len() == 1;
if let Some(arg) = len_args.get(0);
if path_to_local(arg) == path_to_local(base);
then {
if sugg.as_str() == end_str {
sugg::EMPTY.into()
} else {
sugg
}
} else {
match limits {
ast::RangeLimits::Closed => {
sugg + &sugg::ONE.into()
},
ast::RangeLimits::HalfOpen => sugg,
}
}
}
};
let start_str = Sugg::hir(cx, start, "").into();
let end_str: MinifyingSugg<'_> = Sugg::hir(cx, end, "").into();
let print_offset_and_limit = |idx_expr: &IndexExpr<'_>| match idx_expr.idx {
StartKind::Range => (
print_offset(apply_offset(&start_str, &idx_expr.idx_offset)).into_sugg(),
print_limit(
end,
end_str.as_str(),
idx_expr.base,
apply_offset(&end_str, &idx_expr.idx_offset),
)
.into_sugg(),
),
StartKind::Counter { initializer } => {
let counter_start = Sugg::hir(cx, initializer, "").into();
(
print_offset(apply_offset(&counter_start, &idx_expr.idx_offset)).into_sugg(),
print_limit(
end,
end_str.as_str(),
idx_expr.base,
apply_offset(&end_str, &idx_expr.idx_offset) + &counter_start - &start_str,
)
.into_sugg(),
)
},
};
let (dst_offset, dst_limit) = print_offset_and_limit(&dst);
let (src_offset, src_limit) = print_offset_and_limit(&src);
let dst_base_str = snippet(cx, dst.base.span, "???");
let src_base_str = snippet(cx, src.base.span, "???");
let dst = if dst_offset == sugg::EMPTY && dst_limit == sugg::EMPTY {
dst_base_str
} else {
format!(
"{}[{}..{}]",
dst_base_str,
dst_offset.maybe_par(),
dst_limit.maybe_par()
)
.into()
};
format!(
"{}.clone_from_slice(&{}[{}..{}]);",
dst,
src_base_str,
src_offset.maybe_par(),
src_limit.maybe_par()
)
}
/// a wrapper of `Sugg`. Besides what `Sugg` do, this removes unnecessary `0`;
/// and also, it avoids subtracting a variable from the same one by replacing it with `0`.
/// it exists for the convenience of the overloaded operators while normal functions can do the
/// same.
#[derive(Clone)]
struct MinifyingSugg<'a>(Sugg<'a>);
impl<'a> MinifyingSugg<'a> {
fn as_str(&self) -> &str {
let Sugg::NonParen(s) | Sugg::MaybeParen(s) | Sugg::BinOp(_, s) = &self.0;
s.as_ref()
}
fn into_sugg(self) -> Sugg<'a> {
self.0
}
}
impl<'a> From<Sugg<'a>> for MinifyingSugg<'a> {
fn from(sugg: Sugg<'a>) -> Self {
Self(sugg)
}
}
impl std::ops::Add for &MinifyingSugg<'static> {
type Output = MinifyingSugg<'static>;
fn add(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
match (self.as_str(), rhs.as_str()) {
("0", _) => rhs.clone(),
(_, "0") => self.clone(),
(_, _) => (&self.0 + &rhs.0).into(),
}
}
}
impl std::ops::Sub for &MinifyingSugg<'static> {
type Output = MinifyingSugg<'static>;
fn sub(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
match (self.as_str(), rhs.as_str()) {
(_, "0") => self.clone(),
("0", _) => (-rhs.0.clone()).into(),
(x, y) if x == y => sugg::ZERO.into(),
(_, _) => (&self.0 - &rhs.0).into(),
}
}
}
impl std::ops::Add<&MinifyingSugg<'static>> for MinifyingSugg<'static> {
type Output = MinifyingSugg<'static>;
fn add(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
match (self.as_str(), rhs.as_str()) {
("0", _) => rhs.clone(),
(_, "0") => self,
(_, _) => (self.0 + &rhs.0).into(),
}
}
}
impl std::ops::Sub<&MinifyingSugg<'static>> for MinifyingSugg<'static> {
type Output = MinifyingSugg<'static>;
fn sub(self, rhs: &MinifyingSugg<'static>) -> MinifyingSugg<'static> {
match (self.as_str(), rhs.as_str()) {
(_, "0") => self,
("0", _) => (-rhs.0.clone()).into(),
(x, y) if x == y => sugg::ZERO.into(),
(_, _) => (self.0 - &rhs.0).into(),
}
}
}
/// a wrapper around `MinifyingSugg`, which carries a operator like currying
/// so that the suggested code become more efficient (e.g. `foo + -bar` `foo - bar`).
struct Offset {
value: MinifyingSugg<'static>,
sign: OffsetSign,
}
#[derive(Clone, Copy)]
enum OffsetSign {
Positive,
Negative,
}
impl Offset {
fn negative(value: Sugg<'static>) -> Self {
Self {
value: value.into(),
sign: OffsetSign::Negative,
}
}
fn positive(value: Sugg<'static>) -> Self {
Self {
value: value.into(),
sign: OffsetSign::Positive,
}
}
fn empty() -> Self {
Self::positive(sugg::ZERO)
}
}
fn apply_offset(lhs: &MinifyingSugg<'static>, rhs: &Offset) -> MinifyingSugg<'static> {
match rhs.sign {
OffsetSign::Positive => lhs + &rhs.value,
OffsetSign::Negative => lhs - &rhs.value,
}
}
#[derive(Debug, Clone, Copy)]
enum StartKind<'hir> {
Range,
Counter { initializer: &'hir Expr<'hir> },
}
struct IndexExpr<'hir> {
base: &'hir Expr<'hir>,
idx: StartKind<'hir>,
idx_offset: Offset,
}
struct Start<'hir> {
id: HirId,
kind: StartKind<'hir>,
}
fn is_slice_like<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'_>) -> bool {
let is_slice = match ty.kind() {
ty::Ref(_, subty, _) => is_slice_like(cx, subty),
ty::Slice(..) | ty::Array(..) => true,
_ => false,
};
is_slice || is_type_diagnostic_item(cx, ty, sym::vec_type) || is_type_diagnostic_item(cx, ty, sym!(vecdeque_type))
}
fn fetch_cloned_expr<'tcx>(expr: &'tcx Expr<'tcx>) -> &'tcx Expr<'tcx> {
if_chain! {
if let ExprKind::MethodCall(method, _, args, _) = expr.kind;
if method.ident.name == sym::clone;
if args.len() == 1;
if let Some(arg) = args.get(0);
then { arg } else { expr }
}
}
fn get_details_from_idx<'tcx>(
cx: &LateContext<'tcx>,
idx: &Expr<'_>,
starts: &[Start<'tcx>],
) -> Option<(StartKind<'tcx>, Offset)> {
fn get_start<'tcx>(e: &Expr<'_>, starts: &[Start<'tcx>]) -> Option<StartKind<'tcx>> {
let id = path_to_local(e)?;
starts.iter().find(|start| start.id == id).map(|start| start.kind)
}
fn get_offset<'tcx>(cx: &LateContext<'tcx>, e: &Expr<'_>, starts: &[Start<'tcx>]) -> Option<Sugg<'static>> {
match &e.kind {
ExprKind::Lit(l) => match l.node {
ast::LitKind::Int(x, _ty) => Some(Sugg::NonParen(x.to_string().into())),
_ => None,
},
ExprKind::Path(..) if get_start(e, starts).is_none() => Some(Sugg::hir(cx, e, "???")),
_ => None,
}
}
match idx.kind {
ExprKind::Binary(op, lhs, rhs) => match op.node {
BinOpKind::Add => {
let offset_opt = get_start(lhs, starts)
.and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, o)))
.or_else(|| get_start(rhs, starts).and_then(|s| get_offset(cx, lhs, starts).map(|o| (s, o))));
offset_opt.map(|(s, o)| (s, Offset::positive(o)))
},
BinOpKind::Sub => {
get_start(lhs, starts).and_then(|s| get_offset(cx, rhs, starts).map(|o| (s, Offset::negative(o))))
},
_ => None,
},
ExprKind::Path(..) => get_start(idx, starts).map(|s| (s, Offset::empty())),
_ => None,
}
}
fn get_assignment<'tcx>(e: &'tcx Expr<'tcx>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
if let ExprKind::Assign(lhs, rhs, _) = e.kind {
Some((lhs, rhs))
} else {
None
}
}
/// Get assignments from the given block.
/// The returned iterator yields `None` if no assignment expressions are there,
/// filtering out the increments of the given whitelisted loop counters;
/// because its job is to make sure there's nothing other than assignments and the increments.
fn get_assignments<'a, 'tcx>(
Block { stmts, expr, .. }: &'tcx Block<'tcx>,
loop_counters: &'a [Start<'tcx>],
) -> impl Iterator<Item = Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>> + 'a {
// As the `filter` and `map` below do different things, I think putting together
// just increases complexity. (cc #3188 and #4193)
stmts
.iter()
.filter_map(move |stmt| match stmt.kind {
StmtKind::Local(..) | StmtKind::Item(..) => None,
StmtKind::Expr(e) | StmtKind::Semi(e) => Some(e),
})
.chain((*expr).into_iter())
.filter(move |e| {
if let ExprKind::AssignOp(_, place, _) = e.kind {
path_to_local(place).map_or(false, |id| {
!loop_counters
.iter()
// skip the first item which should be `StartKind::Range`
// this makes it possible to use the slice with `StartKind::Range` in the same iterator loop.
.skip(1)
.any(|counter| counter.id == id)
})
} else {
true
}
})
.map(get_assignment)
}
fn get_loop_counters<'a, 'tcx>(
cx: &'a LateContext<'tcx>,
body: &'tcx Block<'tcx>,
expr: &'tcx Expr<'_>,
) -> Option<impl Iterator<Item = Start<'tcx>> + 'a> {
// Look for variables that are incremented once per loop iteration.
let mut increment_visitor = IncrementVisitor::new(cx);
walk_block(&mut increment_visitor, body);
// For each candidate, check the parent block to see if
// it's initialized to zero at the start of the loop.
get_enclosing_block(&cx, expr.hir_id).and_then(|block| {
increment_visitor
.into_results()
.filter_map(move |var_id| {
let mut initialize_visitor = InitializeVisitor::new(cx, expr, var_id);
walk_block(&mut initialize_visitor, block);
initialize_visitor.get_result().map(|(_, initializer)| Start {
id: var_id,
kind: StartKind::Counter { initializer },
})
})
.into()
})
}

627
clippy_lints/src/loops/mod.rs Normal file
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@ -0,0 +1,627 @@
mod empty_loop;
mod explicit_counter_loop;
mod explicit_into_iter_loop;
mod explicit_iter_loop;
mod for_kv_map;
mod for_loops_over_fallibles;
mod iter_next_loop;
mod manual_flatten;
mod manual_memcpy;
mod mut_range_bound;
mod needless_collect;
mod needless_range_loop;
mod never_loop;
mod same_item_push;
mod single_element_loop;
mod utils;
mod while_immutable_condition;
mod while_let_loop;
mod while_let_on_iterator;
use crate::utils::higher;
use rustc_hir::{Expr, ExprKind, LoopSource, Pat};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Span;
use utils::{get_span_of_entire_for_loop, make_iterator_snippet, IncrementVisitor, InitializeVisitor};
declare_clippy_lint! {
/// **What it does:** Checks for for-loops that manually copy items between
/// slices that could be optimized by having a memcpy.
