Avoid repeating common parts of ProgramResults.

dart/tests/try/poi/source_update.dart

+// Copyright (c) 2014, 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 trydart.source_update;
+
+/// Returns [updates] expanded to full compilation units/source files.
+///
+/// [updates] is a convenient way to write updates/patches to a single source
+/// file without repeating common parts.
+///
+/// For example:
+///   ["head ", ["v1", "v2"], " tail"]
+/// expands to:
+///   ["head v1 tail", "head v2 tail"]
+List<String> expandUpdates(List updates) {
+  int outputCount = updates.firstWhere((e) => e is Iterable).length;
+  List<StringBuffer> result = new List<StringBuffer>(outputCount);
+  for (int i = 0; i < outputCount; i++) {
+    result[i] = new StringBuffer();
+  }
+  for (var chunk in updates) {
+    if (chunk is Iterable) {
+      int segmentCount = 0;
+      for (var segment in chunk) {
+        result[segmentCount++].write(segment);
+      }
+      if (segmentCount != outputCount) {
+        throw new ArgumentError(
+            "Expected ${outputCount} segments, "
+            "but found ${segmentCount} in $chunk");
+      }
+    } else {
+      for (StringBuffer buffer in result) {
+        buffer.write(chunk);
+      }
+    }
+  }
+
+  return result.map((e) => '$e').toList();
+}