Change PubPackageResolutionTest to use null safety.

Some tests had some issues migrating to null safety that I
could not immediately hash out, or may warrant some more discussion.
So I've added WithoutNullSafetyMixin, and we can incrementally
migrate these after this CL.

Many tests have little no-op tweaks to make them null safe, like
initializing variables, adding late, making nullable.

Nest steps:
1. Remove `WithNullSafetyMixin` applications.
2. Remove `WithoutNullSafetyMixin` in every position with a TODO for
   #44666.
3. For every file with pair(s) of test classes (one pre-null safety,
   and one null safety), move around test cases so that they generally
   run with null safety, unless they are testing things very specific to
   before and after null safety.

Bug: #44666
Change-Id: I0512dedcda42e864fd580af4842702095937bdb6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/183140
Commit-Queue: Samuel Rawlins <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>

Author: srawlins

pkg/analyzer/test/generated/error_suppression_test.dart

@@ -83,7 +83,7 @@ const y = x; //CONST_INITIALIZED_WITH_NON_CONSTANT_VALUE
     await assertNoErrorsInCode('''
 //ignore_for_file:   unused_element , unnecessary_cast
 int x = (0 as int);  //UNNECESSARY_CAST
-String _foo; //UNUSED_ELEMENT
+String _foo = ''; //UNUSED_ELEMENT
 ''');
   }
 
@@ -98,7 +98,7 @@ int x = (0 as int); // ignore: unnecessary_cast
 //UNNECESSARY_CAST
 int x = (0 as int);
 // ignore: unused_element
-String _foo; //UNUSED_ELEMENT
+String _foo = ''; //UNUSED_ELEMENT
 ''', [
       error(HintCode.UNNECESSARY_CAST, 28, 8),
     ]);
@@ -108,7 +108,7 @@ String _foo; //UNUSED_ELEMENT
     await assertErrorsInCode('''
 //UNNECESSARY_CAST
 int x = (0 as int);
-String _foo; // ignore: $ignoredCode
+String _foo = ''; // ignore: $ignoredCode
 ''', [
       error(HintCode.UNNECESSARY_CAST, 28, 8),
     ]);
@@ -119,7 +119,7 @@ String _foo; // ignore: $ignoredCode
     await assertNoErrorsInCode('''
 import 'package:meta/meta.dart';
 
-int f({@Required('x') int a}) => 0;
+int f({@Required('x') int? a}) => 0;
 
 // ignore: missing_required_param_with_details
 int x = f();
@@ -169,7 +169,7 @@ String y = 3; //INVALID_ASSIGNMENT
     await assertErrorsInCode('''
 int x = (0 as int); //This is the first comment...
 // ignore: $ignoredCode
-String _foo; //UNUSED_ELEMENT
+String _foo = ''; //UNUSED_ELEMENT
 ''', [
       error(HintCode.UNNECESSARY_CAST, 9, 8),
     ]);
@@ -178,7 +178,7 @@ String _foo; //UNUSED_ELEMENT
   test_multiple_ignore_for_files() async {
     await assertNoErrorsInCode('''
 int x = (0 as int); //UNNECESSARY_CAST
-String _foo; //UNUSED_ELEMENT
+String _foo = ''; //UNUSED_ELEMENT
 // ignore_for_file: unnecessary_cast,$ignoredCode
 ''');
   }

pkg/analyzer/test/generated/invalid_code_test.dart

@@ -19,7 +19,10 @@ main() {
 /// errors generated, but we want to make sure that there is at least one,
 /// and analysis finishes without exceptions.
 @reflectiveTest
-class InvalidCodeTest extends PubPackageResolutionTest {
+class InvalidCodeTest extends PubPackageResolutionTest
+    with WithoutNullSafetyMixin {
+  // TODO(https://github.com/dart-lang/sdk/issues/44666): Use null safety in
+  //  test cases.
   test_const_AwaitExpression() async {
     await _assertCanBeAnalyzed(r'''
 const a = await b();

pkg/analyzer/test/generated/non_error_resolver_test.dart

@@ -13,8 +13,8 @@ import '../src/dart/resolution/context_collection_resolution.dart';
 
 main() {
   defineReflectiveSuite(() {
-    defineReflectiveTests(NonErrorResolverTest);
     defineReflectiveTests(NonConstantValueInInitializer);
+    defineReflectiveTests(NonErrorResolverTest);
   });
 }
 
