Elements. Test for https://dart-review.googlesource.com/c/sdk/+/491140

Cover additional topMerge cases that were either untested or only
partially exercised.

Add failure cases for incompatible shapes, including function types with
different formal parameter counts, different type parameter counts,
nullability mismatches, and records whose positional or named fields do
not line up.

Also add positive coverage for records that merge both positional and
named fields in the same type. This makes the expected behavior around
record and function structure more explicit and helps guard the recent
top merge changes against regressions.

Change-Id: I85f3a2206d5c1cfb2a6f31964dc646382d91d227
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/491681
Reviewed-by: Paul Berry <paulberry@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

pkg/analyzer/test/src/dart/element/top_merge_test.dart

@@ -32,6 +32,16 @@ class TopMergeTest extends AbstractTypeSystemTest {
     _check(dynamicType, dynamicType, dynamicType);
   }
 
+  test_function_formalParameters_differentCount() {
+    _checkThrows(
+      functionTypeNone(returnType: voidNone, formalParameters: []),
+      functionTypeNone(
+        returnType: voidNone,
+        formalParameters: [requiredParameter(type: intNone)],
+      ),
+    );
+  }
+
   test_function_parameters_covariant() {
     _check(
       functionTypeNone(
@@ -199,6 +209,15 @@ class TopMergeTest extends AbstractTypeSystemTest {
     );
   }
 
+  test_function_typeParameters_differentCount() {
+    var T = typeParameter('T');
+    var S = typeParameter('S');
+    _checkThrows(
+      functionTypeNone(returnType: voidNone),
+      functionTypeNone(typeParameters: [T, S], returnType: voidNone),
+    );
+  }
+
   test_interface() {
     _check(
       listNone(dynamicType),
@@ -229,6 +248,10 @@ class TopMergeTest extends AbstractTypeSystemTest {
     _check(intQuestion, intQuestion, intQuestion);
   }
 
+  test_nullability_mismatch() {
+    _checkThrows(intQuestion, intNone);
+  }
+
   test_objectQuestion() {
     // NNBD_TOP_MERGE(Object?, Object?) = Object?
     _check(objectQuestion, objectQuestion, objectQuestion);
@@ -260,6 +283,42 @@ class TopMergeTest extends AbstractTypeSystemTest {
       recordTypeNone(namedTypes: {'f': objectQuestion}),
       recordTypeNone(namedTypes: {'f': objectQuestion}),
     );
+
+    _check(
+      recordTypeNone(
+        positionalTypes: [dynamicType],
+        namedTypes: {'f': voidNone},
+      ),
+      recordTypeNone(
+        positionalTypes: [objectQuestion],
+        namedTypes: {'f': objectQuestion},
+      ),
+      recordTypeNone(
+        positionalTypes: [objectQuestion],
+        namedTypes: {'f': objectQuestion},
+      ),
+    );
+  }
+
+  test_record_namedFields_differentCount() {
+    _checkThrows(
+      recordTypeNone(namedTypes: {'a': intNone}),
+      recordTypeNone(namedTypes: {'a': intNone, 'b': intNone}),
+    );
+  }
+
+  test_record_namedFields_differentNames() {
+    _checkThrows(
+      recordTypeNone(namedTypes: {'a': intNone}),
+      recordTypeNone(namedTypes: {'b': intNone}),
+    );
+  }
+
+  test_record_positionalFields_differentCount() {
+    _checkThrows(
+      recordTypeNone(positionalTypes: [intNone]),
+      recordTypeNone(positionalTypes: [intNone, intNone]),
+    );
   }
 
   test_typeParameter() {