[ui/base;css] adding string template expression replacement

ui/base/template_expressions.cc

Index: ui/base/template_expressions.cc
diff --git a/ui/base/template_expressions.cc b/ui/base/template_expressions.cc
new file mode 100644
index 0000000000000000000000000000000000000000..3664db49e3b7a0fcbefc2e13394b919487c75450
--- /dev/null
+++ b/ui/base/template_expressions.cc
@@ -0,0 +1,38 @@
+// Copyright 2015 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 "ui/base/template_expressions.h"
+
+#include "base/logging.h"
+#include "base/strings/utf_string_conversions.h"

[Dan Beam, 2015/07/16 00:21:44]

^ needed?

[dschuyler, 2015/07/16 00:33:18]

Nope, thanks.

Done.

+
+namespace ui {
+
+std::string ReplaceTemplateExpressions(
+    base::StringPiece format_string,
+    const std::map<base::StringPiece, std::string>& substitutions) {
+  std::string formatted;
+  const size_t kValueLengthGuess = 16;
+  formatted.reserve(format_string.length() +
+                    substitutions.size() * kValueLengthGuess);
+  base::StringPiece::const_iterator i = format_string.begin();
+  while (i < format_string.end()) {

[Dan Beam, 2015/07/15 21:56:09]

why not format_string.find("${")?

[dschuyler, 2015/07/16 00:12:29]

imo, it makes the code more complicated that it is currently.

+    if (*i == '$' && i < format_string.end() && i[1] == '{') {
+      size_t offset = i + 2 - format_string.begin();

[Dan Beam, 2015/07/16 00:21:44]

template_start or start

[dschuyler, 2015/07/16 00:33:18]

Done.

+      size_t length = format_string.find('}', offset) - offset;

[Dan Beam, 2015/07/16 00:21:44]

expression_key_size or key_size

[dschuyler, 2015/07/16 00:33:18]

Acknowledged.

+      const auto& replacement = substitutions.find(
+          base::StringPiece(format_string.begin() + offset, length));
+      if (replacement != substitutions.end()) {
+        formatted.append(replacement->second);
+        i += length + 3;
+        continue;
+      }

[Dan Beam, 2015/07/16 00:21:44]

where did we land on

} else {
  NOTREACHED();
}

?

[dschuyler, 2015/07/16 00:33:18]

The current code will leave ${unfound} in the result document.

We can still put in an "else crash" easily enough.  That will break the current
unit tests though.

[dschuyler, 2015/07/16 02:08:42]

I've added a NOTREACHED for unfound keys.

+    }
+    formatted.push_back(*i);
+    ++i;
+  }
+  return formatted;
+}
+
+}  // namespace ui