///
/// **Why is this bad?** It is not as fast as a memcpy.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// # let src = vec![1];
/// # let mut dst = vec![0; 65];
/// for i in 0..src.len() {
/// dst[i + 64] = src[i];
/// }
/// ```
/// Could be written as:
/// ```rust
/// # let src = vec![1];
/// # let mut dst = vec![0; 65];
/// dst[64..(src.len() + 64)].clone_from_slice(&src[..]);
/// ```
pub MANUAL_MEMCPY,
perf,
"manually copying items between slices"
}
declare_clippy_lint! {
/// **What it does:** Checks for looping over the range of `0..len` of some
/// collection just to get the values by index.
///
/// **Why is this bad?** Just iterating the collection itself makes the intent
/// more clear and is probably faster.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// let vec = vec!['a', 'b', 'c'];
/// for i in 0..vec.len() {
/// println!("{}", vec[i]);
/// }
/// ```
/// Could be written as:
/// ```rust
/// let vec = vec!['a', 'b', 'c'];
/// for i in vec {
/// println!("{}", i);
/// }
/// ```
pub NEEDLESS_RANGE_LOOP,
style,
"for-looping over a range of indices where an iterator over items would do"
}
declare_clippy_lint! {
/// **What it does:** Checks for loops on `x.iter()` where `&x` will do, and
/// suggests the latter.
///
/// **Why is this bad?** Readability.
///
/// **Known problems:** False negatives. We currently only warn on some known
/// types.
///
/// **Example:**
/// ```rust
/// // with `y` a `Vec` or slice:
/// # let y = vec![1];
/// for x in y.iter() {
/// // ..
/// }
/// ```
/// can be rewritten to
/// ```rust
/// # let y = vec![1];
/// for x in &y {
/// // ..
/// }
/// ```
pub EXPLICIT_ITER_LOOP,
pedantic,
"for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
}
declare_clippy_lint! {
/// **What it does:** Checks for loops on `y.into_iter()` where `y` will do, and
/// suggests the latter.
///
/// **Why is this bad?** Readability.
///
/// **Known problems:** None
///
/// **Example:**
/// ```rust
/// # let y = vec![1];
/// // with `y` a `Vec` or slice:
/// for x in y.into_iter() {
/// // ..
/// }
/// ```
/// can be rewritten to
/// ```rust
/// # let y = vec![1];
/// for x in y {
/// // ..
/// }
/// ```
pub EXPLICIT_INTO_ITER_LOOP,
pedantic,
"for-looping over `_.into_iter()` when `_` would do"
}
declare_clippy_lint! {
/// **What it does:** Checks for loops on `x.next()`.
///
/// **Why is this bad?** `next()` returns either `Some(value)` if there was a
/// value, or `None` otherwise. The insidious thing is that `Option<_>`
/// implements `IntoIterator`, so that possibly one value will be iterated,
/// leading to some hard to find bugs. No one will want to write such code
/// [except to win an Underhanded Rust
/// Contest](https://www.reddit.com/r/rust/comments/3hb0wm/underhanded_rust_contest/cu5yuhr).
///
/// **Known problems:** None.
///
/// **Example:**
/// ```ignore
/// for x in y.next() {
/// ..
/// }
/// ```
pub ITER_NEXT_LOOP,
correctness,
"for-looping over `_.next()` which is probably not intended"
}
declare_clippy_lint! {
/// **What it does:** Checks for `for` loops over `Option` or `Result` values.
///
/// **Why is this bad?** Readability. This is more clearly expressed as an `if
/// let`.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// # let opt = Some(1);
///
/// // Bad
/// for x in opt {
/// // ..
/// }
///
/// // Good
/// if let Some(x) = opt {
/// // ..
/// }
/// ```
///
/// // or
///
/// ```rust
/// # let res: Result<i32, std::io::Error> = Ok(1);
///
/// // Bad
/// for x in &res {
/// // ..
/// }
///
/// // Good
/// if let Ok(x) = res {
/// // ..
/// }
/// ```
pub FOR_LOOPS_OVER_FALLIBLES,
correctness,
"for-looping over an `Option` or a `Result`, which is more clearly expressed as an `if let`"
}
declare_clippy_lint! {
/// **What it does:** Detects `loop + match` combinations that are easier
/// written as a `while let` loop.
///
/// **Why is this bad?** The `while let` loop is usually shorter and more
/// readable.
///
/// **Known problems:** Sometimes the wrong binding is displayed ([#383](https://github.com/rust-lang/rust-clippy/issues/383)).
///
/// **Example:**
/// ```rust,no_run
/// # let y = Some(1);
/// loop {
/// let x = match y {
/// Some(x) => x,
/// None => break,
/// };
/// // .. do something with x
/// }
/// // is easier written as
/// while let Some(x) = y {
/// // .. do something with x
/// };
/// ```
pub WHILE_LET_LOOP,
complexity,
"`loop { if let { ... } else break }`, which can be written as a `while let` loop"
}
declare_clippy_lint! {
/// **What it does:** Checks for functions collecting an iterator when collect
/// is not needed.
///
/// **Why is this bad?** `collect` causes the allocation of a new data structure,
/// when this allocation may not be needed.
///
/// **Known problems:**
/// None
///
/// **Example:**
/// ```rust
/// # let iterator = vec![1].into_iter();
/// let len = iterator.clone().collect::<Vec<_>>().len();
/// // should be
/// let len = iterator.count();
/// ```
pub NEEDLESS_COLLECT,
perf,
"collecting an iterator when collect is not needed"
}
declare_clippy_lint! {
/// **What it does:** Checks `for` loops over slices with an explicit counter
/// and suggests the use of `.enumerate()`.
///
/// **Why is it bad?** Using `.enumerate()` makes the intent more clear,
/// declutters the code and may be faster in some instances.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// # let v = vec![1];
/// # fn bar(bar: usize, baz: usize) {}
/// let mut i = 0;
/// for item in &v {
/// bar(i, *item);
/// i += 1;
/// }
/// ```
/// Could be written as
/// ```rust
/// # let v = vec![1];
/// # fn bar(bar: usize, baz: usize) {}
/// for (i, item) in v.iter().enumerate() { bar(i, *item); }
/// ```
pub EXPLICIT_COUNTER_LOOP,
complexity,
"for-looping with an explicit counter when `_.enumerate()` would do"
}
declare_clippy_lint! {
/// **What it does:** Checks for empty `loop` expressions.
///
/// **Why is this bad?** These busy loops burn CPU cycles without doing
/// anything. It is _almost always_ a better idea to `panic!` than to have
/// a busy loop.
///
/// If panicking isn't possible, think of the environment and either:
/// - block on something
/// - sleep the thread for some microseconds
/// - yield or pause the thread
///
/// For `std` targets, this can be done with
/// [`std::thread::sleep`](https://doc.rust-lang.org/std/thread/fn.sleep.html)
/// or [`std::thread::yield_now`](https://doc.rust-lang.org/std/thread/fn.yield_now.html).
///
/// For `no_std` targets, doing this is more complicated, especially because
/// `#[panic_handler]`s can't panic. To stop/pause the thread, you will
/// probably need to invoke some target-specific intrinsic. Examples include:
/// - [`x86_64::instructions::hlt`](https://docs.rs/x86_64/0.12.2/x86_64/instructions/fn.hlt.html)
/// - [`cortex_m::asm::wfi`](https://docs.rs/cortex-m/0.6.3/cortex_m/asm/fn.wfi.html)
///
/// **Known problems:** None.
///
/// **Example:**
/// ```no_run
/// loop {}
/// ```
pub EMPTY_LOOP,
style,
"empty `loop {}`, which should block or sleep"
}
declare_clippy_lint! {
/// **What it does:** Checks for `while let` expressions on iterators.
///
/// **Why is this bad?** Readability. A simple `for` loop is shorter and conveys
/// the intent better.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```ignore
/// while let Some(val) = iter() {
/// ..
/// }
/// ```
pub WHILE_LET_ON_ITERATOR,
style,
"using a `while let` loop instead of a for loop on an iterator"
}
declare_clippy_lint! {
/// **What it does:** Checks for iterating a map (`HashMap` or `BTreeMap`) and
/// ignoring either the keys or values.
///
/// **Why is this bad?** Readability. There are `keys` and `values` methods that
/// can be used to express that don't need the values or keys.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```ignore
/// for (k, _) in &map {
/// ..
/// }
/// ```
///
/// could be replaced by
///
/// ```ignore
/// for k in map.keys() {
/// ..
/// }
/// ```
pub FOR_KV_MAP,
style,
"looping on a map using `iter` when `keys` or `values` would do"
}
declare_clippy_lint! {
/// **What it does:** Checks for loops that will always `break`, `return` or
/// `continue` an outer loop.
///
/// **Why is this bad?** This loop never loops, all it does is obfuscating the
/// code.
///
/// **Known problems:** None
///
/// **Example:**
/// ```rust
/// loop {
/// ..;
/// break;
/// }
/// ```
pub NEVER_LOOP,
correctness,
"any loop that will always `break` or `return`"
}
declare_clippy_lint! {
/// **What it does:** Checks for loops which have a range bound that is a mutable variable
///
/// **Why is this bad?** One might think that modifying the mutable variable changes the loop bounds
///
/// **Known problems:** None
///
/// **Example:**
/// ```rust
/// let mut foo = 42;
/// for i in 0..foo {
/// foo -= 1;
/// println!("{}", i); // prints numbers from 0 to 42, not 0 to 21
/// }
/// ```
pub MUT_RANGE_BOUND,
complexity,
"for loop over a range where one of the bounds is a mutable variable"
}
declare_clippy_lint! {
/// **What it does:** Checks whether variables used within while loop condition
/// can be (and are) mutated in the body.
///
/// **Why is this bad?** If the condition is unchanged, entering the body of the loop
/// will lead to an infinite loop.
///
/// **Known problems:** If the `while`-loop is in a closure, the check for mutation of the
/// condition variables in the body can cause false negatives. For example when only `Upvar` `a` is
/// in the condition and only `Upvar` `b` gets mutated in the body, the lint will not trigger.
///
/// **Example:**
/// ```rust
/// let i = 0;
/// while i > 10 {
/// println!("let me loop forever!");
/// }
/// ```
pub WHILE_IMMUTABLE_CONDITION,
correctness,
"variables used within while expression are not mutated in the body"
}
declare_clippy_lint! {
/// **What it does:** Checks whether a for loop is being used to push a constant
/// value into a Vec.
///
/// **Why is this bad?** This kind of operation can be expressed more succinctly with
/// `vec![item;SIZE]` or `vec.resize(NEW_SIZE, item)` and using these alternatives may also
/// have better performance.
