GN: Make file/dir resolving return errors.

tools/gn/source_dir.h

 // 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.
 
 #ifndef TOOLS_GN_SOURCE_DIR_H_
 #define TOOLS_GN_SOURCE_DIR_H_
 
 #include <algorithm>
 #include <string>
 
 #include "base/containers/hash_tables.h"
 #include "base/files/file_path.h"
 #include "base/logging.h"
 #include "base/strings/string_piece.h"
 
+class Err;
 class SourceFile;
+class Value;
 
 // Represents a directory within the source tree. Source dirs begin and end in
 // slashes.
 //
 // If there is one slash at the beginning, it will mean a system-absolute file
 // path. On Windows, absolute system paths will be of the form "/C:/foo/bar".
 //
 // Two slashes at the beginning indicate a path relative to the source root.
 class SourceDir {
  public:
   enum SwapIn { SWAP_IN };
 
   SourceDir();
   explicit SourceDir(const base::StringPiece& p);
   // Swaps the given string in without copies. The given string will be empty
   // after this call.
   SourceDir(SwapIn, std::string* s);
   ~SourceDir();
 
   // Resolves a file or dir name relative to this source directory. Will return
-  // an empty SourceDir/File on error. Empty input is always an error (it's
-  // possible we should say ResolveRelativeDir vs. an empty string should be
-  // the source dir, but we require "." instead).
+  // an empty SourceDir/File on error and set the give *err pointer (required).
+  // Empty input is always an error.
   //
   // If source_root is supplied, these functions will additionally handle the
   // case where the input is a system-absolute but still inside the source
   // tree. This is the case for some external tools.
   SourceFile ResolveRelativeFile(
-      const base::StringPiece& p,
+      const Value& p,
+      Err* err,
       const base::StringPiece& source_root = base::StringPiece()) const;
   SourceDir ResolveRelativeDir(
+      const Value& p,
+      Err* err,
+      const base::StringPiece& source_root = base::StringPiece()) const;
+
+  // Like ResolveRelativeDir but takes a separate value (which gets blamed)
+  // and string to use (in cases where a substring has been extracted from the
+  // value, as with label resolution).
+  SourceDir ResolveRelativeDir(
+      const Value& blame_but_dont_use,
       const base::StringPiece& p,
+      Err* err,
       const base::StringPiece& source_root = base::StringPiece()) const;
 
   // Resolves this source file relative to some given source root. Returns
   // an empty file path on error.
   base::FilePath Resolve(const base::FilePath& source_root) const;
 
   bool is_null() const { return value_.empty(); }
   const std::string& value() const { return value_; }
 
   // Returns true if this path starts with a "//" which indicates a path
@@ skipping 52 matching lines @@
   }
 };
 
 }  // namespace BASE_HASH_NAMESPACE
 
 inline void swap(SourceDir& lhs, SourceDir& rhs) {
   lhs.swap(rhs);
 }
 
 #endif  // TOOLS_GN_SOURCE_DIR_H_