how to git bisect

If something is broken in curl but was working in an older version you can use a technique called bisecting to identify what changes caused the problem.

The first step is to clone the curl repository, https://github.com/curl/curl.git . In the repo the curl releases use tag names in the format curl-X_XX_X, eg 7.44.0 is curl-7_44_0. Each time you build source from the repository using a different commit you should run buildconf first (./buildconf && ./configure && make).

These next two steps are not strictly required but if you're not entirely sure what you're doing you should do them to keep your sanity:

• Checkout from the repo a version you know is good, build it and confirm it's good.
• Checkout from the repo a version you know is bad, build it and confirm it's bad.

Now use git bisect commands to do the bisect. For example, if curl 7.49.1 has some issue that 7.44 does not have:

git bisect start
git bisect bad curl-7_49_1
git bisect good curl-7_44_0

bisect has now checked out the first commit to test. (Note commits are checked out automatically when you bisect.)

• Build but no install (./buildconf && ./configure <opts> && make).
• Confirm libcurl and curl versions match (src/curl -V and compare curl and libcurl versions).
• Attempt to reproduce problem using src/curl. (If problem is not 100% reproducible run multiple times to get an accurate result.)
• Mark each commit good (no problem), bad (problem) or skip (failed to build or problem other than the one you're working on) using one of the respective commands shown below:

git bisect good
git bisect bad
git bisect skip

After you mark a commit another commit will be checked out, and repeat the above set of steps. Assume each step about 1-2min a build, plus however long it takes you to reproduce your issue. A typical bisect should take less than half an hour. You will then eventually end up with the single specific change that introduced the problem.

Alternately, instead of marking the commits manually, you may automate the process by using git bisect run with a script like this one.

When done to cleanup and reset to the commit before bisecting do git bisect reset