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) {
+    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) {
+      var typeName = object is List ? "" : typeName(object) + ":";
+

[gram, 2013/05/17 01:00:30]

Please add a short comment at the start of each of these logical blocks of code
here to explain their function.

[nweiz, 2013/05/17 19:50:56]

Done.

+      var strings = object.map(pp).toList();
+      if (maxItems != null && strings.length > maxItems) {
+        strings.replaceRange(maxItems - 1, strings.length, ['...']);
+      }
+
+      var singleLine = "$typeName[${strings.join(', ')}]";
+      if ((maxLineLength == null ||
+              singleLine.length + indent <= maxLineLength) &&
+          !singleLine.contains("\n")) {
+        return singleLine;
+      }
+
+      return "$typeName[\n" + strings.map((string) {
+        return _indent(indent + 2) + string;
+      }).join(",\n") + "\n" + _indent(indent) + "]";
+    } else if (object is Map) {
+      var strings = object.keys.map((key) {
+        return '${pp(key)}: ${pp(object[key])}';
+      }).toList();
+      if (maxItems != null && strings.length > maxItems) {
+        strings.replaceRange(maxItems - 1, strings.length, ['...']);
+      }
+
+      var singleLine = "{${strings.join(", ")}}";
+      if ((maxLineLength == null ||
+              singleLine.length + indent <= maxLineLength) &&
+          !singleLine.contains("\n")) {
+        return singleLine;
+      }
+
+      return "{\n" + strings.map((string) {
+        return _indent(indent + 2) + string;
+      }).join(",\n") + "\n" + _indent(indent) + "}";
+    } else if (object is String) {
+      var lines = object.split("\n");
+      return "'" + lines.map(escapeString)
+          .join("\\n'\n${_indent(indent + 2)}'") + "'";
+    } else {
+      var value = object.toString().replaceAll("\n", _indent(indent) + "\n");
+      var defaultToString = value.startsWith("Instance of ");
+      if (top) value = "<$value>";
+
+      if (object is num || object is bool || object is Function ||
+          object == null || defaultToString) {
+        return value;
+      } else {
+        var type = typeName(object);
+        // TODO(nweiz): find a public superclass of the object's type to
+        // display once there's a portable API to do that.
+        if (type.startsWith("_")) return value;
+        return "$type:$value";
+      }
+    }
+  }
+
+  return _prettyPrint(object, 0, new Set(), true);
+}
+
+String _indent(int length) => new List.filled(length, ' ').join('');