Disable --follow in `git log` to avoid loading duplicate commit data in infinite scroll

`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

Disable --follow in `git log` to avoid loading duplicate commit data in infinite scroll
ff8cd116 · Stan Hu · 350d6550 · ff8cd116 · ff8cd116
Commit ff8cd116 authored Dec 25, 2015 by Stan Hu
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CHANGELOG CHANGELOG +1 -0

repository.rb app/models/repository.rb +3 -1

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--- a/CHANGELOG
+++ b/CHANGELOG
@@ -10,6 +10,7 @@ v 8.4.0 (unreleased)
  - Add link to merge request on build detail page.

 v 8.3.2 (unreleased)
+  - Disable --follow in `git log` to avoid loading duplicate commit data in infinite scroll (Stan Hu)
  - Enable "Add key" button when user fills in a proper key

 v 8.3.1

--- a/app/models/repository.rb
+++ b/app/models/repository.rb
@@ -76,7 +76,9 @@ class Repository
      path: path,
      limit: limit,
      offset: offset,
-      follow: path.present?
+      # --follow doesn't play well with --skip. See:
+      # https://gitlab.com/gitlab-org/gitlab-ce/issues/3574#note_3040520
+      follow: false
    }

    commits = Gitlab::Git::Commit.where(options)