Fix a bug in unreachableFromMain

Closes https://github.com/dart-lang/sdk/issues/63425

Change-Id: I4bffe8413c56e4d71ae48284c6960085abf33d2f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/505482
Auto-Submit: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Keerti Parthasarathy <keertip@google.com>

pkg/linter/lib/src/rules/unreachable_from_main.dart

@@ -705,8 +705,11 @@ extension on Declaration {
         return self.namePart.typeName.lexeme;
       case ConstructorDeclaration():
         var name = self.name?.lexeme ?? 'new';
-        // TODO(scheglov): support primary constructors
-        return '${self.typeName!.name}.$name';
+        var typeName =
+            self.typeName ??
+            self.declaredFragment?.element.enclosingElement.name ??
+            'unknown';
+        return '$typeName.$name';
       case EnumConstantDeclaration():
         return self.name.lexeme;
       case EnumDeclaration():

pkg/linter/test/rules/unreachable_from_main_test.dart

@@ -624,6 +624,19 @@ void main() {}
     ]);
   }
 
+  test_constructor_named_new() async {
+    // https://github.com/dart-lang/sdk/issues/63425
+    await assertDiagnosticsFromMarkdown(r'''
+void main() {
+  C;
+}
+
+class C {
+  new [!named!]();
+}
+''');
+  }
+
   test_constructor_named_onEnum() async {
     await assertNoDiagnostics(r'''
 void main() {