diff --git a/compiler/rustc_error_messages/locales/en-US/borrowck.ftl b/compiler/rustc_error_messages/locales/en-US/borrowck.ftl
index 0021638c10268..fe77cf23e8f94 100644
--- a/compiler/rustc_error_messages/locales/en-US/borrowck.ftl
+++ b/compiler/rustc_error_messages/locales/en-US/borrowck.ftl
@@ -33,7 +33,7 @@ borrowck_var_here_defined = variable defined here
borrowck_var_here_captured = variable captured here
-borrowck_closure_inferred_mut = inferred to be a `FnMut` closure
+borrowck_closure_inferred_mut = inferred to be a `FnMut` closure
borrowck_returned_closure_escaped =
returns a closure that contains a reference to a captured variable, which then escapes the closure body
diff --git a/compiler/rustc_error_messages/locales/en-US/lint.ftl b/compiler/rustc_error_messages/locales/en-US/lint.ftl
index dca678dff7a79..b1e7cc69a809b 100644
--- a/compiler/rustc_error_messages/locales/en-US/lint.ftl
+++ b/compiler/rustc_error_messages/locales/en-US/lint.ftl
@@ -309,6 +309,7 @@ lint_unused_generator =
.note = generators are lazy and do nothing unless resumed
lint_unused_def = unused {$pre}`{$def}`{$post} that must be used
+ .suggestion = use `let _ = ...` to ignore the resulting value
lint_path_statement_drop = path statement drops value
.suggestion = use `drop` to clarify the intent
diff --git a/compiler/rustc_lint/src/lints.rs b/compiler/rustc_lint/src/lints.rs
index 0c1019545f382..2e447b900e117 100644
--- a/compiler/rustc_lint/src/lints.rs
+++ b/compiler/rustc_lint/src/lints.rs
@@ -1402,6 +1402,21 @@ pub struct UnusedDef<'a, 'b> {
pub cx: &'a LateContext<'b>,
pub def_id: DefId,
pub note: Option<Symbol>,
+ pub suggestion: Option<UnusedDefSuggestion>,
+}
+
+#[derive(Subdiagnostic)]
+pub enum UnusedDefSuggestion {
+ #[suggestion(
+ suggestion,
+ style = "verbose",
+ code = "let _ = ",
+ applicability = "machine-applicable"
+ )]
+ Default {
+ #[primary_span]
+ span: Span,
+ },
}
// Needed because of def_path_str
@@ -1417,6 +1432,9 @@ impl<'a> DecorateLint<'a, ()> for UnusedDef<'_, '_> {
if let Some(note) = self.note {
diag.note(note.as_str());
}
+ if let Some(sugg) = self.suggestion {
+ diag.subdiagnostic(sugg);
+ }
diag
}
diff --git a/compiler/rustc_lint/src/unused.rs b/compiler/rustc_lint/src/unused.rs
index 4c9b3df2dbd33..622601224ff92 100644
--- a/compiler/rustc_lint/src/unused.rs
+++ b/compiler/rustc_lint/src/unused.rs
@@ -1,7 +1,7 @@
use crate::lints::{
PathStatementDrop, PathStatementDropSub, PathStatementNoEffect, UnusedAllocationDiag,
- UnusedAllocationMutDiag, UnusedClosure, UnusedDef, UnusedDelim, UnusedDelimSuggestion,
- UnusedGenerator, UnusedImportBracesDiag, UnusedOp, UnusedResult,
+ UnusedAllocationMutDiag, UnusedClosure, UnusedDef, UnusedDefSuggestion, UnusedDelim,
+ UnusedDelimSuggestion, UnusedGenerator, UnusedImportBracesDiag, UnusedOp, UnusedResult,
};
use crate::Lint;
use crate::{EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext};
@@ -418,6 +418,19 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
);
}
MustUsePath::Def(span, def_id, reason) => {
+ let suggestion = if matches!(
+ cx.tcx.get_diagnostic_name(*def_id),
+ Some(sym::add)
+ | Some(sym::sub)
+ | Some(sym::mul)
+ | Some(sym::div)
+ | Some(sym::rem)
+ | Some(sym::neg),
+ ) {
+ Some(UnusedDefSuggestion::Default { span: span.shrink_to_lo() })
+ } else {
+ None
+ };
cx.emit_spanned_lint(
UNUSED_MUST_USE,
*span,
@@ -427,6 +440,7 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
cx,
def_id: *def_id,
note: *reason,
+ suggestion,
},
);
}
diff --git a/library/core/src/ops/arith.rs b/library/core/src/ops/arith.rs
index cc13db5c9565b..0c7ee9630c6ee 100644
--- a/library/core/src/ops/arith.rs
+++ b/library/core/src/ops/arith.rs
@@ -86,7 +86,8 @@ pub trait Add<Rhs = Self> {
/// ```
/// assert_eq!(12 + 1, 13);
/// ```
- #[must_use]
+ #[must_use = "this returns the result of the operation, without modifying the original"]
+ #[rustc_diagnostic_item = "add"]
#[stable(feature = "rust1", since = "1.0.0")]
fn add(self, rhs: Rhs) -> Self::Output;
}
@@ -195,7 +196,8 @@ pub trait Sub<Rhs = Self> {
/// ```
/// assert_eq!(12 - 1, 11);
/// ```
- #[must_use]
+ #[must_use = "this returns the result of the operation, without modifying the original"]
+ #[rustc_diagnostic_item = "sub"]
#[stable(feature = "rust1", since = "1.0.0")]