/// **Known problems:** None
///
/// **Example:**
/// ```rust
/// let item1 = 2;
/// let item2 = 3;
/// let mut vec: Vec<u8> = Vec::new();
/// for _ in 0..20 {
/// vec.push(item1);
/// }
/// for _ in 0..30 {
/// vec.push(item2);
/// }
/// ```
/// could be written as
/// ```rust
/// let item1 = 2;
/// let item2 = 3;
/// let mut vec: Vec<u8> = vec![item1; 20];
/// vec.resize(20 + 30, item2);
/// ```
pub SAME_ITEM_PUSH,
style,
"the same item is pushed inside of a for loop"
}
declare_clippy_lint! {
/// **What it does:** Checks whether a for loop has a single element.
///
/// **Why is this bad?** There is no reason to have a loop of a
/// single element.
/// **Known problems:** None
///
/// **Example:**
/// ```rust
/// let item1 = 2;
/// for item in &[item1] {
/// println!("{}", item);
/// }
/// ```
/// could be written as
/// ```rust
/// let item1 = 2;
/// let item = &item1;
/// println!("{}", item);
/// ```
pub SINGLE_ELEMENT_LOOP,
complexity,
"there is no reason to have a single element loop"
}
declare_clippy_lint! {
/// **What it does:** Check for unnecessary `if let` usage in a for loop
/// where only the `Some` or `Ok` variant of the iterator element is used.
///
/// **Why is this bad?** It is verbose and can be simplified
/// by first calling the `flatten` method on the `Iterator`.
///
/// **Known problems:** None.
///
/// **Example:**
///
/// ```rust
/// let x = vec![Some(1), Some(2), Some(3)];
/// for n in x {
/// if let Some(n) = n {
/// println!("{}", n);
/// }
/// }
/// ```
/// Use instead:
/// ```rust
/// let x = vec![Some(1), Some(2), Some(3)];
/// for n in x.into_iter().flatten() {
/// println!("{}", n);
/// }
/// ```
pub MANUAL_FLATTEN,
complexity,
"for loops over `Option`s or `Result`s with a single expression can be simplified"
}
declare_lint_pass!(Loops => [
MANUAL_MEMCPY,
MANUAL_FLATTEN,
NEEDLESS_RANGE_LOOP,
EXPLICIT_ITER_LOOP,
EXPLICIT_INTO_ITER_LOOP,
ITER_NEXT_LOOP,
FOR_LOOPS_OVER_FALLIBLES,
WHILE_LET_LOOP,
NEEDLESS_COLLECT,
EXPLICIT_COUNTER_LOOP,
EMPTY_LOOP,
WHILE_LET_ON_ITERATOR,
FOR_KV_MAP,
NEVER_LOOP,
MUT_RANGE_BOUND,
WHILE_IMMUTABLE_CONDITION,
SAME_ITEM_PUSH,
SINGLE_ELEMENT_LOOP,
]);
impl<'tcx> LateLintPass<'tcx> for Loops {
#[allow(clippy::too_many_lines)]
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
if let Some((pat, arg, body, span)) = higher::for_loop(expr) {
// we don't want to check expanded macros
// this check is not at the top of the function
// since higher::for_loop expressions are marked as expansions
if body.span.from_expansion() {
return;
}
check_for_loop(cx, pat, arg, body, expr, span);
}
// we don't want to check expanded macros
if expr.span.from_expansion() {
return;
}
// check for never_loop
never_loop::check(cx, expr);
// check for `loop { if let {} else break }` that could be `while let`
// (also matches an explicit "match" instead of "if let")
// (even if the "match" or "if let" is used for declaration)
if let ExprKind::Loop(ref block, _, LoopSource::Loop, _) = expr.kind {
// also check for empty `loop {}` statements, skipping those in #[panic_handler]
empty_loop::check(cx, expr, block);
while_let_loop::check(cx, expr, block);
}
while_let_on_iterator::check(cx, expr);
if let Some((cond, body)) = higher::while_loop(&expr) {
while_immutable_condition::check(cx, cond, body);
}
needless_collect::check(expr, cx);
}
}
fn check_for_loop<'tcx>(
cx: &LateContext<'tcx>,
pat: &'tcx Pat<'_>,
arg: &'tcx Expr<'_>,
body: &'tcx Expr<'_>,
expr: &'tcx Expr<'_>,
span: Span,
) {
let is_manual_memcpy_triggered = manual_memcpy::check(cx, pat, arg, body, expr);
if !is_manual_memcpy_triggered {
needless_range_loop::check(cx, pat, arg, body, expr);
explicit_counter_loop::check(cx, pat, arg, body, expr);
}
check_for_loop_arg(cx, pat, arg, expr);
for_kv_map::check(cx, pat, arg, body, expr);
mut_range_bound::check(cx, arg, body);
single_element_loop::check(cx, pat, arg, body, expr);
same_item_push::check(cx, pat, arg, body, expr);
manual_flatten::check(cx, pat, arg, body, span);
}
fn check_for_loop_arg(cx: &LateContext<'_>, pat: &Pat<'_>, arg: &Expr<'_>, expr: &Expr<'_>) {
let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
if let ExprKind::MethodCall(ref method, _, ref args, _) = arg.kind {
// just the receiver, no arguments
if args.len() == 1 {
let method_name = &*method.ident.as_str();
// check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
match method_name {
"iter" | "iter_mut" => explicit_iter_loop::check(cx, args, arg, method_name),
"into_iter" => {
explicit_iter_loop::check(cx, args, arg, method_name);
explicit_into_iter_loop::check(cx, args, arg);
},
"next" => {
next_loop_linted = iter_next_loop::check(cx, arg, expr);
},
_ => {},
}
}
}
if !next_loop_linted {
for_loops_over_fallibles::check(cx, pat, arg);
}
}

115
clippy_lints/src/loops/mut_range_bound.rs Normal file
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use super::MUT_RANGE_BOUND;
use crate::utils::{higher, path_to_local, span_lint};
use if_chain::if_chain;
use rustc_hir::{BindingAnnotation, Expr, HirId, Node, PatKind};
use rustc_infer::infer::TyCtxtInferExt;
use rustc_lint::LateContext;
use rustc_middle::ty;
use rustc_span::source_map::Span;
use rustc_typeck::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, PlaceBase, PlaceWithHirId};
pub(super) fn check(cx: &LateContext<'_>, arg: &Expr<'_>, body: &Expr<'_>) {
if let Some(higher::Range {
start: Some(start),
end: Some(end),
..
}) = higher::range(arg)
{
let mut_ids = vec![check_for_mutability(cx, start), check_for_mutability(cx, end)];
if mut_ids[0].is_some() || mut_ids[1].is_some() {
let (span_low, span_high) = check_for_mutation(cx, body, &mut_ids);
mut_warn_with_span(cx, span_low);
mut_warn_with_span(cx, span_high);
}
}
}
fn mut_warn_with_span(cx: &LateContext<'_>, span: Option<Span>) {
if let Some(sp) = span {
span_lint(
cx,
MUT_RANGE_BOUND,
sp,
"attempt to mutate range bound within loop; note that the range of the loop is unchanged",
);
}
}
fn check_for_mutability(cx: &LateContext<'_>, bound: &Expr<'_>) -> Option<HirId> {
if_chain! {
if let Some(hir_id) = path_to_local(bound);
if let Node::Binding(pat) = cx.tcx.hir().get(hir_id);
if let PatKind::Binding(BindingAnnotation::Mutable, ..) = pat.kind;
then {
return Some(hir_id);
}
}
None
}
fn check_for_mutation<'tcx>(
cx: &LateContext<'tcx>,
body: &Expr<'_>,
bound_ids: &[Option<HirId>],
) -> (Option<Span>, Option<Span>) {
let mut delegate = MutatePairDelegate {
cx,
hir_id_low: bound_ids[0],
hir_id_high: bound_ids[1],
span_low: None,
span_high: None,
};
cx.tcx.infer_ctxt().enter(|infcx| {
ExprUseVisitor::new(
&mut delegate,
&infcx,
body.hir_id.owner,
cx.param_env,
cx.typeck_results(),
)
.walk_expr(body);
});
delegate.mutation_span()
}
struct MutatePairDelegate<'a, 'tcx> {
cx: &'a LateContext<'tcx>,
hir_id_low: Option<HirId>,
hir_id_high: Option<HirId>,
span_low: Option<Span>,
span_high: Option<Span>,
}
impl<'tcx> Delegate<'tcx> for MutatePairDelegate<'_, 'tcx> {
fn consume(&mut self, _: &PlaceWithHirId<'tcx>, _: HirId, _: ConsumeMode) {}
fn borrow(&mut self, cmt: &PlaceWithHirId<'tcx>, diag_expr_id: HirId, bk: ty::BorrowKind) {
if let ty::BorrowKind::MutBorrow = bk {
if let PlaceBase::Local(id) = cmt.place.base {
if Some(id) == self.hir_id_low {
self.span_low = Some(self.cx.tcx.hir().span(diag_expr_id))
}
if Some(id) == self.hir_id_high {
self.span_high = Some(self.cx.tcx.hir().span(diag_expr_id))
}
}
}
}
fn mutate(&mut self, cmt: &PlaceWithHirId<'tcx>, diag_expr_id: HirId) {
if let PlaceBase::Local(id) = cmt.place.base {
if Some(id) == self.hir_id_low {
self.span_low = Some(self.cx.tcx.hir().span(diag_expr_id))
}
if Some(id) == self.hir_id_high {
self.span_high = Some(self.cx.tcx.hir().span(diag_expr_id))
}
}
}
}
impl MutatePairDelegate<'_, '_> {
fn mutation_span(&self) -> (Option<Span>, Option<Span>) {
(self.span_low, self.span_high)
}
}

283
clippy_lints/src/loops/needless_collect.rs Normal file
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use super::NEEDLESS_COLLECT;
use crate::utils::sugg::Sugg;
use crate::utils::{
is_type_diagnostic_item, match_trait_method, match_type, path_to_local_id, paths, snippet, span_lint_and_sugg,
span_lint_and_then,
};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::intravisit::{walk_block, walk_expr, NestedVisitorMap, Visitor};
use rustc_hir::{Block, Expr, ExprKind, GenericArg, HirId, Local, Pat, PatKind, QPath, StmtKind};
use rustc_lint::LateContext;
use rustc_middle::hir::map::Map;
use rustc_span::source_map::Span;
use rustc_span::symbol::{sym, Ident};
const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
pub(super) fn check<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
check_needless_collect_direct_usage(expr, cx);
check_needless_collect_indirect_usage(expr, cx);
}
fn check_needless_collect_direct_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
if_chain! {
if let ExprKind::MethodCall(ref method, _, ref args, _) = expr.kind;
if let ExprKind::MethodCall(ref chain_method, _, _, _) = args[0].kind;
if chain_method.ident.name == sym!(collect) && match_trait_method(cx, &args[0], &paths::ITERATOR);
if let Some(ref generic_args) = chain_method.args;
if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
then {
let ty = cx.typeck_results().node_type(ty.hir_id);
