Statement completion framework with a few examples

pkg/analysis_server/lib/src/services/completion/statement/statement_completion.dart

Index: pkg/analysis_server/lib/src/services/completion/statement/statement_completion.dart
diff --git a/pkg/analysis_server/lib/src/services/completion/statement/statement_completion.dart b/pkg/analysis_server/lib/src/services/completion/statement/statement_completion.dart
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index 0000000000000000000000000000000000000000..2814dfa15856e1c04b03192d91f5fdc323c8985b
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+++ b/pkg/analysis_server/lib/src/services/completion/statement/statement_completion.dart
@@ -0,0 +1,410 @@
+// Copyright (c) 2017, 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.
+
+library services.src.completion.statement;
+
+import 'dart:async';
+
+import 'package:analysis_server/plugin/protocol/protocol.dart';
+import 'package:analysis_server/src/protocol_server.dart' hide Element;
+import 'package:analysis_server/src/services/correction/source_buffer.dart';
+import 'package:analysis_server/src/services/correction/source_range.dart';
+import 'package:analysis_server/src/services/correction/util.dart';
+import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/token.dart';
+import 'package:analyzer/dart/element/element.dart';
+import 'package:analyzer/error/error.dart';
+import 'package:analyzer/error/error.dart' as engine;
+import 'package:analyzer/src/dart/ast/utilities.dart';
+import 'package:analyzer/src/dart/error/hint_codes.dart';
+import 'package:analyzer/src/dart/error/syntactic_errors.dart';
+import 'package:analyzer/src/generated/engine.dart';
+import 'package:analyzer/src/generated/java_core.dart';
+import 'package:analyzer/src/generated/source.dart';
+
+/**
+ * An enumeration of possible statement completion kinds.
+ */
+class DartStatementCompletion {
+  static const NO_COMPLETION =
+      const StatementCompletionKind('No_COMPLETION', 'No completion available');
+  static const PLAIN_OLE_ENTER = const StatementCompletionKind(

[scheglov, 2017/04/07 19:36:07]

What means OLE?
And how about more general COM?

[messick, 2017/04/07 20:10:09]

I'll change it something more readable.

+      'PLAIN_OLE_ENTER', "Insert a newline at the end of the current line");
+  static const SIMPLE_SEMICOLON = const StatementCompletionKind(
+      'SIMPLE_SEMICOLON', "Add a semicolon and newline");
+  static const COMPLETE_IF_STMT = const StatementCompletionKind(
+      'COMPLETE_IF_STMT', "Complete if-statement");
+  static const COMPLETE_WHILE_STMT = const StatementCompletionKind(
+      'COMPLETE_WHILE_STMT', "Complete while-statement");
+}
+
+/**
+ * A description of a statement completion.
+ *
+ * Clients may not extend, implement or mix-in this class.
+ */
+class StatementCompletion {
+  /**
+   * A description of the assist being proposed.
+   */
+  final StatementCompletionKind kind;
+
+  /**
+   * The change to be made in order to apply the assist.
+   */
+  final SourceChange change;
+
+  /**
+   * Initialize a newly created completion to have the given [kind] and [change].
+   */
+  StatementCompletion(this.kind, this.change);
+}
+
+/**
+ * The context for computing a statement completion.
+ */
+class StatementCompletionContext {
+  final CompilationUnitElement unitElement;
+  final int selectionOffset;
+  final LineInfo lineInfo;
+  final List<engine.AnalysisError> errors;
+  final CompilationUnit unit;
+  final String file;

[scheglov, 2017/04/07 19:36:07]

The order of fields seems random.
Might be worth to order in the way this information is generated: file,
lineInfo, selectionOffset, unit, unitElement, errors.

[messick, 2017/04/07 20:10:09]

It wasn't random but I can change it to the order you prefer.

