add `--follow` to git log command that shows history

[danielpops]

Feature request description

the --follow flag can be passed to git log for individual files and it will show the history even for files that have moved locations or even repositories.

In sourcegraph, it would be nice if by default, --follow was added to the git log command that generates history / blame annotations.

Is your feature request related to a problem? If so, please describe.

Yes, I cannot see the whole history of a file that has been moved in sourcegraph, and need to clone the repo and view the history manually :(

Describe alternatives you've considered.

I need to clone the repo and view the history manually :(

[danielpops]

Correction: The blame annotations are correct, but the history is not complete

[emidoots]

Thanks for filing this! Just to be clear, the issue is in the history pane like what you see here, correct? https://sourcegraph.com/github.com/sourcegraph/sourcegraph/-/blob/packages/sourcegraph-extension-api/README.md#&tab=history

The blame annotations come from git blame which automatically follows file renames without any additional arguments.

[emidoots]

To future folks who look at this, to implement this we would just need to:

1. Pass a follow flag into the ancestors query we make here: https://sourcegraph.com/github.com/sourcegraph/sourcegraph@1321c950a4936d758b2e9ae3e82bfca7f3230828/-/blob/web/src/repo/RepoRevSidebarCommits.tsx#L79:10
2. Accept that argument here: https://sourcegraph.com/github.com/sourcegraph/sourcegraph@1321c950a4936d758b2e9ae3e82bfca7f3230828/-/blob/cmd/frontend/graphqlbackend/git_commit.go#L187:27
3. Pass that argument into git.Commits here: https://sourcegraph.com/github.com/sourcegraph/sourcegraph@1321c950a4936d758b2e9ae3e82bfca7f3230828/-/blob/cmd/frontend/graphqlbackend/git_commits.go#L56
4. Add it to CommitsOptions and pass it into git log here: https://sourcegraph.com/github.com/sourcegraph/sourcegraph@1321c950a4936d758b2e9ae3e82bfca7f3230828/-/blob/pkg/vcs/git/commits.go#L166:6

While I'm not sure why git log --follow is an option instead of the default, exposing it as the default in Sourcegraph makes sense to me and also seems like it would be a clear advantage over some other history views out there, e.g. GitHub's: isaacs/github#900

Any obvious reason not to enable follow by default? @keegancsmith ?

[keegancsmith]

it is much slower to compute. Renames aren't stored in git. When a file is added/deleted, git will inspect the whole diff looking for a file deleted/added which is similar. To be fair this isn't so bad when following an individual file since most files aren't added/deleted/renamed often so you have 1 or more commits to inspect. However, when running log on a tree this has bad perf easily.

So my guess is we can enable it for logging one file, but not enable it everywhere else. This is probably what most code hosts do (I did not confirm this though)