bjoernager/rust
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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 @@ impl<'tcx> LateLintPass<'tcx> for LetUnderscore {
});
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()),