Fix prefix adjustment hints unnecessarily introducing parens

crates/ide/src/inlay_hints/adjustment.rs

@@ -260,7 +260,7 @@ fn needs_parens_for_adjustment_hints(expr: &ast::Expr, postfix: bool) -> (bool,
     if postfix {
         // postfix ops have higher precedence than any other operator, so we need to wrap
         // any inner expression that is below (except for jumps if they don't have a value)
-        let needs_inner_parens = prec < ExprPrecedence::Unambiguous && {
+        let needs_inner_parens = prec < ExprPrecedence::Postfix && {
             prec != ExprPrecedence::Jump || !expr.is_ret_like_with_no_value()
         };
         // given we are the higher precedence, no parent expression will have stronger requirements
@@ -276,9 +276,12 @@ fn needs_parens_for_adjustment_hints(expr: &ast::Expr, postfix: bool) -> (bool,
             // if we are already wrapped, great, no need to wrap again
             .filter(|it| !matches!(it, ast::Expr::ParenExpr(_)))
             .map(|it| it.precedence());
+
         // if we have no parent, we don't need outer parens to disambiguate
         // otherwise anything with higher precedence than what we insert needs to wrap us
-        let needs_outer_parens = parent.is_some_and(|prec| prec > ExprPrecedence::Prefix);
+        // that means only postfix ops
+        let needs_outer_parens =
+            parent.is_some_and(|parent_prec| parent_prec == ExprPrecedence::Postfix);
         (needs_outer_parens, needs_inner_parens)
     }
 }
@@ -291,7 +294,7 @@ mod tests {
     };
 
     #[test]
-    fn adjustment_hints() {
+    fn adjustment_hints_prefix() {
         check_with_config(
             InlayHintsConfig { adjustment_hints: AdjustmentHints::Always, ..DISABLED_CONFIG },
             r#"
@@ -381,6 +384,8 @@ fn main() {
     &mut Struct[0];
        //^^^^^^(&mut $
        //^^^^^^)
+    let _: (&mut (),) = (&mut (),);
+                       //^^^^^^^&mut *
 }
 
 #[derive(Copy, Clone)]
@@ -472,6 +477,9 @@ fn main() {
   //^^^^^^.&
     &mut Struct[0];
        //^^^^^^.&mut
+    let _: (&mut (),) = (&mut (),);
+                       //^^^^^^^(
+                       //^^^^^^^).*.&mut
 }
 
 #[derive(Copy, Clone)]

crates/syntax/src/ast/prec.rs

@@ -35,7 +35,9 @@ pub enum ExprPrecedence {
     Cast,
     // unary - * ! & &mut
     Prefix,
-    // paths, loops, function calls, array indexing, field expressions, method calls
+    // function calls, array indexing, field expressions, method calls
+    Postfix,
+    // paths, loops,
     Unambiguous,
 }
 
@@ -57,6 +59,7 @@ pub fn precedence(expr: &ast::Expr) -> ExprPrecedence {
         },
 
         Expr::BreakExpr(_)
+        | Expr::BecomeExpr(_)
         | Expr::ContinueExpr(_)
         | Expr::ReturnExpr(_)
         | Expr::YeetExpr(_)
@@ -89,27 +92,27 @@ pub fn precedence(expr: &ast::Expr) -> ExprPrecedence {
 
         Expr::LetExpr(_) | Expr::PrefixExpr(_) | Expr::RefExpr(_) => ExprPrecedence::Prefix,
 
+        Expr::AwaitExpr(_)
+        | Expr::CallExpr(_)
+        | Expr::FieldExpr(_)
+        | Expr::IndexExpr(_)
+        | Expr::MethodCallExpr(_)
+        | Expr::TryExpr(_) => ExprPrecedence::Postfix,
+
         Expr::ArrayExpr(_)
         | Expr::AsmExpr(_)
-        | Expr::AwaitExpr(_)
-        | Expr::BecomeExpr(_)
         | Expr::BlockExpr(_)
-        | Expr::CallExpr(_)
-        | Expr::FieldExpr(_)
         | Expr::ForExpr(_)
         | Expr::FormatArgsExpr(_)
         | Expr::IfExpr(_)
-        | Expr::IndexExpr(_)
         | Expr::Literal(_)
         | Expr::LoopExpr(_)
         | Expr::MacroExpr(_)
         | Expr::MatchExpr(_)
-        | Expr::MethodCallExpr(_)
         | Expr::OffsetOfExpr(_)
         | Expr::ParenExpr(_)
         | Expr::PathExpr(_)
         | Expr::RecordExpr(_)
-        | Expr::TryExpr(_)
         | Expr::TupleExpr(_)
         | Expr::UnderscoreExpr(_)
         | Expr::WhileExpr(_) => ExprPrecedence::Unambiguous,