Add initial prototype for the GN meta-buildsystem.

tools/gn/value_extractors.cc

Index: tools/gn/value_extractors.cc
diff --git a/tools/gn/value_extractors.cc b/tools/gn/value_extractors.cc
new file mode 100644
index 0000000000000000000000000000000000000000..56a2be28b09a3d1413949ad694ace2d6daf1d56c
--- /dev/null
+++ b/tools/gn/value_extractors.cc
@@ -0,0 +1,102 @@
+// 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/value_extractors.h"
+
+#include "tools/gn/err.h"
+#include "tools/gn/label.h"
+#include "tools/gn/source_dir.h"
+#include "tools/gn/source_file.h"
+
+namespace {
+
+// This extractor rejects files with system-absolute file paths. If we need
+// that in the future, we'll have to add some flag to control this.
+struct RelativeFileConverter {
+  RelativeFileConverter(const SourceDir& current_dir_in)
+      : current_dir(current_dir_in) {}
+  bool operator()(const Value& v, SourceFile* out, Err* err) const {
+    if (!v.VerifyTypeIs(Value::STRING, err))
+      return false;
+    *out = current_dir.ResolveRelativeFile(v.string_value());
+    if (out->is_system_absolute()) {
+      *err = Err(v, "System-absolute file path.",
+          "You can't list a system-absolute file path here. Please include "
+          "only files in\nthe source tree. Maybe you meant to begin with two "
+          "slashes to indicate an\nabsolute path in the source tree?");
+      return false;
+    }
+    return true;
+  }
+  const SourceDir& current_dir;
+};
+
+struct RelativeDirConverter {
+  RelativeDirConverter(const SourceDir& current_dir_in)
+      : current_dir(current_dir_in) {}
+  bool operator()(const Value& v, SourceDir* out, Err* err) const {
+    if (!v.VerifyTypeIs(Value::STRING, err))
+      return false;
+    *out = current_dir.ResolveRelativeDir(v.string_value());
+    return true;
+  }
+  const SourceDir& current_dir;
+};
+
+struct LabelResolver {
+  LabelResolver(const SourceDir& current_dir_in,
+                const Label& current_toolchain_in)
+      : current_dir(current_dir_in),
+        current_toolchain(current_toolchain_in) {}
+  bool operator()(const Value& v, Label* out, Err* err) const {
+    if (!v.VerifyTypeIs(Value::STRING, err))
+      return false;
+    *out = Label::Resolve(current_dir, current_toolchain, v, err);
+    return !err->has_error();
+  }
+  const SourceDir& current_dir;
+  const Label& current_toolchain;
+};
+
+}  // namespace
+
+bool ExtractListOfStringValues(const Value& value,
+                               std::vector<std::string>* dest,
+                               Err* err) {
+  if (!value.VerifyTypeIs(Value::LIST, err))
+    return false;
+  const std::vector<Value>& input_list = value.list_value();
+  dest->reserve(input_list.size());
+  for (size_t i = 0; i < input_list.size(); i++) {
+    if (!input_list[i].VerifyTypeIs(Value::STRING, err))
+      return false;
+    dest->push_back(input_list[i].string_value());
+  }
+  return true;
+}
+
+bool ExtractListOfRelativeFiles(const Value& value,
+                                const SourceDir& current_dir,
+                                std::vector<SourceFile>* files,
+                                Err* err) {
+  return ListValueExtractor(value, files, err,
+                            RelativeFileConverter(current_dir));
+}
+
+bool ExtractListOfRelativeDirs(const Value& value,
+                               const SourceDir& current_dir,
+                               std::vector<SourceDir>* dest,
+                               Err* err) {
+  return ListValueExtractor(value, dest, err,
+                            RelativeDirConverter(current_dir));
+}
+
+bool ExtractListOfLabels(const Value& value,
+                         const SourceDir& current_dir,
+                         const Label& current_toolchain,
+                         std::vector<Label>* dest,
+                         Err* err) {
+  return ListValueExtractor(value, dest, err,
+                            LabelResolver(current_dir, current_toolchain));
+}