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rust-clippy/clippy_lints/src/loops.rs

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use itertools::Itertools;
use reexport::*;
use rustc::hir::*;
use rustc::hir::def::Def;
use rustc::hir::def_id::DefId;
use rustc::hir::intravisit::{walk_block, walk_decl, walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor};
use rustc::hir::map::Node::{NodeBlock, NodeExpr, NodeStmt};
use rustc::lint::*;
use rustc::middle::const_val::ConstVal;
use rustc::middle::region;
use rustc::ty::{self, Ty};
use rustc::ty::subst::{Subst, Substs};
use rustc_const_eval::ConstContext;
use std::collections::{HashMap, HashSet};
use syntax::ast;
use utils::sugg;
use utils::{get_enclosing_block, get_parent_expr, higher, in_external_macro, is_integer_literal, is_refutable,
last_path_segment, match_trait_method, match_type, multispan_sugg, snippet, snippet_opt,
span_help_and_lint, span_lint, span_lint_and_sugg, span_lint_and_then};
use utils::paths;
/// **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
/// for i in 0..src.len() {
/// dst[i + 64] = src[i];
/// }
/// ```
declare_lint! {
pub MANUAL_MEMCPY,
Warn,
"manually copying items between slices"
}
/// **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
/// for i in 0..vec.len() {
/// println!("{}", vec[i]);
/// }
/// ```
declare_lint! {
pub NEEDLESS_RANGE_LOOP,
Warn,
"for-looping over a range of indices where an iterator over items would do"
}
/// **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:
/// for x in y.iter() { .. }
/// ```
declare_lint! {
pub EXPLICIT_ITER_LOOP,
Warn,
"for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do"
}
/// **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
/// // with `y` a `Vec` or slice:
/// for x in y.into_iter() { .. }
/// ```
declare_lint! {
pub EXPLICIT_INTO_ITER_LOOP,
Warn,
"for-looping over `_.into_iter()` when `_` would do"
}
/// **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:**
/// ```rust
/// for x in y.next() { .. }
/// ```
declare_lint! {
pub ITER_NEXT_LOOP,
Warn,
"for-looping over `_.next()` which is probably not intended"
}
/// **What it does:** Checks for `for` loops over `Option` values.
///
/// **Why is this bad?** Readability. This is more clearly expressed as an `if
/// let`.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// for x in option { .. }
/// ```
///
/// This should be
/// ```rust
/// if let Some(x) = option { .. }
/// ```
declare_lint! {
pub FOR_LOOP_OVER_OPTION,
Warn,
"for-looping over an `Option`, which is more clearly expressed as an `if let`"
}
/// **What it does:** Checks for `for` loops over `Result` values.
///
/// **Why is this bad?** Readability. This is more clearly expressed as an `if
/// let`.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// for x in result { .. }
/// ```
///
/// This should be
/// ```rust
/// if let Ok(x) = result { .. }
/// ```
declare_lint! {
pub FOR_LOOP_OVER_RESULT,
Warn,
"for-looping over a `Result`, which is more clearly expressed as an `if let`"
}
/// **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).
///
/// **Example:**
/// ```rust
/// 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
/// }
/// ```
declare_lint! {
pub WHILE_LET_LOOP,
Warn,
"`loop { if let { ... } else break }`, which can be written as a `while let` loop"
}
/// **What it does:** Checks for using `collect()` on an iterator without using
/// the result.
///
/// **Why is this bad?** It is more idiomatic to use a `for` loop over the
/// iterator instead.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// vec.iter().map(|x| /* some operation returning () */).collect::<Vec<_>>();
/// ```
declare_lint! {
pub UNUSED_COLLECT,
Warn,
"`collect()`ing an iterator without using the result; this is usually better \
written as a for loop"
}
/// **What it does:** Checks for loops over ranges `x..y` where both `x` and `y`
/// are constant and `x` is greater or equal to `y`, unless the range is
/// reversed or has a negative `.step_by(_)`.
///
/// **Why is it bad?** Such loops will either be skipped or loop until
/// wrap-around (in debug code, this may `panic!()`). Both options are probably
/// not intended.
///
/// **Known problems:** The lint cannot catch loops over dynamically defined
/// ranges. Doing this would require simulating all possible inputs and code
/// paths through the program, which would be complex and error-prone.
///
/// **Example:**
/// ```rust
/// for x in 5..10-5 { .. } // oops, stray `-`
/// ```
declare_lint! {
pub REVERSE_RANGE_LOOP,
Warn,
"iteration over an empty range, such as `10..0` or `5..5`"
}
/// **What it does:** Checks `for` loops over slices with an explicit counter
/// and suggests the use of `.enumerate()`.
///
/// **Why is it bad?** Not only is the version using `.enumerate()` more
/// readable, the compiler is able to remove bounds checks which can lead to
/// faster code in some instances.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// for i in 0..v.len() { foo(v[i]);
/// for i in 0..v.len() { bar(i, v[i]); }
/// ```
declare_lint! {
pub EXPLICIT_COUNTER_LOOP,
Warn,
"for-looping with an explicit counter when `_.enumerate()` would do"
}
/// **What it does:** Checks for empty `loop` expressions.
