GN: Add the ability to trim whitespace from script results.

tools/gn/function_exec_script.cc

Index: tools/gn/function_exec_script.cc
diff --git a/tools/gn/function_exec_script.cc b/tools/gn/function_exec_script.cc
index 9cbb2dd80c45ccd75bad9fc9e2443ee170c6d280..2109522da1d1fb39484e855b02eec80c518337e9 100644
--- a/tools/gn/function_exec_script.cc
+++ b/tools/gn/function_exec_script.cc
@@ -236,8 +236,10 @@ const char kExecScript[] = "exec_script";
 const char kExecScript_Help[] =
     "exec_script: Synchronously run a script and return the output.\n"
     "\n"
-    "  exec_script(filename, arguments, input_conversion,\n"
-    "              [file_dependencies])\n"
+    "  exec_script(filename,\n"
+    "              arguments = [],\n"
+    "              input_conversion = \"\",\n"
+    "              file_dependencies = [])\n"
     "\n"
     "  Runs the given script, returning the stdout of the script. The build\n"
     "  generation will fail if the script does not exist or returns a nonzero\n"
@@ -256,11 +258,15 @@ const char kExecScript_Help[] =
     "\n"
     "  arguments:\n"
     "      A list of strings to be passed to the script as arguments.\n"
+    "      May be unspecified or the empty list which means no arguments.\n"
     "\n"
     "  input_conversion:\n"
     "      Controls how the file is read and parsed.\n"
     "      See \"gn help input_conversion\".\n"
     "\n"
+    "      If unspecified, defaults to the empty string which causes the\n"
+    "      script result to be discarded. exec script will return None.\n"
+    "\n"
     "  dependencies:\n"
     "      (Optional) A list of files that this script reads or otherwise\n"
     "      depends on. These dependencies will be added to the build result\n"
@@ -274,15 +280,19 @@ const char kExecScript_Help[] =
     "\n"
     "  all_lines = exec_script(\"myscript.py\", [some_input], \"list lines\",\n"
     "                          [ rebase_path(\"data_file.txt\", \".\","
-    "                                        root_build_dir) ])\n";
+    "                                        root_build_dir) ])\n"
+    "\n"
+    "  # This example just calls the script with no arguments and discards\n"
+    "  # the result.\n"
+    "  exec_script(\"//foo/bar/myscript.py\")\n";
 
 Value RunExecScript(Scope* scope,
                     const FunctionCallNode* function,
                     const std::vector<Value>& args,
                     Err* err) {
-  if (args.size() != 3 && args.size() != 4) {
+  if (args.size() < 1 || args.size() > 4) {
     *err = Err(function->function(), "Wrong number of arguments to exec_script",
-               "I expected three or four arguments.");
+               "I expected between one and four arguments.");
     return Value();
   }
 
@@ -327,13 +337,16 @@ Value RunExecScript(Scope* scope,
   CommandLine cmdline(python_path);
   cmdline.AppendArgPath(script_path);
 
-  const Value& script_args = args[1];
-  if (!script_args.VerifyTypeIs(Value::LIST, err))
-    return Value();
-  for (size_t i = 0; i < script_args.list_value().size(); i++) {
-    if (!script_args.list_value()[i].VerifyTypeIs(Value::STRING, err))
+  if (args.size() >= 2) {
+    // Optional command-line arguments to the script.
+    const Value& script_args = args[1];
+    if (!script_args.VerifyTypeIs(Value::LIST, err))
       return Value();
-    cmdline.AppendArg(script_args.list_value()[i].string_value());
+    for (size_t i = 0; i < script_args.list_value().size(); i++) {
+      if (!script_args.list_value()[i].VerifyTypeIs(Value::STRING, err))
+        return Value();
+      cmdline.AppendArg(script_args.list_value()[i].string_value());
+    }
   }
 
   // Log command line for debugging help.
@@ -394,7 +407,9 @@ Value RunExecScript(Scope* scope,
     return Value();
   }
 
-  return ConvertInputToValue(output, function, args[2], err);
+  // Default to None value for the input conversion if unspecified.
+  return ConvertInputToValue(output, function,
+                             args.size() >= 3 ? args[2] : Value(), err);
 }
 
 }  // namespace functions