if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
match_type(cx, ty, &paths::BTREEMAP) ||
is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) {
if method.ident.name == sym!(len) {
let span = shorten_needless_collect_span(expr);
span_lint_and_sugg(
cx,
NEEDLESS_COLLECT,
span,
NEEDLESS_COLLECT_MSG,
"replace with",
"count()".to_string(),
Applicability::MachineApplicable,
);
}
if method.ident.name == sym!(is_empty) {
let span = shorten_needless_collect_span(expr);
span_lint_and_sugg(
cx,
NEEDLESS_COLLECT,
span,
NEEDLESS_COLLECT_MSG,
"replace with",
"next().is_none()".to_string(),
Applicability::MachineApplicable,
);
}
if method.ident.name == sym!(contains) {
let contains_arg = snippet(cx, args[1].span, "??");
let span = shorten_needless_collect_span(expr);
span_lint_and_then(
cx,
NEEDLESS_COLLECT,
span,
NEEDLESS_COLLECT_MSG,
|diag| {
let (arg, pred) = contains_arg
.strip_prefix('&')
.map_or(("&x", &*contains_arg), |s| ("x", s));
diag.span_suggestion(
span,
"replace with",
format!(
"any(|{}| x == {})",
arg, pred
),
Applicability::MachineApplicable,
);
}
);
}
}
}
}
}
fn check_needless_collect_indirect_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
if let ExprKind::Block(ref block, _) = expr.kind {
for ref stmt in block.stmts {
if_chain! {
if let StmtKind::Local(
Local { pat: Pat { hir_id: pat_id, kind: PatKind::Binding(_, _, ident, .. ), .. },
init: Some(ref init_expr), .. }
) = stmt.kind;
if let ExprKind::MethodCall(ref method_name, _, &[ref iter_source], ..) = init_expr.kind;
if method_name.ident.name == sym!(collect) && match_trait_method(cx, &init_expr, &paths::ITERATOR);
if let Some(ref generic_args) = method_name.args;
if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
if let ty = cx.typeck_results().node_type(ty.hir_id);
if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
match_type(cx, ty, &paths::LINKED_LIST);
if let Some(iter_calls) = detect_iter_and_into_iters(block, *ident);
if iter_calls.len() == 1;
then {
let mut used_count_visitor = UsedCountVisitor {
cx,
id: *pat_id,
count: 0,
};
walk_block(&mut used_count_visitor, block);
if used_count_visitor.count > 1 {
return;
}
// Suggest replacing iter_call with iter_replacement, and removing stmt
let iter_call = &iter_calls[0];
span_lint_and_then(
cx,
super::NEEDLESS_COLLECT,
stmt.span.until(iter_call.span),
NEEDLESS_COLLECT_MSG,
|diag| {
let iter_replacement = format!("{}{}", Sugg::hir(cx, iter_source, ".."), iter_call.get_iter_method(cx));
diag.multipart_suggestion(
iter_call.get_suggestion_text(),
vec![
(stmt.span, String::new()),
(iter_call.span, iter_replacement)
],
Applicability::MachineApplicable,// MaybeIncorrect,
).emit();
},
);
}
}
}
}
}
struct IterFunction {
func: IterFunctionKind,
span: Span,
}
impl IterFunction {
fn get_iter_method(&self, cx: &LateContext<'_>) -> String {
match &self.func {
IterFunctionKind::IntoIter => String::new(),
IterFunctionKind::Len => String::from(".count()"),
IterFunctionKind::IsEmpty => String::from(".next().is_none()"),
IterFunctionKind::Contains(span) => {
let s = snippet(cx, *span, "..");
if let Some(stripped) = s.strip_prefix('&') {
format!(".any(|x| x == {})", stripped)
} else {
format!(".any(|x| x == *{})", s)
}
},
}
}
fn get_suggestion_text(&self) -> &'static str {
match &self.func {
IterFunctionKind::IntoIter => {
"use the original Iterator instead of collecting it and then producing a new one"
},
IterFunctionKind::Len => {
"take the original Iterator's count instead of collecting it and finding the length"
},
IterFunctionKind::IsEmpty => {
"check if the original Iterator has anything instead of collecting it and seeing if it's empty"
},
IterFunctionKind::Contains(_) => {
"check if the original Iterator contains an element instead of collecting then checking"
},
}
}
}
enum IterFunctionKind {
IntoIter,
Len,
IsEmpty,
Contains(Span),
}
struct IterFunctionVisitor {
uses: Vec<IterFunction>,
seen_other: bool,
target: Ident,
}
impl<'tcx> Visitor<'tcx> for IterFunctionVisitor {
fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
// Check function calls on our collection
if_chain! {
if let ExprKind::MethodCall(method_name, _, ref args, _) = &expr.kind;
if let Some(Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. }) = args.get(0);
if let &[name] = &path.segments;
if name.ident == self.target;
then {
let len = sym!(len);
let is_empty = sym!(is_empty);
let contains = sym!(contains);
match method_name.ident.name {
sym::into_iter => self.uses.push(
IterFunction { func: IterFunctionKind::IntoIter, span: expr.span }
),
name if name == len => self.uses.push(
IterFunction { func: IterFunctionKind::Len, span: expr.span }
),
name if name == is_empty => self.uses.push(
IterFunction { func: IterFunctionKind::IsEmpty, span: expr.span }
),
name if name == contains => self.uses.push(
IterFunction { func: IterFunctionKind::Contains(args[1].span), span: expr.span }
),
_ => self.seen_other = true,
}
return
}
}
// Check if the collection is used for anything else
if_chain! {
if let Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. } = expr;
if let &[name] = &path.segments;
if name.ident == self.target;
then {
self.seen_other = true;
} else {
walk_expr(self, expr);
}
}
}
type Map = Map<'tcx>;
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
NestedVisitorMap::None
}
}
struct UsedCountVisitor<'a, 'tcx> {
cx: &'a LateContext<'tcx>,
id: HirId,
count: usize,
}
impl<'a, 'tcx> Visitor<'tcx> for UsedCountVisitor<'a, 'tcx> {
type Map = Map<'tcx>;
fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
if path_to_local_id(expr, self.id) {
self.count += 1;
} else {
walk_expr(self, expr);
}
}
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
}
}
/// Detect the occurrences of calls to `iter` or `into_iter` for the
/// given identifier
fn detect_iter_and_into_iters<'tcx>(block: &'tcx Block<'tcx>, identifier: Ident) -> Option<Vec<IterFunction>> {
let mut visitor = IterFunctionVisitor {
uses: Vec::new(),
target: identifier,
seen_other: false,
};
visitor.visit_block(block);
if visitor.seen_other { None } else { Some(visitor.uses) }
}
fn shorten_needless_collect_span(expr: &Expr<'_>) -> Span {
if_chain! {
if let ExprKind::MethodCall(.., args, _) = &expr.kind;
if let ExprKind::MethodCall(_, span, ..) = &args[0].kind;
then {
return expr.span.with_lo(span.lo());
}
}
unreachable!();
}

391
clippy_lints/src/loops/needless_range_loop.rs Normal file
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use super::NEEDLESS_RANGE_LOOP;
use crate::utils::visitors::LocalUsedVisitor;
use crate::utils::{
contains_name, has_iter_method, higher, is_integer_const, match_trait_method, multispan_sugg, path_to_local_id,
paths, snippet, span_lint_and_then, sugg, SpanlessEq,
};
use if_chain::if_chain;
use rustc_ast::ast;
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_hir::def::{DefKind, Res};
use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
use rustc_hir::{BinOpKind, BorrowKind, Expr, ExprKind, HirId, Mutability, Pat, PatKind, QPath};
use rustc_lint::LateContext;
use rustc_middle::hir::map::Map;
use rustc_middle::middle::region;
use rustc_middle::ty::{self, Ty};
use rustc_span::symbol::{sym, Symbol};
use std::iter::Iterator;
use std::mem;
/// Checks for looping over a range and then indexing a sequence with it.
/// The iteratee must be a range literal.
#[allow(clippy::too_many_lines)]
pub(super) fn check<'tcx>(
cx: &LateContext<'tcx>,
pat: &'tcx Pat<'_>,
arg: &'tcx Expr<'_>,
body: &'tcx Expr<'_>,
expr: &'tcx Expr<'_>,
) {
if let Some(higher::Range {
start: Some(start),
ref end,
limits,
}) = higher::range(arg)
{
// the var must be a single name
if let PatKind::Binding(_, canonical_id, ident, _) = pat.kind {
let mut visitor = VarVisitor {
cx,
var: canonical_id,
indexed_mut: FxHashSet::default(),
indexed_indirectly: FxHashMap::default(),
indexed_directly: FxHashMap::default(),
referenced: FxHashSet::default(),
nonindex: false,
prefer_mutable: false,
};
walk_expr(&mut visitor, body);
// linting condition: we only indexed one variable, and indexed it directly
if visitor.indexed_indirectly.is_empty() && visitor.indexed_directly.len() == 1 {
let (indexed, (indexed_extent, indexed_ty)) = visitor
.indexed_directly
.into_iter()
.next()
.expect("already checked that we have exactly 1 element");
// ensure that the indexed variable was declared before the loop, see #601
if let Some(indexed_extent) = indexed_extent {
let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
let parent_def_id = cx.tcx.hir().local_def_id(parent_id);
let region_scope_tree = cx.tcx.region_scope_tree(parent_def_id);
let pat_extent = region_scope_tree.var_scope(pat.hir_id.local_id);
if region_scope_tree.is_subscope_of(indexed_extent, pat_extent) {
return;
}
}
// don't lint if the container that is indexed does not have .iter() method
let has_iter = has_iter_method(cx, indexed_ty);
if has_iter.is_none() {
return;
}
// don't lint if the container that is indexed into is also used without
// indexing
if visitor.referenced.contains(&indexed) {
return;
}
let starts_at_zero = is_integer_const(cx, start, 0);
let skip = if starts_at_zero {
String::new()
} else if visitor.indexed_mut.contains(&indexed) && contains_name(indexed, start) {
return;
} else {
format!(".skip({})", snippet(cx, start.span, ".."))
