Rollup merge of #121364 - Urgau:unary_precedence, r=compiler-errors

Implement lint against ambiguous negative literals

This PR implements a lint against ambiguous negative literals with a literal and method calls right after it.

## `ambiguous_negative_literals`

(deny-by-default)

The `ambiguous_negative_literals` lint checks for cases that are confusing between a negative literal and a negation that's not part of the literal.

### Example

```rust,compile_fail
-1i32.abs(); // equals -1, while `(-1i32).abs()` equals 1
```

### Explanation

Method calls take precedence over unary precedence. Setting the precedence explicitly makes the code clearer and avoid potential bugs.

<details>
<summary>Old proposed lint</summary>

## `ambiguous_unary_precedence`

(deny-by-default)

The `ambiguous_unary_precedence` lint checks for use the negative unary operator with a literal and method calls.

### Example

```rust
-1i32.abs(); // equals -1, while `(-1i32).abs()` equals 1
```

### Explanation

Unary operations take precedence on binary operations and method calls take precedence over unary precedence. Setting the precedence explicitly makes the code clearer and avoid potential bugs.

</details>

-----

Note: This is a strip down version of https://github.com/rust-lang/rust/pull/117161, without the binary op precedence.

Fixes https://github.com/rust-lang/rust/issues/117155
`@rustbot` labels +I-lang-nominated
cc `@scottmcm`
r? compiler

6 files changed, 4 insertions, 156 deletions

diff --git a/clippy_lints/src/precedence.rs b/clippy_lints/src/precedence.rs
index ff83725da69..37f5dd5583b 100644
--- a/clippy_lints/src/precedence.rs
+++ b/clippy_lints/src/precedence.rs
@@ -1,38 +1,17 @@
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::source::snippet_with_applicability;
-use rustc_ast::ast::{BinOpKind, Expr, ExprKind, MethodCall, UnOp};
-use rustc_ast::token;
+use rustc_ast::ast::{BinOpKind, Expr, ExprKind};
 use rustc_errors::Applicability;
 use rustc_lint::{EarlyContext, EarlyLintPass};
 use rustc_session::declare_lint_pass;
 use rustc_span::source_map::Spanned;
 
-const ALLOWED_ODD_FUNCTIONS: [&str; 14] = [
-    "asin",
-    "asinh",
-    "atan",
-    "atanh",
-    "cbrt",
-    "fract",
-    "round",
-    "signum",
-    "sin",
-    "sinh",
-    "tan",
-    "tanh",
-    "to_degrees",
-    "to_radians",
-];
-
 declare_clippy_lint! {
     /// ### What it does
     /// Checks for operations where precedence may be unclear
     /// and suggests to add parentheses. Currently it catches the following:
     /// * mixed usage of arithmetic and bit shifting/combining operators without
     /// parentheses
-    /// * a "negative" numeric literal (which is really a unary `-` followed by a
-    /// numeric literal)
-    ///   followed by a method call
     ///
     /// ### Why is this bad?
     /// Not everyone knows the precedence of those operators by
@@ -41,7 +20,6 @@ declare_clippy_lint! {
     ///
     /// ### Example
     /// * `1 << 2 + 3` equals 32, while `(1 << 2) + 3` equals 7
-    /// * `-1i32.abs()` equals -1, while `(-1i32).abs()` equals 1
     #[clippy::version = "pre 1.29.0"]
     pub PRECEDENCE,
     complexity,
@@ -104,38 +82,6 @@ impl EarlyLintPass for Precedence {
                 (false, false) => (),
             }
         }
-
-        if let ExprKind::Unary(UnOp::Neg, operand) = &expr.kind {
-            let mut arg = operand;
-
-            let mut all_odd = true;
-            while let ExprKind::MethodCall(box MethodCall { seg, receiver, .. }) = &arg.kind {
-                let seg_str = seg.ident.name.as_str();
-                all_odd &= ALLOWED_ODD_FUNCTIONS
-                    .iter()
-                    .any(|odd_function| **odd_function == *seg_str);
-                arg = receiver;
-            }
-
-            if !all_odd
-                && let ExprKind::Lit(lit) = &arg.kind
-                && let token::LitKind::Integer | token::LitKind::Float = &lit.kind
-            {
-                let mut applicability = Applicability::MachineApplicable;
-                span_lint_and_sugg(
-                    cx,
-                    PRECEDENCE,
-                    expr.span,
-                    "unary minus has lower precedence than method call",
-                    "consider adding parentheses to clarify your intent",
-                    format!(
-                        "-({})",
-                        snippet_with_applicability(cx, operand.span, "..", &mut applicability)
-                    ),
-                    applicability,
-                );
-            }
-        }
     }
 }
 
diff --git a/tests/ui/precedence.fixed b/tests/ui/precedence.fixed
index cc87de0d90f..c25c2062ace 100644
--- a/tests/ui/precedence.fixed
+++ b/tests/ui/precedence.fixed
@@ -20,40 +20,6 @@ fn main() {
     1 ^ (1 - 1);
     3 | (2 - 1);
     3 & (5 - 2);
-    -(1i32.abs());
-    -(1f32.abs());
-
-    // These should not trigger an error
-    let _ = (-1i32).abs();
-    let _ = (-1f32).abs();
-    let _ = -(1i32).abs();
-    let _ = -(1f32).abs();
-    let _ = -(1i32.abs());
-    let _ = -(1f32.abs());
-
-    // Odd functions should not trigger an error
-    let _ = -1f64.asin();
-    let _ = -1f64.asinh();
-    let _ = -1f64.atan();
-    let _ = -1f64.atanh();
-    let _ = -1f64.cbrt();
-    let _ = -1f64.fract();
-    let _ = -1f64.round();
-    let _ = -1f64.signum();
-    let _ = -1f64.sin();
-    let _ = -1f64.sinh();
-    let _ = -1f64.tan();
-    let _ = -1f64.tanh();
-    let _ = -1f64.to_degrees();
-    let _ = -1f64.to_radians();
-
-    // Chains containing any non-odd function should trigger (issue #5924)
-    let _ = -(1.0_f64.cos().cos());
-    let _ = -(1.0_f64.cos().sin());
-    let _ = -(1.0_f64.sin().cos());
-
-    // Chains of odd functions shouldn't trigger
-    let _ = -1f64.sin().sin();
 
