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Show code suggestions in let_undescore lint messages.

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This commit uses `span_suggestion_verbose` to add what specific code
changes can be done as suggested by the lint--in this case, either binding
the expression to an unused variable or using `std::mem::drop` to drop
the value explicitly.
This commit is contained in:
Aaron Kofsky 2022-06-03 21:33:13 -04:00
parent ae2ac3b4c5
commit eba6c789dc
4 changed files with 79 additions and 21 deletions
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60
compiler/rustc_lint/src/let_underscore.rs
View File

@ -1,6 +1,10 @@
use crate::{LateContext, LateLintPass, LintContext};
use rustc_errors::Applicability;
use rustc_hir as hir;
use rustc_middle::ty::{self, subst::GenericArgKind, Ty};
use rustc_middle::{
lint::LintDiagnosticBuilder,
ty::{self, subst::GenericArgKind, Ty},
};
use rustc_span::Symbol;
declare_lint! {
@ -141,30 +145,60 @@ fn check_local(&mut self, cx: &LateContext<'_>, local: &hir::Local<'_>) {
});
let is_must_use_ty = is_must_use_ty(cx, cx.typeck_results().expr_ty(init));
let is_must_use_func_call = is_must_use_func_call(cx, init);
if is_sync_lock {
cx.struct_span_lint(LET_UNDERSCORE_LOCK, local.span, |lint| {
lint.build("non-binding let on a synchronization lock")
.help("consider binding to an unused variable")
.help("consider explicitly droping with `std::mem::drop`")
.emit();
build_and_emit_lint(
lint,
local,
init.span,
"non-binding let on a synchronization lock",
)
})
} else if is_must_use_ty || is_must_use_func_call {
cx.struct_span_lint(LET_UNDERSCORE_MUST_USE, local.span, |lint| {
lint.build("non-binding let on a expression marked `must_use`")
.help("consider binding to an unused variable")
.help("consider explicitly droping with `std::mem::drop`")
.emit();
build_and_emit_lint(
lint,
local,
init.span,
"non-binding let on a expression marked `must_use`",
);
})
} else if needs_drop {
cx.struct_span_lint(LET_UNDERSCORE_DROP, local.span, |lint| {
lint.build("non-binding let on a type that implements `Drop`")
.help("consider binding to an unused variable")
.help("consider explicitly droping with `std::mem::drop`")
.emit();
build_and_emit_lint(
lint,
local,
init.span,
"non-binding let on a type that implements `Drop`",
);
})
}
}
fn build_and_emit_lint(
lint: LintDiagnosticBuilder<'_, ()>,
local: &hir::Local<'_>,
init_span: rustc_span::Span,
msg: &str,
) {
lint.build(msg)
.span_suggestion_verbose(
local.pat.span,
"consider binding to an unused variable",
"_unused",
Applicability::MachineApplicable,
)
.span_suggestion_verbose(
init_span,
"consider explicitly droping with `std::mem::drop`",
"drop(...)",
Applicability::HasPlaceholders,
)
.emit();
}
// return true if `ty` is a type that is marked as `must_use`
fn is_must_use_ty<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
match ty.kind() {
ty::Adt(adt, _) => has_must_use_attr(cx, adt.did()),

10
src/test/ui/let_underscore/let_underscore_drop.stderr
View File

@ -5,8 +5,14 @@ LL | let _ = NontrivialDrop;
| ^^^^^^^^^^^^^^^^^^^^^^^
|
= note: requested on the command line with `-W let-underscore-drop`
= help: consider binding to an unused variable
= help: consider explicitly droping with `std::mem::drop`
help: consider binding to an unused variable
|
LL | let _unused = NontrivialDrop;
| ~~~~~~~
help: consider explicitly droping with `std::mem::drop`
|
LL | let _ = drop(...);
| ~~~~~~~~~
warning: 1 warning emitted

10
src/test/ui/let_underscore/let_underscore_lock.stderr
View File

@ -5,8 +5,14 @@ LL | let _ = data.lock().unwrap();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: `#[warn(let_underscore_lock)]` on by default
= help: consider binding to an unused variable
= help: consider explicitly droping with `std::mem::drop`
help: consider binding to an unused variable
|
LL | let _unused = data.lock().unwrap();
| ~~~~~~~
help: consider explicitly droping with `std::mem::drop`
|
LL | let _ = drop(...);
| ~~~~~~~~~
warning: 1 warning emitted

20
src/test/ui/let_underscore/let_underscore_must_use.stderr
View File

@ -5,8 +5,14 @@ LL | let _ = MustUseType;
| ^^^^^^^^^^^^^^^^^^^^
|
= note: requested on the command line with `-W let-underscore-must-use`
= help: consider binding to an unused variable
= help: consider explicitly droping with `std::mem::drop`
help: consider binding to an unused variable
|
LL | let _unused = MustUseType;
| ~~~~~~~
help: consider explicitly droping with `std::mem::drop`
|
LL | let _ = drop(...);
| ~~~~~~~~~
warning: non-binding let on a expression marked `must_use`
--> $DIR/let_underscore_must_use.rs:12:5
@ -14,8 +20,14 @@ warning: non-binding let on a expression marked `must_use`
LL | let _ = must_use_function();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= help: consider binding to an unused variable
= help: consider explicitly droping with `std::mem::drop`
help: consider binding to an unused variable
|
LL | let _unused = must_use_function();
| ~~~~~~~
help: consider explicitly droping with `std::mem::drop`
|
LL | let _ = drop(...);
| ~~~~~~~~~
warning: 2 warnings emitted