Make observable transform a barback transform.

pkg/codegen/lib/printer.dart

Index: pkg/codegen/lib/printer.dart
diff --git a/pkg/codegen/lib/printer.dart b/pkg/codegen/lib/printer.dart
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+// Copyright (c) 2013, 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 codegen.printer;
+
+import 'package:source_maps/source_maps.dart';
+
+/**
+ * Helper class to format generated code and keep track of source map
+ * information.
+ */
+class CodePrinter {
+
+  /**
+   * Items recoded by this printer, which can be [String] literals,
+   * other printing helpers such as [Declarations] and [CodePrinter],
+   * and source map information like [Location] and [Span].
+   */
+  List _items = [];
+
+  /** Internal buffer to merge consecutive strings added to this printer. */
+  StringBuffer _buff;
+
+  /** Current indentation, which can be updated from outside this class. */
+  int indent = 0;
+
+  /**
+   * Item used to indicate that the following item is copied from the original
+   * source code, and hence we should preserve source-maps on every new line.
+   */
+  static final _ORIGINAL = new Object();
+
+  CodePrinter(this.indent);
+
+  /**
+   * Adds [object] to this printer. [object] can be a [String], [Declarations],
+   * or a [CodePrinter]. If [object] is a [String], the value is appended
+   * directly, without doing any formatting changes. If you wish to add a line
+   * of code with automatic indentation, use [addLine] instead. [Declarations]
+   * and [CodePrinter] are not processed until [build] gets called later on.
+   * We ensure that [build] emits every object in the order that they were added
+   * to this printer.
+   *
+   * The [location] and [span] parameters indicate the corresponding source map
+   * location of [object] in the original input. Only one, [location] or
+   * [span], should be provided at a time.
+   *
+   * Indicate [isOriginal] when [object] is copied directly from the user code.
+   * Setting [isOriginal] will make this printer propagate source map locations
+   * on every line-break.
+   */
+  void add(object, {Location location, Span span, bool isOriginal: false}) {
+    if (object is! String || location != null || span != null || isOriginal) {
+      _flush();
+      assert(location == null || span == null);
+      if (location != null) _items.add(location);
+      if (span != null) _items.add(span);
+      if (isOriginal) _items.add(_ORIGINAL);
+    }
+
+    if (object is String) {
+      _appendString(object);
+    } else {
+      _items.add(object);
+    }
+  }
+
+  /** Append `2 * indent` spaces to this printer. */
+  void insertIndent() => _indent(indent);
+
+  /**
+   * Add a [line], autoindenting to the current value of [indent]. Note,
+   * indentation is not inferred, so if a line opens or closes an indentation
+   * block, you need to also update [indent] accordingly. Also, indentation is
+   * not adapted for nested code printers. If you add a [CodePrinter] to this
+   * printer, its indentation is set separately and will not include any
+   * the indentation set here.
+   *
+   * The [location] and [span] parameters indicate the corresponding source map
+   * location of [object] in the original input. Only one, [location] or
+   * [span], should be provided at a time.
+   */
+  void addLine(String line, {Location location, Span span}) {
+    if (location != null || span != null) {
+      _flush();
+      assert(location == null || span == null);
+      if (location != null) _items.add(location);
+      if (span != null) _items.add(span);
+    }
+    if (line == null) return;
+    if (line != '') {
+      // We don't indent empty lines.
+      _indent(indent);
+      _appendString(line);
+    }
+    _appendString('\n');
+  }
+
+  /** Appends a string merging it with any previous strings, if possible. */
+  void _appendString(String s) {
+    if (_buff == null) _buff = new StringBuffer();
+    _buff.write(s);
+  }
+
+  /** Adds all of the current [_buff] contents as a string item. */
+  void _flush() {
+    if (_buff != null) {
+      _items.add(_buff.toString());
+      _buff = null;
+    }
+  }
+
+  void _indent(int indent) {
+    for (int i = 0; i < indent; i++) _appendString('  ');
+  }
+
+  /**
+   * Returns a string representation of all the contents appended to this
+   * printer, including source map location tokens.
+   */
+  String toString() {
+    _flush();
+    return (new StringBuffer()..writeAll(_items)).toString();
+  }
+
+  /** [Printer] used during the last call to [build], if any. */
+  Printer _printer;
+
+  /** Returns the text produced after calling [build]. */
+  String get text => _printer.text;
+
+  /** Returns the source-map information produced after calling [build]. */
+  String get map => _printer.map;
+
+  /**
+   * Builds the output of this printer and source map information. After calling
+   * this function, you can use [text] and [map] to retrieve the geenrated code
+   * and source map information, respectively.
+   */
+  void build(String filename) {
+    _build(_printer = new Printer(filename));
+  }
+
+  void _build(Printer printer) {
+    _flush();
+    bool propagate = false;
+    for (var item in _items) {
+      if (item is Declarations) {
+        item._build(printer);
+      } else if (item is CodePrinter) {
+        item._build(printer);
+      } else if (item is String) {
+        printer.add(item, projectMarks: propagate);
+        propagate = false;
+      } else if (item is Location || item is Span) {
+        printer.mark(item);
+      } else if (item == _ORIGINAL) {
+        // we insert booleans when we are about to quote text that was copied
+        // from the original source. In such case, we will propagate marks on
+        // every new-line.
+        propagate = true;
+      } else {
+        throw new UnsupportedError('Unknown item type: $item');
+      }
+    }
+  }
+}
+
+/** A declaration of a field or local variable. */
+class Declaration implements Comparable {
+  final String type;
+  final String name;
+  final Span sourceSpan;
+  final String initializer;
+
+  Declaration(this.type, this.name, this.sourceSpan, [this.initializer]);
+
+  /**
+   * Sort declarations by type, so they can be merged together in a declaration
+   * group.
+   */
+  int compareTo(Declaration other) {
+    if (type != other.type) return type.compareTo(other.type);
+    return name.compareTo(other.name);
+  }
+}
+
+/** A set of declarations grouped together. */
+class Declarations {
+
+  /** All declarations in this group. */
+  final List<Declaration> declarations = <Declaration>[];
+
+  /** Indentation associated with this declaration group. */
+  final int indent;
+
+  /** Whether these declarations are local variables or fields in a class. */
+  final bool isLocal;
+
+  /** Whether types should be prefixed with the "static" keyword. */
+  final bool staticKeyword;
+
+  Declarations(this.indent, {this.isLocal: false, this.staticKeyword: false});
+
+  /** Add a declaration to this group. */
+  void add(String type, String identifier, Span sourceSpan, [String init]) {
+    declarations.add(
+        new Declaration(isLocal ? 'var' : type, identifier, sourceSpan, init));
+  }
+
+  String toString() {
+    var printer = new Printer(null);
+    _build(printer);
+    return printer.text;
+  }
+
+  void _build(Printer printer) {
+    if (declarations.length == 0) return;
+    declarations.sort();
+    var lastType = null;
+    printer.addSpaces(2 * indent);
+    for (var d in declarations) {
+      if (d.type != lastType) {
+        if (lastType != null) {
+          printer.add(';\n');
+          printer.addSpaces(2 * indent);
+        }
+        if (staticKeyword) printer.add('static ');
+        printer.add(d.type);
+        lastType = d.type;
+      } else {
+        printer.add(',');
+      }
+      printer.add(' ');
+      if (d.sourceSpan != null) printer.mark(d.sourceSpan);
+      printer.add(d.name);
+      if (d.initializer != null) {
+        printer..add(' = ')..add(d.initializer);
+      }
+    }
+    printer.add(';\n');
+  }
+}
+