///
/// **Why is this bad?** Those busy loops burn CPU cycles without doing
/// anything. Think of the environment and either block on something or at least
/// make the thread sleep for some microseconds.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// loop {}
/// ```
declare_lint! {
pub EMPTY_LOOP,
Warn,
"empty `loop {}`, which should block or sleep"
}
/// **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:**
/// ```rust
/// while let Some(val) = iter() { .. }
/// ```
declare_lint! {
pub WHILE_LET_ON_ITERATOR,
Warn,
"using a while-let loop instead of a for loop on an iterator"
}
/// **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:**
/// ```rust
/// for (k, _) in &map { .. }
/// ```
///
/// could be replaced by
///
/// ```rust
/// for k in map.keys() { .. }
/// ```
declare_lint! {
pub FOR_KV_MAP,
Warn,
"looping on a map using `iter` when `keys` or `values` would do"
}
/// **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; }
/// ```
declare_lint! {
pub NEVER_LOOP,
Warn,
"any loop that will always `break` or `return`"
}
#[derive(Copy, Clone)]
pub struct Pass;
impl LintPass for Pass {
fn get_lints(&self) -> LintArray {
lint_array!(
MANUAL_MEMCPY,
NEEDLESS_RANGE_LOOP,
EXPLICIT_ITER_LOOP,
EXPLICIT_INTO_ITER_LOOP,
ITER_NEXT_LOOP,
FOR_LOOP_OVER_RESULT,
FOR_LOOP_OVER_OPTION,
WHILE_LET_LOOP,
UNUSED_COLLECT,
REVERSE_RANGE_LOOP,
EXPLICIT_COUNTER_LOOP,
EMPTY_LOOP,
WHILE_LET_ON_ITERATOR,
FOR_KV_MAP,
NEVER_LOOP
)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
if let Some((pat, arg, body)) = higher::for_loop(expr) {
check_for_loop(cx, pat, arg, body, expr);
}
// check for never_loop
match expr.node {
ExprWhile(_, ref block, _) | ExprLoop(ref block, _, _) => if never_loop(block, &expr.id) {
span_lint(cx, NEVER_LOOP, expr.span, "this loop never actually loops");
},
_ => (),
}
// 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 ExprLoop(ref block, _, LoopSource::Loop) = expr.node {
// also check for empty `loop {}` statements
if block.stmts.is_empty() && block.expr.is_none() {
span_lint(
cx,
EMPTY_LOOP,
expr.span,
"empty `loop {}` detected. You may want to either use `panic!()` or add \
`std::thread::sleep(..);` to the loop body.",
);
}
// extract the expression from the first statement (if any) in a block
let inner_stmt_expr = extract_expr_from_first_stmt(block);
// or extract the first expression (if any) from the block
if let Some(inner) = inner_stmt_expr.or_else(|| extract_first_expr(block)) {
if let ExprMatch(ref matchexpr, ref arms, ref source) = inner.node {
// ensure "if let" compatible match structure
match *source {
MatchSource::Normal | MatchSource::IfLetDesugar { .. } => {
if arms.len() == 2 && arms[0].pats.len() == 1 && arms[0].guard.is_none() &&
arms[1].pats.len() == 1 && arms[1].guard.is_none() &&
is_simple_break_expr(&arms[1].body)
{
if in_external_macro(cx, expr.span) {
return;
}
// NOTE: we used to make 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).
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(cx, arms[0].pats[0].span, ".."),
snippet(cx, matchexpr.span, "..")
),
);
}
},
_ => (),
}
}
}
}
if let ExprMatch(ref match_expr, ref arms, MatchSource::WhileLetDesugar) = expr.node {
let pat = &arms[0].pats[0].node;
if let (
&PatKind::TupleStruct(ref qpath, ref pat_args, _),
&ExprMethodCall(ref method_path, _, ref method_args),
) = (pat, &match_expr.node)
{
let iter_expr = &method_args[0];
let lhs_constructor = last_path_segment(qpath);
if method_path.name == "next" && match_trait_method(cx, match_expr, &paths::ITERATOR) &&
lhs_constructor.name == "Some" && !is_refutable(cx, &pat_args[0]) &&
!is_iterator_used_after_while_let(cx, iter_expr) &&
!is_nested(cx, expr, &method_args[0])
{
let iterator = snippet(cx, method_args[0].span, "_");
let loop_var = snippet(cx, pat_args[0].span, "_");
span_lint_and_sugg(
cx,
WHILE_LET_ON_ITERATOR,
expr.span,
"this loop could be written as a `for` loop",
"try",
format!("for {} in {} {{ .. }}", loop_var, iterator),
);
}
}
}
}
fn check_stmt(&mut self, cx: &LateContext<'a, 'tcx>, stmt: &'tcx Stmt) {
if let StmtSemi(ref expr, _) = stmt.node {
if let ExprMethodCall(ref method, _, ref args) = expr.node {
if args.len() == 1 && method.name == "collect" && match_trait_method(cx, expr, &paths::ITERATOR) {
span_lint(
cx,
UNUSED_COLLECT,
expr.span,
