GN: Allow setting the path to Python

tools/gn/setup.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/setup.h"
 
 #include <stdlib.h>
 #include <algorithm>
 #include <sstream>
 #include <utility>
@@ skipping 281 matching lines @@
   Err err;
   if (!dotfile_scope_.CheckForUnusedVars(&err)) {
     err.PrintToStdout();
     return false;
   }
 
   if (fill_arguments_) {
     if (!FillArguments(*cmdline))
       return false;
   }
-  FillPythonPath();
+  FillPythonPath(*cmdline);
 
   return true;
 }
 
 bool Setup::Run() {
   RunPreMessageLoop();
   if (!scheduler_.Run())
     return false;
   return RunPostMessageLoop();
 }
@@ skipping 274 matching lines @@
           "\nwhich doesn't seem to contain a previously-generated build.")
           .PrintToStdout();
       return false;
     }
   }
 
   build_settings_.SetBuildDir(resolved);
   return true;
 }
 
-void Setup::FillPythonPath() {
+void Setup::FillPythonPath(const base::CommandLine& cmdline) {
   // Trace this since it tends to be a bit slow on Windows.
   ScopedTrace setup_trace(TraceItem::TRACE_SETUP, "Fill Python Path");
+  if (cmdline.HasSwitch(switches::kScriptExecutable)) {
+    build_settings_.set_python_path(
+        cmdline.GetSwitchValuePath(switches::kScriptExecutable));
+  } else {
 #if defined(OS_WIN)
-  base::FilePath python_path = FindWindowsPython();
-  if (python_path.empty()) {
-    scheduler_.Log("WARNING", "Could not find python on path, using "
-        "just \"python.exe\"");
-    python_path = base::FilePath(kPythonExeName);
+    base::FilePath python_path = FindWindowsPython();
+    if (python_path.empty()) {
+      scheduler_.Log("WARNING", "Could not find python on path, using "
+          "just \"python.exe\"");
+      python_path = base::FilePath(kPythonExeName);
+    }
+    build_settings_.set_python_path(python_path.NormalizePathSeparatorsTo('/'));
+#else
+    build_settings_.set_python_path(base::FilePath("python"));
+#endif
   }
-  build_settings_.set_python_path(python_path.NormalizePathSeparatorsTo('/'));
-#else
-  build_settings_.set_python_path(base::FilePath("python"));
-#endif
 }
 
 bool Setup::RunConfigFile() {
   if (scheduler_.verbose_logging())
     scheduler_.Log("Got dotfile", FilePathToUTF8(dotfile_name_));
 
   dotfile_input_file_.reset(new InputFile(SourceFile("//.gn")));
   if (!dotfile_input_file_->Load(dotfile_name_)) {
     Err(Location(), "Could not load dotfile.",
         "The file \"" + FilePathToUTF8(dotfile_name_) + "\" cound't be loaded")
@@ skipping 105 matching lines @@
       if (err.has_error()) {
         err.PrintToStdout();
         return false;
       }
     }
     build_settings_.set_exec_script_whitelist(std::move(whitelist));
   }
 
   return true;
 }