};
let mut end_is_start_plus_val = false;
let take = if let Some(end) = *end {
let mut take_expr = end;
if let ExprKind::Binary(ref op, ref left, ref right) = end.kind {
if let BinOpKind::Add = op.node {
let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
if start_equal_left {
take_expr = right;
} else if start_equal_right {
take_expr = left;
}
end_is_start_plus_val = start_equal_left | start_equal_right;
}
}
if is_len_call(end, indexed) || is_end_eq_array_len(cx, end, limits, indexed_ty) {
String::new()
} else if visitor.indexed_mut.contains(&indexed) && contains_name(indexed, take_expr) {
return;
} else {
match limits {
ast::RangeLimits::Closed => {
let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
format!(".take({})", take_expr + sugg::ONE)
},
ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
}
}
} else {
String::new()
};
let (ref_mut, method) = if visitor.indexed_mut.contains(&indexed) {
("mut ", "iter_mut")
} else {
("", "iter")
};
let take_is_empty = take.is_empty();
let mut method_1 = take;
let mut method_2 = skip;
if end_is_start_plus_val {
mem::swap(&mut method_1, &mut method_2);
}
if visitor.nonindex {
span_lint_and_then(
cx,
NEEDLESS_RANGE_LOOP,
expr.span,
&format!("the loop variable `{}` is used to index `{}`", ident.name, indexed),
|diag| {
multispan_sugg(
diag,
"consider using an iterator",
vec![
(pat.span, format!("({}, <item>)", ident.name)),
(
arg.span,
format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2),
),
],
);
},
);
} else {
let repl = if starts_at_zero && take_is_empty {
format!("&{}{}", ref_mut, indexed)
} else {
format!("{}.{}(){}{}", indexed, method, method_1, method_2)
};
span_lint_and_then(
cx,
NEEDLESS_RANGE_LOOP,
expr.span,
&format!("the loop variable `{}` is only used to index `{}`", ident.name, indexed),
|diag| {
multispan_sugg(
diag,
"consider using an iterator",
vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
);
},
);
}
}
}
}
}
fn is_len_call(expr: &Expr<'_>, var: Symbol) -> bool {
if_chain! {
if let ExprKind::MethodCall(ref method, _, ref len_args, _) = expr.kind;
if len_args.len() == 1;
if method.ident.name == sym!(len);
if let ExprKind::Path(QPath::Resolved(_, ref path)) = len_args[0].kind;
if path.segments.len() == 1;
if path.segments[0].ident.name == var;
then {
return true;
}
}
false
}
fn is_end_eq_array_len<'tcx>(
cx: &LateContext<'tcx>,
end: &Expr<'_>,
limits: ast::RangeLimits,
indexed_ty: Ty<'tcx>,
) -> bool {
if_chain! {
if let ExprKind::Lit(ref lit) = end.kind;
if let ast::LitKind::Int(end_int, _) = lit.node;
if let ty::Array(_, arr_len_const) = indexed_ty.kind();
if let Some(arr_len) = arr_len_const.try_eval_usize(cx.tcx, cx.param_env);
then {
return match limits {
ast::RangeLimits::Closed => end_int + 1 >= arr_len.into(),
ast::RangeLimits::HalfOpen => end_int >= arr_len.into(),
};
}
}
false
}
struct VarVisitor<'a, 'tcx> {
/// context reference
cx: &'a LateContext<'tcx>,
/// var name to look for as index
var: HirId,
/// indexed variables that are used mutably
indexed_mut: FxHashSet<Symbol>,
/// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
indexed_indirectly: FxHashMap<Symbol, Option<region::Scope>>,
/// subset of `indexed` of vars that are indexed directly: `v[i]`
/// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
indexed_directly: FxHashMap<Symbol, (Option<region::Scope>, Ty<'tcx>)>,
/// Any names that are used outside an index operation.
/// Used to detect things like `&mut vec` used together with `vec[i]`
referenced: FxHashSet<Symbol>,
/// has the loop variable been used in expressions other than the index of
/// an index op?
nonindex: bool,
/// Whether we are inside the `$` in `&mut $` or `$ = foo` or `$.bar`, where bar
/// takes `&mut self`
prefer_mutable: bool,
}
impl<'a, 'tcx> VarVisitor<'a, 'tcx> {
fn check(&mut self, idx: &'tcx Expr<'_>, seqexpr: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) -> bool {
if_chain! {
// the indexed container is referenced by a name
if let ExprKind::Path(ref seqpath) = seqexpr.kind;
if let QPath::Resolved(None, ref seqvar) = *seqpath;
if seqvar.segments.len() == 1;
then {
let index_used_directly = path_to_local_id(idx, self.var);
let indexed_indirectly = {
let mut used_visitor = LocalUsedVisitor::new(self.cx, self.var);
walk_expr(&mut used_visitor, idx);
used_visitor.used
};
if indexed_indirectly || index_used_directly {
if self.prefer_mutable {
self.indexed_mut.insert(seqvar.segments[0].ident.name);
}
let res = self.cx.qpath_res(seqpath, seqexpr.hir_id);
match res {
Res::Local(hir_id) => {
let parent_id = self.cx.tcx.hir().get_parent_item(expr.hir_id);
let parent_def_id = self.cx.tcx.hir().local_def_id(parent_id);
let extent = self.cx.tcx.region_scope_tree(parent_def_id).var_scope(hir_id.local_id);
if indexed_indirectly {
self.indexed_indirectly.insert(seqvar.segments[0].ident.name, Some(extent));
}
if index_used_directly {
self.indexed_directly.insert(
seqvar.segments[0].ident.name,
(Some(extent), self.cx.typeck_results().node_type(seqexpr.hir_id)),
);
}
return false; // no need to walk further *on the variable*
}
Res::Def(DefKind::Static | DefKind::Const, ..) => {
if indexed_indirectly {
self.indexed_indirectly.insert(seqvar.segments[0].ident.name, None);
}
if index_used_directly {
self.indexed_directly.insert(
seqvar.segments[0].ident.name,
(None, self.cx.typeck_results().node_type(seqexpr.hir_id)),
);
}
return false; // no need to walk further *on the variable*
}
_ => (),
}
}
}
}
true
}
}
impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
type Map = Map<'tcx>;
fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
if_chain! {
// a range index op
if let ExprKind::MethodCall(ref meth, _, ref args, _) = expr.kind;
if (meth.ident.name == sym::index && match_trait_method(self.cx, expr, &paths::INDEX))
|| (meth.ident.name == sym::index_mut && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
if !self.check(&args[1], &args[0], expr);
then { return }
}
if_chain! {
// an index op
if let ExprKind::Index(ref seqexpr, ref idx) = expr.kind;
if !self.check(idx, seqexpr, expr);
then { return }
}
if_chain! {
// directly using a variable
if let ExprKind::Path(QPath::Resolved(None, path)) = expr.kind;
if let Res::Local(local_id) = path.res;
then {
if local_id == self.var {
self.nonindex = true;
} else {
// not the correct variable, but still a variable
self.referenced.insert(path.segments[0].ident.name);
}
}
}
let old = self.prefer_mutable;
match expr.kind {
ExprKind::AssignOp(_, ref lhs, ref rhs) | ExprKind::Assign(ref lhs, ref rhs, _) => {
self.prefer_mutable = true;
self.visit_expr(lhs);
self.prefer_mutable = false;
self.visit_expr(rhs);
},
ExprKind::AddrOf(BorrowKind::Ref, mutbl, ref expr) => {
if mutbl == Mutability::Mut {
self.prefer_mutable = true;
}
self.visit_expr(expr);
},
ExprKind::Call(ref f, args) => {
self.visit_expr(f);
for expr in args {
let ty = self.cx.typeck_results().expr_ty_adjusted(expr);
self.prefer_mutable = false;
if let ty::Ref(_, _, mutbl) = *ty.kind() {
if mutbl == Mutability::Mut {
self.prefer_mutable = true;
}
}
self.visit_expr(expr);
}
},
ExprKind::MethodCall(_, _, args, _) => {
let def_id = self.cx.typeck_results().type_dependent_def_id(expr.hir_id).unwrap();
for (ty, expr) in self.cx.tcx.fn_sig(def_id).inputs().skip_binder().iter().zip(args) {
self.prefer_mutable = false;
if let ty::Ref(_, _, mutbl) = *ty.kind() {
if mutbl == Mutability::Mut {
self.prefer_mutable = true;
}
}
self.visit_expr(expr);
}
},
ExprKind::Closure(_, _, body_id, ..) => {
let body = self.cx.tcx.hir().body(body_id);
self.visit_expr(&body.value);
},
_ => walk_expr(self, expr),
}
self.prefer_mutable = old;
}
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
NestedVisitorMap::None
}
}

172
clippy_lints/src/loops/never_loop.rs Normal file
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use super::NEVER_LOOP;
use crate::utils::span_lint;
use rustc_hir::{Block, Expr, ExprKind, HirId, InlineAsmOperand, Stmt, StmtKind};
use rustc_lint::LateContext;
use std::iter::{once, Iterator};
pub(super) fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
if let ExprKind::Loop(ref block, _, _, _) = expr.kind {
match never_loop_block(block, expr.hir_id) {
NeverLoopResult::AlwaysBreak => span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops"),
NeverLoopResult::MayContinueMainLoop | NeverLoopResult::Otherwise => (),
}
}
}
enum NeverLoopResult {
// A break/return always get triggered but not necessarily for the main loop.
AlwaysBreak,
// A continue may occur for the main loop.
MayContinueMainLoop,
Otherwise,
}
#[must_use]
fn absorb_break(arg: &NeverLoopResult) -> NeverLoopResult {
match *arg {
NeverLoopResult::AlwaysBreak | NeverLoopResult::Otherwise => NeverLoopResult::Otherwise,
NeverLoopResult::MayContinueMainLoop => NeverLoopResult::MayContinueMainLoop,
}
}
// Combine two results for parts that are called in order.
#[must_use]
fn combine_seq(first: NeverLoopResult, second: NeverLoopResult) -> NeverLoopResult {
match first {
NeverLoopResult::AlwaysBreak | NeverLoopResult::MayContinueMainLoop => first,
NeverLoopResult::Otherwise => second,
}
}
// Combine two results where both parts are called but not necessarily in order.
#[must_use]
fn combine_both(left: NeverLoopResult, right: NeverLoopResult) -> NeverLoopResult {
match (left, right) {
(NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
NeverLoopResult::MayContinueMainLoop
},
(NeverLoopResult::AlwaysBreak, _) | (_, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
(NeverLoopResult::Otherwise, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
}
}
// Combine two results where only one of the part may have been executed.
#[must_use]
fn combine_branches(b1: NeverLoopResult, b2: NeverLoopResult) -> NeverLoopResult {
match (b1, b2) {
(NeverLoopResult::AlwaysBreak, NeverLoopResult::AlwaysBreak) => NeverLoopResult::AlwaysBreak,
(NeverLoopResult::MayContinueMainLoop, _) | (_, NeverLoopResult::MayContinueMainLoop) => {
NeverLoopResult::MayContinueMainLoop
},
(NeverLoopResult::Otherwise, _) | (_, NeverLoopResult::Otherwise) => NeverLoopResult::Otherwise,
}
}
fn never_loop_block(block: &Block<'_>, main_loop_id: HirId) -> NeverLoopResult {
let stmts = block.stmts.iter().map(stmt_to_expr);
let expr = once(block.expr.as_deref());
let mut iter = stmts.chain(expr).flatten();
never_loop_expr_seq(&mut iter, main_loop_id)
}
fn never_loop_expr_seq<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
es.map(|e| never_loop_expr(e, main_loop_id))
.fold(NeverLoopResult::Otherwise, combine_seq)
}
fn stmt_to_expr<'tcx>(stmt: &Stmt<'tcx>) -> Option<&'tcx Expr<'tcx>> {
match stmt.kind {
StmtKind::Semi(ref e, ..) | StmtKind::Expr(ref e, ..) => Some(e),
StmtKind::Local(ref local) => local.init.as_deref(),
_ => None,
}
}
fn never_loop_expr(expr: &Expr<'_>, main_loop_id: HirId) -> NeverLoopResult {
match expr.kind {
ExprKind::Box(ref e)
| ExprKind::Unary(_, ref e)
| ExprKind::Cast(ref e, _)
| ExprKind::Type(ref e, _)
| ExprKind::Field(ref e, _)
| ExprKind::AddrOf(_, _, ref e)
| ExprKind::Struct(_, _, Some(ref e))
| ExprKind::Repeat(ref e, _)
| ExprKind::DropTemps(ref e) => never_loop_expr(e, main_loop_id),
ExprKind::Array(ref es) | ExprKind::MethodCall(_, _, ref es, _) | ExprKind::Tup(ref es) => {
never_loop_expr_all(&mut es.iter(), main_loop_id)
},
ExprKind::Call(ref e, ref es) => never_loop_expr_all(&mut once(&**e).chain(es.iter()), main_loop_id),
ExprKind::Binary(_, ref e1, ref e2)
| ExprKind::Assign(ref e1, ref e2, _)
| ExprKind::AssignOp(_, ref e1, ref e2)
| ExprKind::Index(ref e1, ref e2) => never_loop_expr_all(&mut [&**e1, &**e2].iter().cloned(), main_loop_id),
ExprKind::Loop(ref b, _, _, _) => {
// Break can come from the inner loop so remove them.
