Flow analysis is not available outside of function bodies and initial…

…izers.

This fixes a group of crashes during fuzz testing.

FAILURE: z({=?[
[NoSuchMethodError: The getter 'flow' was called on null.
Receiver: null
Tried calling: flow
#0      Object.noSuchMethod (dart:core-patch/object_patch.dart:54:5)
flutter#1      ResolverVisitor.startNullAwareIndexExpression (package:analyzer/src/generated/resolver.dart:743:21)
flutter#2      ResolverVisitor.visitIndexExpression (package:analyzer/src/generated/resolver.dart:1552:5)
flutter#3      IndexExpressionImpl.accept (package:analyzer/src/dart/ast/ast.dart:5993:49)
flutter#4      AstResolver.resolve (package:analyzer/src/summary2/ast_resolver.dart:85:10)
#5      DefaultValueResolver._parameter (package:analyzer/src/summary2/default_value_resolver.dart:107:18)
flutter#6      DefaultValueResolver._parameters (package:analyzer/src/summary2/default_value_resolver.dart:121:7)
flutter#7      DefaultValueResolver._function (package:analyzer/src/summary2/default_value_resolver.dart:89:5)
flutter#8      DefaultValueResolver.resolve (package:analyzer/src/summary2/default_value_resolver.dart:47:9)
flutter#9      LibraryBuilder.resolveDefaultValues (package:analyzer/src/summary2/library_builder.dart:313:43)
flutter#10     Linker._resolveDefaultValues (package:analyzer/src/summary2/link.dart:230:15)
flutter#11     Linker._buildOutlines (package:analyzer/src/summary2/link.dart:89:5)
flutter#12     Linker.link (package:analyzer/src/summary2/link.dart:69:5)
flutter#13     link (package:analyzer/src/summary2/link.dart:33:10)


Change-Id: I6145a1f728d432be8d0fa55235858e091030461c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/175187
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>

pkg/analyzer/lib/src/generated/resolver.dart

@@ -739,7 +739,7 @@ class ResolverVisitor extends ScopedVisitor {
 
   void startNullAwareIndexExpression(IndexExpression node) {
     if (_migratableAstInfoProvider.isIndexExpressionNullAware(node) &&
-        _isNonNullableByDefault) {
+        _flowAnalysis != null) {
       _flowAnalysis.flow.nullAwareAccess_rightBegin(
           node.target, node.realTarget.staticType ?? typeProvider.dynamicType);
       _unfinishedNullShorts.add(node.nullShortingTermination);
@@ -750,7 +750,7 @@ class ResolverVisitor extends ScopedVisitor {
     PropertyAccess node,
   ) {
     if (_migratableAstInfoProvider.isPropertyAccessNullAware(node) &&
-        _isNonNullableByDefault) {
+        _flowAnalysis != null) {
       var target = node.target;
       if (target is SimpleIdentifier && target.staticElement is ClassElement) {
         // `?.` to access static methods is equivalent to `.`, so do nothing.
@@ -948,7 +948,7 @@ class ResolverVisitor extends ScopedVisitor {
     InferenceContext.setTypeFromNode(node.target, node);
     node.target.accept(this);
 
-    if (node.isNullAware && _isNonNullableByDefault) {
+    if (node.isNullAware && _flowAnalysis != null) {
       _flowAnalysis.flow.nullAwareAccess_rightBegin(
           node.target, node.target.staticType ?? typeProvider.dynamicType);
       _unfinishedNullShorts.add(node.nullShortingTermination);
@@ -1652,7 +1652,7 @@ class ResolverVisitor extends ScopedVisitor {
     target?.accept(this);
 
     if (_migratableAstInfoProvider.isMethodInvocationNullAware(node) &&
-        _isNonNullableByDefault) {
+        _flowAnalysis != null) {
       if (target is SimpleIdentifier && target.staticElement is ClassElement) {
         // `?.` to access static methods is equivalent to `.`, so do nothing.
       } else {

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

@@ -16,6 +16,19 @@ main() {
 
 @reflectiveTest
 class IndexExpressionTest extends PubPackageResolutionTest {
+  test_invalid_inDefaultValue_nullAware() async {
+    await assertInvalidTestCode(r'''
+void f({a = b?[0]}) {}
+''');
+
+    assertIndexExpression(
+      findNode.index('[0]'),
+      readElement: null,
+      writeElement: null,
+      type: 'dynamic',
+    );
+  }
+
   test_read() async {
     await assertNoErrorsInCode(r'''
 class A {

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

@@ -1703,6 +1703,20 @@ class B extends A {
     assertSuperExpression(invocation.target);
   }
 
+  test_invalid_inDefaultValue_nullAware() async {
+    await assertInvalidTestCode('''
+void f({a = b?.foo()}) {}
+''');
+
+    assertMethodInvocation2(
+      findNode.methodInvocation('?.foo()'),
+      element: null,
+      typeArgumentTypes: [],
+      invokeType: 'dynamic',
+      type: 'dynamic',
+    );
+  }
+
   test_namedArgument() async {
     var question = typeToStringWithNullability ? '?' : '';
     await assertNoErrorsInCode('''

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

@@ -238,6 +238,30 @@ void f() {
     }
   }
 
+  test_invalid_inDefaultValue_nullAware() async {
+    await assertInvalidTestCode('''
+void f({a = b?.foo}) {}
+''');
+
+    assertPropertyAccess2(
+      findNode.propertyAccess('?.foo'),
+      element: null,
+      type: 'dynamic',
+    );
+  }
+
+  test_invalid_inDefaultValue_nullAware_cascade() async {
+    await assertInvalidTestCode('''
+void f({a = b?..foo}) {}
+''');
+
+    assertPropertyAccess2(
+      findNode.propertyAccess('?..foo'),
+      element: null,
+      type: 'dynamic',
+    );
+  }
+
   test_ofExtension_read() async {
     await assertNoErrorsInCode('''
 class A {}

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

@@ -448,6 +448,13 @@ mixin ResolutionTest implements ResourceProviderMixin {
         expectedPrefix: expectedPrefix);
   }
 
+  /// Resolve the [code], and ensure that it can be resolved without a crash,
+  /// and is invalid, i.e. produces a diagnostic.
+  Future<void> assertInvalidTestCode(String code) async {
+    await resolveTestCode(code);
+    assertHasTestErrors();
+  }
+
   void assertInvokeType(Expression node, String expected) {
     DartType actual;
     if (node is BinaryExpression) {