Implement clang tool that converts std::string("") to std::string().

tools/clang/scripts/update.sh

 #!/usr/bin/env bash
 # Copyright (c) 2012 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.
 
 # This script will check out llvm and clang into third_party/llvm and build it.
 
 # Do NOT CHANGE this if you don't know what you're doing -- see
 # https://code.google.com/p/chromium/wiki/UpdatingClang
 # Reverting problematic clang rolls is safe, though.
@@ skipping 357 matching lines @@
   fi
 
   # Build ASan runtime for Android.
   cd "${LLVM_BUILD_DIR}"
   make -C tools/clang/runtime/ LLVM_ANDROID_TOOLCHAIN_DIR="../../../../${TC}"
   cd -
 fi
 
 # Build Chrome-specific clang tools. Paths in this list should be relative to
 # tools/clang.
-CHROME_TOOL_DIRS="plugins"
+CHROME_TOOL_DIRS="empty_string plugins"

[Nico, 2013/03/27 16:35:29]

Hm, this means that everyone building clang locally will build lots of tools
over time. Maybe there could be a build-tool $toolname script instead, which
does the stuff below? Then people who want to use a tool can call that for the
tool they care about, and update.sh could call it to build the plugin.

[dcheng, 2013/03/28 00:10:17]

I added (another) command-line argument instead, so I can just use $LLVM_DIR and
${NUM_JOBS}. It defaults to just plugins so people who don't care about tooling
can just omit the argument completely.

 # For each tool directory, copy it into the clang tree and use clang's build
 # system to compile it.
 for CHROME_TOOL_DIR in ${CHROME_TOOL_DIRS}; do
   TOOL_SRC_DIR="${THIS_DIR}/../${CHROME_TOOL_DIR}"
   TOOL_DST_DIR="${LLVM_DIR}/tools/clang/tools/chrome-${CHROME_TOOL_DIR}"
   TOOL_BUILD_DIR="${LLVM_BUILD_DIR}/tools/clang/tools/chrome-${CHROME_TOOL_DIR}"
   rm -rf "${TOOL_DST_DIR}"
   cp -R "${TOOL_SRC_DIR}" "${TOOL_DST_DIR}"
   rm -rf "${TOOL_BUILD_DIR}"
   mkdir -p "${TOOL_BUILD_DIR}"
   cp "${TOOL_SRC_DIR}/Makefile" "${TOOL_BUILD_DIR}"
   MACOSX_DEPLOYMENT_TARGET=10.5 make -j"${NUM_JOBS}" -C "${TOOL_BUILD_DIR}"
 done
 
 if [[ -n "$run_tests" ]]; then
   # Run a few tests.
   PLUGIN_SRC_DIR="${THIS_DIR}/../plugins"
   "${PLUGIN_SRC_DIR}/tests/test.sh" "${LLVM_BUILD_DIR}/Release+Asserts"
   cd "${LLVM_BUILD_DIR}"
   make check-all
   cd -
 fi
 
 # After everything is done, log success for this revision.
 echo "${CLANG_REVISION}" > "${STAMP_FILE}"