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wxWidgets/docs/contributing/how-to-update-third-party-library.md
Vadim Zeitlin e1c54ff032 Update 3rd party libraries updating instructions 
Explain how to do it now when Git submodules are used for them instead
of speaking about svn vendor branches.
2017-11-11 15:35:35 +01:00

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How to update a third party library to a newer version

  1. 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.

  1. Submodules

Normally all third party libraries should be managed using Git submodules. Currently only zlib and libpng use them, but this will be extended to the other third party libraries (i.e. expat, libjpeg and libtiff) soon.

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.

  1. 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, test the build under MSW and under Unix using --disable-sys-libs configure option, and 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
  1. 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 submodule and create a PR to test them as usual.

  1. Special instructions for 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).