+
+  StatementCompletionContext(this.unitElement, this.selectionOffset,
+      this.lineInfo, this.errors, this.file, this.unit) {
+    if (unitElement.context == null) {
+      throw new Error(); // not reached; see getStatementCompletion()
+    }
+  }
+}
+
+/**
+ * A description of a class of statement completions. Instances are intended to
+ * hold the information that is common across a number of completions and to be
+ * shared by those completions.
+ *
+ * Clients may not extend, implement or mix-in this class.
+ */
+class StatementCompletionKind {
+  /**
+   * The name of this kind of statement completion, used for debugging.
+   */
+  final String name;
+
+  /**
+   * A human-readable description of the changes that will be applied by this
+   * kind of statement completion.
+   */
+  final String message;
+
+  /**
+   * Initialize a newly created kind of statement completion to have the given
+   * [name] and [message].
+   */
+  const StatementCompletionKind(this.name, this.message);
+
+  @override
+  String toString() => name;
+}
+
+/**
+ * The computer for Dart statement completions.
+ */
+class StatementCompletionProcessor {
+  static final NO_COMPLETION = new StatementCompletion(
+      DartStatementCompletion.NO_COMPLETION, new SourceChange("", edits: []));
+
+  final StatementCompletionContext statementContext;
+  final AnalysisContext analysisContext;
+  final CorrectionUtils utils;
+  int fileStamp;
+  AstNode node;
+  StatementCompletion completion;
+  SourceChange change = new SourceChange('statement-completion');
+  List errors = <engine.AnalysisError>[];
+  final Map<String, LinkedEditGroup> linkedPositionGroups =
+      <String, LinkedEditGroup>{};
+  Position exitPosition = null;
+
+  StatementCompletionProcessor(this.statementContext)
+      : analysisContext = statementContext.unitElement.context,
+        utils = new CorrectionUtils(statementContext.unit) {
+    fileStamp = analysisContext.getModificationStamp(source);
+  }
+
+  String get eol => utils.endOfLine;
+
+  String get file => statementContext.file;
+
+  LineInfo get lineInfo => statementContext.lineInfo;
+
+  int get requestLine => lineInfo.getLocation(selectionOffset).lineNumber;
+
+  int get selectionOffset => statementContext.selectionOffset;
+
+  Source get source => statementContext.unitElement.source;
+
+  CompilationUnit get unit => statementContext.unit;
+
+  CompilationUnitElement get unitElement => statementContext.unitElement;
+
+  Future<StatementCompletion> compute() async {
+    // If the source was changed between the constructor and running
+    // this asynchronous method, it is not safe to use the unit.
+    if (analysisContext.getModificationStamp(source) != fileStamp) {
+      return NO_COMPLETION;
+    }
+    node = new NodeLocator(selectionOffset).searchWithin(unit);
+    if (node == null) {
+      return NO_COMPLETION;
+    }
+    // TODO(messick): This needs to work for declarations.
+    node = node.getAncestor((n) => n is Statement);
+    for (engine.AnalysisError error in statementContext.errors) {
+      if (error.offset >= node.offset &&
+          error.offset <= node.offset + node.length) {
