diff --git a/compiler/rustc_lint/messages.ftl b/compiler/rustc_lint/messages.ftl index 3fa43296dfcac..b2f88b0d57350 100644 --- a/compiler/rustc_lint/messages.ftl +++ b/compiler/rustc_lint/messages.ftl @@ -78,6 +78,11 @@ lint_builtin_deprecated_attr_used = use of deprecated attribute `{$name}`: no lo lint_builtin_deref_nullptr = dereferencing a null pointer .label = this code causes undefined behavior when executed +lint_builtin_double_negations = use of a double negation + .note = the prefix `--` could be misinterpreted as a decrement operator which exists in other languages + .note_decrement = use `-= 1` if you meant to decrement the value + .add_parens_suggestion = add parentheses for clarity + lint_builtin_ellipsis_inclusive_range_patterns = `...` range patterns are deprecated .suggestion = use `..=` for an inclusive range diff --git a/compiler/rustc_lint/src/builtin.rs b/compiler/rustc_lint/src/builtin.rs index 1fa6f96660e73..31b4675eff44b 100644 --- a/compiler/rustc_lint/src/builtin.rs +++ b/compiler/rustc_lint/src/builtin.rs @@ -51,6 +51,7 @@ use crate::errors::BuiltinEllipsisInclusiveRangePatterns; use crate::lints::{ BuiltinAnonymousParams, BuiltinConstNoMangle, BuiltinDeprecatedAttrLink, BuiltinDeprecatedAttrLinkSuggestion, BuiltinDeprecatedAttrUsed, BuiltinDerefNullptr, + BuiltinDoubleNegations, BuiltinDoubleNegationsAddParens, BuiltinEllipsisInclusiveRangePatternsLint, BuiltinExplicitOutlives, BuiltinExplicitOutlivesSuggestion, BuiltinFeatureIssueNote, BuiltinIncompleteFeatures, BuiltinIncompleteFeaturesHelp, BuiltinInternalFeatures, BuiltinKeywordIdents, @@ -1555,6 +1556,58 @@ impl<'tcx> LateLintPass<'tcx> for TrivialConstraints { } } +declare_lint! { + /// The `double_negations` lint detects expressions of the form `--x`. + /// + /// ### Example + /// + /// ```rust + /// fn main() { + /// let x = 1; + /// let _b = --x; + /// } + /// ``` + /// + /// {{produces}} + /// + /// ### Explanation + /// + /// Negating something twice is usually the same as not negating it at all. + /// However, a double negation in Rust can easily be confused with the + /// prefix decrement operator that exists in many languages derived from C. + /// Use `-(-x)` if you really wanted to negate the value twice. + /// + /// To decrement a value, use `x -= 1` instead. + pub DOUBLE_NEGATIONS, + Warn, + "detects expressions of the form `--x`" +} + +declare_lint_pass!( + /// Lint for expressions of the form `--x` that can be confused with C's + /// prefix decrement operator. + DoubleNegations => [DOUBLE_NEGATIONS] +); + +impl EarlyLintPass for DoubleNegations { + #[inline] + fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) { + // only lint on the innermost `--` in a chain of `-` operators, + // even if there are 3 or more negations + if let ExprKind::Unary(UnOp::Neg, ref inner) = expr.kind + && let ExprKind::Unary(UnOp::Neg, ref inner2) = inner.kind + && !matches!(inner2.kind, ExprKind::Unary(UnOp::Neg, _)) + { + cx.emit_span_lint(DOUBLE_NEGATIONS, expr.span, BuiltinDoubleNegations { + add_parens: BuiltinDoubleNegationsAddParens { + start_span: inner.span.shrink_to_lo(), + end_span: inner.span.shrink_to_hi(), + }, + }); + } + } +} + declare_lint_pass!( /// Does nothing as a lint pass, but registers some `Lint`s /// which are used by other parts of the compiler. @@ -1573,7 +1626,8 @@ declare_lint_pass!( UNSTABLE_FEATURES, UNREACHABLE_PUB, TYPE_ALIAS_BOUNDS, - TRIVIAL_BOUNDS + TRIVIAL_BOUNDS, + DOUBLE_NEGATIONS ] ); diff --git a/compiler/rustc_lint/src/lib.rs b/compiler/rustc_lint/src/lib.rs index 86112277504a8..70b46f022d42b 100644 --- a/compiler/rustc_lint/src/lib.rs +++ b/compiler/rustc_lint/src/lib.rs @@ -181,6 +181,7 @@ early_lint_methods!( UnusedDocComment: UnusedDocComment, Expr2024: Expr2024, Precedence: Precedence, + DoubleNegations: DoubleNegations, ] ] ); diff --git a/compiler/rustc_lint/src/lints.rs b/compiler/rustc_lint/src/lints.rs index 000f4b697bd68..53cc490ef01e5 100644 --- a/compiler/rustc_lint/src/lints.rs +++ b/compiler/rustc_lint/src/lints.rs @@ -343,6 +343,24 @@ pub(crate) struct BuiltinTrivialBounds<'a> { pub predicate: Clause<'a>, } +#[derive(LintDiagnostic)] +#[diag(lint_builtin_double_negations)] +#[note(lint_note)] +#[note(lint_note_decrement)] +pub(crate) struct BuiltinDoubleNegations { + #[subdiagnostic] + pub add_parens: BuiltinDoubleNegationsAddParens, +} + +#[derive(Subdiagnostic)] +#[multipart_suggestion(lint_add_parens_suggestion, applicability = "maybe-incorrect")] +pub(crate) struct BuiltinDoubleNegationsAddParens { + #[suggestion_part(code = "(")] + pub start_span: Span, + #[suggestion_part(code = ")")] + pub end_span: Span, +} + #[derive(LintDiagnostic)] pub(crate) enum