Issue 57035. Fix for exception when asking class alias constructors.

Bug: #57035
Change-Id: I48aa20815b56c49f08e22509126f74891e694644
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/393960
Commit-Queue: Konstantin Shcheglov <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>

Author: scheglov

pkg/analyzer/lib/src/dart/element/element.dart

@@ -490,9 +490,6 @@ class ClassElementImpl extends ClassOrMixinElementImpl
       return;
     }
 
-    // Assign to break a possible infinite recursion during computing.
-    _constructors = const <ConstructorElementImpl>[];
-
     var superType = supertype;
     if (superType == null) {
       // Shouldn't ever happen, since the only classes with no supertype are
@@ -503,6 +500,9 @@ class ClassElementImpl extends ClassOrMixinElementImpl
       return;
     }
 
+    // Assign to break a possible infinite recursion during computing.
+    _constructors = const <ConstructorElementImpl>[];
+
     var superElement = superType.element as ClassElementImpl;
 
     var constructorsToForward = superElement.constructors

pkg/analyzer/test/src/summary/elements/class_test.dart

@@ -26355,6 +26355,18 @@ library
 ''');
   }
 
+  test_classAlias_constructors_beforeOtherProperties() async {
+    // https://github.com/dart-lang/sdk/issues/57035
+    var library = await buildLibrary('''
+abstract mixin class A {}
+mixin M {}
+class X = A with M;
+''');
+
+    var X = library.getClass('X')!;
+    expect(X.constructors, hasLength(1));
+  }
+
   test_classAlias_constructors_default() async {
     var library = await buildLibrary('''
 class A {}