🐣 GN: Print the import trail when parse errors occur.

tools/gn/location.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/location.h"
 
 #include <tuple>
 
 #include "base/logging.h"
 #include "base/strings/string_number_conversions.h"
 #include "tools/gn/input_file.h"
 
 Location::Location()
     : file_(nullptr),
       line_number_(-1),
       column_number_(-1) {
 }
 
 Location::Location(const InputFile* file,
                    int line_number,
                    int column_number,
                    int byte)
     : file_(file),
       line_number_(line_number),
       column_number_(column_number),
       byte_(byte) {
 }
 
+bool Location::is_null() const {
+  return *this == Location();
+}
+
 bool Location::operator==(const Location& other) const {
   return other.file_ == file_ &&
          other.line_number_ == line_number_ &&
          other.column_number_ == column_number_;
 }
 
 bool Location::operator!=(const Location& other) const {
   return !operator==(other);
 }
 
@@ skipping 24 matching lines @@
 
 LocationRange::LocationRange() {
 }
 
 LocationRange::LocationRange(const Location& begin, const Location& end)
     : begin_(begin),
       end_(end) {
   DCHECK(begin_.file() == end_.file());
 }
 
+bool LocationRange::is_null() const {
+  return begin_.is_null();  // No need to check both for the null case.
+}
+
 LocationRange LocationRange::Union(const LocationRange& other) const {
   DCHECK(begin_.file() == other.begin_.file());
   return LocationRange(
       begin_ < other.begin_ ? begin_ : other.begin_,
       end_ < other.end_ ? other.end_ : end_);
 }