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Notes about the tools/icu subdirectory

This directory contains tools, data, and information about the ICU (International Components for Unicode) integration. ICU is used to provide internationalization functionality.

  • patches/ are one-off patches, actually entire source file replacements, organized by ICU version number.
  • icu_small.json controls the "small" (English only) ICU. It is input to
  • icu-generic.gyp is the build file used for most ICU builds within ICU.
  • icu-system.gyp is an alternate build file used when --with-intl=system-icu is invoked. It builds against the pkg-config located ICU.
  • is source for the iculslocs utility, invoked by as part of repackaging. Not used separately. See source for more details.
  • — empty function to convince gyp to use a C++ compiler.
  • — you are here
  • — this is used during upgrade (see guide below)

How to upgrade ICU

  • Make sure your Node.js workspace is clean (clean git status) should be sufficient.
  • Configure Node.js with the specific ICU version you want to upgrade to, for example:
./configure \
    --with-intl=full-icu \

Note in theory, the equivalent vcbuild.bat commands should work also, but the commands below are makefile-centric.

  • If there are ICU version-specific changes needed, you may need to make changes in icu-generic.gyp or add patch files to tools/icu/patches.

    • Specifically, look for the lists in sources! in the icu-generic.gyp for files to exclude.
  • Verify the Node.js build works:

make test-ci

Also running

new Intl.DateTimeFormat('es', {month: 'long'}).format(new Date(9E8));

…Should return enero not January.

  • Now, copy deps/icu over to deps/icu-small
python tools/icu/
  • Now, do a clean rebuild of Node.js to test:
make -k distclean
  • Test this newly default-generated Node.js;
new Intl.DateTimeFormat('es', {month: 'long'}).format(new Date(9E8));

(This should print your updated ICU version number, and also January again.)

You are ready to check in the updated deps/small-icu. This is a big commit, so make this a separate commit from the smaller changes.

  • Now, rebuild the Node.js license.
# clean up - remove deps/icu
make clean
  • Update the URL and hash for the full ICU file in tools/icu/current_ver.dep. It should match the ICU URL used in the first step. When this is done, the following should build with small ICU.
# clean up
rm -rf out deps/icu deps/icu4c*
./configure --with-intl=small-icu --download=all
make test-ci
  • commit the change to tools/icu/current_ver.dep and LICENSE files.

    • Note: To simplify review, I often will “pre-land” this patch, meaning that I run the patch through curl -L | git am -3 --whitespace=fix per the collaborator’s guide… and then push that patched branch into my PR's branch. This reduces the whitespace changes that show up in the PR, since the final land will eliminate those anyway.

Postscript about the tools

The files in this directory were written for the Node.js effort. It was the intent of their author (Steven R. Loomis / srl295) to merge them upstream into ICU, pending much discussion within the ICU-TC.

icu_small.json is somewhat node-specific as it specifies a "small ICU" configuration file for the script. and iculslocs.cpp may themselves be superseded by components built into ICU in the future. As of this writing, however, the tools are separate entities within Node.js, although theyare being scrutinized by interested members of the ICU-TC. The “upstream” ICU bugs are given below.

  • #10919 (experimental branch - may copy any source patches here)
  • #10922 (data packaging improvements)
  • #10923 (rewrite data building in python)
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