rust/clippy_lints/src/ranges.rs

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use clippy_utils::consts::{constant, Constant};
use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg, span_lint_and_then};
use clippy_utils::source::{snippet, snippet_opt, snippet_with_applicability};
use clippy_utils::sugg::Sugg;
use clippy_utils::{get_parent_expr, in_constant, is_integer_const, meets_msrv, msrvs, single_segment_path};
use clippy_utils::{higher, SpanlessEq};
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use if_chain::if_chain;
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use rustc_ast::ast::RangeLimits;
use rustc_errors::Applicability;
use rustc_hir::{BinOpKind, Expr, ExprKind, PathSegment, QPath};
use rustc_lint::{LateContext, LateLintPass, LintContext};
use rustc_middle::ty;
use rustc_semver::RustcVersion;
use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::source_map::{Span, Spanned};
use rustc_span::sym;
use rustc_span::symbol::Ident;
use std::cmp::Ordering;
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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()`.
///
/// ### Example
/// ```rust
/// # let x = vec![1];
/// x.iter().zip(0..x.len());
/// ```
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/// Could be written as
/// ```rust
/// # let x = vec![1];
/// x.iter().enumerate();
/// ```
pub RANGE_ZIP_WITH_LEN,
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complexity,
"zipping iterator with a range when `enumerate()` would do"
}
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declare_clippy_lint! {
/// ### What it does
/// Checks for exclusive ranges where 1 is added to the
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/// 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
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/// expression is not wrapped in a pair but starts with an opening parenthesis
/// and ends with a closing one.
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/// I.e., `let _ = (f()+1)..(f()+1)` results in `let _ = ((f()+1)..=f())`.
///
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/// 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.
///
/// This will cause a warning that cannot be fixed if the consumer of the
/// range only accepts a specific range type, instead of the generic
/// `RangeBounds` trait
/// ([#3307](https://github.com/rust-lang/rust-clippy/issues/3307)).
///
/// ### Example
/// ```rust,ignore
/// for x..(y+1) { .. }
/// ```
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/// Could be written as
/// ```rust,ignore
/// for x..=y { .. }
/// ```
pub RANGE_PLUS_ONE,
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pedantic,
"`x..(y+1)` reads better as `x..=y`"
}
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declare_clippy_lint! {
/// ### What it does
/// Checks for inclusive ranges where 1 is subtracted from
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/// 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
/// This will cause a warning that cannot be fixed if
/// the consumer of the range only accepts a specific range type, instead of
/// the generic `RangeBounds` trait
/// ([#3307](https://github.com/rust-lang/rust-clippy/issues/3307)).
///
/// ### Example
/// ```rust,ignore
/// for x..=(y-1) { .. }
/// ```
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/// Could be written as
/// ```rust,ignore
/// for x..y { .. }
/// ```
pub RANGE_MINUS_ONE,
pedantic,
"`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.
///
/// ### 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_clippy_lint! {
/// ### What it does
/// Checks for expressions like `x >= 3 && x < 8` that could
/// be more readably expressed as `(3..8).contains(x)`.
///
/// ### Why is this bad?
/// `contains` expresses the intent better and has less
/// failure modes (such as fencepost errors or using `||` instead of `&&`).