"you are collect()ing an iterator and throwing away the result. \
Consider using an explicit for loop to exhaust the iterator",
);
}
}
}
}
}
fn never_loop(block: &Block, id: &NodeId) -> bool {
!contains_continue_block(block, id) && loop_exit_block(block)
}
fn contains_continue_block(block: &Block, dest: &NodeId) -> bool {
block.stmts.iter().any(|e| contains_continue_stmt(e, dest)) ||
block
.expr
.as_ref()
.map_or(false, |e| contains_continue_expr(e, dest))
}
fn contains_continue_stmt(stmt: &Stmt, dest: &NodeId) -> bool {
match stmt.node {
StmtSemi(ref e, _) | StmtExpr(ref e, _) => contains_continue_expr(e, dest),
StmtDecl(ref d, _) => contains_continue_decl(d, dest),
}
}
fn contains_continue_decl(decl: &Decl, dest: &NodeId) -> bool {
match decl.node {
DeclLocal(ref local) => local
.init
.as_ref()
.map_or(false, |e| contains_continue_expr(e, dest)),
_ => false,
}
}
fn contains_continue_expr(expr: &Expr, dest: &NodeId) -> bool {
match expr.node {
ExprRet(Some(ref e)) |
ExprBox(ref e) |
ExprUnary(_, ref e) |
ExprCast(ref e, _) |
ExprType(ref e, _) |
ExprField(ref e, _) |
ExprTupField(ref e, _) |
ExprAddrOf(_, ref e) |
ExprRepeat(ref e, _) => contains_continue_expr(e, dest),
ExprArray(ref es) | ExprMethodCall(_, _, ref es) | ExprTup(ref es) => {
es.iter().any(|e| contains_continue_expr(e, dest))
},
ExprCall(ref e, ref es) => {
contains_continue_expr(e, dest) || es.iter().any(|e| contains_continue_expr(e, dest))
},
ExprBinary(_, ref e1, ref e2) |
ExprAssign(ref e1, ref e2) |
ExprAssignOp(_, ref e1, ref e2) |
ExprIndex(ref e1, ref e2) => [e1, e2].iter().any(|e| contains_continue_expr(e, dest)),
ExprIf(ref e, ref e2, ref e3) => [e, e2]
.iter()
.chain(e3.as_ref().iter())
.any(|e| contains_continue_expr(e, dest)),
ExprWhile(ref e, ref b, _) => contains_continue_expr(e, dest) || contains_continue_block(b, dest),
ExprMatch(ref e, ref arms, _) => {
contains_continue_expr(e, dest) || arms.iter().any(|a| contains_continue_expr(&a.body, dest))
},
ExprBlock(ref block) => contains_continue_block(block, dest),
ExprStruct(_, _, ref base) => base.as_ref()
.map_or(false, |e| contains_continue_expr(e, dest)),
ExprAgain(d) => d.target_id.opt_id().map_or(false, |id| id == *dest),
_ => false,
}
}
fn loop_exit_block(block: &Block) -> bool {
block.stmts.iter().any(|e| loop_exit_stmt(e)) || block.expr.as_ref().map_or(false, |e| loop_exit_expr(e))
}
fn loop_exit_stmt(stmt: &Stmt) -> bool {
match stmt.node {
StmtSemi(ref e, _) | StmtExpr(ref e, _) => loop_exit_expr(e),
StmtDecl(ref d, _) => loop_exit_decl(d),
}
}
fn loop_exit_decl(decl: &Decl) -> bool {
match decl.node {
DeclLocal(ref local) => local.init.as_ref().map_or(false, |e| loop_exit_expr(e)),
_ => false,
}
}
fn loop_exit_expr(expr: &Expr) -> bool {
match expr.node {
ExprBox(ref e) |
ExprUnary(_, ref e) |
ExprCast(ref e, _) |
ExprType(ref e, _) |
ExprField(ref e, _) |
ExprTupField(ref e, _) |
ExprAddrOf(_, ref e) |
ExprRepeat(ref e, _) => loop_exit_expr(e),
ExprArray(ref es) | ExprMethodCall(_, _, ref es) | ExprTup(ref es) => es.iter().any(|e| loop_exit_expr(e)),
ExprCall(ref e, ref es) => loop_exit_expr(e) || es.iter().any(|e| loop_exit_expr(e)),
ExprBinary(_, ref e1, ref e2) |
ExprAssign(ref e1, ref e2) |
ExprAssignOp(_, ref e1, ref e2) |
ExprIndex(ref e1, ref e2) => [e1, e2].iter().any(|e| loop_exit_expr(e)),
ExprIf(ref e, ref e2, ref e3) => {
loop_exit_expr(e) || e3.as_ref().map_or(false, |e| loop_exit_expr(e)) && loop_exit_expr(e2)
},
ExprWhile(ref e, ref b, _) => loop_exit_expr(e) || loop_exit_block(b),
ExprMatch(ref e, ref arms, _) => loop_exit_expr(e) || arms.iter().all(|a| loop_exit_expr(&a.body)),
ExprBlock(ref b) => loop_exit_block(b),
ExprBreak(_, _) | ExprAgain(_) | ExprRet(_) => true,
_ => false,
}
}
fn check_for_loop<'a, 'tcx>(
cx: &LateContext<'a, 'tcx>,
pat: &'tcx Pat,
arg: &'tcx Expr,
body: &'tcx Expr,
expr: &'tcx Expr,
) {
check_for_loop_range(cx, pat, arg, body, expr);
check_for_loop_reverse_range(cx, arg, expr);
check_for_loop_arg(cx, pat, arg, expr);
check_for_loop_explicit_counter(cx, arg, body, expr);
check_for_loop_over_map_kv(cx, pat, arg, body, expr);
detect_manual_memcpy(cx, pat, arg, body, expr);
}
fn same_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: DefId) -> bool {
if_let_chain! {[
let ExprPath(ref qpath) = expr.node,
let QPath::Resolved(None, ref path) = *qpath,
path.segments.len() == 1,
// our variable!
