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Auto merge of #7607 - dswij:mut-range-bound-break, r=flip1995

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`mut_range_bound` check for immediate break after mutation

closes #7532

`mut_range_bound` ignores mutation on range bounds that is placed immediately before break. Still warns if the break is not always reachable.

changelog: [`mut_range_bound`] ignore range bound mutations before immediate break
This commit is contained in:
bors 2021-09-08 08:14:17 +00:00
commit f35678401c
4 changed files with 158 additions and 41 deletions
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15
clippy_lints/src/loops/mod.rs
View File

@ -397,6 +397,21 @@ declare_clippy_lint! {
/// ### Why is this bad?
/// One might think that modifying the mutable variable changes the loop bounds
///
/// ### Known problems
/// False positive when mutation is followed by a `break`, but the `break` is not immediately
/// after the mutation:
///
/// ```rust
/// let mut x = 5;
/// for _ in 0..x {
/// x += 1; // x is a range bound that is mutated
/// ..; // some other expression
/// break; // leaves the loop, so mutation is not an issue
/// }
/// ```
///
/// False positive on nested loops ([#6072](https://github.com/rust-lang/rust-clippy/issues/6072))
///
/// ### Example
/// ```rust
/// let mut foo = 42;

98
clippy_lints/src/loops/mut_range_bound.rs
View File

@ -1,24 +1,27 @@
use super::MUT_RANGE_BOUND;
use clippy_utils::diagnostics::span_lint;
use clippy_utils::{higher, path_to_local};
use clippy_utils::diagnostics::span_lint_and_note;
use clippy_utils::{get_enclosing_block, higher, path_to_local};
use if_chain::if_chain;
use rustc_hir::{BindingAnnotation, Expr, HirId, Node, PatKind};
use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
use rustc_hir::{BindingAnnotation, Expr, ExprKind, HirId, Node, PatKind};
use rustc_infer::infer::TyCtxtInferExt;
use rustc_lint::LateContext;
use rustc_middle::hir::map::Map;
use rustc_middle::{mir::FakeReadCause, ty};
use rustc_span::source_map::Span;
use rustc_typeck::expr_use_visitor::{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::hir(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);
if_chain! {
if let Some(higher::Range {
start: Some(start),
end: Some(end),
..
}) = higher::Range::hir(arg);
let (mut_id_start, mut_id_end) = (check_for_mutability(cx, start), check_for_mutability(cx, end));
if mut_id_start.is_some() || mut_id_end.is_some();
then {
let (span_low, span_high) = check_for_mutation(cx, body, mut_id_start, mut_id_end);
mut_warn_with_span(cx, span_low);
mut_warn_with_span(cx, span_high);
}
@ -27,11 +30,13 @@ pub(super) fn check(cx: &LateContext<'_>, arg: &Expr<'_>, body: &Expr<'_>) {
fn mut_warn_with_span(cx: &LateContext<'_>, span: Option<Span>) {
if let Some(sp) = span {
span_lint(
span_lint_and_note(
cx,
MUT_RANGE_BOUND,
sp,
"attempt to mutate range bound within loop; note that the range of the loop is unchanged",
"attempt to mutate range bound within loop",
None,
"the range of the loop is unchanged",
);
}
}
@ -51,12 +56,13 @@ fn check_for_mutability(cx: &LateContext<'_>, bound: &Expr<'_>) -> Option<HirId>
fn check_for_mutation<'tcx>(
cx: &LateContext<'tcx>,
body: &Expr<'_>,
bound_ids: &[Option<HirId>],
bound_id_start: Option<HirId>,
bound_id_end: Option<HirId>,
) -> (Option<Span>, Option<Span>) {
let mut delegate = MutatePairDelegate {
cx,
hir_id_low: bound_ids[0],
hir_id_high: bound_ids[1],
hir_id_low: bound_id_start,
hir_id_high: bound_id_end,
span_low: None,
span_high: None,
};
@ -70,6 +76,7 @@ fn check_for_mutation<'tcx>(
)
.walk_expr(body);
});
delegate.mutation_span()
}
@ -87,10 +94,10 @@ impl<'tcx> Delegate<'tcx> for MutatePairDelegate<'_, 'tcx> {
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 {
if Some(id) == self.hir_id_low && !BreakAfterExprVisitor::is_found(self.cx, diag_expr_id) {
self.span_low = Some(self.cx.tcx.hir().span(diag_expr_id));
}
if Some(id) == self.hir_id_high {
if Some(id) == self.hir_id_high && !BreakAfterExprVisitor::is_found(self.cx, diag_expr_id) {
self.span_high = Some(self.cx.tcx.hir().span(diag_expr_id));
}
}
@ -99,10 +106,10 @@ impl<'tcx> Delegate<'tcx> for MutatePairDelegate<'_, 'tcx> {
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 {
if Some(id) == self.hir_id_low && !BreakAfterExprVisitor::is_found(self.cx, diag_expr_id) {
self.span_low = Some(self.cx.tcx.hir().span(diag_expr_id));
}
if Some(id) == self.hir_id_high {
if Some(id) == self.hir_id_high && !BreakAfterExprVisitor::is_found(self.cx, diag_expr_id) {
self.span_high = Some(self.cx.tcx.hir().span(diag_expr_id));
}
}
@ -116,3 +123,52 @@ impl MutatePairDelegate<'_, '_> {
(self.span_low, self.span_high)
}
}
struct BreakAfterExprVisitor {
hir_id: HirId,
past_expr: bool,
past_candidate: bool,
break_after_expr: bool,
}
impl BreakAfterExprVisitor {
pub fn is_found(cx: &LateContext<'_>, hir_id: HirId) -> bool {
let mut visitor = BreakAfterExprVisitor {
hir_id,
past_expr: false,
past_candidate: false,
break_after_expr: false,
};
get_enclosing_block(cx, hir_id).map_or(false, |block| {
visitor.visit_block(block);
visitor.break_after_expr
})
}
}
impl intravisit::Visitor<'tcx> for BreakAfterExprVisitor {
type Map = Map<'tcx>;
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
NestedVisitorMap::None
}
fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
if self.past_candidate {
return;
}
if expr.hir_id == self.hir_id {
self.past_expr = true;
} else if self.past_expr {
if matches!(&expr.kind, ExprKind::Break(..)) {
self.break_after_expr = true;
}
self.past_candidate = true;
} else {
intravisit::walk_expr(self, expr);
}
}
}

