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  12. 25 Dec, 2015 2 commits
    • Valery Sizov's avatar
    • Stan Hu's avatar
      Disable --follow in `git log` to avoid loading duplicate commit data in infinite scroll · ff8cd116
      Stan Hu authored
      `git` doesn't work properly when `--follow` and `--skip` are specified together. We could even be **omitting commits in the Web log** as a result.
      Here are the gory details. Let's say you ran:
      git log -n=5 --skip=2 README
      This is the working case since it omits `--follow`. This is what happens:
      1. `git` starts at `HEAD` and traverses down the tree until it finds the top-most commit relevant to README.
      2. Once this is found, this commit is returned via `get_revision_1()`.
      3. If the `skip_count` is positive, decrement and repeat step 2. Otherwise go onto step 4.
      4. `show_log()` gets called with that commit.
      5. Repeat step 1 until we have all five entries.
      That's exactly what we want. What happens when you use `--follow`? You have to understand how step 1 is performed:
      * When you specify a pathspec on the command-line (e.g. README), a flag `prune` [gets set here](https://github.com/git/git/blob/master/revision.c#L2351).
      * If the `prune` flag is active, `get_commit_action()` determines whether the commit should be [scanned for matching paths](https://github.com/git/git/blob/master/revision.c#L2989).
      * In the case of `--follow`, however, `prune` is [disabled here](https://github.com/git/git/blob/master/revision.c#L2350).
      * As a result, a commit is never scanned for matching paths and therefore never pruned. `HEAD` will always get returned as the first commit, even if it's not relevant to the README.
      * Making matters worse, the `--skip` in the example above would actually skip every other after `HEAD` N times. If README were changed in these skipped commits, we would actually miss information!
      Since git uses a matching algorithm to determine whether a file was renamed, I
      believe `git` needs to generate a diff of each commit to do this and traverse
      each commit one-by-one to do this. I think that's the rationale for disabling
      the `prune` functionality since you can't just do a simple string comparison.
      Closes #4181, #4229, #3574, #2410
  13. 24 Dec, 2015 4 commits