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Rollup merge of #112529 - jieyouxu:block-expr-unused-must-use, r=oli-obk

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Extend `unused_must_use` to cover block exprs

Given code like

```rust
#[must_use]
fn foo() -> i32 {
    42
}

fn warns() {
    {
        foo();
    }
}

fn does_not_warn() {
    {
        foo()
    };
}

fn main() {
    warns();
    does_not_warn();
}
```

### Before This PR

```
warning: unused return value of `foo` that must be used
 --> test.rs:8:9
  |
8 |         foo();
  |         ^^^^^
  |
  = note: `#[warn(unused_must_use)]` on by default
help: use `let _ = ...` to ignore the resulting value
  |
8 |         let _ = foo();
  |         +++++++

warning: 1 warning emitted
```

### After This PR

```
warning: unused return value of `foo` that must be used
 --> test.rs:8:9
  |
8 |         foo();
  |         ^^^^^
  |
  = note: `#[warn(unused_must_use)]` on by default
help: use `let _ = ...` to ignore the resulting value
  |
8 |         let _ = foo();
  |         +++++++

warning: unused return value of `foo` that must be used
  --> test.rs:14:9
   |
14 |         foo()
   |         ^^^^^
   |
help: use `let _ = ...` to ignore the resulting value
   |
14 |         let _ = foo();
   |         +++++++      +

warning: 2 warnings emitted
```

Fixes #104253.
This commit is contained in:
Guillaume Gomez 2023-06-15 22:04:56 +02:00 • committed by GitHub
commit d233522418
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GPG key ID: 4AEE18F83AFDEB23
19 changed files with 289 additions and 65 deletions
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53
compiler/rustc_lint/src/lints.rs
View file

@ -1555,8 +1555,29 @@ pub struct UnusedOp<'a> {
pub op: &'a str,
#[label]
pub label: Span,
#[suggestion(style = "verbose", code = "let _ = ", applicability = "maybe-incorrect")]
pub suggestion: Span,
#[subdiagnostic]
pub suggestion: UnusedOpSuggestion,
}
#[derive(Subdiagnostic)]
pub enum UnusedOpSuggestion {
#[suggestion(
lint_suggestion,
style = "verbose",
code = "let _ = ",
applicability = "maybe-incorrect"
)]
NormalExpr {
#[primary_span]
span: Span,
},
#[multipart_suggestion(lint_suggestion, style = "verbose", applicability = "maybe-incorrect")]
BlockTailExpr {
#[suggestion_part(code = "let _ = ")]
before_span: Span,
#[suggestion_part(code = ";")]
after_span: Span,
},
}
#[derive(LintDiagnostic)]
@ -1599,15 +1620,25 @@ pub struct UnusedDef<'a, 'b> {
}
#[derive(Subdiagnostic)]
#[suggestion(
lint_suggestion,
style = "verbose",
code = "let _ = ",
applicability = "maybe-incorrect"
)]
pub struct UnusedDefSuggestion {
#[primary_span]
pub span: Span,
pub enum UnusedDefSuggestion {
#[suggestion(
lint_suggestion,
style = "verbose",
code = "let _ = ",
applicability = "maybe-incorrect"
)]
NormalExpr {
#[primary_span]
span: Span,
},
#[multipart_suggestion(lint_suggestion, style = "verbose", applicability = "maybe-incorrect")]
BlockTailExpr {
#[suggestion_part(code = "let _ = ")]
before_span: Span,
#[suggestion_part(code = ";")]
after_span: Span,
},
}
// Needed because of def_path_str