absorb_break(&never_loop_block(b, main_loop_id))
},
ExprKind::If(ref e, ref e2, ref e3) => {
let e1 = never_loop_expr(e, main_loop_id);
let e2 = never_loop_expr(e2, main_loop_id);
let e3 = e3
.as_ref()
.map_or(NeverLoopResult::Otherwise, |e| never_loop_expr(e, main_loop_id));
combine_seq(e1, combine_branches(e2, e3))
},
ExprKind::Match(ref e, ref arms, _) => {
let e = never_loop_expr(e, main_loop_id);
if arms.is_empty() {
e
} else {
let arms = never_loop_expr_branch(&mut arms.iter().map(|a| &*a.body), main_loop_id);
combine_seq(e, arms)
}
},
ExprKind::Block(ref b, _) => never_loop_block(b, main_loop_id),
ExprKind::Continue(d) => {
let id = d
.target_id
.expect("target ID can only be missing in the presence of compilation errors");
if id == main_loop_id {
NeverLoopResult::MayContinueMainLoop
} else {
NeverLoopResult::AlwaysBreak
}
},
ExprKind::Break(_, ref e) | ExprKind::Ret(ref e) => e.as_ref().map_or(NeverLoopResult::AlwaysBreak, |e| {
combine_seq(never_loop_expr(e, main_loop_id), NeverLoopResult::AlwaysBreak)
}),
ExprKind::InlineAsm(ref asm) => asm
.operands
.iter()
.map(|(o, _)| match o {
InlineAsmOperand::In { expr, .. }
| InlineAsmOperand::InOut { expr, .. }
| InlineAsmOperand::Const { expr }
| InlineAsmOperand::Sym { expr } => never_loop_expr(expr, main_loop_id),
InlineAsmOperand::Out { expr, .. } => never_loop_expr_all(&mut expr.iter(), main_loop_id),
InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
never_loop_expr_all(&mut once(in_expr).chain(out_expr.iter()), main_loop_id)
},
})
.fold(NeverLoopResult::Otherwise, combine_both),
ExprKind::Struct(_, _, None)
| ExprKind::Yield(_, _)
| ExprKind::Closure(_, _, _, _, _)
| ExprKind::LlvmInlineAsm(_)
| ExprKind::Path(_)
| ExprKind::ConstBlock(_)
| ExprKind::Lit(_)
| ExprKind::Err => NeverLoopResult::Otherwise,
}
}
fn never_loop_expr_all<'a, T: Iterator<Item = &'a Expr<'a>>>(es: &mut T, main_loop_id: HirId) -> NeverLoopResult {
es.map(|e| never_loop_expr(e, main_loop_id))
.fold(NeverLoopResult::Otherwise, combine_both)
}
fn never_loop_expr_branch<'a, T: Iterator<Item = &'a Expr<'a>>>(e: &mut T, main_loop_id: HirId) -> NeverLoopResult {
e.map(|e| never_loop_expr(e, main_loop_id))
.fold(NeverLoopResult::AlwaysBreak, combine_branches)
}

169
clippy_lints/src/loops/same_item_push.rs Normal file
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use super::SAME_ITEM_PUSH;
use crate::utils::{implements_trait, is_type_diagnostic_item, snippet_with_macro_callsite, span_lint_and_help};
use if_chain::if_chain;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
use rustc_hir::{BindingAnnotation, Block, Expr, ExprKind, Node, Pat, PatKind, Stmt, StmtKind};
use rustc_lint::LateContext;
use rustc_middle::hir::map::Map;
use rustc_span::symbol::sym;
use std::iter::Iterator;
/// Detects for loop pushing the same item into a Vec
pub(super) fn check<'tcx>(
cx: &LateContext<'tcx>,
pat: &'tcx Pat<'_>,
_: &'tcx Expr<'_>,
body: &'tcx Expr<'_>,
_: &'tcx Expr<'_>,
) {
fn emit_lint(cx: &LateContext<'_>, vec: &Expr<'_>, pushed_item: &Expr<'_>) {
let vec_str = snippet_with_macro_callsite(cx, vec.span, "");
let item_str = snippet_with_macro_callsite(cx, pushed_item.span, "");
span_lint_and_help(
cx,
SAME_ITEM_PUSH,
vec.span,
"it looks like the same item is being pushed into this Vec",
None,
&format!(
"try using vec![{};SIZE] or {}.resize(NEW_SIZE, {})",
item_str, vec_str, item_str
),
)
}
if !matches!(pat.kind, PatKind::Wild) {
return;
}
// Determine whether it is safe to lint the body
let mut same_item_push_visitor = SameItemPushVisitor {
should_lint: true,
vec_push: None,
cx,
};
walk_expr(&mut same_item_push_visitor, body);
if same_item_push_visitor.should_lint {
if let Some((vec, pushed_item)) = same_item_push_visitor.vec_push {
let vec_ty = cx.typeck_results().expr_ty(vec);
let ty = vec_ty.walk().nth(1).unwrap().expect_ty();
if cx
.tcx
.lang_items()
.clone_trait()
.map_or(false, |id| implements_trait(cx, ty, id, &[]))
{
// Make sure that the push does not involve possibly mutating values
match pushed_item.kind {
ExprKind::Path(ref qpath) => {
match cx.qpath_res(qpath, pushed_item.hir_id) {
// immutable bindings that are initialized with literal or constant
Res::Local(hir_id) => {
if_chain! {
let node = cx.tcx.hir().get(hir_id);
if let Node::Binding(pat) = node;
if let PatKind::Binding(bind_ann, ..) = pat.kind;
if !matches!(bind_ann, BindingAnnotation::RefMut | BindingAnnotation::Mutable);
let parent_node = cx.tcx.hir().get_parent_node(hir_id);
if let Some(Node::Local(parent_let_expr)) = cx.tcx.hir().find(parent_node);
if let Some(init) = parent_let_expr.init;
then {
match init.kind {
// immutable bindings that are initialized with literal
ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
// immutable bindings that are initialized with constant
ExprKind::Path(ref path) => {
if let Res::Def(DefKind::Const, ..) = cx.qpath_res(path, init.hir_id) {
emit_lint(cx, vec, pushed_item);
}
}
_ => {},
}
}
}
},
// constant
Res::Def(DefKind::Const, ..) => emit_lint(cx, vec, pushed_item),
_ => {},
}
},
ExprKind::Lit(..) => emit_lint(cx, vec, pushed_item),
_ => {},
}
}
}
}
}
// Scans the body of the for loop and determines whether lint should be given
struct SameItemPushVisitor<'a, 'tcx> {
should_lint: bool,
// this field holds the last vec push operation visited, which should be the only push seen
vec_push: Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)>,
cx: &'a LateContext<'tcx>,
}
impl<'a, 'tcx> Visitor<'tcx> for SameItemPushVisitor<'a, 'tcx> {
type Map = Map<'tcx>;
fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
match &expr.kind {
// Non-determinism may occur ... don't give a lint
ExprKind::Loop(..) | ExprKind::Match(..) => self.should_lint = false,
ExprKind::Block(block, _) => self.visit_block(block),
_ => {},
}
}
fn visit_block(&mut self, b: &'tcx Block<'_>) {
for stmt in b.stmts.iter() {
self.visit_stmt(stmt);
}
}
fn visit_stmt(&mut self, s: &'tcx Stmt<'_>) {
let vec_push_option = get_vec_push(self.cx, s);
if vec_push_option.is_none() {
// Current statement is not a push so visit inside
match &s.kind {
StmtKind::Expr(expr) | StmtKind::Semi(expr) => self.visit_expr(&expr),
_ => {},
}
} else {
// Current statement is a push ...check whether another
// push had been previously done
if self.vec_push.is_none() {
self.vec_push = vec_push_option;
} else {
// There are multiple pushes ... don't lint
self.should_lint = false;
}
}
}
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
NestedVisitorMap::None
}
}
// Given some statement, determine if that statement is a push on a Vec. If it is, return
// the Vec being pushed into and the item being pushed
fn get_vec_push<'tcx>(cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>)> {
if_chain! {
// Extract method being called
if let StmtKind::Semi(semi_stmt) = &stmt.kind;
if let ExprKind::MethodCall(path, _, args, _) = &semi_stmt.kind;
// Figure out the parameters for the method call
if let Some(self_expr) = args.get(0);
if let Some(pushed_item) = args.get(1);
// Check that the method being called is push() on a Vec
if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(self_expr), sym::vec_type);
if path.ident.name.as_str() == "push";
then {
return Some((self_expr, pushed_item))
}
}
None
}

42
clippy_lints/src/loops/single_element_loop.rs Normal file
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@ -0,0 +1,42 @@
use super::{get_span_of_entire_for_loop, SINGLE_ELEMENT_LOOP};
use crate::utils::{indent_of, single_segment_path, snippet, span_lint_and_sugg};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::{BorrowKind, Expr, ExprKind, Pat, PatKind};
use rustc_lint::LateContext;
pub(super) fn check<'tcx>(
cx: &LateContext<'tcx>,
pat: &'tcx Pat<'_>,
arg: &'tcx Expr<'_>,
body: &'tcx Expr<'_>,
expr: &'tcx Expr<'_>,
) {
if_chain! {
if let ExprKind::AddrOf(BorrowKind::Ref, _, ref arg_expr) = arg.kind;
if let PatKind::Binding(.., target, _) = pat.kind;
if let ExprKind::Array([arg_expression]) = arg_expr.kind;
if let ExprKind::Path(ref list_item) = arg_expression.kind;
if let Some(list_item_name) = single_segment_path(list_item).map(|ps| ps.ident.name);
if let ExprKind::Block(ref block, _) = body.kind;
if !block.stmts.is_empty();
then {
let for_span = get_span_of_entire_for_loop(expr);
let mut block_str = snippet(cx, block.span, "..").into_owned();
block_str.remove(0);
block_str.pop();
span_lint_and_sugg(
cx,
SINGLE_ELEMENT_LOOP,
for_span,
"for loop over a single element",
"try",
format!("{{\n{}let {} = &{};{}}}", " ".repeat(indent_of(cx, block.stmts[0].span).unwrap_or(0)), target.name, list_item_name, block_str),
Applicability::MachineApplicable
)
}
}
}

350
clippy_lints/src/loops/utils.rs Normal file
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@ -0,0 +1,350 @@
use crate::utils::{
get_parent_expr, get_trait_def_id, has_iter_method, implements_trait, is_integer_const, path_to_local,
path_to_local_id, paths, sugg,
};
use if_chain::if_chain;
use rustc_data_structures::fx::FxHashMap;
use rustc_errors::Applicability;
use rustc_hir::intravisit::{walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor};
use rustc_hir::{BinOpKind, BorrowKind, Expr, ExprKind, HirId, Mutability, Pat, PatKind, Stmt, StmtKind};
use rustc_lint::LateContext;
use rustc_middle::hir::map::Map;
use rustc_span::source_map::Span;
use rustc_span::symbol::Symbol;
use std::iter::Iterator;
#[derive(Debug, PartialEq)]
enum IncrementVisitorVarState {
Initial, // Not examined yet
IncrOnce, // Incremented exactly once, may be a loop counter
DontWarn,
}
/// Scan a for loop for variables that are incremented exactly once and not used after that.
