make automated pull PR title more clear

[tshepang]

This more clearly indicates that we are pulling from a given repository

[tgross35]

Is the rustc commit ID available at this time? It would be nice if the body also said Sync to rust-lang/rust@9c6a4b05bc3d5e7 or similar, to have a quick cross ref for the commit.

[tgross35]

Actually, could it just pick the merge commit message and use that for the title+body? It should be the last commit at this point, so I think --title="$(git log -1 --format=%s)" --body="$(git log -1 --format=%b)" would work.

That would mention rust-lang/rust, the specific commit, as well as link the diff and link back to josh-sync (e.g. rust-lang/compiler-builtins@66ffdef). The downside is that for repos that use merge commits, you get the same message repeated twice in history.

[tshepang]

@tgross35 nice suggestion there... I added your title suggestion to the body instead

[Kobzol]

This would require some changes in subtree repos, which I'm not sure is worth it (https://github.com/rust-lang/rust/blob/0d162b25edd5bf0dba9a22e83b614f1113e90474/src/tools/rust-analyzer/triagebot.toml#L20, https://github.com/rust-lang/rust/blob/71963027884c9d995173aca298b0fe614e145bde/library/compiler-builtins/triagebot.toml#L7).

Changing the PR message would be nice though. I think we could just use --fill-verbose (https://cli.github.com/manual/gh_pr_create) to autofill the latest commit of the pull into the PR body.