94
compiler/rustc_lint/src/unused.rs
View file

@ -1,7 +1,8 @@
use crate::lints::{
PathStatementDrop, PathStatementDropSub, PathStatementNoEffect, UnusedAllocationDiag,
UnusedAllocationMutDiag, UnusedClosure, UnusedDef, UnusedDefSuggestion, UnusedDelim,
UnusedDelimSuggestion, UnusedGenerator, UnusedImportBracesDiag, UnusedOp, UnusedResult,
UnusedDelimSuggestion, UnusedGenerator, UnusedImportBracesDiag, UnusedOp, UnusedOpSuggestion,
UnusedResult,
};
use crate::Lint;
use crate::{EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext};
@ -93,7 +94,15 @@ declare_lint_pass!(UnusedResults => [UNUSED_MUST_USE, UNUSED_RESULTS]);
impl<'tcx> LateLintPass<'tcx> for UnusedResults {
fn check_stmt(&mut self, cx: &LateContext<'_>, s: &hir::Stmt<'_>) {
let hir::StmtKind::Semi(expr) = s.kind else { return; };
let hir::StmtKind::Semi(mut expr) = s.kind else { return; };
let mut expr_is_from_block = false;
while let hir::ExprKind::Block(blk, ..) = expr.kind
&& let hir::Block { expr: Some(e), .. } = blk
{
expr = e;
expr_is_from_block = true;
}
if let hir::ExprKind::Ret(..) = expr.kind {
return;
@ -113,6 +122,7 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
expr.span,
"output of future returned by ",
"",
expr_is_from_block,
)
{
// We have a bare `foo().await;` on an opaque type from an async function that was
@ -125,13 +135,13 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
let must_use_result = is_ty_must_use(cx, ty, &expr, expr.span);
let type_lint_emitted_or_suppressed = match must_use_result {
Some(path) => {
emit_must_use_untranslated(cx, &path, "", "", 1, false);
emit_must_use_untranslated(cx, &path, "", "", 1, false, expr_is_from_block);
true
}
None => false,
};
let fn_warned = check_fn_must_use(cx, expr);
let fn_warned = check_fn_must_use(cx, expr, expr_is_from_block);
if !fn_warned && type_lint_emitted_or_suppressed {
// We don't warn about unused unit or uninhabited types.
@ -176,7 +186,14 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
UnusedOp {
op: must_use_op,
label: expr.span,
suggestion: expr.span.shrink_to_lo(),
suggestion: if expr_is_from_block {
UnusedOpSuggestion::BlockTailExpr {
before_span: expr.span.shrink_to_lo(),
after_span: expr.span.shrink_to_hi(),
}
} else {
UnusedOpSuggestion::NormalExpr { span: expr.span.shrink_to_lo() }
},
},
);
op_warned = true;
@ -186,7 +203,11 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
cx.emit_spanned_lint(UNUSED_RESULTS, s.span, UnusedResult { ty });
}
fn check_fn_must_use(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> bool {
fn check_fn_must_use(
cx: &LateContext<'_>,
expr: &hir::Expr<'_>,
expr_is_from_block: bool,
) -> bool {
let maybe_def_id = match expr.kind {
hir::ExprKind::Call(ref callee, _) => {
match callee.kind {
@ -207,7 +228,14 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
_ => None,
};
if let Some(def_id) = maybe_def_id {
check_must_use_def(cx, def_id, expr.span, "return value of ", "")
check_must_use_def(
cx,
def_id,
expr.span,
"return value of ",
"",
expr_is_from_block,
)
} else {
false
}
@ -350,6 +378,7 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
span: Span,
descr_pre_path: &str,
descr_post_path: &str,
expr_is_from_block: bool,
) -> bool {
is_def_must_use(cx, def_id, span)
.map(|must_use_path| {
@ -360,6 +389,7 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
descr_post_path,
1,
false,
expr_is_from_block,
)
})
.is_some()
@ -373,6 +403,7 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
descr_post: &str,
plural_len: usize,
is_inner: bool,
expr_is_from_block: bool,
) {
let plural_suffix = pluralize!(plural_len);
@ -380,21 +411,51 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
MustUsePath::Suppressed => {}
MustUsePath::Boxed(path) => {
let descr_pre = &format!("{}boxed ", descr_pre);
emit_must_use_untranslated(cx, path, descr_pre, descr_post, plural_len, true);
emit_must_use_untranslated(
cx,
path,
descr_pre,
descr_post,
plural_len,
true,
expr_is_from_block,
);
}
MustUsePath::Opaque(path) => {
let descr_pre = &format!("{}implementer{} of ", descr_pre, plural_suffix);
emit_must_use_untranslated(cx, path, descr_pre, descr_post, plural_len, true);
emit_must_use_untranslated(
cx,
path,
descr_pre,
descr_post,
plural_len,
true,
expr_is_from_block,
);
}
MustUsePath::TraitObject(path) => {
let descr_post = &format!(" trait object{}{}", plural_suffix, descr_post);
emit_must_use_untranslated(cx, path, descr_pre, descr_post, plural_len, true);
emit_must_use_untranslated(
cx,
path,
descr_pre,
descr_post,
plural_len,
true,
expr_is_from_block,
);
}
MustUsePath::TupleElement(elems) => {
for (index, path) in elems {
let descr_post = &format!(" in tuple element {}", index);
emit_must_use_untranslated(
cx, path, descr_pre, descr_post, plural_len, true,
cx,
path,
descr_pre,
descr_post,
plural_len,
true,
expr_is_from_block,
);
}
}
@ -407,6 +468,7 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
descr_post,
plural_len.saturating_add(usize::try_from(*len).unwrap_or(usize::MAX)),
true,
expr_is_from_block,
);
}
MustUsePath::Closure(span) => {
@ -433,8 +495,14 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
cx,
def_id: *def_id,
note: *reason,
suggestion: (!is_inner)
.then_some(UnusedDefSuggestion { span: span.shrink_to_lo() }),
suggestion: (!is_inner).then_some(if expr_is_from_block {
UnusedDefSuggestion::BlockTailExpr {
before_span: span.shrink_to_lo(),
after_span: span.shrink_to_hi(),
}
} else {
UnusedDefSuggestion::NormalExpr { span: span.shrink_to_lo() }
}),
},
);
}