Fix parsing switch statement with SwitchPatternCaseImpl when the patt…

…erns feature is disabled.

Bug: #50553
Change-Id: Icd87d422ebf899d4a0d56ab4b7e476ab60949ad4
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/272387
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Samuel Rawlins <srawlins@google.com>

pkg/analyzer/lib/src/fasta/ast_builder.dart

@@ -975,12 +975,16 @@ class AstBuilder extends StackListener {
     assert(optional(':', colon));
     debugEvent("CaseMatch");
 
+    WhenClauseImpl? whenClause;
+    if (when != null) {
+      var expression = pop() as ExpressionImpl;
+      whenClause = WhenClauseImpl(
+        whenKeyword: when,
+        expression: expression,
+      );
+    }
+
     if (_featureSet.isEnabled(Feature.patterns)) {
-      WhenClauseImpl? whenClause;
-      if (when != null) {
-        var expression = pop() as ExpressionImpl;
-        whenClause = WhenClauseImpl(whenKeyword: when, expression: expression);
-      }
       var pattern = pop() as DartPatternImpl;
       push(
         SwitchPatternCaseImpl(

pkg/analyzer/test/src/fasta/ast_builder_test.dart

@@ -1333,6 +1333,32 @@ SuperFormalParameter
   superKeyword: super
   period: .
   name: a
+''');
+  }
+
+  void test_switchStatement_withPatternCase_whenDisabled() {
+    var parseResult = parseStringWithErrors(r'''
+// @dart = 2.18
+void f(Object value) {
+  switch (value) {
+    case (int a,) when a == 0:
+  }
+}
+''');
+    parseResult.assertErrors([
+      error(ParserErrorCode.EXPECTED_TOKEN, 72, 1),
+    ]);
+
+    var node = parseResult.findNode.switchCase('case');
+    assertParsedNodeText(node, r'''
+SwitchCase
+  keyword: case
+  expression: ParenthesizedExpression
+    leftParenthesis: (
+    expression: SimpleIdentifier
+      token: int
+    rightParenthesis: )
+  colon: :
 ''');
   }
 }