cx.tables.qpath_def(qpath, expr.hir_id).def_id() == var
], {
return true;
}}
false
}
struct Offset {
value: String,
negate: bool,
}
impl Offset {
fn negative(s: String) -> Self {
Self {
value: s,
negate: true,
}
}
fn positive(s: String) -> Self {
Self {
value: s,
negate: false,
}
}
}
struct FixedOffsetVar {
var_name: String,
offset: Offset,
}
fn is_slice_like<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: Ty) -> bool {
let is_slice = match ty.sty {
ty::TyRef(_, ref subty) => is_slice_like(cx, subty.ty),
ty::TySlice(..) | ty::TyArray(..) => true,
_ => false,
};
is_slice || match_type(cx, ty, &paths::VEC) || match_type(cx, ty, &paths::VEC_DEQUE)
}
fn get_fixed_offset_var<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &Expr, var: DefId) -> Option<FixedOffsetVar> {
fn extract_offset<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, e: &Expr, var: DefId) -> Option<String> {
match e.node {
ExprLit(ref l) => match l.node {
ast::LitKind::Int(x, _ty) => Some(x.to_string()),
_ => None,
},
ExprPath(..) if !same_var(cx, e, var) => Some(snippet_opt(cx, e.span).unwrap_or_else(|| "??".into())),
_ => None,
}
}
if let ExprIndex(ref seqexpr, ref idx) = expr.node {
let ty = cx.tables.expr_ty(seqexpr);
if !is_slice_like(cx, ty) {
return None;
}
let offset = match idx.node {
ExprBinary(op, ref lhs, ref rhs) => match op.node {
BinOp_::BiAdd => {
let offset_opt = if same_var(cx, lhs, var) {
extract_offset(cx, rhs, var)
} else if same_var(cx, rhs, var) {
extract_offset(cx, lhs, var)
} else {
None
};
offset_opt.map(Offset::positive)
},
BinOp_::BiSub if same_var(cx, lhs, var) => extract_offset(cx, rhs, var).map(Offset::negative),
_ => None,
},
ExprPath(..) => if same_var(cx, idx, var) {
Some(Offset::positive("0".into()))
} else {
None
},
_ => None,
};
offset.map(|o| {
FixedOffsetVar {
var_name: snippet_opt(cx, seqexpr.span).unwrap_or_else(|| "???".into()),
offset: o,
}
})
} else {
None
}
}
fn get_indexed_assignments<'a, 'tcx>(
cx: &LateContext<'a, 'tcx>,
body: &Expr,
var: DefId,
) -> Vec<(FixedOffsetVar, FixedOffsetVar)> {
fn get_assignment<'a, 'tcx>(
cx: &LateContext<'a, 'tcx>,
e: &Expr,
var: DefId,
) -> Option<(FixedOffsetVar, FixedOffsetVar)> {
if let Expr_::ExprAssign(ref lhs, ref rhs) = e.node {
match (get_fixed_offset_var(cx, lhs, var), get_fixed_offset_var(cx, rhs, var)) {
(Some(offset_left), Some(offset_right)) => Some((offset_left, offset_right)),
_ => None,
}
} else {
None
}
}
if let Expr_::ExprBlock(ref b) = body.node {
let Block {
ref stmts,
ref expr,
..
} = **b;
stmts
.iter()
.map(|stmt| match stmt.node {
Stmt_::StmtDecl(..) => None,
Stmt_::StmtExpr(ref e, _node_id) | Stmt_::StmtSemi(ref e, _node_id) => Some(get_assignment(cx, e, var)),
})
.chain(
expr.as_ref()
.into_iter()
.map(|e| Some(get_assignment(cx, &*e, var))),
)
.filter_map(|op| op)
.collect::<Option<Vec<_>>>()
.unwrap_or_else(|| vec![])
} else {
get_assignment(cx, body, var).into_iter().collect()
}
}
/// Check for for loops that sequentially copy items from one slice-like
/// object to another.
fn detect_manual_memcpy<'a, 'tcx>(
cx: &LateContext<'a, '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(_, def_id, _, _) = pat.node {
let print_sum = |arg1: &Offset, arg2: &Offset| -> String {
match (&arg1.value[..], arg1.negate, &arg2.value[..], arg2.negate) {
("0", _, "0", _) => "".into(),
("0", _, x, false) | (x, false, "0", false) => x.into(),
("0", _, x, true) | (x, false, "0", true) => format!("-{}", x),
(x, false, y, false) => format!("({} + {})", x, y),
(x, false, y, true) => format!("({} - {})", x, y),
(x, true, y, false) => format!("({} - {})", y, x),
(x, true, y, true) => format!("-({} + {})", x, y),
}
};
let print_limit = |end: &Option<&Expr>, offset: Offset, var_name: &str| if let Some(end) = *end {
if_let_chain! {[
let ExprMethodCall(ref method, _, ref len_args) = end.node,
method.name == "len",
len_args.len() == 1,
let Some(arg) = len_args.get(0),
snippet(cx, arg.span, "??") == var_name,
], {
return if offset.negate {
format!("({} - {})", snippet(cx, end.span, "<src>.len()"), offset.value)
} else {
"".to_owned()
};
}}
let end_str = match limits {
ast::RangeLimits::Closed => {
let end = sugg::Sugg::hir(cx, end, "<count>");
format!("{}", end + sugg::ONE)
},
ast::RangeLimits::HalfOpen => format!("{}", snippet(cx, end.span, "..")),
};
print_sum(&Offset::positive(end_str), &offset)
} else {
"..".into()
};
// The only statements in the for loops can be indexed assignments from
// indexed retrievals.
let manual_copies = get_indexed_assignments(cx, body, def_id);
let big_sugg = manual_copies
.into_iter()
.map(|(dst_var, src_var)| {
let start_str = Offset::positive(snippet_opt(cx, start.span).unwrap_or_else(|| "".into()));
let dst_offset = print_sum(&start_str, &dst_var.offset);
let dst_limit = print_limit(end, dst_var.offset, &dst_var.var_name);
let src_offset = print_sum(&start_str, &src_var.offset);
let src_limit = print_limit(end, src_var.offset, &src_var.var_name);
let dst = if dst_offset == "" && dst_limit == "" {
dst_var.var_name
} else {
format!("{}[{}..{}]", dst_var.var_name, dst_offset, dst_limit)
};
format!("{}.clone_from_slice(&{}[{}..{}])", dst, src_var.var_name, src_offset, src_limit)
})
.join("\n ");
if !big_sugg.is_empty() {
span_lint_and_sugg(
cx,
MANUAL_MEMCPY,
expr.span,
"it looks like you're manually copying between slices",
"try replacing the loop by",
big_sugg,
);
}
}
}
}
/// Check for looping over a range and then indexing a sequence with it.
/// The iteratee must be a range literal.
fn check_for_loop_range<'a, 'tcx>(
cx: &LateContext<'a, '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(_, def_id, ref ident, _) = pat.node {
let mut visitor = VarVisitor {
cx: cx,
var: def_id,
indexed: HashMap::new(),
referenced: HashSet::new(),
nonindex: false,
};
walk_expr(&mut visitor, body);
// linting condition: we only indexed one variable
if visitor.indexed.len() == 1 {
let (indexed, indexed_extent) = visitor
.indexed
.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(expr.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 into is also used without
// indexing
if visitor.referenced.contains(&indexed) {
return;
}
let starts_at_zero = is_integer_literal(start, 0);
let skip = if starts_at_zero {
"".to_owned()
} else {
format!(".skip({})", snippet(cx, start.span, ".."))
