Add initial prototype for the GN meta-buildsystem.

tools/gn/string_utils.cc

Index: tools/gn/string_utils.cc
diff --git a/tools/gn/string_utils.cc b/tools/gn/string_utils.cc
new file mode 100644
index 0000000000000000000000000000000000000000..14d296a51e2bc727ffd59194beae1d09053ad645
--- /dev/null
+++ b/tools/gn/string_utils.cc
@@ -0,0 +1,168 @@
+// 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/string_utils.h"
+
+#include "tools/gn/err.h"
+#include "tools/gn/scope.h"
+#include "tools/gn/token.h"
+#include "tools/gn/tokenizer.h"
+#include "tools/gn/value.h"
+
+namespace {
+
+// Constructs an Err indicating a range inside a string. We assume that the
+// token has quotes around it that are not counted by the offset.
+Err ErrInsideStringToken(const Token& token, size_t offset, size_t size,
+                         const std::string& msg,
+                         const std::string& help = std::string()) {
+  // The "+1" is skipping over the " at the beginning of the token.
+  Location begin_loc(token.location().file(),
+                     token.location().line_number(),
+                     token.location().char_offset() + offset + 1);
+  Location end_loc(token.location().file(),
+                   token.location().line_number(),
+                   token.location().char_offset() + offset + 1 + size);
+  return Err(LocationRange(begin_loc, end_loc), msg, help);
+}
+
+// Given the character input[i] indicating the $ in a string, locates the
+// identifier and places its range in |*identifier|, and updates |*i| to
+// point to the last character consumed.
+//
+// On error returns false and sets the error.
+bool LocateInlineIdenfitier(const Token& token,
+                            const char* input, size_t size,
+                            size_t* i,
+                            base::StringPiece* identifier,
+                            Err* err) {
+  size_t dollars_index = *i;
+  (*i)++;
+  if (*i == size) {
+    *err = ErrInsideStringToken(token, dollars_index, 1, "$ at end of string.",
+        "I was expecting an identifier after the $.");
+    return false;
+  }
+
+  bool has_brackets;
+  if (input[*i] == '{') {
+    (*i)++;
+    if (*i == size) {
+      *err = ErrInsideStringToken(token, dollars_index, 2,
+          "${ at end of string.",
+          "I was expecting an identifier inside the ${...}.");
+      return false;
+    }
+    has_brackets = true;
+  } else {
+    has_brackets = false;
+  }
+
+  // First char is special.
+  if (!Tokenizer::IsIdentifierFirstChar(input[*i])) {
+    *err = ErrInsideStringToken(
+        token, dollars_index, *i - dollars_index + 1,
+        "$ not followed by an identifier char.",
+        "It you want a literal $ use \"\\$\".");
+    return false;
+  }
+  size_t begin_offset = *i;
+  (*i)++;
+
+  // Find the first non-identifier char following the string.
+  while (*i < size && Tokenizer::IsIdentifierContinuingChar(input[*i]))
+    (*i)++;
+  size_t end_offset = *i;
+
+  // If we started with a bracket, validate that there's an ending one. Leave
+  // *i pointing to the last char we consumed (backing up one).
+  if (has_brackets) {
+    if (*i == size) {
+      *err = ErrInsideStringToken(token, dollars_index, *i - dollars_index,
+                                  "Unterminated ${...");
+      return false;
+    } else if (input[*i] != '}') {
+      *err = ErrInsideStringToken(token, *i, 1, "Not an identifier in string expansion.",
+          "The contents of ${...} should be an identifier. "
+          "This character is out of sorts.");
+      return false;
+    }
+    // We want to consume the bracket but also back up one, so *i is unchanged.
+  } else {
+    (*i)--;
+  }
+
+  *identifier = base::StringPiece(&input[begin_offset],
+                                  end_offset - begin_offset);
+  return true;
+}
+
+bool AppendIdentifierValue(Scope* scope,
+                           const Token& token,
+                           const base::StringPiece& identifier,
+                           std::string* output,
+                           Err* err) {
+  const Value* value = scope->GetValue(identifier, true);
+  if (!value) {
+    // We assume the identifier points inside the token.
+    *err = ErrInsideStringToken(
+        token, identifier.data() - token.value().data() - 1, identifier.size(),
+        "Undefined identifier in string expansion.",
+        std::string("\"") + identifier + "\" is not currently in scope.");
+    return false;
+  }
+
+  output->append(value->ToString());
+  return true;
+}
+
+}  // namespace
+
+bool ExpandStringLiteral(Scope* scope,
+                         const Token& literal,
+                         Value* result,
+                         Err* err) {
+  DCHECK(literal.type() == Token::STRING);
+  DCHECK(literal.value().size() > 1);  // Should include quotes.
+  DCHECK(result->type() == Value::STRING);  // Should be already set.
+
+  // The token includes the surrounding quotes, so strip those off.
+  const char* input = &literal.value().data()[1];
+  size_t size = literal.value().size() - 2;
+
+  std::string& output = result->string_value();
+  output.reserve(size);
+  for (size_t i = 0; i < size; i++) {
+    if (input[i] == '\\') {
+      if (i < size - 1) {
+        switch (input[i + 1]) {
+          case '\\':
+          case '"':
+          case '$':
+            output.push_back(input[i + 1]);
+            i++;
+            continue;
+          default:  // Everything else has no meaning: pass the literal.
+            break;
+        }
+      }
+      output.push_back(input[i]);
+    } else if (input[i] == '$') {
+      base::StringPiece identifier;
+      if (!LocateInlineIdenfitier(literal, input, size, &i, &identifier, err))
+        return false;
+      if (!AppendIdentifierValue(scope, literal, identifier, &output, err))
+        return false;
+    } else {
+      output.push_back(input[i]);
+    }
+  }
+  return true;
+}
+
+std::string RemovePrefix(const std::string& str, const std::string& prefix) {
+  CHECK(str.size() >= prefix.size() &&
+        str.compare(0, prefix.size(), prefix) == 0);
+  return str.substr(prefix.size());
+}