+        if (error.errorCode is! HintCode) {
+          errors.add(error);
+        }
+      }
+    }
+
+    if (_complete_ifStatement() ||
+        _complete_whileStatement() ||
+        _complete_simpleSemicolon() ||
+        _complete_plainOleEnter()) {
+      return completion;
+    }
+    return NO_COMPLETION;
+  }
+
+  void _addIndentEdit(SourceRange range, String oldIndent, String newIndent) {
+    SourceEdit edit = utils.createIndentEdit(range, oldIndent, newIndent);
+    doSourceChange_addElementEdit(change, unitElement, edit);
+  }
+
+  void _addInsertEdit(int offset, String text) {
+    SourceEdit edit = new SourceEdit(offset, 0, text);
+    doSourceChange_addElementEdit(change, unitElement, edit);
+  }
+
+  void _addReplaceEdit(SourceRange range, String text) {
+    SourceEdit edit = new SourceEdit(range.offset, range.length, text);
+    doSourceChange_addElementEdit(change, unitElement, edit);
+  }
+
+  void _appendEmptyBraces(SourceBuilder sb, [bool needsExitMark = false]) {
+    sb.append(' {');
+    sb.append(eol);
+    String indent = utils.getLinePrefix(selectionOffset);
+    sb.append(indent);
+    sb.append(utils.getIndent(1));
+    if (needsExitMark) {
+      sb.setExitOffset();
+    }
+    sb.append(eol);
+    sb.append(indent);
+    sb.append('}');
+  }
+
+  int _appendNewlinePlusIndent() {
+    // Append a newline plus proper indent and another newline.
+    // Return the position before the second newline.
+    String indent = utils.getLinePrefix(selectionOffset);
+    int loc = utils.getLineNext(selectionOffset);
+    _addInsertEdit(loc, indent + eol);
+    return loc + indent.length;
+  }
+
+  bool _complete_ifOrWhileStatement(
+      _IfWhileStructure ifNode, StatementCompletionKind kind) {
+    String text = utils.getNodeText(node);
+    if (text.endsWith(eol)) {
+      text = text.substring(0, text.length - eol.length);
+    }
+    SourceBuilder sb;
+    bool needsExit = false;
+    if (ifNode.leftParenthesis.lexeme.isEmpty) {
+      if (!ifNode.rightParenthesis.lexeme.isEmpty) {
+        // Quite unlikely to see this so don't try to fix it.
+        return false;
+      }
+      int len = ifNode.keyword.length;
+      if (text.length == len ||
+          !text.substring(len, len + 1).contains(new RegExp(r'\s'))) {
+        sb = new SourceBuilder(file, ifNode.offset + len);
+        sb.append(' ');
+      } else {
+        sb = new SourceBuilder(file, ifNode.offset + len + 1);
+      }
+      sb.append('(');
+      sb.setExitOffset();
+      sb.append(')');
+    } else {
+      if (_isEmptyExpression(ifNode.condition)) {
+        exitPosition = _newPosition(ifNode.leftParenthesis.offset + 1);
+        sb = new SourceBuilder(file, ifNode.rightParenthesis.offset + 1);
+      } else {
+        sb = new SourceBuilder(file, ifNode.rightParenthesis.offset + 1);
+        needsExit = true;
+      }
+    }
+    if (ifNode.block is EmptyStatement) {
+      _appendEmptyBraces(sb, needsExit);
+    }
+    _insertBuilder(sb);
+    _setCompletion(kind);
+    return true;
+  }
+
+  bool _complete_ifStatement() {
+    if (errors.isEmpty) {
+      return false;
+    }
+    IfStatement ifNode = node.getAncestor((n) => n is IfStatement);

