Issue 665072 has been merged into this issue.

The solution is to check logs between two git hashes OLD_HASH..NEW_HASH : empty -> backward rolling; not empty -> forward rolling.

But for v8, this won't work because V8 revisions which are referenced by Chromium's DEPS are not from master branch.
V8 and WebRTC have commit position footers produced by gnumbd, so we should check those instead.

Note that this might not work not just for v8. It really depends whether commits being rolled to are from the same branch or not. For example, I have no idea about skia, catapult and pdfium which all use the same deps roller logic. Perhaps ask borenet@

Sorry, I'm not aware of the context here.  The skia/catapult/nacl/pdfium rollers don't roll backwards and only roll commits on the master branch, so the logic is basically:

git log <last roll rev>..origin/master

Timestamps never enter the picture. Is this for a new roller?  If so, why not use the Skia roller?

you've answered my question :)
Since you only roll commits from master branch, then git log will indeed be sufficient as one commit will always be parent of another one (transitively).

Thanks borenet@ and tandrii@!

The context here is to detect whether a roll is forward or backward for an arbitrary dependency in DEPS. For those rollers, they are rolling forward; but upon a revert of the rolling CL (e.g. to fix breakage), it is backward.

This detection is needed for Findit to analyze test or compile failures on Waterfall and then infer the culprits.

@stgao, can we not look at the CL itself like we already do for detecting whether a CL is reverting another or not? Or is there no clean mapping from rolls to CLs?

wrengr@, I'm not sure if I understand your question/suggestion correctly.

The new approach I described above is to not look at the information of individual commit; but instead checking whether a commit is a parent of another. And this won't work for V8 as suggested by tandrii@. And the solution is to look at the commit position footer.

When mapping a DEPS rolling to the commits of that rolled dependency, we just grab the changelogs between the two commits referred to by the DEPS file.

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