Prevent a cast exception in convert-to-if-null

I wasn't able to find a case that reproduced the exception. I suspect
that this means that we won't produce a fix in at least one case where
we could be. If you have ideas for how to reproduce, let me know.

Bug: 43432
Change-Id: Id1a2ffec281d6622792253358243c0fad4387f6d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/162922
Commit-Queue: Brian Wilkerson <[email protected]>
Reviewed-by: Konstantin Shcheglov <[email protected]>

Author: bwilkerson

pkg/analysis_server/lib/src/services/correction/dart/convert_to_if_null.dart

@@ -16,27 +16,28 @@ class ConvertToIfNull extends CorrectionProducer {
 
   @override
   Future<void> compute(ChangeBuilder builder) async {
-    var conditional = node.thisOrAncestorOfType<ConditionalExpression>();
-    if (conditional == null) {
-      return;
-    }
-    var condition = conditional.condition as BinaryExpression;
-    Expression nullableExpression;
-    Expression defaultExpression;
-    if (condition.operator.type == TokenType.EQ_EQ) {
-      nullableExpression = conditional.elseExpression;
-      defaultExpression = conditional.thenExpression;
-    } else {
-      nullableExpression = conditional.thenExpression;
-      defaultExpression = conditional.elseExpression;
-    }
-    await builder.addDartFileEdit(file, (builder) {
-      builder.addReplacement(range.node(conditional), (builder) {
-        builder.write(utils.getNodeText(nullableExpression));
-        builder.write(' ?? ');
-        builder.write(utils.getNodeText(defaultExpression));
+    var node = this.node;
+    if (node is ConditionalExpression &&
+        node.offset == errorOffset &&
+        node.length == errorLength) {
+      var condition = node.condition as BinaryExpression;
+      Expression nullableExpression;
+      Expression defaultExpression;
+      if (condition.operator.type == TokenType.EQ_EQ) {
+        nullableExpression = node.elseExpression;
+        defaultExpression = node.thenExpression;
+      } else {
+        nullableExpression = node.thenExpression;
+        defaultExpression = node.elseExpression;
+      }
+      await builder.addDartFileEdit(file, (builder) {
+        builder.addReplacement(range.node(node), (builder) {
+          builder.write(utils.getNodeText(nullableExpression));
+          builder.write(' ?? ');
+          builder.write(utils.getNodeText(defaultExpression));
+        });
       });
-    });
+    }
   }
 
   /// Return an instance of this class. Used as a tear-off in `FixProcessor`.

pkg/analysis_server/test/src/services/correction/fix/convert_to_if_null_test.dart

@@ -4,6 +4,7 @@
 
 import 'package:analysis_server/src/services/correction/fix.dart';
 import 'package:analysis_server/src/services/linter/lint_names.dart';
+import 'package:analyzer/src/dart/error/lint_codes.dart';
 import 'package:analyzer_plugin/utilities/fixes/fixes.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
@@ -36,6 +37,33 @@ void f(String s) {
 ''');
   }
 
+  Future<void> test_malformed() async {
+    await resolveTestUnit('''
+void f(String s, bool b) {
+  print(b ? s != null ? s : : null);
+}
+''');
+    await assertNoFix(errorFilter: (error) {
+      var code = error.errorCode;
+      return code is LintCode &&
+          code.name == LintNames.prefer_if_null_operators;
+    });
+  }
+
+  Future<void> test_malformed_parentheses() async {
+    // https://github.com/dart-lang/sdk/issues/43432
+    await resolveTestUnit('''
+void f(String s, bool b) {
+  print(b ? (s != null ? s : ) : null);
+}
+''');
+    await assertNoFix(errorFilter: (error) {
+      var code = error.errorCode;
+      return code is LintCode &&
+          code.name == LintNames.prefer_if_null_operators;
+    });
+  }
+
   Future<void> test_notEqual() async {
     await resolveTestUnit('''
 void f(String s) {