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Instructions for updating to a new SOFA version and releasing ERFA

We welcome contributors who would like to help with the steps of updating to a new version of SOFA! The latter parts of the release process must be done by a maintainer with permissions, but the first part can (and should) be done as a pull request by anyone.

Updating SOFA

These steps can be done by anyone, as they use the Pull Request workflow which places no contraints on who has permissions to submit code changes.

  • Clone your fork of the ERFA repository from github (if you have not already), and change to the ERFA directory.
  • Create a new branch from the latest master branch in the ERFA repo.
  • If a new version of SOFA exists, run sofa_deriver.py from the erfa-fetch repository in its own directory. That will create a directory called erfa inside the erfa-fetch directory, and you should copy its contents to the src directory of erfa. Add any new C files or header files added by SOFA to src/meson.build, as appropriate.
  • Use git diff in erfa to inspect the changes, ensuring that you are not overwriting intentional changes between SOFA and ERFA (the README from the previous version is generally your friend here.)
  • Update the SOFA_VERSION define in both meson.build and configure.ac to reflect the new SOFA version.
  • Update the SOFA version mentioned in README.rst to reflect what's now in, as well as any relevant changes in the "Differences from SOFA" section or any other part of the README that your changes might have affected. This usually requires specifying the upcoming version of ERFA - since that isn't definite until release time, put x.y.z as the version, and leave it to the release maintainer to fill that in with the correct version (see below).
  • Commit the changes and push them up to your fork.
  • Create a Pull Request to the main ERFA repository. It is helpful to mention in the PR description if the changes in that SOFA version are backwards-compatible or not, as that helps the maintainers know how to update the version numbers when they do the release (described in more detail in the "Version numbering" section below).
  • A maintainer will check the Pull Request and merge once it's reviewed.

Releasing ERFA

These steps should be done by a maintainer, as they require specific Github permissions.

  • Update the version number in the project() version field of meson.build as well as AC_INIT in configure.ac to the version number you are about to release. Follow the instructions in the Version numbering "Package version number" section below.
  • Update the version info of the shared library in the libtool_version variable of meson.build and ERFA_LIB_VERSION_INFO in configure.ac. Follow the instructions in Version numbering "Shared library version info" section below.
  • Update the README.rst to reference the version you filled in above (it may be x.y.z if a maintainer followed the processes described above). Ensure the list of changes is accurate for this new version.
  • Commit these changes using git commit, with a commit message like Preparing release v0.0.1.
  • Run meson setup builddir: you need meson installed. If no errors appear, this will create a build.ninja file in the build directory, as well as a config.h. To avoid possible trouble, check that in the latter, PACKAGE_VERSION is set correctly.
  • Run meson test -C builddir, which will build the library and run the tests - make sure they pass before proceeding. (This is already done by continuous integration in Github so it really should pass, but better to be safe than sorry!)
  • Run meson dist -C builddir: this creates the distribution tarball, unpackages it and runs the check inside the untarred directory. The resulting tarball will be named e.g., erfa-0.0.1.tar.gz and will be placed in builddir/meson-dist (its filename will be printed out as well).
  • Tag the current commit with the version number. A signed tag is preferred if you have an a signing key (e.g., do git tag -s v0.0.1).
  • Push up your changes and the new tag to github: git push --tags origin master. (The command here assumes the git remote "origin" points to the "liberfa/erfa" repository. If not, substitute the appropriate name.)
  • Go to the "liberfa/erfa" repository for the github page, and click on the "releases" banner, "tags", and then the tag name you just pushed up. Click on the "..." button and choose "Create release". to change this tag to a release (Note that the details of how you find this option might change depending on what Github has decided recently, but the goal is to get to the "draft new release" page for the existing tag.)
  • Put the version number as the title (e.g., v0.0.1) and for the description put See `README.rst` for release notes.
  • Upload the tarball you created (e.g., erfa-0.0.1.tar.gz) by dropping it in the area that says "Attach binaries for this release by dropping them here or selecting them."
  • Click the "Publish release" button.
  • Update the release listing on Github Pages to include this release: Do git checkout gh-pages, add a new <li>...</li> entry for the release in index.html, do git commit, and then git push origin gh-pages. Or just edit it directly on the Github web interface if that's more your thing.

Version numbering

ERFA needs to provide two different version numbers. You need to update both. The first is the package version number or version number proper. ERFA uses semantic versioning to create this number. For more on this choice, see liberfa/erfa#6.

The second number is shared library version info. When a program has been linked with the ERFA shared library, the dynamic linker checks the version info of the library requested by the program with those of the libraries present if the system. This version info is important to binary distributions (such as Linux distributions). ERFA uses libtool versioning.

Package version number

Semantic versioning dictates how to change the version number according to changes to the API of the library. In the case of ERFA the API is:

  • The public C macros defined in erfam.h
  • The names, return types, number of arguments and types of the functions in erfa.h

To update the package version, the release manager has to check the relevant information about the release, such as:

If the version is given in the form MAJOR.MINOR.PATCH, then

  • if there is a backwards incompatible change (function removed, types of arguments altered, macros renamed...) then increase MAJOR by one and set the others to zero.
  • else if there is backwards compatible change (new function added or new macro added) then do not change MAJOR, increase MINOR by one and set PATCH to zero.
  • else
    you are either fixing a bug or making other improvements. Increase patch by one and do not change the others.

Change the version number in README.rst and the project() version argument.

Shared library version info

For the shared library version info, we are only interested in a subset of the API, the interfaces of the shared library. As the C macros are interpolated away at compile time, the interfaces in the ERFA shared library are:

  • The names, return types, number of arguments and types of the functions

Again, the release manager has to review the relevant information:

The shared library version info is stored in three numbers called current, revision and age. These numbers appear in the variable libtool_version in the mentioned order.

If the version is given in the form CURRENT,REVISION,AGE then

  • if there is a backwards incompatible change (function removed, types of arguments altered...) then increase CURRENT by one and set the others to zero (c,r,a -> c+1,0,0).
  • else if there is backwards compatible change (new function added) then increase both CURRENT and AGE by one, set REVISON to zero (c,r,a -> c+1,0,a+1).
  • else if the library code has been modified at all then increase REVISION by one (c,r,a -> c,r+1,a)
  • else
    do not change the version info (c,r,a -> c,r,a)

Change the version info in libtool_version

Examples

We start with ERFA version 1.0.0 and library version info 0,0,0

  • SOFA makes a new release. A function is added and two functions change their arguments. This is a backawars incompatible change, so the new package will have version 2.0.0 and the shared library version info will be 1,0,0
  • We forgot to add README.rst to the release. We make a new one. The change is a bugfix (no API changes), the new release will be 2.0.1. The shared library version is not modified (no changes in the library source code).
  • SOFA makes a new release. They just add a new function. The new package version will be 2.1.0. The shared library info will be 2,0,1 (both current and age are incremented).
  • SOFA makes a new relase fixing some bugs in the code without changing the API. New package version is 2.1.1. The shared library version is 2,1,1
  • A contributor finds a bug in ERFA. The fix doesn't change the API. New package version is 2.1.2. The shared library version is 2,2,1
  • SOFA makes a new release incorporating the bug fix and adding new functions. The new package version is 2.2.0. The shared library version is 3,0,2
  • SOFA makes a new release removing functions. This is a backawars incompatible change, so the new package will have version 3.0.0 and the shared library version info will be 4,0,0