};
let take = if let Some(end) = *end {
if is_len_call(end, &indexed) {
"".to_owned()
} else {
match limits {
ast::RangeLimits::Closed => {
let end = sugg::Sugg::hir(cx, end, "<count>");
format!(".take({})", end + sugg::ONE)
},
ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, end.span, "..")),
}
}
} else {
"".to_owned()
};
if visitor.nonindex {
span_lint_and_then(
cx,
NEEDLESS_RANGE_LOOP,
expr.span,
&format!("the loop variable `{}` is used to index `{}`", ident.node, indexed),
|db| {
multispan_sugg(
db,
"consider using an iterator".to_string(),
vec![
(pat.span, format!("({}, <item>)", ident.node)),
(arg.span, format!("{}.iter().enumerate(){}{}", indexed, take, skip)),
],
);
},
);
} else {
let repl = if starts_at_zero && take.is_empty() {
format!("&{}", indexed)
} else {
format!("{}.iter(){}{}", indexed, take, skip)
};
span_lint_and_then(
cx,
NEEDLESS_RANGE_LOOP,
expr.span,
&format!("the loop variable `{}` is only used to index `{}`.", ident.node, indexed),
|db| {
multispan_sugg(
db,
"consider using an iterator".to_string(),
vec![(pat.span, "<item>".to_string()), (arg.span, repl)],
);
},
);
}
}
}
}
}
fn is_len_call(expr: &Expr, var: &Name) -> bool {
if_let_chain! {[
let ExprMethodCall(ref method, _, ref len_args) = expr.node,
len_args.len() == 1,
method.name == "len",
let ExprPath(QPath::Resolved(_, ref path)) = len_args[0].node,
path.segments.len() == 1,
path.segments[0].name == *var
], {
return true;
}}
false
}
fn check_for_loop_reverse_range(cx: &LateContext, arg: &Expr, expr: &Expr) {
// if this for loop is iterating over a two-sided range...
if let Some(higher::Range {
start: Some(start),
end: Some(end),
limits,
}) = higher::range(arg)
{
// ...and both sides are compile-time constant integers...
let parent_item = cx.tcx.hir.get_parent(arg.id);
let parent_def_id = cx.tcx.hir.local_def_id(parent_item);
let substs = Substs::identity_for_item(cx.tcx, parent_def_id);
let constcx = ConstContext::new(cx.tcx, cx.param_env.and(substs), cx.tables);
if let Ok(start_idx) = constcx.eval(start) {
if let Ok(end_idx) = constcx.eval(end) {
// ...and the start index is greater than the end index,
// this loop will never run. This is often confusing for developers
// who think that this will iterate from the larger value to the
// smaller value.
let (sup, eq) = match (start_idx, end_idx) {
(ConstVal::Integral(start_idx), ConstVal::Integral(end_idx)) => {
(start_idx > end_idx, start_idx == end_idx)
},
_ => (false, false),
};
if sup {
let start_snippet = snippet(cx, start.span, "_");
let end_snippet = snippet(cx, end.span, "_");
let dots = if limits == ast::RangeLimits::Closed {
"..."
} else {
".."
};
span_lint_and_then(
cx,
REVERSE_RANGE_LOOP,
expr.span,
"this range is empty so this for loop will never run",
|db| {
db.span_suggestion(
arg.span,
"consider using the following if you are attempting to iterate over this \
range in reverse",
format!(
"({end}{dots}{start}).rev()",
end = end_snippet,
dots = dots,
start = start_snippet
),
);
},
);
} else if eq && limits != ast::RangeLimits::Closed {
// if they are equal, it's also problematic - this loop
// will never run.
span_lint(
cx,
REVERSE_RANGE_LOOP,
expr.span,
"this range is empty so this for loop will never run",
);
}
}
}
}
}
fn lint_iter_method(cx: &LateContext, args: &[Expr], arg: &Expr, method_name: &str) {
let object = snippet(cx, args[0].span, "_");
let muta = if method_name == "iter_mut" {
"mut "
} else {
""
};
span_lint_and_sugg(
cx,
EXPLICIT_ITER_LOOP,
arg.span,
"it is more idiomatic to loop over references to containers instead of using explicit \
iteration methods",
"to write this more concisely, try",
format!("&{}{}", muta, object),
)
}
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 ExprMethodCall(ref method, _, ref args) = arg.node {
// just the receiver, no arguments
if args.len() == 1 {
let method_name = &*method.name.as_str();
// check for looping over x.iter() or x.iter_mut(), could use &x or &mut x
if method_name == "iter" || method_name == "iter_mut" {
if is_ref_iterable_type(cx, &args[0]) {
lint_iter_method(cx, args, arg, method_name);
}
} else if method_name == "into_iter" && match_trait_method(cx, arg, &paths::INTO_ITERATOR) {
let def_id = cx.tables.type_dependent_defs()[arg.hir_id].def_id();
let substs = cx.tables.node_substs(arg.hir_id);
let method_type = cx.tcx.type_of(def_id).subst(cx.tcx, substs);
let fn_arg_tys = method_type.fn_sig(cx.tcx).inputs();
assert_eq!(fn_arg_tys.skip_binder().len(), 1);
if fn_arg_tys.skip_binder()[0].is_region_ptr() {
lint_iter_method(cx, args, arg, method_name);
} else {
let object = snippet(cx, args[0].span, "_");
span_lint_and_sugg(
cx,
EXPLICIT_INTO_ITER_LOOP,
arg.span,
"it is more idiomatic to loop over containers instead of using explicit \
iteration methods`",
"to write this more concisely, try",
object.to_string(),
);
}
} else if method_name == "next" && 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",
);
next_loop_linted = true;
}
}
}
if !next_loop_linted {
check_arg_type(cx, pat, arg);
}
}
/// Check for `for` loops over `Option`s and `Results`
fn check_arg_type(cx: &LateContext, pat: &Pat, arg: &Expr) {
let ty = cx.tables.expr_ty(arg);
if match_type(cx, ty, &paths::OPTION) {
span_help_and_lint(
cx,
FOR_LOOP_OVER_OPTION,
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, "_")
),
&format!(
"consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
snippet(cx, pat.span, "_"),
snippet(cx, arg.span, "_")
),
);
} else if match_type(cx, ty, &paths::RESULT) {
span_help_and_lint(
cx,
FOR_LOOP_OVER_RESULT,
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, "_")
),
&format!(
"consider replacing `for {0} in {1}` with `if let Ok({0}) = {1}`",
snippet(cx, pat.span, "_"),
snippet(cx, arg.span, "_")
),
);
}
}
fn check_for_loop_explicit_counter<'a, 'tcx>(
cx: &LateContext<'a, 'tcx>,
arg: &'tcx Expr,
body: &'tcx Expr,
expr: &'tcx Expr,
) {
// Look for variables that are incremented once per loop iteration.
