Add pretty-printing to unittest and more thoroughly print values.

pkg/unittest/lib/src/pretty_print.dart

+// 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 pretty_print;
+
+import 'utils.dart';
+
+/**
+ * Returns a pretty-printed representation of [object].
+ *
+ * If [maxLineLength] is passed, this will attempt to ensure that each line is
+ * no longer than [maxLineLength] characters long. This isn't guaranteed, since
+ * individual objects may have string representations that are too long, but
+ * most lines will be less than [maxLineLength] long.
+ *
+ * If [maxItems] is passed, [Iterable]s and [Map]s will only print their first
+ * [maxItems] members or key/value pairs, respectively.
+ */
+String prettyPrint(object, {int maxLineLength, int maxItems}) {
+  String _prettyPrint(object, int indent, Set seen, bool top) {
+    // Avoid looping infinitely on recursively-nested data structures.
+    if (seen.contains(object)) return "(recursive)";
+    seen = seen.union(new Set.from([object]));
+    String pp(child) => _prettyPrint(child, indent + 2, seen, false);
+
+    if (object is Iterable) {
+      // Print the type name for non-List iterables.
+      var typeName = object is List ? "" : typeName(object) + ":";
+
+      // Truncate the list of strings if it's longer than [maxItems].
+      var strings = object.map(pp).toList();
+      if (maxItems != null && strings.length > maxItems) {
+        strings.replaceRange(maxItems - 1, strings.length, ['...']);
+      }
+
+      // If the printed string is short and doesn't contain a newline, print it
+      // as a single line.
+      var singleLine = "$typeName[${strings.join(', ')}]";
+      if ((maxLineLength == null ||
+              singleLine.length + indent <= maxLineLength) &&
+          !singleLine.contains("\n")) {
+        return singleLine;
+      }
+
+      // Otherwise, print each member on its own line.
+      return "$typeName[\n" + strings.map((string) {
+        return _indent(indent + 2) + string;
+      }).join(",\n") + "\n" + _indent(indent) + "]";
+    } else if (object is Map) {
+      // Convert the contents of the map to string representations.
+      var strings = object.keys.map((key) {
+        return '${pp(key)}: ${pp(object[key])}';
+      }).toList();
+
+      // Truncate the list of strings if it's longer than [maxItems].
+      if (maxItems != null && strings.length > maxItems) {
+        strings.replaceRange(maxItems - 1, strings.length, ['...']);
+      }
+
+      // If the printed string is short and doesn't contain a newline, print it
+      // as a single line.
+      var singleLine = "{${strings.join(", ")}}";
+      if ((maxLineLength == null ||
+              singleLine.length + indent <= maxLineLength) &&
+          !singleLine.contains("\n")) {
+        return singleLine;
+      }
+
+      // Otherwise, print each key/value pair on its own line.
+      return "{\n" + strings.map((string) {
+        return _indent(indent + 2) + string;
+      }).join(",\n") + "\n" + _indent(indent) + "}";
+    } else if (object is String) {
+      // Escape strings and print each line on its own line.
+      var lines = object.split("\n");
+      return "'" + lines.map(escapeString)
+          .join("\\n'\n${_indent(indent + 2)}'") + "'";
+    } else {
+      var value = object.toString().replaceAll("\n", _indent(indent) + "\n");
+      var defaultToString = value.startsWith("Instance of ");
+
+      // If this is the top-level call to [prettyPrint], wrap the value on angle
+      // brackets to set it apart visually.
+      if (top) value = "<$value>";
+
+      // Print the type of objects with custom [toString] methods. Primitive
+      // objects and objects that don't implement a custom [toString] don't need
+      // to have their types printed.
+      if (object is num || object is bool || object is Function ||
+          object == null || defaultToString) {
+        return value;
+      } else {
+        return "${typeName(object)}:$value";

[gram, 2013/05/17 20:38:33]

The latest version has a lot of "Unknown:<value>" cases. Can we skip the type if
it is going to print as Unknown? 'Unknown" doesn't seem to add much value.

[nweiz, 2013/05/17 21:07:21]

Changed to "?" as per offline discussion.

+      }
+    }
+  }
+
+  return _prettyPrint(object, 0, new Set(), true);
+}
+
+String _indent(int length) => new List.filled(length, ' ').join('');