[analyzer] Dot shorthands: Allow potentially constant DotShorthandPropertyAccesses.

When we test for potentially-constant constants (ie. in asserts), we need to also test whether the identifier of a `DotShorthandPropertyAccess` is constant or not.

This CL adds one bit of logic and a few unit tests.
The language test `language/dot_shorthands/equality/equality_test` also covers this behavior and is passing.

Bug: https://github.com/dart-lang/sdk/issues/59835
Change-Id: I4e3daeb008c7dbadbb71d988012bf2e521df2e84
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/424661
Reviewed-by: Chloe Stefantsova <cstefantsova@google.com>
Commit-Queue: Kallen Tu <kallentu@google.com>

pkg/analyzer/lib/src/dart/constant/potentially_constant.dart

diff --git a/pkg/analyzer/lib/src/dart/constant/potentially_constant.dart b/pkg/analyzer/lib/src/dart/constant/potentially_constant.dart
index a21edbf..993e851 100644
--- a/pkg/analyzer/lib/src/dart/constant/potentially_constant.dart
+++ b/pkg/analyzer/lib/src/dart/constant/potentially_constant.dart
@@ -72,6 +72,10 @@
       return;
     }
 
+    if (node is DotShorthandPropertyAccess) {
+      return _identifier(node.propertyName);
+    }
+
     if (node is StringInterpolation) {
       for (var component in node.elements) {
         if (component is InterpolationExpression) {

pkg/analyzer/test/src/dart/resolution/dot_shorthand_property_access_test.dart

diff --git a/pkg/analyzer/test/src/dart/resolution/dot_shorthand_property_access_test.dart b/pkg/analyzer/test/src/dart/resolution/dot_shorthand_property_access_test.dart
index 6b6c17a..2d1ab7e 100644
--- a/pkg/analyzer/test/src/dart/resolution/dot_shorthand_property_access_test.dart
+++ b/pkg/analyzer/test/src/dart/resolution/dot_shorthand_property_access_test.dart
@@ -97,6 +97,55 @@
 ''');
   }
 
+  test_const_assert_class() async {
+    await assertNoErrorsInCode(r'''
+class Integer {
+  static const Integer one = const Integer._(1);
+  final int integer;
+  Integer(this.integer);
+  const Integer._(this.integer);
+}
+
+class CAssert {
+  const CAssert.one(Integer i): assert(i == .one);
+}
+''');
+
+    var node = findNode.singleDotShorthandPropertyAccess;
+    assertResolvedNodeText(node, r'''
+DotShorthandPropertyAccess
+  period: .
+  propertyName: SimpleIdentifier
+    token: one
+    element: <testLibraryFragment>::@class::Integer::@getter::one#element
+    staticType: Integer
+  correspondingParameter: dart:core::<fragment>::@class::Object::@method::==::@parameter::other#element
+  staticType: Integer
+''');
+  }
+
+  test_const_assert_enum() async {
+    await assertNoErrorsInCode(r'''
+enum Color { red, green, blue }
+
+class CAssert {
+  const CAssert.blue(Color color): assert(color == .blue);
+}
+''');
+
+    var node = findNode.singleDotShorthandPropertyAccess;
+    assertResolvedNodeText(node, r'''
+DotShorthandPropertyAccess
+  period: .
+  propertyName: SimpleIdentifier
+    token: blue
+    element: <testLibraryFragment>::@enum::Color::@getter::blue#element
+    staticType: Color
+  correspondingParameter: dart:core::<fragment>::@class::Object::@method::==::@parameter::other#element
+  staticType: Color
+''');
+  }
+
   test_const_class() async {
     await assertNoErrorsInCode('''
 class C {