let mut visitor = IncrementVisitor {
cx: cx,
states: HashMap::new(),
depth: 0,
done: false,
};
walk_expr(&mut visitor, body);
// For each candidate, check the parent block to see if
// it's initialized to zero at the start of the loop.
let map = &cx.tcx.hir;
let parent_scope = map.get_enclosing_scope(expr.id)
.and_then(|id| map.get_enclosing_scope(id));
if let Some(parent_id) = parent_scope {
if let NodeBlock(block) = map.get(parent_id) {
for (id, _) in visitor
.states
.iter()
.filter(|&(_, v)| *v == VarState::IncrOnce)
{
let mut visitor2 = InitializeVisitor {
cx: cx,
end_expr: expr,
var_id: *id,
state: VarState::IncrOnce,
name: None,
depth: 0,
past_loop: false,
};
walk_block(&mut visitor2, block);
if visitor2.state == VarState::Warn {
if let Some(name) = visitor2.name {
span_lint(
cx,
EXPLICIT_COUNTER_LOOP,
expr.span,
&format!(
"the variable `{0}` is used as a loop counter. Consider using `for ({0}, \
item) in {1}.enumerate()` or similar iterators",
name,
snippet(cx, arg.span, "_")
),
);
}
}
}
}
}
}
/// Check for the `FOR_KV_MAP` lint.
fn check_for_loop_over_map_kv<'a, 'tcx>(
cx: &LateContext<'a, '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.node {
if pat.len() == 2 {
let arg_span = arg.span;
let (new_pat_span, kind, ty, mutbl) = match cx.tables.expr_ty(arg).sty {
ty::TyRef(_, ref tam) => match (&pat[0].node, &pat[1].node) {
(key, _) if pat_is_wild(key, body) => (pat[1].span, "value", tam.ty, tam.mutbl),
(_, value) if pat_is_wild(value, body) => (pat[0].span, "key", tam.ty, MutImmutable),
_ => return,
},
_ => return,
};
let mutbl = match mutbl {
MutImmutable => "",
MutMutable => "_mut",
};
let arg = match arg.node {
ExprAddrOf(_, ref expr) => &**expr,
_ => arg,
};
if match_type(cx, ty, &paths::HASHMAP) || 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),
|db| {
let map = sugg::Sugg::hir(cx, arg, "map");
multispan_sugg(
db,
"use the corresponding method".into(),
vec![
(pat_span, snippet(cx, new_pat_span, kind).into_owned()),
(arg_span, format!("{}.{}s{}()", map.maybe_par(), kind, mutbl)),
],
);
},
);
}
}
}
}
/// Return true if the pattern is a `PatWild` or an ident prefixed with `'_'`.
fn pat_is_wild<'tcx>(pat: &'tcx PatKind, body: &'tcx Expr) -> bool {
match *pat {
PatKind::Wild => true,
PatKind::Binding(_, _, ident, None) if ident.node.as_str().starts_with('_') => {
let mut visitor = UsedVisitor {
var: ident.node,
used: false,
};
walk_expr(&mut visitor, body);
!visitor.used
},
_ => false,
}
}
fn match_var(expr: &Expr, var: Name) -> bool {
if let ExprPath(QPath::Resolved(None, ref path)) = expr.node {
if path.segments.len() == 1 && path.segments[0].name == var {
return true;
}
}
false
}
struct UsedVisitor {
var: ast::Name, // var to look for
used: bool, // has the var been used otherwise?
}
impl<'tcx> Visitor<'tcx> for UsedVisitor {
fn visit_expr(&mut self, expr: &'tcx Expr) {
if match_var(expr, self.var) {
self.used = true;
} else {
walk_expr(self, expr);
}
}
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
NestedVisitorMap::None
}
}
struct DefIdUsedVisitor<'a, 'tcx: 'a> {
cx: &'a LateContext<'a, 'tcx>,
def_id: DefId,
used: bool,
}
impl<'a, 'tcx: 'a> Visitor<'tcx> for DefIdUsedVisitor<'a, 'tcx> {
fn visit_expr(&mut self, expr: &'tcx Expr) {
if same_var(self.cx, expr, self.def_id) {
self.used = true;
} else {
walk_expr(self, expr);
}
}
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
NestedVisitorMap::None
}
}
struct VarVisitor<'a, 'tcx: 'a> {
/// context reference
cx: &'a LateContext<'a, 'tcx>,
/// var name to look for as index
var: DefId,
/// indexed variables, the extend is `None` for global
indexed: HashMap<Name, Option<region::Scope>>,
/// Any names that are used outside an index operation.
