Support script response files in GN.

tools/gn/variables.cc

Index: tools/gn/variables.cc
diff --git a/tools/gn/variables.cc b/tools/gn/variables.cc
index d4e978d334a6e195d89583cee94ccab79609a0f6..5a9b8404ce88f0cf761733f006ba6c5623d9a21d 100644
--- a/tools/gn/variables.cc
+++ b/tools/gn/variables.cc
@@ -1164,6 +1164,45 @@ const char kPublicDeps_Help[] =
     "    public_deps = [ \":c\" ]\n"
     "  }\n";
 
+const char kResponseFileContents[] = "response_file_contents";
+const char kResponseFileContents_HelpShort[] =
+    "response_file_contents: [string list] Contents of .rsp file for actions.";
+const char kResponseFileContents_Help[] =
+    "response_file_contents: Contents of a response file for actions.\n"
+    "\n"
+    "  Sometimes the arguments passed to a script can be too long for the\n"
+    "  system's command-line capabilities. This is especially the case on\n"
+    "  Windows where the maximum command-line length is less than 8K. A\n"
+    "  response file allows you to pass an unlimited amount of data to a\n"
+    "  script in a temporary file for an action or action_foreach target.\n"
+    "\n"
+    "  If the response_file_contents variable is defined and non-empty, the\n"
+    "  list will be treated as script args (including possibly substitution\n"
+    "  patterns) that will be written to a temporary file at build time.\n"
+    "  The name of the temporary file will be substituted for\n"
+    "  \"{{response_file_name}}\" in the script args.\n"
+    "\n"
+    "  The response file contents will always be quoted and escaped\n"
+    "  according to Unix shell rules. To parse the response file, the Python\n"
+    "  script should use \"shlex.split(file_contents)\".\n"
+    "\n"
+    "Example\n"
+    "\n"
+    "  action(\"process_lots_of_files\") {\n"
+    "    script = \"process.py\",\n"
+    "    inputs = [ ... huge list of files ... ]\n"
+    "\n"
+    "    # Write all the inputs to a response file for the script. Also,\n"
+    "    # make the paths relative to the script working directory.\n"
+    "    response_file_contents = rebase_path(inputs, root_build_dir)\n"
+    "\n"
+    "    # The script expects the name of the response file in --file-list.\n"
+    "    args = [\n"
+    "      \"--enable-foo\",\n"
+    "      \"--file-list={{response_file_name}}\",\n"
+    "    ]\n"
+    "  }\n";
+
 const char kScript[] = "script";
 const char kScript_HelpShort[] =
     "script: [file name] Script file for actions.";
@@ -1358,6 +1397,7 @@ const VariableInfoMap& GetTargetVariables() {
     INSERT_VARIABLE(Public)
     INSERT_VARIABLE(PublicConfigs)
     INSERT_VARIABLE(PublicDeps)
+    INSERT_VARIABLE(ResponseFileContents)
     INSERT_VARIABLE(Script)
     INSERT_VARIABLE(Sources)
     INSERT_VARIABLE(Testonly)