Remove default value checking in GN, adds getenv function, reorders parameters to rebase_path.

tools/gn/functions.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/functions.h"
 
 #include <iostream>
 
+#include "base/environment.h"
 #include "base/strings/string_util.h"
 #include "tools/gn/config.h"
 #include "tools/gn/config_values_generator.h"
 #include "tools/gn/err.h"
 #include "tools/gn/input_file.h"
 #include "tools/gn/parse_tree.h"
 #include "tools/gn/scheduler.h"
 #include "tools/gn/scope.h"
 #include "tools/gn/settings.h"
 #include "tools/gn/token.h"
@@ skipping 335 matching lines @@
     *err = Err(function, "Bad argument to defined().",
         "defined() takes one argument which should be an identifier.");
     return Value();
   }
 
   if (scope->GetValue(identifier->value().value()))
     return Value(function, true);
   return Value(function, false);
 }
 
+// getenv ----------------------------------------------------------------------
+
+const char kGetEnv[] = "getenv";
+const char kGetEnv_Help[] =
+    "getenv: Get an environment variable.\n"
+    "\n"
+    "  value = getenv(env_var_name)\n"
+    "\n"
+    "  Returns the value of the given enironment variable. If the value is\n"
+    "  not found, it will try to look up the variable with the \"opposite\"\n"
+    "  case (based on the case of the first letter of the variable), but\n"
+    "  is otherwise case-sensitive.\n"
+    "\n"
+    "  If the environment variable is not found, the empty string will be\n"
+    "  returned. Note: it might be nice to extend this if we had the concept\n"
+    "  of \"none\" in the language to indicate lookup failure.\n"
+    "\n"
+    "Example:\n"
+    "\n"
+    "  home_dir = getenv(\"HOME\")\n";
+
+Value RunGetEnv(Scope* scope,
+                const FunctionCallNode* function,
+                const std::vector<Value>& args,
+                Err* err) {
+  if (!EnsureSingleStringArg(function, args, err))
+    return Value();
+
+  scoped_ptr<base::Environment> env(base::Environment::Create());
+
+  std::string result;
+  if (!env->GetVar(args[0].string_value().c_str(), &result))
+    return Value(function, "");  // Not found, return empty string.
+  return Value(function, result);
+}
+
 // import ----------------------------------------------------------------------
 
 const char kImport[] = "import";
 const char kImport_Help[] =
     "import: Import a file into the current scope.\n"
     "\n"
     "  The import command loads the rules and variables resulting from\n"
     "  executing the given file into the current scope.\n"
     "\n"
     "  By convention, imported files are named with a .gni extension.\n"
@@ skipping 165 matching lines @@
 
     INSERT_FUNCTION(Assert)
     INSERT_FUNCTION(Component)
     INSERT_FUNCTION(Config)
     INSERT_FUNCTION(Copy)
     INSERT_FUNCTION(Custom)
     INSERT_FUNCTION(DeclareArgs)
     INSERT_FUNCTION(Defined)
     INSERT_FUNCTION(ExecScript)
     INSERT_FUNCTION(Executable)
+    INSERT_FUNCTION(GetEnv)
     INSERT_FUNCTION(Group)
     INSERT_FUNCTION(Import)
     INSERT_FUNCTION(Print)
     INSERT_FUNCTION(ProcessFileTemplate)
     INSERT_FUNCTION(ReadFile)
     INSERT_FUNCTION(RebasePath)
     INSERT_FUNCTION(SetDefaults)
     INSERT_FUNCTION(SetDefaultToolchain)
     INSERT_FUNCTION(SetSourcesAssignmentFilter)
     INSERT_FUNCTION(SharedLibrary)
@@ skipping 73 matching lines @@
     return found_function->second.executed_block_runner(
         function, args.list_value(), &block_scope, err);
   }
 
   // Otherwise it's a no-block function.
   return found_function->second.no_block_runner(scope, function,
                                                 args.list_value(), err);
 }
 
 }  // namespace functions