fix(parser): allow parenthesized private-in expressions (#28284)

Parenthesized private-in expressions are valid even when parentheses are
omitted from the AST. Precedence parsing already rejects an
unparenthesized private-in on the right.

AI-assisted implementation.

crates/oxc_parser/src/diagnostics.rs

@@ -836,10 +836,6 @@ parser_diagnostics! {
             .with_label(span)
     };
 
-    private_in_private(span: Span) => {
-        OxcDiagnostic::error("Unexpected right-hand side of private-in expression").with_label(span)
-    };
-
     unexpected_private_identifier(span: Span) => {
         OxcDiagnostic::error("Unexpected private identifier").with_label(span)
     };

crates/oxc_parser/src/js/expression.rs

@@ -209,9 +209,8 @@ impl<'a, C: Config> ParserImpl<'a, C> {
         }
         self.expect(Kind::In);
         let right = self.parse_binary_expression_or_higher(Precedence::Compare);
-        if let Expression::PrivateInExpression(private_in_expr) = right {
-            return self.fatal_error(diagnostics::private_in_private(private_in_expr.span));
-        }
+        // The precedence check rejects an unparenthesized private-in on the right.
+        // A parenthesized one is valid, even when its parentheses are omitted from the AST.
         Expression::new_private_in_expression(self.end_span(lhs_start), left, right, self)
     }
 

tasks/coverage/misc/pass/private-in-parentheses.js

@@ -0,0 +1,8 @@
+class PrivateInParentheses {
+  #outer;
+  #inner;
+
+  check(value) {
+    return #outer in (#inner in value);
+  }
+}

tasks/coverage/snapshots/codegen_misc.snap

@@ -1,3 +1,3 @@
 codegen_misc Summary:
-AST Parsed     : 114/114 (100.00%)
-Positive Passed: 114/114 (100.00%)
+AST Parsed     : 115/115 (100.00%)
+Positive Passed: 115/115 (100.00%)

tasks/coverage/snapshots/formatter_misc.snap

@@ -1,3 +1,3 @@
 formatter_misc Summary:
-AST Parsed     : 114/114 (100.00%)
-Positive Passed: 114/114 (100.00%)
+AST Parsed     : 115/115 (100.00%)
+Positive Passed: 115/115 (100.00%)

tasks/coverage/snapshots/lexer_misc.snap

@@ -1,3 +1,3 @@
 lexer_misc Summary:
-AST Parsed     : 369/369 (100.00%)
-Positive Passed: 369/369 (100.00%)
+AST Parsed     : 370/370 (100.00%)
+Positive Passed: 370/370 (100.00%)

tasks/coverage/snapshots/parser_misc.snap

@@ -1,6 +1,6 @@
 parser_misc Summary:
-AST Parsed     : 114/114 (100.00%)
-Positive Passed: 114/114 (100.00%)
+AST Parsed     : 115/115 (100.00%)
+Positive Passed: 115/115 (100.00%)
 Negative Passed: 257/257 (100.00%)
 
   × TS(1275): 'accessor' modifier can only appear on a property declaration.

tasks/coverage/snapshots/semantic_misc.snap

@@ -1,6 +1,6 @@
 semantic_misc Summary:
-AST Parsed     : 114/114 (100.00%)
-Positive Passed: 108/114 (94.74%)
+AST Parsed     : 115/115 (100.00%)
+Positive Passed: 109/115 (94.78%)
 semantic Error: tasks/coverage/misc/pass/declare-let-private.ts
 Bindings mismatch:
 after transform: ScopeId(0): ["private"]

tasks/coverage/snapshots/transformer_misc.snap

@@ -1,3 +1,3 @@
 transformer_misc Summary:
-AST Parsed     : 114/114 (100.00%)
-Positive Passed: 114/114 (100.00%)
+AST Parsed     : 115/115 (100.00%)
+Positive Passed: 115/115 (100.00%)