[Brian Wilkerson, 2017/04/07 19:17:14]

Given that this can travel an indeterminate distance up the AST, isn't there a
danger of getting an unintended if statement?

[messick, 2017/04/07 20:10:09]

Yes, that's a good point. Since the conditional expression can be arbitrarily
complex, what's the recommended way of finding the statement that contains it?
Something like:

node.getAncesotor((n) => n is! Expression)

perhaps? And then check the statement type.

[Brian Wilkerson, 2017/04/07 21:23:37]

If you know it's contained in a statement (as opposed to a field initializer,
for example) then `n is Statement` would work. You just need to guard against
something like

if (cond1) {
  while (cond2) ^
}

finding the 'if' statement when there's a closer statement.

If you do just look for the nearest enclosing statement, you might want to
compute it once and pass it in to the appropriate _complete methods.

+    if (ifNode != null) {
+      if (ifNode.elseKeyword != null) {
+        return false;
+      }
+      var stmt = new _IfWhileStructure(ifNode.ifKeyword, ifNode.leftParenthesis,
+          ifNode.condition, ifNode.rightParenthesis, ifNode.thenStatement);
+      return _complete_ifOrWhileStatement(
+          stmt, DartStatementCompletion.COMPLETE_IF_STMT);
+    }
+    return false;
+  }
+
+  bool _complete_plainOleEnter() {
+    int offset;
+    if (!errors.isEmpty) {
+      offset = selectionOffset;
+    } else {
+      String indent = utils.getLinePrefix(selectionOffset);
+      int loc = utils.getLineNext(selectionOffset);
+      _addInsertEdit(loc, indent + eol);
+      offset = loc + indent.length + eol.length;
+    }
+    _setCompletionAt(DartStatementCompletion.PLAIN_OLE_ENTER, offset);
+    return true;
+  }
+
+  bool _complete_simpleSemicolon() {
+    if (errors.length != 1) {
+      return false;
+    }
+    var error = _findError(ParserErrorCode.EXPECTED_TOKEN, partialMatch: "';'");
+    if (error != null) {
+      int insertOffset = error.offset + error.length;
+      _addInsertEdit(insertOffset, ';');
+      int offset = _appendNewlinePlusIndent() + 1 /* ';' */;
+      _setCompletionAt(DartStatementCompletion.SIMPLE_SEMICOLON, offset);
+      return true;
+    }
+    return false;
+  }
+
+  bool _complete_whileStatement() {
+    if (errors.isEmpty) {
+      return false;
+    }
+    WhileStatement whileNode = node.getAncestor((n) => n is WhileStatement);
+    if (whileNode != null) {
+      var stmt = new _IfWhileStructure(
+          whileNode.whileKeyword,
+          whileNode.leftParenthesis,
+          whileNode.condition,
+          whileNode.rightParenthesis,
+          whileNode.body);
+      return _complete_ifOrWhileStatement(
+          stmt, DartStatementCompletion.COMPLETE_WHILE_STMT);
+    }
+    return false;
+  }
+
+  engine.AnalysisError _findError(ErrorCode code, {partialMatch: null}) {
+    var error =
+        errors.firstWhere((err) => err.errorCode == code, orElse: () => null);
+    if (error != null) {
+      if (partialMatch != null) {
+        return error.message.contains(partialMatch) ? error : null;
+      }
+      return error;
+    }
+    return null;
+  }
+
+  LinkedEditGroup _getLinkedPosition(String groupId) {
+    LinkedEditGroup group = linkedPositionGroups[groupId];
+    if (group == null) {
+      group = new LinkedEditGroup.empty();
+      linkedPositionGroups[groupId] = group;
+    }
+    return group;
+  }
+
+  void _insertBuilder(SourceBuilder builder, [int length = 0]) {
+    {
+      SourceRange range = rangeStartLength(builder.offset, length);
+      String text = builder.toString();
+      _addReplaceEdit(range, text);
+    }
+    // add linked positions
+    builder.linkedPositionGroups.forEach((String id, LinkedEditGroup group) {
+      LinkedEditGroup fixGroup = _getLinkedPosition(id);
+      group.positions.forEach((Position position) {
+        fixGroup.addPosition(position, group.length);
+      });
+      group.suggestions.forEach((LinkedEditSuggestion suggestion) {
+        fixGroup.addSuggestion(suggestion);
+      });
+    });
+    // add exit position
+    {
+      int exitOffset = builder.exitOffset;
+      if (exitOffset != null) {
+        exitPosition = _newPosition(exitOffset);
+      }
+    }
+  }
+
+  bool _isEmptyExpression(Expression expr) {
+    if (expr is! SimpleIdentifier) {
+      return false;
+    }
+    SimpleIdentifier id = expr as SimpleIdentifier;
+    return id.length == 0;
+  }
+
+  Position _newPosition(int offset) {
+    return new Position(file, offset);
+  }
+
+  void _setCompletion(StatementCompletionKind kind, [List args]) {
+    assert(exitPosition != null);
+    change.selection = exitPosition;
+    change.message = formatList(kind.message, args);
+    linkedPositionGroups.values
+        .forEach((group) => change.addLinkedEditGroup(group));
+    completion = new StatementCompletion(kind, change);
+  }
+
+  void _setCompletionAt(StatementCompletionKind kind, int offset, [List args]) {
+    exitPosition = _newPosition(offset);
+    _setCompletion(kind, args);
+  }
+}
+
+// Encapsulate common structure of if-statement and while-statement.
+class _IfWhileStructure {
+  final Token keyword;
+  final Token leftParenthesis, rightParenthesis;
+  final Expression condition;
+  final Statement block;
+
+  _IfWhileStructure(this.keyword, this.leftParenthesis, this.condition,
+      this.rightParenthesis, this.block);
+
+  int get offset => keyword.offset;
+}