wxWidgets/docs/contributing/how-to-update-third-party-library.md

How to update a third party library to a newer version

Introduction

wxWidgets includes several third party libraries, i.e. libraries which are used by wxWidgets and distributed with it but which we don't maintain nor even modify, inasmuch as possible, ourselves. These libraries are developed by their maintainers and from time to time we need to replace the versions used by wxWidgets with newer versions.

Submodules

All third party libraries are managed using Git submodules. This includes 3rdparty/catch and expat, jpeg, png, tiff and zlib subdirectories of src.

As always with submodules, updating a library involves updating its sources in the submodule, pushing this submodule out and then committing the changes in the top-level repository.

Updating the submodule

All submodules use master branch for the upstream master and wx for the version used by wxWidgets. To update the latter, just merge the appropriate commit from master into wx, e.g.

$ cd src/expat
$ git checkout wx
$ git merge R_x_y_z # For the latest x.y.z release

After resolving any conflicts, commit the result.

Special instructions for specific libraries

Some libraries, notably those for which we store the generated build files in our submodules, require extra actions to be undertaken after merging with the upstream:

libexpat

Run buildconf.sh to update the generated files and commit the changes.

libpng

We use a special hack for libpng as we want to prefix all its symbols with wx_ but don't want to use its build system which makes this easily possible (perhaps we should, but for now we don't). So, when upgrading libpng, you need to perform an extra step after merging the new version (and before committing your changes):

Create a temporary build directory and run libpng configure from it using --with-libpng-prefix=wx_ option. Then run make pnglibconf.h pngprefix.h to create these files in the build directory. Next, search for the line containing PNG_ZLIB_VERNUM in the pnglibconf.h and set it to 0 to disable zlib version checks (this looks dangerous but seems to be unavoidable with the current build system). And then, finally, copy these files to src/png subdirectory of the wxWidgets source tree, overwriting the versions there.

Notice that config.h generated by libpng configure is not used, we build it without -DHAVE_CONFIG_H as it works just fine without it on any ANSI C system (i.e. anywhere by now).

libtiff

Run autogen.sh to update the generated files and commit the changes.

zlib

Check for the newly added public systems in zlib.map and update zconf.h to include if necessary -- at least with zlib 1.2.12 release this file wasn't updated at all in the upstream version, resulting in problems such as #22280. If zconf.h is updated, you probably already had to resolve the conflicts in it, as our file differs from the upstream version due to having the changes from Z_PREFIX PR included in it.

Updating the main repository

If there are any changes to the source files used by the library, update the corresponding build/bakefiles/$lib.bkl file (e.g. expat.bkl for Expat) and rerun bakefile to regenerate most of the makefiles and project files. Currently you will need to update build/msw/wx_wx$lib.vcxproj{,.filters} files manually.

Commit these changes and the changes to the submodule itself, but don't push them to GitHub yet.

Test and push

The updates need to be tested under MSW and under Unix using --disable-sys-libs configure option.

If everything seems to work, push the updated branch out. Notice that you may want to use the ssh GitHub repository URL instead of the default (because more convenient for checking them out) HTTPS one:

$ git push --set-upstream git@github.com:wxWidgets/libexpat.git wx

Finally, create a PR to let the CI builds to run and test changes too. If no problems are found, merge the PR as usual.