fn sub(self, rhs: Rhs) -> Self::Output;
}
@@ -325,7 +327,8 @@ pub trait Mul<Rhs = Self> {
/// ```
/// assert_eq!(12 * 2, 24);
/// ```
- #[must_use]
+ #[must_use = "this returns the result of the operation, without modifying the original"]
+ #[rustc_diagnostic_item = "mul"]
#[stable(feature = "rust1", since = "1.0.0")]
fn mul(self, rhs: Rhs) -> Self::Output;
}
@@ -459,7 +462,8 @@ pub trait Div<Rhs = Self> {
/// ```
/// assert_eq!(12 / 2, 6);
/// ```
- #[must_use]
+ #[must_use = "this returns the result of the operation, without modifying the original"]
+ #[rustc_diagnostic_item = "div"]
#[stable(feature = "rust1", since = "1.0.0")]
fn div(self, rhs: Rhs) -> Self::Output;
}
@@ -562,7 +566,8 @@ pub trait Rem<Rhs = Self> {
/// ```
/// assert_eq!(12 % 10, 2);
/// ```
- #[must_use]
+ #[must_use = "this returns the result of the operation, without modifying the original"]
+ #[rustc_diagnostic_item = "rem"]
#[stable(feature = "rust1", since = "1.0.0")]
fn rem(self, rhs: Rhs) -> Self::Output;
}
@@ -678,7 +683,8 @@ pub trait Neg {
/// let x: i32 = 12;
/// assert_eq!(-x, -12);
/// ```
- #[must_use]
+ #[must_use = "this returns the result of the operation, without modifying the original"]
+ #[rustc_diagnostic_item = "neg"]
#[stable(feature = "rust1", since = "1.0.0")]
fn neg(self) -> Self::Output;
}
diff --git a/tests/ui/lint/unused/issue-103320-must-use-ops.rs b/tests/ui/lint/unused/issue-103320-must-use-ops.rs
new file mode 100644
index 0000000000000..597d312fa5ecb
--- /dev/null
+++ b/tests/ui/lint/unused/issue-103320-must-use-ops.rs
@@ -0,0 +1,27 @@
+// check-pass
+
+#![warn(unused_must_use)]
+#![feature(never_type)]
+
+use std::ops::Add;
+use std::ops::Sub;
+use std::ops::Mul;
+use std::ops::Div;
+use std::ops::Rem;
+
+fn main() {
+ let x = 2_u32;
+ (x.add(4), x.sub(4), x.mul(4), x.div(4), x.rem(4));
+
+ x.add(4); //~ WARN unused return value of `add` that must be used
+
+ x.sub(4); //~ WARN unused return value of `sub` that must be used
+
+ x.mul(4); //~ WARN unused return value of `mul` that must be used
+
+ x.div(4); //~ WARN unused return value of `div` that must be used
+
+ x.rem(4); //~ WARN unused return value of `rem` that must be used
+
+ println!("{}", x);
+}
diff --git a/tests/ui/lint/unused/issue-103320-must-use-ops.stderr b/tests/ui/lint/unused/issue-103320-must-use-ops.stderr
new file mode 100644
index 0000000000000..57439ec6a8fdb
--- /dev/null
+++ b/tests/ui/lint/unused/issue-103320-must-use-ops.stderr
@@ -0,0 +1,67 @@
+warning: unused return value of `add` that must be used
+ --> $DIR/issue-103320-must-use-ops.rs:16:5
+ |
+LL | x.add(4);
+ | ^^^^^^^^
+ |
+ = note: this returns the result of the operation, without modifying the original
+note: the lint level is defined here
+ --> $DIR/issue-103320-must-use-ops.rs:3:9
+ |
+LL | #![warn(unused_must_use)]
+ | ^^^^^^^^^^^^^^^
+help: use `let _ = ...` to ignore the resulting value
+ |
+LL | let _ = x.add(4);
+ | +++++++
+
+warning: unused return value of `sub` that must be used
+ --> $DIR/issue-103320-must-use-ops.rs:18:5
+ |
+LL | x.sub(4);
+ | ^^^^^^^^
+ |
+ = note: this returns the result of the operation, without modifying the original
+help: use `let _ = ...` to ignore the resulting value
+ |
+LL | let _ = x.sub(4);
+ | +++++++
+
+warning: unused return value of `mul` that must be used
+ --> $DIR/issue-103320-must-use-ops.rs:20:5
+ |
+LL | x.mul(4);
+ | ^^^^^^^^
+ |
+ = note: this returns the result of the operation, without modifying the original
+help: use `let _ = ...` to ignore the resulting value
+ |
+LL | let _ = x.mul(4);
+ | +++++++
+
+warning: unused return value of `div` that must be used
+ --> $DIR/issue-103320-must-use-ops.rs:22:5
+ |
+LL | x.div(4);
+ | ^^^^^^^^
+ |
+ = note: this returns the result of the operation, without modifying the original
+help: use `let _ = ...` to ignore the resulting value
+ |
+LL | let _ = x.div(4);
+ | +++++++
+
+warning: unused return value of `rem` that must be used
+ --> $DIR/issue-103320-must-use-ops.rs:24:5
+ |
+LL | x.rem(4);
+ | ^^^^^^^^
+ |
+ = note: this returns the result of the operation, without modifying the original
+help: use `let _ = ...` to ignore the resulting value
+ |
+LL | let _ = x.rem(4);
+ | +++++++
+
+warning: 5 warnings emitted
+