fix demorgan assist to handle method call

Author: Natural-selection1

crates/ide-assists/src/handlers/apply_demorgan.rs

@@ -132,6 +132,19 @@ pub(crate) fn apply_demorgan(acc: &mut Assists, ctx: &AssistContext<'_>) -> Opti
                 .filter(|prefix_expr| matches!(prefix_expr.op_kind(), Some(ast::UnaryOp::Not)))
                 .map(ast::Expr::PrefixExpr);
 
+            // Check if the parenthesized expression is the receiver of a method call
+            let is_method_receiver = paren_expr
+                .as_ref()
+                .and_then(|paren_expr| paren_expr.syntax().parent())
+                .and_then(ast::MethodCallExpr::cast)
+                .is_some_and(|method_call| {
+                    paren_expr.as_ref().is_some_and(|paren_expr| {
+                        method_call
+                            .receiver()
+                            .is_some_and(|receiver| receiver.syntax() == paren_expr.syntax())
+                    })
+                });
+
             let mut editor;
             if let Some(paren_expr) = paren_expr {
                 if let Some(neg_expr) = neg_expr {
@@ -151,7 +164,18 @@ pub(crate) fn apply_demorgan(acc: &mut Assists, ctx: &AssistContext<'_>) -> Opti
                     cov_mark::hit!(demorgan_double_parens);
                     editor = builder.make_editor(paren_expr.syntax());
 
-                    editor.replace(paren_expr.syntax(), add_bang_paren(&make, demorganed).syntax());
+                    // If this is a method receiver, we need to keep parentheses around the negated expression
+                    if is_method_receiver {
+                        editor.replace(
+                            paren_expr.syntax(),
+                            make.expr_paren(add_bang_paren(&make, demorganed)).syntax(),
+                        );
+                    } else {
+                        editor.replace(
+                            paren_expr.syntax(),
+                            add_bang_paren(&make, demorganed).syntax(),
+                        );
+                    }
                 }
             } else {
                 editor = builder.make_editor(bin_expr.syntax());
@@ -636,4 +660,31 @@ fn main() {
 "#,
         );
     }
+
+    #[test]
+    fn demorgan_method_call_receiver() {
+        check_assist(
+            apply_demorgan,
+            "fn f() { (x ||$0 !y).then_some(42) }",
+            "fn f() { (!(!x && y)).then_some(42) }",
+        );
+    }
+
+    #[test]
+    fn demorgan_method_call_receiver_complex() {
+        check_assist(
+            apply_demorgan,
+            "fn f() { (a && b ||$0 c && d).then_some(42) }",
+            "fn f() { (!(!(a && b) && !(c && d))).then_some(42) }",
+        );
+    }
+
+    #[test]
+    fn demorgan_method_call_receiver_chained() {
+        check_assist(
+            apply_demorgan,
+            "fn f() { (a ||$0 b).then_some(42).or(Some(0)) }",
+            "fn f() { (!(!a && !b)).then_some(42).or(Some(0)) }",
+        );
+    }
 }