pub(super) struct IncrementVisitor<'a, 'tcx> {
cx: &'a LateContext<'tcx>, // context reference
states: FxHashMap<HirId, IncrementVisitorVarState>, // incremented variables
depth: u32, // depth of conditional expressions
done: bool,
}
impl<'a, 'tcx> IncrementVisitor<'a, 'tcx> {
pub(super) fn new(cx: &'a LateContext<'tcx>) -> Self {
Self {
cx,
states: FxHashMap::default(),
depth: 0,
done: false,
}
}
pub(super) fn into_results(self) -> impl Iterator<Item = HirId> {
self.states.into_iter().filter_map(|(id, state)| {
if state == IncrementVisitorVarState::IncrOnce {
Some(id)
} else {
None
}
})
}
}
impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
type Map = Map<'tcx>;
fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
if self.done {
return;
}
// If node is a variable
if let Some(def_id) = path_to_local(expr) {
if let Some(parent) = get_parent_expr(self.cx, expr) {
let state = self.states.entry(def_id).or_insert(IncrementVisitorVarState::Initial);
if *state == IncrementVisitorVarState::IncrOnce {
*state = IncrementVisitorVarState::DontWarn;
return;
}
match parent.kind {
ExprKind::AssignOp(op, ref lhs, ref rhs) => {
if lhs.hir_id == expr.hir_id {
*state = if op.node == BinOpKind::Add
&& is_integer_const(self.cx, rhs, 1)
&& *state == IncrementVisitorVarState::Initial
&& self.depth == 0
{
IncrementVisitorVarState::IncrOnce
} else {
// Assigned some other value or assigned multiple times
IncrementVisitorVarState::DontWarn
};
}
},
ExprKind::Assign(ref lhs, _, _) if lhs.hir_id == expr.hir_id => {
*state = IncrementVisitorVarState::DontWarn
},
ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
*state = IncrementVisitorVarState::DontWarn
},
_ => (),
}
}
walk_expr(self, expr);
} else if is_loop(expr) || is_conditional(expr) {
self.depth += 1;
walk_expr(self, expr);
self.depth -= 1;
} else if let ExprKind::Continue(_) = expr.kind {
self.done = true;
} else {
walk_expr(self, expr);
}
}
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
NestedVisitorMap::None
}
}
enum InitializeVisitorState<'hir> {
Initial, // Not examined yet
Declared(Symbol), // Declared but not (yet) initialized
Initialized {
name: Symbol,
initializer: &'hir Expr<'hir>,
},
DontWarn,
}
/// Checks whether a variable is initialized at the start of a loop and not modified
/// and used after the loop.
pub(super) struct InitializeVisitor<'a, 'tcx> {
cx: &'a LateContext<'tcx>, // context reference
end_expr: &'tcx Expr<'tcx>, // the for loop. Stop scanning here.
var_id: HirId,
state: InitializeVisitorState<'tcx>,
depth: u32, // depth of conditional expressions
past_loop: bool,
}
impl<'a, 'tcx> InitializeVisitor<'a, 'tcx> {
pub(super) fn new(cx: &'a LateContext<'tcx>, end_expr: &'tcx Expr<'tcx>, var_id: HirId) -> Self {
Self {
cx,
end_expr,
var_id,
state: InitializeVisitorState::Initial,
depth: 0,
past_loop: false,
}
}
pub(super) fn get_result(&self) -> Option<(Symbol, &'tcx Expr<'tcx>)> {
if let InitializeVisitorState::Initialized { name, initializer } = self.state {
Some((name, initializer))
} else {
None
}
}
}
impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
type Map = Map<'tcx>;
fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
// Look for declarations of the variable
if_chain! {
if let StmtKind::Local(ref local) = stmt.kind;
if local.pat.hir_id == self.var_id;
if let PatKind::Binding(.., ident, _) = local.pat.kind;
then {
self.state = local.init.map_or(InitializeVisitorState::Declared(ident.name), |init| {
InitializeVisitorState::Initialized {
initializer: init,
name: ident.name,
}
})
}
}
walk_stmt(self, stmt);
}
fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
if matches!(self.state, InitializeVisitorState::DontWarn) {
return;
}
if expr.hir_id == self.end_expr.hir_id {
self.past_loop = true;
return;
}
// No need to visit expressions before the variable is
// declared
if matches!(self.state, InitializeVisitorState::Initial) {
return;
}
// If node is the desired variable, see how it's used
if path_to_local_id(expr, self.var_id) {
if self.past_loop {
self.state = InitializeVisitorState::DontWarn;
return;
}
if let Some(parent) = get_parent_expr(self.cx, expr) {
match parent.kind {
ExprKind::AssignOp(_, ref lhs, _) if lhs.hir_id == expr.hir_id => {
self.state = InitializeVisitorState::DontWarn;
},
ExprKind::Assign(ref lhs, ref rhs, _) if lhs.hir_id == expr.hir_id => {
self.state = if_chain! {
if self.depth == 0;
if let InitializeVisitorState::Declared(name)
| InitializeVisitorState::Initialized { name, ..} = self.state;
then {
InitializeVisitorState::Initialized { initializer: rhs, name }
} else {
InitializeVisitorState::DontWarn
}
}
},
ExprKind::AddrOf(BorrowKind::Ref, mutability, _) if mutability == Mutability::Mut => {
self.state = InitializeVisitorState::DontWarn
},
_ => (),
}
}
walk_expr(self, expr);
} else if !self.past_loop && is_loop(expr) {
self.state = InitializeVisitorState::DontWarn;
} else if is_conditional(expr) {
self.depth += 1;
walk_expr(self, expr);
self.depth -= 1;
} else {
walk_expr(self, expr);
}
}
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
}
}
fn is_loop(expr: &Expr<'_>) -> bool {
matches!(expr.kind, ExprKind::Loop(..))
}
fn is_conditional(expr: &Expr<'_>) -> bool {
matches!(expr.kind, ExprKind::If(..) | ExprKind::Match(..))
}
#[derive(PartialEq, Eq)]
pub(super) enum Nesting {
Unknown, // no nesting detected yet
RuledOut, // the iterator is initialized or assigned within scope
LookFurther, // no nesting detected, no further walk required
}
use self::Nesting::{LookFurther, RuledOut, Unknown};
pub(super) struct LoopNestVisitor {
pub(super) hir_id: HirId,
pub(super) iterator: HirId,
pub(super) nesting: Nesting,
}
impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
type Map = Map<'tcx>;
fn visit_stmt(&mut self, stmt: &'tcx Stmt<'_>) {
if stmt.hir_id == self.hir_id {
self.nesting = LookFurther;
} else if self.nesting == Unknown {
walk_stmt(self, stmt);
}
}
fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
if self.nesting != Unknown {
return;
}
if expr.hir_id == self.hir_id {
self.nesting = LookFurther;
return;
}
match expr.kind {
ExprKind::Assign(ref path, _, _) | ExprKind::AssignOp(_, ref path, _) => {
if path_to_local_id(path, self.iterator) {
self.nesting = RuledOut;
}
},
_ => walk_expr(self, expr),
}
}
fn visit_pat(&mut self, pat: &'tcx Pat<'_>) {
if self.nesting != Unknown {
return;
}
if let PatKind::Binding(_, id, ..) = pat.kind {
if id == self.iterator {
self.nesting = RuledOut;
return;
}
}
walk_pat(self, pat)
}
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
NestedVisitorMap::None
}
}
// this function assumes the given expression is a `for` loop.
pub(super) fn get_span_of_entire_for_loop(expr: &Expr<'_>) -> Span {
// for some reason this is the only way to get the `Span`
// of the entire `for` loop
if let ExprKind::Match(_, arms, _) = &expr.kind {
arms[0].body.span
} else {
unreachable!()
}
}
/// If `arg` was the argument to a `for` loop, return the "cleanest" way of writing the
/// actual `Iterator` that the loop uses.
pub(super) fn make_iterator_snippet(cx: &LateContext<'_>, arg: &Expr<'_>, applic_ref: &mut Applicability) -> String {
let impls_iterator = get_trait_def_id(cx, &paths::ITERATOR).map_or(false, |id| {
implements_trait(cx, cx.typeck_results().expr_ty(arg), id, &[])
});
if impls_iterator {
format!(
"{}",
sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
)
} else {
// (&x).into_iter() ==> x.iter()
// (&mut x).into_iter() ==> x.iter_mut()
match &arg.kind {
ExprKind::AddrOf(BorrowKind::Ref, mutability, arg_inner)
if has_iter_method(cx, cx.typeck_results().expr_ty(&arg_inner)).is_some() =>
{
let meth_name = match mutability {
Mutability::Mut => "iter_mut",
Mutability::Not => "iter",
};
format!(
"{}.{}()",
sugg::Sugg::hir_with_applicability(cx, &arg_inner, "_", applic_ref).maybe_par(),
meth_name,
)
}
_ => format!(
"{}.into_iter()",
sugg::Sugg::hir_with_applicability(cx, arg, "_", applic_ref).maybe_par()
),
}
}
}

139
clippy_lints/src/loops/while_immutable_condition.rs Normal file
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use super::WHILE_IMMUTABLE_CONDITION;
use crate::consts::constant;
use crate::utils::span_lint_and_then;
use crate::utils::usage::mutated_variables;
use if_chain::if_chain;
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_hir::def::{DefKind, Res};
use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
use rustc_hir::{def_id, Expr, ExprKind, HirId, QPath};
use rustc_lint::LateContext;
use rustc_middle::hir::map::Map;
use std::iter::Iterator;
pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, cond: &'tcx Expr<'_>, expr: &'tcx Expr<'_>) {
if constant(cx, cx.typeck_results(), cond).is_some() {
// A pure constant condition (e.g., `while false`) is not linted.