BuiltinEllipsisInclusiveRangePatternsLint { #[diag(lint_builtin_ellipsis_inclusive_range_patterns)] diff --git a/tests/ui/lint/lint-double-negations.rs b/tests/ui/lint/lint-double-negations.rs new file mode 100644 index 0000000000000..43e61dd7c1327 --- /dev/null +++ b/tests/ui/lint/lint-double-negations.rs @@ -0,0 +1,9 @@ +//@ check-pass +fn main() { + let x = 1; + -x; + -(-x); + --x; //~ WARN use of a double negation + ---x; //~ WARN use of a double negation + let _y = --(-x); //~ WARN use of a double negation +} diff --git a/tests/ui/lint/lint-double-negations.stderr b/tests/ui/lint/lint-double-negations.stderr new file mode 100644 index 0000000000000..9367f74be546d --- /dev/null +++ b/tests/ui/lint/lint-double-negations.stderr @@ -0,0 +1,42 @@ +warning: use of a double negation + --> $DIR/lint-double-negations.rs:6:5 + | +LL | --x; + | ^^^ + | + = note: the prefix `--` could be misinterpreted as a decrement operator which exists in other languages + = note: use `-= 1` if you meant to decrement the value + = note: `#[warn(double_negations)]` on by default +help: add parentheses for clarity + | +LL | -(-x); + | + + + +warning: use of a double negation + --> $DIR/lint-double-negations.rs:7:6 + | +LL | ---x; + | ^^^ + | + = note: the prefix `--` could be misinterpreted as a decrement operator which exists in other languages + = note: use `-= 1` if you meant to decrement the value +help: add parentheses for clarity + | +LL | --(-x); + | + + + +warning: use of a double negation + --> $DIR/lint-double-negations.rs:8:14 + | +LL | let _y = --(-x); + | ^^^^^^ + | + = note: the prefix `--` could be misinterpreted as a decrement operator which exists in other languages + = note: use `-= 1` if you meant to decrement the value +help: add parentheses for clarity + | +LL | let _y = -(-(-x)); + | + + + +warning: 3 warnings emitted + diff --git a/tests/ui/lint/lint-type-overflow2.rs b/tests/ui/lint/lint-type-overflow2.rs index f007b45b8479d..ac7420326c893 100644 --- a/tests/ui/lint/lint-type-overflow2.rs +++ b/tests/ui/lint/lint-type-overflow2.rs @@ -4,6 +4,7 @@ fn main() { let x2: i8 = --128; //~ ERROR literal out of range for `i8` + //~| WARN use of a double negation let x = -3.40282357e+38_f32; //~ ERROR literal out of range for `f32` let x = 3.40282357e+38_f32; //~ ERROR literal out of range for `f32` diff --git a/tests/ui/lint/lint-type-overflow2.stderr b/tests/ui/lint/lint-type-overflow2.stderr index eb593d062f218..2cfb18e9fe924 100644 --- a/tests/ui/lint/lint-type-overflow2.stderr +++ b/tests/ui/lint/lint-type-overflow2.stderr @@ -1,3 +1,17 @@ +warning: use of a double negation + --> $DIR/lint-type-overflow2.rs:6:18 + | +LL | let x2: i8 = --128; + | ^^^^^ + | + = note: the prefix `--` could be misinterpreted as a decrement operator which exists in other languages + = note: use `-= 1` if you meant to decrement the value + = note: `#[warn(double_negations)]` on by default +help: add parentheses for clarity + | +LL | let x2: i8 = -(-128); + | + + + error: literal out of range for `i8` --> $DIR/lint-type-overflow2.rs:6:20 | @@ -13,7 +27,7 @@ LL | #![deny(overflowing_literals)] | ^^^^^^^^^^^^^^^^^^^^ error: literal out of range for `f32` - --> $DIR/lint-type-overflow2.rs:8:14 + --> $DIR/lint-type-overflow2.rs:9:14 | LL | let x = -3.40282357e+38_f32; | ^^^^^^^^^^^^^^^^^^ @@ -21,7 +35,7 @@ LL | let x = -3.40282357e+38_f32; = note: the literal `3.40282357e+38_f32` does not fit into the type `f32` and will be converted to `f32::INFINITY` error: literal out of range for `f32` - --> $DIR/lint-type-overflow2.rs:9:14 + --> $DIR/lint-type-overflow2.rs:10:14 | LL | let x = 3.40282357e+38_f32; | ^^^^^^^^^^^^^^^^^^ @@ -29,7 +43,7 @@ LL | let x = 3.40282357e+38_f32; = note: the literal `3.40282357e+38_f32` does not fit into the type `f32` and will be converted to `f32::INFINITY` error: literal out of range for `f64` - --> $DIR/lint-type-overflow2.rs:10:14 + --> $DIR/lint-type-overflow2.rs:11:14 | LL | let x = -1.7976931348623159e+308_f64; | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ @@ -37,12 +51,12 @@ LL | let x = -1.7976931348623159e+308_f64; = note: the literal `1.7976931348623159e+308_f64` does not fit into the type `f64` and will be converted to `f64::INFINITY` error: literal out of range for `f64` - --> $DIR/lint-type-overflow2.rs:11:14 + --> $DIR/lint-type-overflow2.rs:12:14 | LL | let x = 1.7976931348623159e+308_f64; | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ | = note: the literal `1.7976931348623159e+308_f64` does not fit into the type `f64` and will be converted to `f64::INFINITY` -error: aborting due to 5 previous errors +error: aborting due to 5 previous errors; 1 warning emitted