From 05939a8d38959b1ff418a0f54663eaba0f5e3108 Mon Sep 17 00:00:00 2001
From: A4-Tacks <wdsjxhno1001@163.com>
Date: Wed, 14 Jan 2026 17:54:23 +0800
Subject: [PATCH] Fix false positive precedence in `(2 as i32) < 3`

Example
---
```rust
fn f() { _ = $0(1 as u32) << 10; }
```

**Before this PR**

This is syntax error

```rust
fn f() { _ = 1 as u32 << 10; }
```

**After this PR**

Assist not applicable
---
 .../src/handlers/remove_parentheses.rs        |  6 +++++
 .../crates/syntax/src/ast/prec.rs             | 24 +++++++++++++++----
 2 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/src/tools/rust-analyzer/crates/ide-assists/src/handlers/remove_parentheses.rs b/src/tools/rust-analyzer/crates/ide-assists/src/handlers/remove_parentheses.rs
index aa4d2bcadb01..f07da489e23a 100644
--- a/src/tools/rust-analyzer/crates/ide-assists/src/handlers/remove_parentheses.rs
+++ b/src/tools/rust-analyzer/crates/ide-assists/src/handlers/remove_parentheses.rs
@@ -321,6 +321,12 @@ mod tests {
         );
     }
 
+    #[test]
+    fn remove_parens_conflict_cast_before_l_angle() {
+        check_assist_not_applicable(remove_parentheses, r#"fn f() { _ = $0(1 as u32) << 10; }"#);
+        check_assist_not_applicable(remove_parentheses, r#"fn f() { _ = $0(1 as u32) < 10; }"#);
+    }
+
     #[test]
     fn remove_parens_double_paren_stmt() {
         check_assist(
diff --git a/src/tools/rust-analyzer/crates/syntax/src/ast/prec.rs b/src/tools/rust-analyzer/crates/syntax/src/ast/prec.rs
index 8c88224a761a..d99cf492616e 100644
--- a/src/tools/rust-analyzer/crates/syntax/src/ast/prec.rs
+++ b/src/tools/rust-analyzer/crates/syntax/src/ast/prec.rs
@@ -154,6 +154,11 @@ fn check_ancestry(ancestor: &SyntaxNode, descendent: &SyntaxNode) -> bool {
     bail()
 }
 
+fn next_token_of(node: &SyntaxNode) -> Option<ast::SyntaxToken> {
+    let last = node.last_token()?;
+    skip_trivia_token(last.next_token()?, Direction::Next)
+}
+
 impl Expr {
     pub fn precedence(&self) -> ExprPrecedence {
         precedence(self)
@@ -197,6 +202,8 @@ impl Expr {
         if is_parent_call_expr && is_field_expr {
             return true;
         }
+        let place_of_parent =
+            || place_of.ancestors().find(|it| it.parent().is_none_or(|p| &p == parent.syntax()));
 
         // Special-case block weirdness
         if parent.child_is_followed_by_a_block() {
@@ -226,15 +233,24 @@ impl Expr {
         // For `&&`, we avoid introducing `<ret-like> && <expr>` into a binary chain.
 
         if self.precedence() == ExprPrecedence::Jump
-            && let Some(node) =
-                place_of.ancestors().find(|it| it.parent().is_none_or(|p| &p == parent.syntax()))
-            && let Some(next) =
-                node.last_token().and_then(|t| skip_trivia_token(t.next_token()?, Direction::Next))
+            && let Some(node) = place_of_parent()
+            && let Some(next) = next_token_of(&node)
             && matches!(next.kind(), T![||] | T![&&])
         {
             return true;
         }
 
+        // Special-case `2 as x < 3`
+        if let ast::Expr::CastExpr(it) = self
+            && let Some(ty) = it.ty()
+            && ty.syntax().last_token().and_then(|it| ast::NameLike::cast(it.parent()?)).is_some()
+            && let Some(node) = place_of_parent()
+            && let Some(next) = next_token_of(&node)
+            && matches!(next.kind(), T![<] | T![<<])
+        {
+            return true;
+        }
+
         if self.is_paren_like()
             || parent.is_paren_like()
             || self.is_prefix()