Fix for NPE when no flow for 'if' statement.

FAILURE: typedef:(:<>(s{if
[NoSuchMethodError: The method 'ifStatement_thenBegin' was called on null.
Receiver: null
Tried calling: ifStatement_thenBegin(Instance of 'SimpleIdentifierImpl'), #0      Object.noSuchMethod (dart:core-patch/object_patch.dart:54:5)
flutter#1      ResolverVisitor.visitIfStatement (package:analyzer/src/generated/resolver.dart:1556:26)
flutter#2      IfStatementImpl.accept (package:analyzer/src/dart/ast/ast.dart:5705:49)
flutter#3      NodeListImpl.accept (package:analyzer/src/dart/ast/ast.dart:7611:20)
flutter#4      BlockImpl.visitChildren (package:analyzer/src/dart/ast/ast.dart:1087:17)
#5      ResolverVisitor.visitNode (package:analyzer/src/generated/resolver.dart:1743:10)
flutter#6      UnifyingAstVisitor.visitBlock (package:analyzer/dart/ast/visitor.dart:3143:31)
flutter#7      ScopedVisitor.visitBlock.<anonymous closure> (package:analyzer/src/generated/resolver.dart:2467:13)
flutter#8      ScopedVisitor._withDeclaredLocals (package:analyzer/src/generated/resolver.dart:3061:8)
flutter#9      ScopedVisitor.visitBlock (package:analyzer/src/generated/resolver.dart:2466:5)
flutter#10     BlockImpl.accept (package:analyzer/src/dart/ast/ast.dart:1083:49)
flutter#11     BlockFunctionBodyImpl.visitChildren (package:analyzer/src/dart/ast/ast.dart:1042:13)
flutter#12     ResolverVisitor.visitNode (package:analyzer/src/generated/resolver.dart:1743:10)
flutter#13     UnifyingAstVisitor.visitBlockFunctionBody (package:analyzer/dart/ast/visitor.dart:3146:55)
flutter#14     ScopedVisitor.visitBlockFunctionBody (package:analyzer/src/generated/resolver.dart:2476:13)
flutter#15     ResolverVisitor.visitBlockFunctionBody (package:analyzer/src/generated/resolver.dart:954:13)
flutter#16     BlockFunctionBodyImpl.accept (package:analyzer/src/dart/ast/ast.dart:1038:49)
flutter#17     FunctionExpressionImpl.visitChildren (package:analyzer/src/dart/ast/ast.dart:5010:12)
flutter#18     FunctionExpressionResolver.resolve (package:analyzer/src/dart/resolver/function_expression_resolver.dart:65:10)
flutter#19     ResolverVisitor.visitFunctionExpression (package:analyzer/src/generated/resolver.dart:1457:37)
flutter#20     FunctionExpressionImpl.accept (package:analyzer/src/dart/ast/ast.dart:5004:49)
#21     DefaultFormalParameterImpl.visitChildren (package:analyzer/src/dart/ast/ast.dart:3008:20)
#22     ResolverVisitor.visitNode (package:analyzer/src/generated/resolver.dart:1743:10)
#23     UnifyingAstVisitor.visitDefaultFormalParameter (package:analyzer/dart/ast/visitor.dart:3198:65)
#24     ResolverVisitor.visitDefaultFormalParameter (package:analyzer/src/generated/resolver.dart:1239:11)
#25     DefaultFormalParameterImpl.accept (package:analyzer/src/dart/ast/ast.dart:3003:15)
#26     NodeListImpl.accept (package:analyzer/src/dart/ast/ast.dart:7611:20)
#27     FormalParameterListImpl.visitChildren (package:analyzer/src/dart/ast/ast.dart:4493:17)
#28     ResolverVisitor.visitNode (package:analyzer/src/generated/resolver.dart:1743:10)
#29     UnifyingAstVisitor.visitFormalParameterList (package:analyzer/dart/ast/visitor.dart:3258:59)
#30     ScopedVisitor.visitFormalParameterList (package:analyzer/src/generated/resolver.dart:2717:11)
#31     FormalParameterListImpl.accept (package:analyzer/src/dart/ast/ast.dart:4489:49)
#32     FunctionTypeAliasImpl.visitChildren (package:analyzer/src/dart/ast/ast.dart:5166:18)
#33     ResolverVisitor.visitNode (package:analyzer/src/generated/resolver.dart:1743:10)
#34     UnifyingAstVisitor.visitFunctionTypeAlias (package:analyzer/dart/ast/visitor.dart:3285:55)
#35     ScopedVisitor.visitFunctionTypeAliasInScope (package:analyzer/src/generated/resolver.dart:2819:11)
#36     ResolverVisitor.visitFunctionTypeAliasInScope (package:analyzer/src/generated/resolver.dart:1490:11)
#37     ScopedVisitor.visitFunctionTypeAlias (package:analyzer/src/generated/resolver.dart:2812:7)
#38     ResolverVisitor.visitFunctionTypeAlias (package:analyzer/src/generated/resolver.dart:1482:13)
#39     FunctionTypeAliasImpl.accept (package:analyzer/src/dart/ast/ast.dart:5158:49)
#40     ResolverVisitor.visitCompilationUnit (package:analyzer/src/generated/resolver.dart:1088:23)
#41     CompilationUnitImpl.accept (package:analyzer/src/dart/ast/ast.dart:2134:49)
#42     LibraryAnalyzer._resolveFile (package:analyzer/src/dart/analysis/library_analyzer.dart:706:10)


R=brianwilkerson@google.com

Change-Id: I72bf7219d55d0bf53beae11f977f8fb840dd8e2e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/175908
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>

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

@@ -1516,7 +1516,7 @@ class ResolverVisitor extends ScopedVisitor {
 
     CollectionElement thenElement = node.thenElement;
     if (_flowAnalysis != null) {
-      _flowAnalysis.flow.ifStatement_thenBegin(condition);
+      _flowAnalysis.flow?.ifStatement_thenBegin(condition);
       thenElement.accept(this);
     } else {
       _promoteManager.visitIfElement_thenElement(
@@ -1556,7 +1556,7 @@ class ResolverVisitor extends ScopedVisitor {
 
     Statement thenStatement = node.thenStatement;
     if (_flowAnalysis != null) {
-      _flowAnalysis.flow.ifStatement_thenBegin(condition);
+      _flowAnalysis.flow?.ifStatement_thenBegin(condition);
       visitStatementInScope(thenStatement);
       nullSafetyDeadCodeVerifier?.flowEnd(thenStatement);
     } else {

pkg/analyzer/test/generated/invalid_code_test.dart

@@ -395,6 +395,18 @@ var v = <T>();
 ''');
   }
 
+  test_inDefaultValue_noFlow_ifExpression() async {
+    await _assertCanBeAnalyzed('''
+typedef void F({a = [if (true) 0]});
+''');
+  }
+
+  test_inDefaultValue_noFlow_ifStatement() async {
+    await _assertCanBeAnalyzed('''
+typedef void F([a = () { if (true) 0; }]);
+''');
+  }
+
   test_issue_40837() async {
     await _assertCanBeAnalyzed('''
 class A {