return;
}
let mut var_visitor = VarCollectorVisitor {
cx,
ids: FxHashSet::default(),
def_ids: FxHashMap::default(),
skip: false,
};
var_visitor.visit_expr(cond);
if var_visitor.skip {
return;
}
let used_in_condition = &var_visitor.ids;
let no_cond_variable_mutated = if let Some(used_mutably) = mutated_variables(expr, cx) {
used_in_condition.is_disjoint(&used_mutably)
} else {
return;
};
let mutable_static_in_cond = var_visitor.def_ids.iter().any(|(_, v)| *v);
let mut has_break_or_return_visitor = HasBreakOrReturnVisitor {
has_break_or_return: false,
};
has_break_or_return_visitor.visit_expr(expr);
let has_break_or_return = has_break_or_return_visitor.has_break_or_return;
if no_cond_variable_mutated && !mutable_static_in_cond {
span_lint_and_then(
cx,
WHILE_IMMUTABLE_CONDITION,
cond.span,
"variables in the condition are not mutated in the loop body",
|diag| {
diag.note("this may lead to an infinite or to a never running loop");
if has_break_or_return {
diag.note("this loop contains `return`s or `break`s");
diag.help("rewrite it as `if cond { loop { } }`");
}
},
);
}
}
struct HasBreakOrReturnVisitor {
has_break_or_return: bool,
}
impl<'tcx> Visitor<'tcx> for HasBreakOrReturnVisitor {
type Map = Map<'tcx>;
fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
if self.has_break_or_return {
return;
}
match expr.kind {
ExprKind::Ret(_) | ExprKind::Break(_, _) => {
self.has_break_or_return = true;
return;
},
_ => {},
}
walk_expr(self, expr);
}
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
NestedVisitorMap::None
}
}
/// Collects the set of variables in an expression
/// Stops analysis if a function call is found
/// Note: In some cases such as `self`, there are no mutable annotation,
/// All variables definition IDs are collected
struct VarCollectorVisitor<'a, 'tcx> {
cx: &'a LateContext<'tcx>,
ids: FxHashSet<HirId>,
def_ids: FxHashMap<def_id::DefId, bool>,
skip: bool,
}
impl<'a, 'tcx> VarCollectorVisitor<'a, 'tcx> {
fn insert_def_id(&mut self, ex: &'tcx Expr<'_>) {
if_chain! {
if let ExprKind::Path(ref qpath) = ex.kind;
if let QPath::Resolved(None, _) = *qpath;
let res = self.cx.qpath_res(qpath, ex.hir_id);
then {
match res {
Res::Local(hir_id) => {
self.ids.insert(hir_id);
},
Res::Def(DefKind::Static, def_id) => {
let mutable = self.cx.tcx.is_mutable_static(def_id);
self.def_ids.insert(def_id, mutable);
},
_ => {},
}
}
}
}
}
impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
type Map = Map<'tcx>;
fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
match ex.kind {
ExprKind::Path(_) => self.insert_def_id(ex),
// If there is any function/method call… we just stop analysis
ExprKind::Call(..) | ExprKind::MethodCall(..) => self.skip = true,
_ => walk_expr(self, ex),
}
}
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
NestedVisitorMap::None
}
}

87
clippy_lints/src/loops/while_let_loop.rs Normal file
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use super::WHILE_LET_LOOP;
use crate::utils::{snippet_with_applicability, span_lint_and_sugg};
use rustc_errors::Applicability;
use rustc_hir::{Block, Expr, ExprKind, MatchSource, StmtKind};
use rustc_lint::{LateContext, LintContext};
use rustc_middle::lint::in_external_macro;
pub(super) fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, loop_block: &'tcx Block<'_>) {
// extract the expression from the first statement (if any) in a block
let inner_stmt_expr = extract_expr_from_first_stmt(loop_block);
// or extract the first expression (if any) from the block
if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(loop_block)) {
if let ExprKind::Match(ref matchexpr, ref arms, ref source) = inner.kind {
// ensure "if let" compatible match structure
match *source {
MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
if arms.len() == 2
&& arms[0].guard.is_none()
&& arms[1].guard.is_none()
&& is_simple_break_expr(&arms[1].body)
{
if in_external_macro(cx.sess(), expr.span) {
return;
}
// NOTE: we used to build a body here instead of using
// ellipsis, this was removed because:
// 1) it was ugly with big bodies;
// 2) it was not indented properly;
// 3) it wasn’t very smart (see #675).
let mut applicability = Applicability::HasPlaceholders;
span_lint_and_sugg(
cx,
WHILE_LET_LOOP,
expr.span,
"this loop could be written as a `while let` loop",
"try",
format!(
"while let {} = {} {{ .. }}",
snippet_with_applicability(cx, arms[0].pat.span, "..", &mut applicability),
snippet_with_applicability(cx, matchexpr.span, "..", &mut applicability),
),
applicability,
);
}
},
_ => (),
}
}
}
}
/// If a block begins with a statement (possibly a `let` binding) and has an
/// expression, return it.
fn extract_expr_from_first_stmt<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
if block.stmts.is_empty() {
return None;
}
if let StmtKind::Local(ref local) = block.stmts[0].kind {
local.init //.map(|expr| expr)
} else {
None
}
}
/// If a block begins with an expression (with or without semicolon), return it.
fn extract_first_expr<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
match block.expr {
Some(ref expr) if block.stmts.is_empty() => Some(expr),
None if !block.stmts.is_empty() => match block.stmts[0].kind {
StmtKind::Expr(ref expr) | StmtKind::Semi(ref expr) => Some(expr),
StmtKind::Local(..) | StmtKind::Item(..) => None,
},
_ => None,
}
}
/// Returns `true` if expr contains a single break expr without destination label
/// and
/// passed expression. The expression may be within a block.
fn is_simple_break_expr(expr: &Expr<'_>) -> bool {
match expr.kind {
ExprKind::Break(dest, ref passed_expr) if dest.label.is_none() && passed_expr.is_none() => true,
ExprKind::Block(ref b, _) => extract_first_expr(b).map_or(false, |subexpr| is_simple_break_expr(subexpr)),
_ => false,
}
}

171
clippy_lints/src/loops/while_let_on_iterator.rs Normal file
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use super::utils::{LoopNestVisitor, Nesting};
use super::WHILE_LET_ON_ITERATOR;
use crate::utils::usage::mutated_variables;
use crate::utils::{
get_enclosing_block, get_trait_def_id, implements_trait, is_refutable, last_path_segment, match_trait_method,
path_to_local, path_to_local_id, paths, snippet_with_applicability, span_lint_and_sugg,
};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::intravisit::{walk_block, walk_expr, NestedVisitorMap, Visitor};
use rustc_hir::{Expr, ExprKind, HirId, MatchSource, Node, PatKind};
use rustc_lint::LateContext;
use rustc_middle::hir::map::Map;
use rustc_span::symbol::sym;
pub(super) fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
if let ExprKind::Match(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.kind {
let pat = &arms[0].pat.kind;
if let (
&PatKind::TupleStruct(ref qpath, ref pat_args, _),
&ExprKind::MethodCall(ref method_path, _, ref method_args, _),
) = (pat, &match_expr.kind)
{
let iter_expr = &method_args[0];
// Don't lint when the iterator is recreated on every iteration
if_chain! {
if let ExprKind::MethodCall(..) | ExprKind::Call(..) = iter_expr.kind;
if let Some(iter_def_id) = get_trait_def_id(cx, &paths::ITERATOR);
if implements_trait(cx, cx.typeck_results().expr_ty(iter_expr), iter_def_id, &[]);
then {
return;
}
}
let lhs_constructor = last_path_segment(qpath);
if method_path.ident.name == sym::next
&& match_trait_method(cx, match_expr, &paths::ITERATOR)
&& lhs_constructor.ident.name == sym::Some
&& (pat_args.is_empty()
|| !is_refutable(cx, &pat_args[0])
&& !is_used_inside(cx, iter_expr, &arms[0].body)
&& !is_iterator_used_after_while_let(cx, iter_expr)
&& !is_nested(cx, expr, &method_args[0]))
{
let mut applicability = Applicability::MachineApplicable;
let iterator = snippet_with_applicability(cx, method_args[0].span, "_", &mut applicability);
let loop_var = if pat_args.is_empty() {
"_".to_string()
} else {
snippet_with_applicability(cx, pat_args[0].span, "_", &mut applicability).into_owned()
};
span_lint_and_sugg(
cx,
WHILE_LET_ON_ITERATOR,
expr.span.with_hi(match_expr.span.hi()),
"this loop could be written as a `for` loop",
"try",
format!("for {} in {}", loop_var, iterator),
applicability,
);
}
}
}
}
fn is_used_inside<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, container: &'tcx Expr<'_>) -> bool {
let def_id = match path_to_local(expr) {
Some(id) => id,
None => return false,
};
if let Some(used_mutably) = mutated_variables(container, cx) {
if used_mutably.contains(&def_id) {
return true;
}
}
false
}
fn is_iterator_used_after_while_let<'tcx>(cx: &LateContext<'tcx>, iter_expr: &'tcx Expr<'_>) -> bool {
let def_id = match path_to_local(iter_expr) {
Some(id) => id,
None => return false,
};
let mut visitor = VarUsedAfterLoopVisitor {
def_id,
iter_expr_id: iter_expr.hir_id,
past_while_let: false,
var_used_after_while_let: false,
};
if let Some(enclosing_block) = get_enclosing_block(cx, def_id) {
walk_block(&mut visitor, enclosing_block);
}
visitor.var_used_after_while_let
}
fn is_nested(cx: &LateContext<'_>, match_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
if_chain! {
if let Some(loop_block) = get_enclosing_block(cx, match_expr.hir_id);
let parent_node = cx.tcx.hir().get_parent_node(loop_block.hir_id);
if let Some(Node::Expr(loop_expr)) = cx.tcx.hir().find(parent_node);
then {
return is_loop_nested(cx, loop_expr, iter_expr)
}
}
false
}
fn is_loop_nested(cx: &LateContext<'_>, loop_expr: &Expr<'_>, iter_expr: &Expr<'_>) -> bool {
let mut id = loop_expr.hir_id;
let iter_id = if let Some(id) = path_to_local(iter_expr) {
id
} else {
return true;
};
loop {
let parent = cx.tcx.hir().get_parent_node(id);
if parent == id {
return false;
}
match cx.tcx.hir().find(parent) {
Some(Node::Expr(expr)) => {
if let ExprKind::Loop(..) = expr.kind {
return true;
};
},
Some(Node::Block(block)) => {
let mut block_visitor = LoopNestVisitor {
hir_id: id,
iterator: iter_id,
nesting: Nesting::Unknown,
};
walk_block(&mut block_visitor, block);
if block_visitor.nesting == Nesting::RuledOut {
return false;
}
},
Some(Node::Stmt(_)) => (),
_ => {
return false;
},
}
id = parent;
}
}
struct VarUsedAfterLoopVisitor {
def_id: HirId,
iter_expr_id: HirId,
past_while_let: bool,
var_used_after_while_let: bool,
}
impl<'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor {
type Map = Map<'tcx>;
fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
if self.past_while_let {
if path_to_local_id(expr, self.def_id) {
self.var_used_after_while_let = true;
}
} else if self.iter_expr_id == expr.hir_id {
self.past_while_let = true;
}
walk_expr(self, expr);
}
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
NestedVisitorMap::None
}
}