assist to insert null checks

(still WIP)

Change-Id: Icca46e4a9fbca43f00151d99cb24935e18c97294
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/117589
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Phil Quitslund <[email protected]>

Author: pq

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

@@ -31,6 +31,8 @@ class DartAssistContextImpl implements DartAssistContext {
  * An enumeration of possible assist kinds.
  */
 class DartAssistKind {
+  static const ADD_NOT_NULL_ASSERT = const AssistKind(
+      'dart.assist.addNotNullAssert', 30, "Add a not-null assertion");
   static const ADD_TYPE_ANNOTATION = const AssistKind(
       'dart.assist.addTypeAnnotation', 30, "Add type annotation");
   static const ASSIGN_TO_LOCAL_VARIABLE = const AssistKind(

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

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 import 'dart:collection';
+import 'dart:math';
 
 import 'package:analysis_server/plugin/edit/assist/assist_core.dart';
 import 'package:analysis_server/plugin/edit/assist/assist_dart.dart';
@@ -61,6 +62,7 @@ class AssistProcessor extends BaseProcessor {
     )) {
       await _addProposals_addTypeAnnotation();
     }
+    await _addProposal_addNotNullAssert();
     await _addProposal_assignToLocalVariable();
     await _addProposal_convertClassToMixin();
     await _addProposal_convertDocumentationIntoBlock();
@@ -225,6 +227,42 @@ class AssistProcessor extends BaseProcessor {
     assists.add(new Assist(kind, change));
   }
 
+  Future<void> _addProposal_addNotNullAssert() async {
+    if (node is SimpleIdentifier) {
+      if (node.parent is FormalParameter) {
+        final exp = node.parent.thisOrAncestorMatching(
+            (node) => node is FunctionExpression || node is MethodDeclaration);
+        var body;
+        if (exp is FunctionExpression) {
+          body = exp.body;
+        } else if (exp is MethodDeclaration) {
+          body = exp.body;
+        }
+        if (body is BlockFunctionBody) {
+          final changeBuilder = _newDartChangeBuilder();
+          await changeBuilder.addFileEdit(file, (DartFileEditBuilder builder) {
+            final id = (node as SimpleIdentifier).name;
+            final prefix = utils.getNodePrefix(exp);
+            final indent = utils.getIndent(1);
+            // todo (pq): follow-ups:
+            // 1. if the end token is on the same line as the body
+            // we should add an `eol` before the assert as well.
+            // 2. also, consider asking the block for the list of statements and
+            // adding the statement to the beginning of the list, special casing
+            // when there are no statements (or when there's a single statement
+            // and the whole block is on the same line).
+            final int offset = min(utils.getLineNext(body.beginToken.offset),
+                body.endToken.offset);
+            builder.addSimpleInsertion(
+                offset, '$prefix${indent}assert($id != null);$eol');
+            _addAssistFromBuilder(
+                changeBuilder, DartAssistKind.ADD_NOT_NULL_ASSERT);
+          });
+        }
+      }
+    }
+  }
+
   Future<void> _addProposal_assignToLocalVariable() async {
     // prepare enclosing ExpressionStatement
     ExpressionStatement expressionStatement;

pkg/analysis_server/test/src/services/correction/assist/add_not_null_assert.dart

@@ -0,0 +1,55 @@
+// Copyright (c) 2019, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:analysis_server/src/services/correction/assist.dart';
+import 'package:analyzer_plugin/utilities/assist/assist.dart';
+import 'package:test_reflective_loader/test_reflective_loader.dart';
+
+import 'assist_processor.dart';
+
+main() {
+  defineReflectiveSuite(() {
+    defineReflectiveTests(AddNotNullAssert);
+  });
+}
+
+@reflectiveTest
+class AddNotNullAssert extends AssistProcessorTest {
+  @override
+  AssistKind get kind => DartAssistKind.ADD_NOT_NULL_ASSERT;
+
+  test_function_expressionBody_noAssert() async {
+    await resolveTestUnit('''
+int double(int x) => x * 2;
+''');
+    // todo (pq): support expression bodies.
+    await assertNoAssistAt('x');
+  }
+
+  test_function_noAssert() async {
+    await resolveTestUnit('''
+foo(int x) {
+}
+''');
+    await assertHasAssistAt('x', '''
+foo(int x) {
+  assert(x != null);
+}
+''');
+  }
+
+  test_method_noAssert() async {
+    await resolveTestUnit('''
+class A {
+  foo(int x) {
+  }
+}''');
+    await assertHasAssistAt('x', '''
+class A {
+  foo(int x) {
+    assert(x != null);
+  }
+}''');
+  }
+}

pkg/analysis_server/test/src/services/correction/assist/test_all.dart

@@ -4,6 +4,7 @@
 
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
+import 'add_not_null_assert.dart' as add_not_null_assert;
 import 'add_type_annotation_test.dart' as add_type_annotation;
 import 'assign_to_local_variable_test.dart' as assign_to_local_variable;
 import 'convert_class_to_mixin_test.dart' as convert_class_to_mixin;
@@ -82,6 +83,7 @@ import 'use_curly_braces_test.dart' as use_curly_braces;
 
 main() {
   defineReflectiveSuite(() {
+    add_not_null_assert.main();
     add_type_annotation.main();
     assign_to_local_variable.main();
     convert_class_to_mixin.main();