/// Used to detect things like `&mut vec` used together with `vec[i]`
referenced: HashSet<Name>,
/// has the loop variable been used in expressions other than the index of
/// an index op?
nonindex: bool,
}
impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
fn visit_expr(&mut self, expr: &'tcx Expr) {
if_let_chain! {[
// an index op
let ExprIndex(ref seqexpr, ref idx) = expr.node,
// the indexed container is referenced by a name
let ExprPath(ref seqpath) = seqexpr.node,
let QPath::Resolved(None, ref seqvar) = *seqpath,
seqvar.segments.len() == 1,
], {
let index_used = same_var(self.cx, idx, self.var) || {
let mut used_visitor = DefIdUsedVisitor {
cx: self.cx,
def_id: self.var,
used: false,
};
walk_expr(&mut used_visitor, idx);
used_visitor.used
};
if index_used {
let def = self.cx.tables.qpath_def(seqpath, seqexpr.hir_id);
match def {
Def::Local(..) | Def::Upvar(..) => {
let def_id = def.def_id();
let node_id = self.cx.tcx.hir.as_local_node_id(def_id).expect("local/upvar are local nodes");
let hir_id = self.cx.tcx.hir.node_to_hir_id(node_id);
let parent_id = self.cx.tcx.hir.get_parent(expr.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);
self.indexed.insert(seqvar.segments[0].name, Some(extent));
return; // no need to walk further *on the variable*
}
Def::Static(..) | Def::Const(..) => {
self.indexed.insert(seqvar.segments[0].name, None);
return; // no need to walk further *on the variable*
}
_ => (),
}
}
}}
if_let_chain! {[
// directly using a variable
let ExprPath(ref qpath) = expr.node,
let QPath::Resolved(None, ref path) = *qpath,
path.segments.len() == 1,
], {
if self.cx.tables.qpath_def(qpath, expr.hir_id).def_id() == self.var {
// we are not indexing anything, record that
self.nonindex = true;
} else {
// not the correct variable, but still a variable
self.referenced.insert(path.segments[0].name);
}
}}
walk_expr(self, expr);
}
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
NestedVisitorMap::None
}
}
fn is_iterator_used_after_while_let<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, iter_expr: &'tcx Expr) -> bool {
let def_id = match var_def_id(cx, iter_expr) {
Some(id) => id,
None => return false,
};
let mut visitor = VarUsedAfterLoopVisitor {
cx: cx,
def_id: def_id,
iter_expr_id: iter_expr.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
}
struct VarUsedAfterLoopVisitor<'a, 'tcx: 'a> {
cx: &'a LateContext<'a, 'tcx>,
def_id: NodeId,
iter_expr_id: NodeId,
past_while_let: bool,
var_used_after_while_let: bool,
}
impl<'a, 'tcx> Visitor<'tcx> for VarUsedAfterLoopVisitor<'a, 'tcx> {
fn visit_expr(&mut self, expr: &'tcx Expr) {
if self.past_while_let {
if Some(self.def_id) == var_def_id(self.cx, expr) {
self.var_used_after_while_let = true;
}
} else if self.iter_expr_id == expr.id {
self.past_while_let = true;
}
walk_expr(self, expr);
}
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
NestedVisitorMap::None
}
}
/// Return true if the type of expr is one that provides `IntoIterator` impls
/// for `&T` and `&mut T`, such as `Vec`.
#[cfg_attr(rustfmt, 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.tables.expr_ty(e);
is_iterable_array(ty) ||
match_type(cx, ty, &paths::VEC) ||
match_type(cx, ty, &paths::LINKED_LIST) ||
match_type(cx, ty, &paths::HASHMAP) ||
match_type(cx, ty, &paths::HASHSET) ||
match_type(cx, ty, &paths::VEC_DEQUE) ||
match_type(cx, ty, &paths::BINARY_HEAP) ||
match_type(cx, ty, &paths::BTREEMAP) ||
match_type(cx, ty, &paths::BTREESET)
}
fn is_iterable_array(ty: Ty) -> bool {
// IntoIterator is currently only implemented for array sizes <= 32 in rustc
match ty.sty {
ty::TyArray(_, 0...32) => true,
_ => false,
}
}
/// If a block begins with a statement (possibly a `let` binding) and has an
/// expression, return it.
fn extract_expr_from_first_stmt(block: &Block) -> Option<&Expr> {
if block.stmts.is_empty() {
return None;
}
if let StmtDecl(ref decl, _) = block.stmts[0].node {
if let DeclLocal(ref local) = decl.node {
if let Some(ref expr) = local.init {
Some(expr)
} else {
None
}
} else {
None
}
} else {
None
}
}
/// If a block begins with an expression (with or without semicolon), return it.
fn extract_first_expr(block: &Block) -> Option<&Expr> {
match block.expr {
Some(ref expr) if block.stmts.is_empty() => Some(expr),
None if !block.stmts.is_empty() => match block.stmts[0].node {
StmtExpr(ref expr, _) | StmtSemi(ref expr, _) => Some(expr),
StmtDecl(..) => None,
},
_ => None,
}
}
/// Return 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.node {
ExprBreak(dest, ref passed_expr) if dest.ident.is_none() && passed_expr.is_none() => true,
ExprBlock(ref b) => {
match extract_first_expr(b) {
Some(subexpr) => is_simple_break_expr(subexpr),
None => false,
}
},
_ => false,
}
}
// 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.
#[derive(PartialEq)]
enum VarState {
Initial, // Not examined yet
IncrOnce, // Incremented exactly once, may be a loop counter
Declared, // Declared but not (yet) initialized to zero
Warn,
DontWarn,
}
/// Scan a for loop for variables that are incremented exactly once.
