Add an error for empty script names in GN.

tools/gn/action_target_generator.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/action_target_generator.h"
 
 #include "tools/gn/build_settings.h"
 #include "tools/gn/err.h"
 #include "tools/gn/filesystem_utils.h"
 #include "tools/gn/parse_tree.h"
@@ skipping 76 matching lines @@
   // If this gets called, the target type requires a script, so error out
   // if it doesn't have one.
   const Value* value = scope_->GetValue(variables::kScript, true);
   if (!value) {
     *err_ = Err(function_call_, "This target type requires a \"script\".");
     return;
   }
   if (!value->VerifyTypeIs(Value::STRING, err_))
     return;
 
-  target_->action_values().set_script(
-      scope_->GetSourceDir().ResolveRelativeFile(value->string_value()));
+  SourceFile script_file =
+      scope_->GetSourceDir().ResolveRelativeFile(value->string_value());
+  if (script_file.value().empty()) {
+    *err_ = Err(*value, "script name is empty");
+    return;
+  }
+  target_->action_values().set_script(script_file);
 }
 
 void ActionTargetGenerator::FillScriptArgs() {
   const Value* value = scope_->GetValue(variables::kArgs, true);
   if (!value)
     return;
 
   std::vector<std::string> args;
   if (!ExtractListOfStringValues(*value, &args, err_))
     return;
@@ skipping 32 matching lines @@
     if (!FileListHasPattern(outputs)) {
       *err_ = Err(function_call_,
           "action_foreach should have a pattern in the output.",
           "An action_foreach target should have a source expansion pattern in\n"
           "it to map source file to unique output file name. Otherwise, the\n"
           "build system can't determine when your script needs to be run.");
       return;
     }
   }
 }