///
/// ### Example
/// ```rust
/// // given
/// let x = 6;
///
/// assert!(x >= 3 && x < 8);
/// ```
/// Use instead:
/// ```rust
///# let x = 6;
/// assert!((3..8).contains(&x));
/// ```
pub MANUAL_RANGE_CONTAINS,
style,
"manually reimplementing {`Range`, `RangeInclusive`}`::contains`"
}
pub struct Ranges {
msrv: Option<RustcVersion>,
}
impl Ranges {
#[must_use]
pub fn new(msrv: Option<RustcVersion>) -> Self {
Self { msrv }
}
}
impl_lint_pass!(Ranges => [
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RANGE_ZIP_WITH_LEN,
RANGE_PLUS_ONE,
RANGE_MINUS_ONE,
REVERSED_EMPTY_RANGES,
MANUAL_RANGE_CONTAINS,
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]);
impl<'tcx> LateLintPass<'tcx> for Ranges {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
match expr.kind {
ExprKind::MethodCall(path, _, args, _) => {
check_range_zip_with_len(cx, path, args, expr.span);
},
ExprKind::Binary(ref op, l, r) => {
if meets_msrv(self.msrv.as_ref(), &msrvs::RANGE_CONTAINS) {
check_possible_range_contains(cx, op.node, l, r, expr);
}
},
_ => {},
}
check_exclusive_range_plus_one(cx, expr);
check_inclusive_range_minus_one(cx, expr);
check_reversed_empty_range(cx, expr);
}
extract_msrv_attr!(LateContext);
}
fn check_possible_range_contains(cx: &LateContext<'_>, op: BinOpKind, l: &Expr<'_>, r: &Expr<'_>, expr: &Expr<'_>) {
if in_constant(cx, expr.hir_id) {
return;
}
let span = expr.span;
let combine_and = match op {
BinOpKind::And | BinOpKind::BitAnd => true,
BinOpKind::Or | BinOpKind::BitOr => false,
_ => return,
};
// value, name, order (higher/lower), inclusiveness
if let (Some((lval, lname, name_span, lval_span, lord, linc)), Some((rval, rname, _, rval_span, rord, rinc))) =
(check_range_bounds(cx, l), check_range_bounds(cx, r))
{
// we only lint comparisons on the same name and with different
// direction
if lname != rname || lord == rord {
return;
}
let ord = Constant::partial_cmp(cx.tcx, cx.typeck_results().expr_ty(l), &lval, &rval);
if combine_and && ord == Some(rord) {
// order lower bound and upper bound
let (l_span, u_span, l_inc, u_inc) = if rord == Ordering::Less {
(lval_span, rval_span, linc, rinc)
} else {
(rval_span, lval_span, rinc, linc)
};
// we only lint inclusive lower bounds
if !l_inc {
return;
}
let (range_type, range_op) = if u_inc {
("RangeInclusive", "..=")
} else {
("Range", "..")
};
let mut applicability = Applicability::MachineApplicable;
let name = snippet_with_applicability(cx, name_span, "_", &mut applicability);
let lo = snippet_with_applicability(cx, l_span, "_", &mut applicability);
let hi = snippet_with_applicability(cx, u_span, "_", &mut applicability);
let space = if lo.ends_with('.') { " " } else { "" };
span_lint_and_sugg(
cx,
MANUAL_RANGE_CONTAINS,
span,
&format!("manual `{}::contains` implementation", range_type),
"use",
format!("({}{}{}{}).contains(&{})", lo, space, range_op, hi, name),
applicability,
);
} else if !combine_and && ord == Some(lord) {
// `!_.contains(_)`
// order lower bound and upper bound
let (l_span, u_span, l_inc, u_inc) = if lord == Ordering::Less {
(lval_span, rval_span, linc, rinc)
} else {
(rval_span, lval_span, rinc, linc)
};
if l_inc {
return;
}
let (range_type, range_op) = if u_inc {
("Range", "..")
} else {
("RangeInclusive", "..=")
};
let mut applicability = Applicability::MachineApplicable;
let name = snippet_with_applicability(cx, name_span, "_", &mut applicability);
let lo = snippet_with_applicability(cx, l_span, "_", &mut applicability);
let hi = snippet_with_applicability(cx, u_span, "_", &mut applicability);
let space = if lo.ends_with('.') { " " } else { "" };
span_lint_and_sugg(
cx,
MANUAL_RANGE_CONTAINS,
span,
&format!("manual `!{}::contains` implementation", range_type),
"use",
format!("!({}{}{}{}).contains(&{})", lo, space, range_op, hi, name),
applicability,
);
}
}
}
fn check_range_bounds(cx: &LateContext<'_>, ex: &Expr<'_>) -> Option<(Constant, Ident, Span, Span, Ordering, bool)> {
if let ExprKind::Binary(ref op, l, r) = ex.kind {
let (inclusive, ordering) = match op.node {
BinOpKind::Gt => (false, Ordering::Greater),
BinOpKind::Ge => (true, Ordering::Greater),
BinOpKind::Lt => (false, Ordering::Less),
BinOpKind::Le => (true, Ordering::Less),
_ => return None,
};
if let Some(id) = match_ident(l) {
if let Some((c, _)) = constant(cx, cx.typeck_results(), r) {