@@ -53,7 +53,10 @@ void main() {
 }
 
 @reflectiveTest
-class NonErrorResolverTest extends PubPackageResolutionTest {
+class NonErrorResolverTest extends PubPackageResolutionTest
+    with WithoutNullSafetyMixin {
+  // TODO(https://github.com/dart-lang/sdk/issues/44666): Use null safety in
+  //  test cases.
   test_ambiguousExport() async {
     newFile("$testPackageLibPath/lib1.dart", content: r'''
 library lib1;

pkg/analyzer/test/generated/resolver_test.dart

@@ -277,7 +277,10 @@ class StaticTypeVerifier extends GeneralizingAstVisitor<void> {
 /// The class `StrictModeTest` contains tests to ensure that the correct errors
 /// and warnings are reported when the analysis engine is run in strict mode.
 @reflectiveTest
-class StrictModeTest extends PubPackageResolutionTest {
+class StrictModeTest extends PubPackageResolutionTest
+    with WithoutNullSafetyMixin {
+  // TODO(https://github.com/dart-lang/sdk/issues/44666): Use null safety in
+  //  test cases.
   test_assert_is() async {
     await assertErrorsInCode(r'''
 int f(num n) {
@@ -417,7 +420,10 @@ int f() {
 }
 
 @reflectiveTest
-class TypePropagationTest extends PubPackageResolutionTest {
+class TypePropagationTest extends PubPackageResolutionTest
+    with WithoutNullSafetyMixin {
+  // TODO(https://github.com/dart-lang/sdk/issues/44666): Use null safety in
+  //  test cases.
   test_assignment_null() async {
     String code = r'''
 main() {

pkg/analyzer/test/generated/resolver_test_case.dart

@@ -285,7 +285,11 @@ class ResolutionVerifier extends RecursiveAstVisitor<void> {
 }
 
 /// Shared infrastructure for [StaticTypeAnalyzer2Test].
-class StaticTypeAnalyzer2TestShared extends PubPackageResolutionTest {
+class StaticTypeAnalyzer2TestShared extends PubPackageResolutionTest
+    with WithoutNullSafetyMixin {
+  // TODO(https://github.com/dart-lang/sdk/issues/44666): Use null safety in
+  //  test cases.
+
   /// Looks up the identifier with [name] and validates that its type type
   /// stringifies to [type] and that its generics match the given stringified
   /// output.

pkg/analyzer/test/generated/simple_resolver_test.dart

@@ -530,7 +530,7 @@ f() {
     await assertNoErrorsInCode(r'''
 typedef bool P(e);
 class A {
-  P p;
+  late P p;
   m(e) {
     if (p(e)) {}
   }
@@ -604,7 +604,7 @@ import 'lib2.dart';
 main() {
   foo = 0;
 }
-A a;''');
+A a = A();''');
     verifyTestResolved();
   }
 
@@ -693,11 +693,11 @@ main() {
   test_indexExpression_typeParameters() async {
     await assertNoErrorsInCode(r'''
 f() {
-  List<int> a;
+  List<int> a = [];
   a[0];
-  List<List<int>> b;
+  List<List<int>> b = [];
   b[0][0];
-  List<List<List<int>>> c;
+  List<List<List<int>>> c = [];
   c[0][0][0];
 }''');
     verifyTestResolved();
@@ -706,10 +706,10 @@ f() {
   test_indexExpression_typeParameters_invalidAssignmentWarning() async {
     await assertErrorsInCode(r'''
 f() {
-  List<List<int>> b;
+  List<List<int>> b = [];
   b[0][0] = 'hi';
 }''', [
-      error(CompileTimeErrorCode.INVALID_ASSIGNMENT, 39, 4),
+      error(CompileTimeErrorCode.INVALID_ASSIGNMENT, 44, 4),
     ]);
     verifyTestResolved();
   }
@@ -854,7 +854,7 @@ const A = null;
     await assertNoErrorsInCode(r'''
 const A = null;
 class C {
-  @A int f;
+  @A int f = 1;
 }''');
     verifyTestResolved();
 
@@ -1077,7 +1077,7 @@ class A {
   test_methodCascades_withSetter() async {
     await assertNoErrorsInCode(r'''
 class A {
-  String name;
+  String name = '';
   void m1() {}
   void m2() {}
   void m() {