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Extend unused_must_use to cover block exprs #112529

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Jun 16, 2023
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Extend unused_must_use to cover block exprs #112529

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2 changes: 1 addition & 1 deletion compiler/rustc_arena/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -67,7 +67,7 @@ struct ArenaChunk<T = u8> {

unsafe impl<#[may_dangle] T> Drop for ArenaChunk<T> {
fn drop(&mut self) {
unsafe { Box::from_raw(self.storage.as_mut()) };
unsafe { drop(Box::from_raw(self.storage.as_mut())) }
}
}

Expand Down
53 changes: 42 additions & 11 deletions compiler/rustc_lint/src/lints.rs
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Expand Up @@ -1534,8 +1534,29 @@ 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)]
Expand Down Expand Up @@ -1578,15 +1599,25 @@ 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
Expand Down
94 changes: 81 additions & 13 deletions compiler/rustc_lint/src/unused.rs
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Original file line number Diff line number Diff line change
@@ -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};
Expand Down Expand Up @@ -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;
Expand All @@ -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
Expand All @@ -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.
Expand Down Expand Up @@ -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;
Expand All @@ -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 {
Expand All @@ -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
}
Expand Down Expand Up @@ -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| {
Expand All @@ -360,6 +389,7 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
descr_post_path,
1,
false,
expr_is_from_block,
)
})
.is_some()
Expand All @@ -373,28 +403,59 @@ 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);

match path {
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,
);
}
}
Expand All @@ -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) => {
Expand All @@ -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() }
}),
},
);
}
Expand Down
2 changes: 1 addition & 1 deletion library/core/src/primitive_docs.rs
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Expand Up @@ -308,7 +308,7 @@ mod prim_never {}
///
/// ```no_run
/// // Undefined behaviour
/// unsafe { char::from_u32_unchecked(0x110000) };
/// let _ = unsafe { char::from_u32_unchecked(0x110000) };
/// ```
///
/// USVs are also the exact set of values that may be encoded in UTF-8. Because
Expand Down
2 changes: 1 addition & 1 deletion library/core/tests/ptr.rs
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Expand Up @@ -1001,7 +1001,7 @@ fn nonnull_tagged_pointer_with_provenance() {
assert_eq!(p.tag(), 3);
assert_eq!(unsafe { *p.pointer().as_ptr() }, 10);

unsafe { Box::from_raw(p.pointer().as_ptr()) };
unsafe { drop(Box::from_raw(p.pointer().as_ptr())) };

/// A non-null pointer type which carries several bits of metadata and maintains provenance.
#[repr(transparent)]
Expand Down
2 changes: 1 addition & 1 deletion library/std/src/primitive_docs.rs
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Expand Up @@ -308,7 +308,7 @@ mod prim_never {}
///
/// ```no_run
/// // Undefined behaviour
/// unsafe { char::from_u32_unchecked(0x110000) };
/// let _ = unsafe { char::from_u32_unchecked(0x110000) };
/// ```
///
/// USVs are also the exact set of values that may be encoded in UTF-8. Because
Expand Down
3 changes: 2 additions & 1 deletion src/tools/clippy/tests/ui/transmute_ptr_to_ref.fixed
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Expand Up @@ -2,6 +2,7 @@

#![warn(clippy::transmute_ptr_to_ref)]
#![allow(clippy::match_single_binding)]
#![allow(unused_must_use)]

unsafe fn _ptr_to_ref<T, U>(p: *const T, m: *mut T, o: *const U, om: *mut U) {
let _: &T = &*p;
Expand Down Expand Up @@ -38,7 +39,7 @@ fn _issue1231() {

type Bar<'a> = &'a u8;
let raw = 42 as *const i32;
unsafe { &*(raw as *const u8) };
let _ = unsafe { &*(raw as *const u8) };
}

unsafe fn _issue8924<'a, 'b, 'c>(x: *const &'a u32, y: *const &'b u32) -> &'c &'b u32 {
Expand Down
3 changes: 2 additions & 1 deletion src/tools/clippy/tests/ui/transmute_ptr_to_ref.rs
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Expand Up @@ -2,6 +2,7 @@

#![warn(clippy::transmute_ptr_to_ref)]
#![allow(clippy::match_single_binding)]
#![allow(unused_must_use)]

unsafe fn _ptr_to_ref<T, U>(p: *const T, m: *mut T, o: *const U, om: *mut U) {
let _: &T = std::mem::transmute(p);
Expand Down Expand Up @@ -38,7 +39,7 @@ fn _issue1231() {

type Bar<'a> = &'a u8;
let raw = 42 as *const i32;
unsafe { std::mem::transmute::<_, Bar>(raw) };
let _ = unsafe { std::mem::transmute::<_, Bar>(raw) };
}

unsafe fn _issue8924<'a, 'b, 'c>(x: *const &'a u32, y: *const &'b u32) -> &'c &'b u32 {
Expand Down
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