Refactor GN source expansions.

tools/gn/substitution_pattern.h

Index: tools/gn/substitution_pattern.h
diff --git a/tools/gn/substitution_pattern.h b/tools/gn/substitution_pattern.h
new file mode 100644
index 0000000000000000000000000000000000000000..70fc5eb375a00e4fcc909feaa0d648c9a62e7ea9
--- /dev/null
+++ b/tools/gn/substitution_pattern.h
@@ -0,0 +1,61 @@
+// Copyright 2014 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_SUBSTITUTION_PATTERN_H_
+#define TOOLS_GN_SUBSTITUTION_PATTERN_H_
+
+#include <string>
+#include <vector>
+
+#include "tools/gn/substitution_type.h"
+
+class Err;
+class ParseNode;
+class Value;
+
+// Represents a string with {{substitution_patterns}} in them.
+class SubstitutionPattern {
+ public:
+  struct Subrange {
+    Subrange();
+    Subrange(SubstitutionType t, const std::string& l = std::string());
+    ~Subrange();
+
+    SubstitutionType type;
+
+    // When type_ == LITERAL, this specifies the literal.
+    std::string literal;
+  };
+
+  SubstitutionPattern();
+  ~SubstitutionPattern();
+
+  // Parses the given string and fills in the pattern. The pattern must only
+  // be initialized once. On failure, returns false and sets the error.
+  bool Parse(const Value& value, Err* err);
+  bool Parse(const std::string& str, const ParseNode* origin, Err* err);
+
+  // Returns the pattern as a string with substitutions in them.
+  std::string AsString() const;
+
+  // Sets the bits in the given vector corresponding to the substitutions used
+  // by this pattern. SUBSTITUTION_LITERAL is ignored.
+  void FillRequiredTypes(bool required_types[SUBSTITUTION_NUM_TYPES]) const;
+
+  // Returns a vector listing the substitutions used by this pattern, not
+  // counting SUBSTITUTION_LITERAL.
+  const std::vector<SubstitutionType>& required_types() const {
+    return required_types_;
+  }
+
+  const std::vector<Subrange>& ranges() const { return ranges_; }
+  bool empty() const { return ranges_.empty(); }
+
+ private:
+  std::vector<Subrange> ranges_;
+
+  std::vector<SubstitutionType> required_types_;
+};
+
+#endif  // TOOLS_GN_SUBSTITUTION_PATTERN_H_