Add testonly flag to GN

tools/gn/variables.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "tools/gn/variables.h"
 
 namespace variables {
 
 // Built-in variables ----------------------------------------------------------
 
@@ skipping 720 matching lines @@
     "  \"gn help action_foreach\").\n";
 
 const char kSources[] = "sources";
 const char kSources_HelpShort[] =
     "sources: [file list] Source files for a target.";
 const char kSources_Help[] =
     "sources: Source files for a target\n"
     "\n"
     "  A list of files relative to the current buildfile.\n";
 
+const char kTestonly[] = "testonly";
+const char kTestonly_HelpShort[] =
+    "testonly: [boolean] Declares a target must only be used for testing.";
+const char kTestonly_Help[] =
+    "testonly: Declares a target must only be used for testing.\n"
+    "\n"
+    "  Boolean. Defaults to false.\n"
+    "\n"
+    "  When a target is marked \"testonly = true\", it must only be depended\n"
+    "  on by other test-only targets. Otherwise, GN will issue an error\n"
+    "  that the depenedency is not allowed.\n"
+    "\n"
+    "  This feature is intended to prevent accidentally shipping test code\n"
+    "  in a final product.\n"
+    "\n"
+    "Example\n"
+    "\n"
+    "  source_set(\"test_support\") {\n"
+    "    testonly = true\n"
+    "    ...\n"
+    "  }\n";
+
 const char kVisibility[] = "visibility";
 const char kVisibility_HelpShort[] =
     "visibility: [label list] A list of labels that can depend on a target.";
 const char kVisibility_Help[] =
     "visibility: A list of labels that can depend on a target.\n"
     "\n"
     "  A label or a list of labels and label patterns that define which\n"
     "  targets can depend on the current one. These permissions are checked\n"
     "  via then \"check\" command (see \"gn help check\").\n"
     "\n"
@@ skipping 98 matching lines @@
     INSERT_VARIABLE(Inputs)
     INSERT_VARIABLE(Ldflags)
     INSERT_VARIABLE(Libs)
     INSERT_VARIABLE(LibDirs)
     INSERT_VARIABLE(OutputExtension)
     INSERT_VARIABLE(OutputName)
     INSERT_VARIABLE(Outputs)
     INSERT_VARIABLE(Public)
     INSERT_VARIABLE(Script)
     INSERT_VARIABLE(Sources)
+    INSERT_VARIABLE(Testonly)
     INSERT_VARIABLE(Visibility)
   }
   return info_map;
 }
 
 #undef INSERT_VARIABLE
 
 }  // namespace variables