39
tests/ui/mut_range_bound.rs
View File

@ -1,14 +1,6 @@
#![allow(unused)]
fn main() {
mut_range_bound_upper();
mut_range_bound_lower();
mut_range_bound_both();
mut_range_bound_no_mutation();
immut_range_bound();
mut_borrow_range_bound();
immut_borrow_range_bound();
}
fn main() {}
fn mut_range_bound_upper() {
let mut m = 4;
@ -61,3 +53,32 @@ fn immut_range_bound() {
continue;
} // no warning
}
fn mut_range_bound_break() {
let mut m = 4;
for i in 0..m {
if m == 4 {
m = 5; // no warning because of immediate break
break;
}
}
}
fn mut_range_bound_no_immediate_break() {
let mut m = 4;
for i in 0..m {
m = 2; // warning because it is not immediately followed by break
if m == 4 {
break;
}
}
let mut n = 3;
for i in n..10 {
if n == 4 {
n = 1; // FIXME: warning because is is not immediately followed by break
let _ = 2;
break;
}
}
}

47
tests/ui/mut_range_bound.stderr
View File

@ -1,34 +1,59 @@
error: attempt to mutate range bound within loop; note that the range of the loop is unchanged
--> $DIR/mut_range_bound.rs:16:9
error: attempt to mutate range bound within loop
--> $DIR/mut_range_bound.rs:8:9
|
LL | m = 5;
| ^
|
= note: `-D clippy::mut-range-bound` implied by `-D warnings`
= note: the range of the loop is unchanged
error: attempt to mutate range bound within loop; note that the range of the loop is unchanged
--> $DIR/mut_range_bound.rs:23:9
error: attempt to mutate range bound within loop
--> $DIR/mut_range_bound.rs:15:9
|
LL | m *= 2;
| ^
|
= note: the range of the loop is unchanged
error: attempt to mutate range bound within loop; note that the range of the loop is unchanged
--> $DIR/mut_range_bound.rs:31:9
error: attempt to mutate range bound within loop
--> $DIR/mut_range_bound.rs:23:9
|
LL | m = 5;
| ^
|
= note: the range of the loop is unchanged
error: attempt to mutate range bound within loop; note that the range of the loop is unchanged
--> $DIR/mut_range_bound.rs:32:9
error: attempt to mutate range bound within loop
--> $DIR/mut_range_bound.rs:24:9
|
LL | n = 7;
| ^
|
= note: the range of the loop is unchanged
error: attempt to mutate range bound within loop; note that the range of the loop is unchanged
--> $DIR/mut_range_bound.rs:46:22
error: attempt to mutate range bound within loop
--> $DIR/mut_range_bound.rs:38:22
|
LL | let n = &mut m; // warning
| ^
|
= note: the range of the loop is unchanged
error: aborting due to 5 previous errors
error: attempt to mutate range bound within loop
--> $DIR/mut_range_bound.rs:70:9
|
LL | m = 2; // warning because it is not immediately followed by break
| ^
|
= note: the range of the loop is unchanged
error: attempt to mutate range bound within loop
--> $DIR/mut_range_bound.rs:79:13
|
LL | n = 1; // FIXME: warning because is is not immediately followed by break
| ^
|
= note: the range of the loop is unchanged
error: aborting due to 7 previous errors