Refactor GN source expansions.

tools/gn/substitution_pattern.cc

Index: tools/gn/substitution_pattern.cc
diff --git a/tools/gn/substitution_pattern.cc b/tools/gn/substitution_pattern.cc
new file mode 100644
index 0000000000000000000000000000000000000000..b589aaeaa400d11579cbcd92dd9c0f8d3efe5b4e
--- /dev/null
+++ b/tools/gn/substitution_pattern.cc
@@ -0,0 +1,111 @@
+// 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.
+
+#include "tools/gn/substitution_pattern.h"
+
+#include "base/strings/string_number_conversions.h"
+#include "tools/gn/err.h"
+#include "tools/gn/value.h"
+
+SubstitutionPattern::Subrange::Subrange()
+    : type(SUBSTITUTION_LITERAL) {
+}
+
+SubstitutionPattern::Subrange::Subrange(SubstitutionType t,
+                                        const std::string& l)
+    : type(t),
+      literal(l) {
+}
+
+SubstitutionPattern::Subrange::~Subrange() {
+}
+
+SubstitutionPattern::SubstitutionPattern() {
+}
+
+SubstitutionPattern::~SubstitutionPattern() {
+}
+
+bool SubstitutionPattern::Parse(const Value& value, Err* err) {
+  if (!value.VerifyTypeIs(Value::STRING, err))
+    return false;
+  return Parse(value.string_value(), value.origin(), err);
+}
+
+bool SubstitutionPattern::Parse(const std::string& str,
+                                const ParseNode* origin,
+                                Err* err) {
+  DCHECK(ranges_.empty());  // Should only be called once.
+
+  size_t cur = 0;
+  while (true) {
+    size_t next = str.find("{{", cur);
+
+    // Pick up everything from the previous spot to here as a literal.
+    if (next == std::string::npos) {
+      if (cur != str.size())
+        ranges_.push_back(Subrange(SUBSTITUTION_LITERAL, str.substr(cur)));
+      break;
+    } else if (next > cur) {
+      ranges_.push_back(
+          Subrange(SUBSTITUTION_LITERAL, str.substr(cur, next - cur)));
+    }
+
+    // Find which specific pattern this corresponds to.
+    bool found_match = false;
+    for (size_t i = SUBSTITUTION_FIRST_PATTERN;
+         i < SUBSTITUTION_NUM_TYPES; i++) {
+      const char* cur_pattern = kSubstitutionNames[i];
+      size_t cur_len = strlen(cur_pattern);
+      if (str.compare(next, cur_len, cur_pattern) == 0) {
+        ranges_.push_back(Subrange(static_cast<SubstitutionType>(i)));
+        cur = next + cur_len;
+        found_match = true;
+        break;
+      }
+    }
+
+    // Expect all occurrances of {{ to resolve to a pattern.
+    if (!found_match) {
+      // Could make this error message more friendly if it comes up a lot. But
+      // most people will not be writing substitution patterns and the code
+      // to exactly indicate the error location is tricky.
+      *err = Err(origin, "Unknown substitution pattern",
+          "Found a {{ at offset " +
+          base::SizeTToString(next) +
+          " and did not find a known substitution following it.");
+      ranges_.clear();
+      return false;
+    }
+  }
+
+  // Fill required types vector.
+  bool required_type_bits[SUBSTITUTION_NUM_TYPES] = {0};
+  FillRequiredTypes(required_type_bits);
+
+  for (size_t i = SUBSTITUTION_FIRST_PATTERN; i < SUBSTITUTION_NUM_TYPES; i++) {
+    if (required_type_bits[i])
+      required_types_.push_back(static_cast<SubstitutionType>(i));
+  }
+  return true;
+}
+
+std::string SubstitutionPattern::AsString() const {
+  std::string result;
+  for (size_t i = 0; i < ranges_.size(); i++) {
+    if (ranges_[i].type == SUBSTITUTION_LITERAL)
+      result.append(ranges_[i].literal);
+    else
+      result.append(kSubstitutionNames[ranges_[i].type]);
+  }
+  return result;
+}
+
+void SubstitutionPattern::FillRequiredTypes(
+    bool required_types[SUBSTITUTION_NUM_TYPES]) const {
+  for (size_t i = 0; i < ranges_.size(); i++) {
+    if (ranges_[i].type != SUBSTITUTION_LITERAL)
+      required_types[static_cast<size_t>(ranges_[i].type)] = true;
+  }
+}