Migration: Add if-statement and block-statement support to FixBuilder.

Change-Id: I3e3f0b3824a9a51b63f9ee8ffbe414415fc2b2e1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/121340
Reviewed-by: Mike Fairhurst <mfairhurst@google.com>

Author: stereotype441

pkg/nnbd_migration/lib/src/fix_builder.dart

@@ -232,12 +232,34 @@ abstract class FixBuilder extends GeneralizingAstVisitor<DartType> {
     }
   }
 
+  @override
+  DartType visitBlock(Block node) {
+    for (var statement in node.statements) {
+      statement.accept(this);
+    }
+    return null;
+  }
+
   @override
   DartType visitExpressionStatement(ExpressionStatement node) {
     visitSubexpression(node.expression, UnknownInferredType.instance);
     return null;
   }
 
+  @override
+  DartType visitIfStatement(IfStatement node) {
+    visitSubexpression(node.condition, _typeProvider.boolType);
+    _flowAnalysis.ifStatement_thenBegin(node.condition);
+    node.thenStatement.accept(this);
+    bool hasElse = node.elseStatement != null;
+    if (hasElse) {
+      _flowAnalysis.ifStatement_elseBegin();
+      node.elseStatement.accept(this);
+    }
+    _flowAnalysis.ifStatement_end(hasElse);
+    return null;
+  }
+
   @override
   DartType visitListLiteral(ListLiteral node) {
     DartType contextType;

pkg/nnbd_migration/test/fix_builder_test.dart

@@ -509,6 +509,19 @@ _f(_C<int, String/*?*/> c, String/*?*/ s) => c + s;
     visitSubexpression(findNode.binary('c +'), 'int');
   }
 
+  test_block() async {
+    await analyze('''
+_f(int/*?*/ x, int/*?*/ y) {
+  { // block
+    x + 1;
+    y + 1;
+  }
+}
+''');
+    visitStatement(findNode.statement('{ // block'),
+        nullChecked: {findNode.simple('x + 1'), findNode.simple('y + 1')});
+  }
+
   test_booleanLiteral() async {
     await analyze('''
 f() => true;
@@ -533,6 +546,45 @@ _f(int/*!*/ x, int/*?*/ y) {
         nullChecked: {findNode.simple('y;')});
   }
 
+  test_ifStatement_flow_promote_in_else() async {
+    await analyze('''
+_f(int/*?*/ x) {
+  if (x == null) {
+    x + 1;
+  } else {
+    x + 2;
+  }
+}
+''');
+    visitStatement(findNode.statement('if'),
+        nullChecked: {findNode.simple('x + 1')});
+  }
+
+  test_ifStatement_flow_promote_in_then() async {
+    await analyze('''
+_f(int/*?*/ x) {
+  if (x != null) {
+    x + 1;
+  } else {
+    x + 2;
+  }
+}
+''');
+    visitStatement(findNode.statement('if'),
+        nullChecked: {findNode.simple('x + 2')});
+  }
+
+  test_ifStatement_flow_promote_in_then_no_else() async {
+    await analyze('''
+_f(int/*?*/ x) {
+  if (x != null) {
+    x + 1;
+  }
+}
+''');
+    visitStatement(findNode.statement('if'));
+  }
+
   test_integerLiteral() async {
     await analyze('''
 f() => 1;