struct IncrementVisitor<'a, 'tcx: 'a> {
cx: &'a LateContext<'a, 'tcx>, // context reference
states: HashMap<NodeId, VarState>, // incremented variables
depth: u32, // depth of conditional expressions
done: bool,
}
impl<'a, 'tcx> Visitor<'tcx> for IncrementVisitor<'a, 'tcx> {
fn visit_expr(&mut self, expr: &'tcx Expr) {
if self.done {
return;
}
// If node is a variable
if let Some(def_id) = var_def_id(self.cx, expr) {
if let Some(parent) = get_parent_expr(self.cx, expr) {
let state = self.states.entry(def_id).or_insert(VarState::Initial);
match parent.node {
ExprAssignOp(op, ref lhs, ref rhs) => {
if lhs.id == expr.id {
if op.node == BiAdd && is_integer_literal(rhs, 1) {
*state = match *state {
VarState::Initial if self.depth == 0 => VarState::IncrOnce,
_ => VarState::DontWarn,
};
} else {
// Assigned some other value
*state = VarState::DontWarn;
}
}
},
ExprAssign(ref lhs, _) if lhs.id == expr.id => *state = VarState::DontWarn,
ExprAddrOf(mutability, _) if mutability == MutMutable => *state = VarState::DontWarn,
_ => (),
}
}
} else if is_loop(expr) {
self.states.clear();
self.done = true;
return;
} else if is_conditional(expr) {
self.depth += 1;
walk_expr(self, expr);
self.depth -= 1;
return;
}
walk_expr(self, expr);
}
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
NestedVisitorMap::None
}
}
/// Check whether a variable is initialized to zero at the start of a loop.
struct InitializeVisitor<'a, 'tcx: 'a> {
cx: &'a LateContext<'a, 'tcx>, // context reference
end_expr: &'tcx Expr, // the for loop. Stop scanning here.
var_id: NodeId,
state: VarState,
name: Option<Name>,
depth: u32, // depth of conditional expressions
past_loop: bool,
}
impl<'a, 'tcx> Visitor<'tcx> for InitializeVisitor<'a, 'tcx> {
fn visit_decl(&mut self, decl: &'tcx Decl) {
// Look for declarations of the variable
if let DeclLocal(ref local) = decl.node {
if local.pat.id == self.var_id {
if let PatKind::Binding(_, _, ref ident, _) = local.pat.node {
self.name = Some(ident.node);
self.state = if let Some(ref init) = local.init {
if is_integer_literal(init, 0) {
VarState::Warn
} else {
VarState::Declared
}
} else {
VarState::Declared
}
}
}
}
walk_decl(self, decl);
}
fn visit_expr(&mut self, expr: &'tcx Expr) {
if self.state == VarState::DontWarn {
return;
}
if expr == self.end_expr {
self.past_loop = true;
return;
}
// No need to visit expressions before the variable is
// declared
if self.state == VarState::IncrOnce {
return;
}
// If node is the desired variable, see how it's used
if var_def_id(self.cx, expr) == Some(self.var_id) {
if let Some(parent) = get_parent_expr(self.cx, expr) {
match parent.node {
ExprAssignOp(_, ref lhs, _) if lhs.id == expr.id => {
self.state = VarState::DontWarn;
},
ExprAssign(ref lhs, ref rhs) if lhs.id == expr.id => {
self.state = if is_integer_literal(rhs, 0) && self.depth == 0 {
VarState::Warn
} else {
VarState::DontWarn
}
},
ExprAddrOf(mutability, _) if mutability == MutMutable => self.state = VarState::DontWarn,
_ => (),
}
}
if self.past_loop {
self.state = VarState::DontWarn;
return;
}
} else if !self.past_loop && is_loop(expr) {
self.state = VarState::DontWarn;
return;
} else if is_conditional(expr) {
self.depth += 1;
walk_expr(self, expr);
self.depth -= 1;
return;
}
walk_expr(self, expr);
}
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
NestedVisitorMap::None
}
}
fn var_def_id(cx: &LateContext, expr: &Expr) -> Option<NodeId> {
if let ExprPath(ref qpath) = expr.node {
let path_res = cx.tables.qpath_def(qpath, expr.hir_id);
if let Def::Local(def_id) = path_res {
let node_id = cx.tcx
.hir
.as_local_node_id(def_id)
.expect("That DefId should be valid");
return Some(node_id);
}
}
None
}
fn is_loop(expr: &Expr) -> bool {
match expr.node {
ExprLoop(..) | ExprWhile(..) => true,
_ => false,
}
}
fn is_conditional(expr: &Expr) -> bool {
match expr.node {
ExprIf(..) | ExprMatch(..) => true,
_ => false,
}
}
fn is_nested(cx: &LateContext, match_expr: &Expr, iter_expr: &Expr) -> bool {
if_let_chain! {[
let Some(loop_block) = get_enclosing_block(cx, match_expr.id),
let Some(map::Node::NodeExpr(loop_expr)) = cx.tcx.hir.find(cx.tcx.hir.get_parent_node(loop_block.id)),
], {
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.id;
let iter_name = if let Some(name) = path_name(iter_expr) {
name
} 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(NodeExpr(expr)) => match expr.node {
ExprLoop(..) | ExprWhile(..) => {
return true;
},
_ => (),
},
Some(NodeBlock(block)) => {
let mut block_visitor = LoopNestVisitor {
id: id,
iterator: iter_name,
nesting: Unknown,
};
walk_block(&mut block_visitor, block);
if block_visitor.nesting == RuledOut {
return false;
}
},
Some(NodeStmt(_)) => (),
_ => {
return false;
},
}
id = parent;
}
}
#[derive(PartialEq, Eq)]
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};
struct LoopNestVisitor {
id: NodeId,
iterator: Name,
nesting: Nesting,
}
impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
fn visit_stmt(&mut self, stmt: &'tcx Stmt) {
if stmt.node.id() == self.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.id == self.id {
self.nesting = LookFurther;
return;
}
match expr.node {
ExprAssign(ref path, _) | ExprAssignOp(_, ref path, _) => if match_var(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(_, _, span_name, _) = pat.node {
if self.iterator == span_name.node {
self.nesting = RuledOut;
return;
}
}
walk_pat(self, pat)
}
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
NestedVisitorMap::None
}
}
fn path_name(e: &Expr) -> Option<Name> {
if let ExprPath(QPath::Resolved(_, ref path)) = e.node {
let segments = &path.segments;
if segments.len() == 1 {
return Some(segments[0].name);
}
};
None
}
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