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apicompat checks recent changes to a Go project for backwards incompatible changes


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Build Status Coverage Status GoDoc

apicompat is a tool to check for the introduction of backwards incompatible changes.


  • Guarantees that all consumers of a library will still build without failure
  • Only checks exported declarations
  • There are no false positives (if there are, it's a bug)
  • Not every backwards incompatible change can be detected, swapping argument parameters and other changes still need to be considered by the library author
  • Can be simply consumed as a library
  • Is in its infancy, see Status, feedback and review appreciated
  • Was originally named abicheck during early development

Secondary tasks could include:

  • Detecting current semver and suggesting an appropriate increase
  • Listing all changes for help in writing release notes/commit messages.

Try at or via CLI:

go get -u
cd /your/project/dir/with/committed/changes

Proposed Arguments

apicompat also comes with a command line tool, as well as being used as a library, the following are the proposed flags and arguments for the command line tool.

-vcs    (auto|git|svn|etc) - Version control system to use (default: auto)
-before revision           - Revisions to check as before  (default: if unstaged changes, check those, else check last two commits)
-after  revision           - Revisions to check as after   (default: if unstaged changes, check those, else check last two commits)
-vcsDir path               - Path to root VCS directory    (default: let VCS tool search)
-all                       - Show non-breaking changes as well as breaking (default: false)

apicompat        # current package only
apicompat ./...  # check subdirectory packages

Another tool, called abichanges may also be included which will list all detected changes to assist in producing release notes.


apicompat is currently under heavy development and refactoring. This initial version was a proof of concept and shortcuts were taken. The current tasks are focused on (but not limited to):

  • Adding Mercurial, SVN and potentially other VCS systems
  • Improve VCS options such as:
    • Detection of VCS and flag to overwrite
    • Choosing base VCS path to allow running for a different directory
    • Filtering vendor/ directories (if this is the best place to do it, or leave it to go/type ast packages)
    • Check subdirectories if ran from a subdirectory of the VCS (currently checks all committed code)
  • Add docs, flow diagram and fixing of existing docs
  • Improve output formats (such as vim quickfix)
  • Move these tasks to GitHub issues
  • Once all other steps have been completed, performance will be investigated


This uses golden masters for the tests, currently (and only due to time constraints) testdata/ directory contains before.go and after.go, which are before and after versions of a test package, each time go test is ran, the output is compared to testdata/exp.txt, which should not change.

If adding new test cases, you should expect the test to fail as the code changes should create a difference with exp.txt. Then, you'll need to update the golden master (see below), and commit those changes. If you add a new test case to before.go and after.go, and the tests still pass, you've uncovered a bug within apicompat which will need a code change to fix, once code has change, the tests should fail, so update the master, review all your changes and commit.

  • This uses golden master testdata/exp.txt for the tests
  • Run tests with: go test
  • Update master with: go test -args update
  • Alternatively to do a test run: go install && ( cd testgit; ./ && apicompat )


apicompat checks recent changes to a Go project for backwards incompatible changes







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