Fix overflowing_literals lint with repeated negation

Fixes #158295

The `overflowing_literal` lint is, I believe, supposed to consider the
literal and not the surrounding context when deciding whether to lint.
This is in contrast to the `arithmetic_overflow` lint, which only
considers code that executes at run time, which excludes the negation
inside a literal.

According to [the reference](https://doc.rust-lang.org/1.96.0/reference/expressions/operator-expr.html#r-expr.operator.int-overflow.unary-neg),
a negation in front of an integer does not result in an overflow.
I think of this as: a negation, and only one negation, in front of
an integer, is "part of" the integer. Therefore,
the `overflowing_literal` lint should consider that when linting.
It should not consider the second or third negation.

Therefore, this commit changes `overflowing_literals` so that it only
lints on `128_i8` when there is no preceding negation at all. This is
in contrast to the previous behavior, which lints on `128_i8` preceded
by an even number of negations.

Author: theemathas

compiler/rustc_lint/src/types.rs

@@ -567,12 +567,8 @@ impl<'tcx> LateLintPass<'tcx> for TypeLimits {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx hir::Expr<'tcx>) {
         match e.kind {
             hir::ExprKind::Unary(hir::UnOp::Neg, expr) => {
-                // Propagate negation, if the negation itself isn't negated
-                if self.last_visited_negation.is_none_or(|negation| negation.negated_id != e.hir_id)
-                {
-                    self.last_visited_negation =
-                        Some(NegationInfo { negation_span: e.span, negated_id: expr.hir_id });
-                }
+                self.last_visited_negation =
+                    Some(NegationInfo { negation_span: e.span, negated_id: expr.hir_id });
             }
             hir::ExprKind::Binary(binop, ref l, ref r) => {
                 if is_comparison(binop.node) {

tests/ui/lint/lint-type-overflow3.rs

@@ -9,16 +9,13 @@ fn main() {
     //~^ ERROR literal out of range for `i8`
     let x: i8 = -128;
     let x: i8 = --128; //~ WARN use of a double negation
-    //~^ ERROR literal out of range for `i8`
-    //~| ERROR this arithmetic operation will overflow
+    //~^ ERROR this arithmetic operation will overflow
     let x: i8 = ---128; //~ WARN use of a double negation
     //~^ ERROR this arithmetic operation will overflow
     let x: i8 = ----128; //~ WARN use of a double negation
-    //~^ ERROR literal out of range for `i8`
-    //~| ERROR this arithmetic operation will overflow
+    //~^ ERROR this arithmetic operation will overflow
     let x: i8 = -----128; //~ WARN use of a double negation
     //~^ ERROR this arithmetic operation will overflow
     let x: i8 = ------128; //~ WARN use of a double negation
-    //~^ ERROR literal out of range for `i8`
-    //~| ERROR this arithmetic operation will overflow
+    //~^ ERROR this arithmetic operation will overflow
 }

tests/ui/lint/lint-type-overflow3.stderr

@@ -13,7 +13,7 @@ LL |     let x: i8 = -(-128);
    |                  +    +
 
 warning: use of a double negation
-  --> $DIR/lint-type-overflow3.rs:14:18
+  --> $DIR/lint-type-overflow3.rs:13:18
    |
 LL |     let x: i8 = ---128;
    |                  ^^^^^
@@ -26,7 +26,7 @@ LL |     let x: i8 = --(-128);
    |                   +    +
 
 warning: use of a double negation
-  --> $DIR/lint-type-overflow3.rs:16:19
+  --> $DIR/lint-type-overflow3.rs:15:19
    |
 LL |     let x: i8 = ----128;
    |                   ^^^^^
@@ -39,7 +39,7 @@ LL |     let x: i8 = ---(-128);
    |                    +    +
 
 warning: use of a double negation
-  --> $DIR/lint-type-overflow3.rs:19:20
+  --> $DIR/lint-type-overflow3.rs:17:20
    |
 LL |     let x: i8 = -----128;
    |                    ^^^^^
@@ -52,7 +52,7 @@ LL |     let x: i8 = ----(-128);
    |                     +    +
 
 warning: use of a double negation
-  --> $DIR/lint-type-overflow3.rs:21:21
+  --> $DIR/lint-type-overflow3.rs:19:21
    |
 LL |     let x: i8 = ------128;
    |                     ^^^^^
@@ -77,25 +77,25 @@ LL | #![deny(overflowing_literals, arithmetic_overflow)]
    |                               ^^^^^^^^^^^^^^^^^^^
 
 error: this arithmetic operation will overflow
-  --> $DIR/lint-type-overflow3.rs:14:18
+  --> $DIR/lint-type-overflow3.rs:13:18
    |
 LL |     let x: i8 = ---128;
    |                  ^^^^^ attempt to negate `i8::MIN`, which would overflow
 
 error: this arithmetic operation will overflow
-  --> $DIR/lint-type-overflow3.rs:16:19
+  --> $DIR/lint-type-overflow3.rs:15:19
    |
 LL |     let x: i8 = ----128;
    |                   ^^^^^ attempt to negate `i8::MIN`, which would overflow
 
 error: this arithmetic operation will overflow
-  --> $DIR/lint-type-overflow3.rs:19:20
+  --> $DIR/lint-type-overflow3.rs:17:20
    |
 LL |     let x: i8 = -----128;
    |                    ^^^^^ attempt to negate `i8::MIN`, which would overflow
 
 error: this arithmetic operation will overflow
-  --> $DIR/lint-type-overflow3.rs:21:21
+  --> $DIR/lint-type-overflow3.rs:19:21
    |
 LL |     let x: i8 = ------128;
    |                     ^^^^^ attempt to negate `i8::MIN`, which would overflow
@@ -114,32 +114,5 @@ note: the lint level is defined here
 LL | #![deny(overflowing_literals, arithmetic_overflow)]
    |         ^^^^^^^^^^^^^^^^^^^^
 
-error: literal out of range for `i8`
-  --> $DIR/lint-type-overflow3.rs:11:19
-   |
-LL |     let x: i8 = --128;
-   |                   ^^^
-   |
-   = note: the literal `128` does not fit into the type `i8` whose range is `-128..=127`
-   = help: consider using the type `u8` instead
-
-error: literal out of range for `i8`
-  --> $DIR/lint-type-overflow3.rs:16:21
-   |
-LL |     let x: i8 = ----128;
-   |                     ^^^
-   |
-   = note: the literal `128` does not fit into the type `i8` whose range is `-128..=127`
-   = help: consider using the type `u8` instead
-
-error: literal out of range for `i8`
-  --> $DIR/lint-type-overflow3.rs:21:23
-   |
-LL |     let x: i8 = ------128;
-   |                       ^^^
-   |
-   = note: the literal `128` does not fit into the type `i8` whose range is `-128..=127`
-   = help: consider using the type `u8` instead
-
-error: aborting due to 9 previous errors; 5 warnings emitted
+error: aborting due to 6 previous errors; 5 warnings emitted