Make observable transform a barback transform.

pkg/codegen/lib/refactor.dart

+// 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.
+
+/**
+ * Tools to help implement refactoring like transformations to Dart code.
+ *
+ * [TextEditTransaction] supports making a series of changes to a text buffer.
+ * [guessIndent] helps to guess the appropriate indentiation for the new code.
+ */
+library codegen.refactor;
+
+import 'printer.dart';
+import 'package:source_maps/span.dart';
+
+const $CR = 13;
+const $LF = 10;
+const $TAB = 9;
+const $SPACE = 32;
+
+/**
+ * Editable text transaction. Applies a series of edits using original location
+ * information, and composes them into the edited string.
+ */
+class TextEditTransaction {
+  final SourceFile file;
+  final String original;
+  final _edits = <_TextEdit>[];
+
+  TextEditTransaction(this.original, this.file);
+
+  bool get hasEdits => _edits.length > 0;
+
+  /**
+   * Edit the original text, replacing text on the range [begin] and [end]
+   * with the [replacement]. [replacement] can be either a string or a
+   * [CodePrinter].
+   */
+  void edit(int begin, int end, replacement) {
+    _edits.add(new _TextEdit(begin, end, replacement));
+  }
+
+  /** Create a source map [Location] for [offset]. */
+  Location _loc(int offset) =>
+      file != null ? file.location(offset) : null;
+
+  /**
+   * Applies all pending [edit]s and returns the rewritten string.
+   * If no edits were made, returns the [original] string.
+   * Throws [UnsupportedError] if the edits were overlapping.
+   */
+  CodePrinter commit() {
+    var printer = new CodePrinter(0);
+    if (_edits.length == 0) {
+      printer.add(original, location: _loc(0), isOriginal: true);
+      return printer;
+    }
+
+    // Sort edits by start location.
+    _edits.sort();
+
+    int consumed = 0;
+    for (var edit in _edits) {
+      if (consumed > edit.begin) {
+        var sb = new StringBuffer();
+        sb..write(file.location(edit.begin).formatString)
+            ..write(': overlapping edits. Insert at offset ')
+            ..write(edit.begin)
+            ..write(' but have consumed ')
+            ..write(consumed)
+            ..write(' input characters. List of edits:');
+        for (var e in _edits) sb..write('\n    ')..write(e);
+        throw new UnsupportedError(sb.toString());
+      }
+
+      // Add characters from the original string between this edit and the last
+      // one, if any.
+      var betweenEdits = original.substring(consumed, edit.begin);
+      printer..add(betweenEdits, location: _loc(consumed), isOriginal: true)
+             ..add(edit.replace, location: _loc(edit.begin));
+      consumed = edit.end;
+    }
+
+    // Add any text from the end of the original string that was not replaced.
+    printer.add(original.substring(consumed),
+        location: _loc(consumed), isOriginal: true);
+    return printer;
+  }
+}
+
+class _TextEdit implements Comparable<_TextEdit> {
+  final int begin;
+  final int end;
+
+  /** The replacement used by the edit, can be a string or a [CodePrinter]. */
+  final replace;
+
+  _TextEdit(this.begin, this.end, this.replace);
+
+  int get length => end - begin;
+
+  String toString() => '(Edit @ $begin,$end: "$replace")';
+
+  int compareTo(_TextEdit other) {
+    int diff = begin - other.begin;
+    if (diff != 0) return diff;
+    return end - other.end;
+  }
+}
+
+/**
+ * Finds and returns all whitespace characters at the start of the current line.
+ */
+String guessIndent(String code, int charOffset) {
+  // Find the beginning of the line
+  int lineStart = 0;
+  for (int i = charOffset - 1; i >= 0; i--) {
+    var c = code.codeUnitAt(i);
+    if (c == $LF || c == $CR) {
+      lineStart = i + 1;
+      break;
+    }
+  }
+
+  // Grab all the whitespace
+  int whitespaceEnd = code.length;
+  for (int i = lineStart; i < code.length; i++) {
+    var c = code.codeUnitAt(i);
+    if (c != $SPACE && c != $TAB) {
+      whitespaceEnd = i;
+      break;
+    }
+  }
+
+  return code.substring(lineStart, whitespaceEnd);
+}
+