rust-clippy/clippy_lints/src/ranges.rs

345 lines
12 KiB
Rust

use crate::consts::{constant, Constant};
use if_chain::if_chain;
use rustc_ast::ast::RangeLimits;
use rustc_errors::Applicability;
use rustc_hir::{BinOpKind, Expr, ExprKind, QPath};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty;
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Spanned;
use std::cmp::Ordering;
use crate::utils::sugg::Sugg;
use crate::utils::{get_parent_expr, is_integer_const, snippet, snippet_opt, span_lint, span_lint_and_then};
use crate::utils::{higher, SpanlessEq};
declare_clippy_lint! {
/// **What it does:** Checks for zipping a collection with the range of
/// `0.._.len()`.
///
/// **Why is this bad?** The code is better expressed with `.enumerate()`.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// # let x = vec![1];
/// x.iter().zip(0..x.len());
/// ```
/// Could be written as
/// ```rust
/// # let x = vec![1];
/// x.iter().enumerate();
/// ```
pub RANGE_ZIP_WITH_LEN,
complexity,
"zipping iterator with a range when `enumerate()` would do"
}
declare_clippy_lint! {
/// **What it does:** Checks for exclusive ranges where 1 is added to the
/// upper bound, e.g., `x..(y+1)`.
///
/// **Why is this bad?** The code is more readable with an inclusive range
/// like `x..=y`.
///
/// **Known problems:** Will add unnecessary pair of parentheses when the
/// expression is not wrapped in a pair but starts with a opening parenthesis
/// and ends with a closing one.
/// I.e., `let _ = (f()+1)..(f()+1)` results in `let _ = ((f()+1)..=f())`.
///
/// Also in many cases, inclusive ranges are still slower to run than
/// exclusive ranges, because they essentially add an extra branch that
/// LLVM may fail to hoist out of the loop.
///
/// **Example:**
/// ```rust,ignore
/// for x..(y+1) { .. }
/// ```
/// Could be written as
/// ```rust,ignore
/// for x..=y { .. }
/// ```
pub RANGE_PLUS_ONE,
pedantic,
"`x..(y+1)` reads better as `x..=y`"
}
declare_clippy_lint! {
/// **What it does:** Checks for inclusive ranges where 1 is subtracted from
/// the upper bound, e.g., `x..=(y-1)`.
///
/// **Why is this bad?** The code is more readable with an exclusive range
/// like `x..y`.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust,ignore
/// for x..=(y-1) { .. }
/// ```
/// Could be written as
/// ```rust,ignore
/// for x..y { .. }
/// ```
pub RANGE_MINUS_ONE,
complexity,
"`x..=(y-1)` reads better as `x..y`"
}
declare_clippy_lint! {
/// **What it does:** Checks for range expressions `x..y` where both `x` and `y`
/// are constant and `x` is greater or equal to `y`.
///
/// **Why is this bad?** Empty ranges yield no values so iterating them is a no-op.
/// Moreover, trying to use a reversed range to index a slice will panic at run-time.
///
/// **Known problems:** None.
///
/// **Example:**
///
/// ```rust,no_run
/// fn main() {
/// (10..=0).for_each(|x| println!("{}", x));
///
/// let arr = [1, 2, 3, 4, 5];
/// let sub = &arr[3..1];
/// }
/// ```
/// Use instead:
/// ```rust
/// fn main() {
/// (0..=10).rev().for_each(|x| println!("{}", x));
///
/// let arr = [1, 2, 3, 4, 5];
/// let sub = &arr[1..3];
/// }
/// ```
pub REVERSED_EMPTY_RANGES,
correctness,
"reversing the limits of range expressions, resulting in empty ranges"
}
declare_lint_pass!(Ranges => [
RANGE_ZIP_WITH_LEN,
RANGE_PLUS_ONE,
RANGE_MINUS_ONE,
REVERSED_EMPTY_RANGES,
]);
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Ranges {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
if let ExprKind::MethodCall(ref path, _, ref args) = expr.kind {
let name = path.ident.as_str();
if name == "zip" && args.len() == 2 {
let iter = &args[0].kind;
let zip_arg = &args[1];
if_chain! {
// `.iter()` call
if let ExprKind::MethodCall(ref iter_path, _, ref iter_args ) = *iter;
if iter_path.ident.name == sym!(iter);
// range expression in `.zip()` call: `0..x.len()`
if let Some(higher::Range { start: Some(start), end: Some(end), .. }) = higher::range(cx, zip_arg);
if is_integer_const(cx, start, 0);
// `.len()` call
if let ExprKind::MethodCall(ref len_path, _, ref len_args) = end.kind;
if len_path.ident.name == sym!(len) && len_args.len() == 1;
// `.iter()` and `.len()` called on same `Path`
if let ExprKind::Path(QPath::Resolved(_, ref iter_path)) = iter_args[0].kind;
if let ExprKind::Path(QPath::Resolved(_, ref len_path)) = len_args[0].kind;