return Some((c, id, l.span, r.span, ordering, inclusive));
}
} else if let Some(id) = match_ident(r) {
if let Some((c, _)) = constant(cx, cx.typeck_results(), l) {
return Some((c, id, r.span, l.span, ordering.reverse(), inclusive));
}
}
}
None
}
fn match_ident(e: &Expr<'_>) -> Option<Ident> {
if let ExprKind::Path(ref qpath) = e.kind {
if let Some(seg) = single_segment_path(qpath) {
if seg.args.is_none() {
return Some(seg.ident);
}
}
}
None
}
fn check_range_zip_with_len(cx: &LateContext<'_>, path: &PathSegment<'_>, args: &[Expr<'_>], span: Span) {
if_chain! {
if path.ident.as_str() == "zip";
if let [iter, zip_arg] = args;
// `.iter()` call
if let ExprKind::MethodCall(iter_path, _, iter_args, _) = iter.kind;
if iter_path.ident.name == sym::iter;
// range expression in `.zip()` call: `0..x.len()`
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if let Some(higher::Range { start: Some(start), end: Some(end), .. }) = higher::Range::hir(zip_arg);
if is_integer_const(cx, start, 0);
// `.len()` call
if let ExprKind::MethodCall(len_path, _, 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(_, iter_path)) = iter_args[0].kind;
if let ExprKind::Path(QPath::Resolved(_, len_path)) = len_args[0].kind;
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if SpanlessEq::new(cx).eq_path_segments(&iter_path.segments, &len_path.segments);
then {
span_lint(cx,
RANGE_ZIP_WITH_LEN,
span,
&format!("it is more idiomatic to use `{}.iter().enumerate()`",
snippet(cx, iter_args[0].span, "_"))
);
}
}
}
// 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
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}) = higher::Range::hir(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! {
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if let Some(higher::Range { start, end: Some(end), limits: RangeLimits::Closed }) = higher::Range::hir(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_for_loop_arg(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
let mut cur_expr = expr;
while let Some(parent_expr) = get_parent_expr(cx, cur_expr) {
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match higher::ForLoop::hir(parent_expr) {
Some(higher::ForLoop { arg, .. }) if arg.hir_id == expr.hir_id => return true,
_ => cur_expr = parent_expr,
}
}
false
}
fn is_empty_range(limits: RangeLimits, ordering: Ordering) -> bool {
match limits {
RangeLimits::HalfOpen => ordering != Ordering::Less,
RangeLimits::Closed => ordering == Ordering::Greater,
}
}
if_chain! {
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if let Some(higher::Range { start: Some(start), end: Some(end), limits }) = higher::Range::hir(expr);
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let ty = cx.typeck_results().expr_ty(start);
if let ty::Int(_) | ty::Uint(_) = ty.kind();
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if let Some((start_idx, _)) = constant(cx, cx.typeck_results(), start);
if let Some((end_idx, _)) = constant(cx, cx.typeck_results(), 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) {
// Avoid linting `N..N` as it has proven to be useful, see #5689 and #5628 ...
if ordering != Ordering::Equal {
span_lint(
cx,
REVERSED_EMPTY_RANGES,
expr.span,
"this range is reversed and using it to index a slice will panic at run-time",
);
}
// ... except in for loop arguments for backwards compatibility with `reverse_range_loop`
} else if ordering != Ordering::Equal || is_for_loop_arg(cx, expr) {
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>> {
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match expr.kind {
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ExprKind::Binary(
Spanned {
node: BinOpKind::Add, ..
},
lhs,
rhs,
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) => {
if is_integer_const(cx, lhs, 1) {
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Some(rhs)
} else if is_integer_const(cx, rhs, 1) {
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Some(lhs)
} else {
None
}
},
_ => None,
}
}
fn y_minus_one<'t>(cx: &LateContext<'_>, expr: &'t Expr<'_>) -> Option<&'t Expr<'t>> {
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match expr.kind {
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ExprKind::Binary(
Spanned {
node: BinOpKind::Sub, ..
},
lhs,
rhs,
) if is_integer_const(cx, rhs, 1) => Some(lhs),
_ => None,
}
}