     let b = 3;
     trip!(b * 8);
diff --git a/tests/ui/precedence.rs b/tests/ui/precedence.rs
index 00c18d92b5f..dc242ecf4c7 100644
--- a/tests/ui/precedence.rs
+++ b/tests/ui/precedence.rs
@@ -20,40 +20,6 @@ fn main() {
     1 ^ 1 - 1;
     3 | 2 - 1;
     3 & 5 - 2;
-    -1i32.abs();
-    -1f32.abs();
-
-    // These should not trigger an error
-    let _ = (-1i32).abs();
-    let _ = (-1f32).abs();
-    let _ = -(1i32).abs();
-    let _ = -(1f32).abs();
-    let _ = -(1i32.abs());
-    let _ = -(1f32.abs());
-
-    // Odd functions should not trigger an error
-    let _ = -1f64.asin();
-    let _ = -1f64.asinh();
-    let _ = -1f64.atan();
-    let _ = -1f64.atanh();
-    let _ = -1f64.cbrt();
-    let _ = -1f64.fract();
-    let _ = -1f64.round();
-    let _ = -1f64.signum();
-    let _ = -1f64.sin();
-    let _ = -1f64.sinh();
-    let _ = -1f64.tan();
-    let _ = -1f64.tanh();
-    let _ = -1f64.to_degrees();
-    let _ = -1f64.to_radians();
-
-    // Chains containing any non-odd function should trigger (issue #5924)
-    let _ = -1.0_f64.cos().cos();
-    let _ = -1.0_f64.cos().sin();
-    let _ = -1.0_f64.sin().cos();
-
-    // Chains of odd functions shouldn't trigger
-    let _ = -1f64.sin().sin();
 
     let b = 3;
     trip!(b * 8);
diff --git a/tests/ui/precedence.stderr b/tests/ui/precedence.stderr
index 47e61326219..8057c25a5e4 100644
--- a/tests/ui/precedence.stderr
+++ b/tests/ui/precedence.stderr
@@ -43,35 +43,5 @@ error: operator precedence can trip the unwary
 LL |     3 & 5 - 2;
    |     ^^^^^^^^^ help: consider parenthesizing your expression: `3 & (5 - 2)`
 
-error: unary minus has lower precedence than method call
-  --> tests/ui/precedence.rs:23:5
-   |
-LL |     -1i32.abs();
-   |     ^^^^^^^^^^^ help: consider adding parentheses to clarify your intent: `-(1i32.abs())`
-
-error: unary minus has lower precedence than method call
-  --> tests/ui/precedence.rs:24:5
-   |
-LL |     -1f32.abs();
-   |     ^^^^^^^^^^^ help: consider adding parentheses to clarify your intent: `-(1f32.abs())`
-
-error: unary minus has lower precedence than method call
-  --> tests/ui/precedence.rs:51:13
-   |
-LL |     let _ = -1.0_f64.cos().cos();
-   |             ^^^^^^^^^^^^^^^^^^^^ help: consider adding parentheses to clarify your intent: `-(1.0_f64.cos().cos())`
-
-error: unary minus has lower precedence than method call
-  --> tests/ui/precedence.rs:52:13
-   |
-LL |     let _ = -1.0_f64.cos().sin();
-   |             ^^^^^^^^^^^^^^^^^^^^ help: consider adding parentheses to clarify your intent: `-(1.0_f64.cos().sin())`
-
-error: unary minus has lower precedence than method call
-  --> tests/ui/precedence.rs:53:13
-   |
-LL |     let _ = -1.0_f64.sin().cos();
-   |             ^^^^^^^^^^^^^^^^^^^^ help: consider adding parentheses to clarify your intent: `-(1.0_f64.sin().cos())`
-
-error: aborting due to 12 previous errors
+error: aborting due to 7 previous errors
 
diff --git a/tests/ui/unnecessary_cast.fixed b/tests/ui/unnecessary_cast.fixed
index 288541362cd..c43e50761bd 100644
--- a/tests/ui/unnecessary_cast.fixed
+++ b/tests/ui/unnecessary_cast.fixed
@@ -206,7 +206,7 @@ mod fixable {
 
     fn issue_9563() {
         let _: f64 = (-8.0_f64).exp();
-        #[allow(clippy::precedence)]
+        #[allow(ambiguous_negative_literals)]
         let _: f64 = -8.0_f64.exp(); // should suggest `-8.0_f64.exp()` here not to change code behavior
     }
 
diff --git a/tests/ui/unnecessary_cast.rs b/tests/ui/unnecessary_cast.rs
index eef3a42e351..4a5ca231315 100644
--- a/tests/ui/unnecessary_cast.rs
+++ b/tests/ui/unnecessary_cast.rs
@@ -206,7 +206,7 @@ mod fixable {
 
     fn issue_9563() {
         let _: f64 = (-8.0 as f64).exp();
-        #[allow(clippy::precedence)]
+        #[allow(ambiguous_negative_literals)]
         let _: f64 = -(8.0 as f64).exp(); // should suggest `-8.0_f64.exp()` here not to change code behavior
     }