if SpanlessEq::new(cx).eq_path_segments(&iter_path.segments, &len_path.segments);
then {
span_lint(cx,
RANGE_ZIP_WITH_LEN,
expr.span,
&format!("It is more idiomatic to use `{}.iter().enumerate()`",
snippet(cx, iter_args[0].span, "_")));
}
}
}
}
check_exclusive_range_plus_one(cx, expr);
check_inclusive_range_minus_one(cx, expr);
check_reversed_empty_range(cx, expr);
}
}
// exclusive range plus one: `x..(y+1)`
fn check_exclusive_range_plus_one(cx: &LateContext<'_, '_>, expr: &Expr<'_>) {
if_chain! {
if let Some(higher::Range {
start,
end: Some(end),
limits: RangeLimits::HalfOpen
}) = higher::range(cx, expr);
if let Some(y) = y_plus_one(cx, end);
then {
let span = if expr.span.from_expansion() {
expr.span
.ctxt()
.outer_expn_data()
.call_site
} else {
expr.span
};
span_lint_and_then(
cx,
RANGE_PLUS_ONE,
span,
"an inclusive range would be more readable",
|diag| {
let start = start.map_or(String::new(), |x| Sugg::hir(cx, x, "x").to_string());
let end = Sugg::hir(cx, y, "y");
if let Some(is_wrapped) = &snippet_opt(cx, span) {
if is_wrapped.starts_with('(') && is_wrapped.ends_with(')') {
diag.span_suggestion(
span,
"use",
format!("({}..={})", start, end),
Applicability::MaybeIncorrect,
);
} else {
diag.span_suggestion(
span,
"use",
format!("{}..={}", start, end),
Applicability::MachineApplicable, // snippet
);
}
}
},
);
}
}
}
// inclusive range minus one: `x..=(y-1)`
fn check_inclusive_range_minus_one(cx: &LateContext<'_, '_>, expr: &Expr<'_>) {
if_chain! {
if let Some(higher::Range { start, end: Some(end), limits: RangeLimits::Closed }) = higher::range(cx, expr);
if let Some(y) = y_minus_one(cx, end);
then {
span_lint_and_then(
cx,
RANGE_MINUS_ONE,
expr.span,
"an exclusive range would be more readable",
|diag| {
let start = start.map_or(String::new(), |x| Sugg::hir(cx, x, "x").to_string());
let end = Sugg::hir(cx, y, "y");
diag.span_suggestion(
expr.span,
"use",
format!("{}..{}", start, end),
Applicability::MachineApplicable, // snippet
);
},
);
}
}
}
fn check_reversed_empty_range(cx: &LateContext<'_, '_>, expr: &Expr<'_>) {
fn inside_indexing_expr(cx: &LateContext<'_, '_>, expr: &Expr<'_>) -> bool {
matches!(
get_parent_expr(cx, expr),
Some(Expr {
kind: ExprKind::Index(..),
..
})
)
}
fn is_empty_range(limits: RangeLimits, ordering: Ordering) -> bool {
match limits {
RangeLimits::HalfOpen => ordering != Ordering::Less,
RangeLimits::Closed => ordering == Ordering::Greater,
}
}
if_chain! {
if let Some(higher::Range { start: Some(start), end: Some(end), limits }) = higher::range(cx, expr);
let ty = cx.tables.expr_ty(start);
if let ty::Int(_) | ty::Uint(_) = ty.kind;
if let Some((start_idx, _)) = constant(cx, cx.tables, start);
if let Some((end_idx, _)) = constant(cx, cx.tables, end);
if let Some(ordering) = Constant::partial_cmp(cx.tcx, ty, &start_idx, &end_idx);
if is_empty_range(limits, ordering);
then {
if inside_indexing_expr(cx, expr) {
let (reason, outcome) = if ordering == Ordering::Equal {
("empty", "always yield an empty slice")
} else {
("reversed", "panic at run-time")
};
span_lint(
cx,
REVERSED_EMPTY_RANGES,
expr.span,
&format!("this range is {} and using it to index a slice will {}", reason, outcome),
);
} else {
span_lint_and_then(
cx,
REVERSED_EMPTY_RANGES,
expr.span,
"this range is empty so it will yield no values",
|diag| {
if ordering != Ordering::Equal {
let start_snippet = snippet(cx, start.span, "_");
let end_snippet = snippet(cx, end.span, "_");
let dots = match limits {
RangeLimits::HalfOpen => "..",
RangeLimits::Closed => "..="
};
diag.span_suggestion(
expr.span,
"consider using the following if you are attempting to iterate over this \
range in reverse",
format!("({}{}{}).rev()", end_snippet, dots, start_snippet),
Applicability::MaybeIncorrect,
);
}
},
);
}
}
}
}
fn y_plus_one<'t>(cx: &LateContext<'_, '_>, expr: &'t Expr<'_>) -> Option<&'t Expr<'t>> {
match expr.kind {
ExprKind::Binary(
Spanned {
node: BinOpKind::Add, ..
},
ref lhs,
ref rhs,
) => {
if is_integer_const(cx, lhs, 1) {
Some(rhs)
} else if is_integer_const(cx, rhs, 1) {
Some(lhs)
} else {
None
}
},
_ => None,
}
}
fn y_minus_one<'t>(cx: &LateContext<'_, '_>, expr: &'t Expr<'_>) -> Option<&'t Expr<'t>> {
match expr.kind {
ExprKind::Binary(
Spanned {
node: BinOpKind::Sub, ..
},
ref lhs,
ref rhs,
) if is_integer_const(cx, rhs, 1) => Some(lhs),
_ => None,
}
}