Branches merged on GitHub with "Squash and merge" or "Rebase and merge" are
never deleted by git branch --delete-merged, because their tips are not
reachable from the upstream. This treats such a branch as merged when some
upstream commit contains all of its changes, and names that commit in the
output:

Deleted branch topic (was 1a2b3c4, landed as 9f8e7d6).

This series finds the first upstream commit since the fork point that has
the branch's version of every file the branch changed, comparing only object
ids. With --squashed, a file that upstream also changed counts when merging
the branch's version into upstream's leaves it unchanged. Timed on my clone
with 65 branches, this takes 0.5s.

Other approaches:

 * Full merge-ort test merge per upstream commit: about 9s, because it
   builds a whole tree for every commit.
 * range-diff pairing for rebases: about 10s. It pairs on diffs alone,
   ignoring log messages, so it found nothing extra.
 * Patch ids: not tried. They tell whether a commit is the same patch, but
   deleting a branch only needs a commit that contains its changes. They
   miss a squash that was touched up and changes next to upstream edits, and
   they read file contents for every upstream commit touching the branch's
   files.

Changes in v3:

 * Split into multiple commits, one for rebase merges and one for squash
   merges.
 * By default a branch counts as merged when an upstream commit has its
   exact version of every file it changed. This never reads file contents,
   so it stays cheap in a partial clone. It finds rebase merges, and squash
   merges where upstream left those files alone.
 * Replace --no-squashed with an opt-in --squashed, which also finds
   branches merged after upstream changed the same files by merging those
   files.
 * Add a test for a rebase merge, and check that a squash onto changed files
   is kept without --squashed and deleted with it.

Changes in v2:

 * Diff each upstream commit once and share the result between all branches,
   faster than v1.
 * Fix a branch merged with a merge commit being reported as "landed as" the
   merge when another branch was searched first, and add a test for it. Show
   the topic commit itself in "landed as" for work that arrived through a
   merge.
 * Use git merge --squash as the example in the commit message and mention
   GitHub's squash and rebase buttons.
 * Add --no-squashed to skip the squash search.

Harald Nordgren (3):
  branch: move the deleteMerged opt-out check into a helper
  branch: let --delete-merged find rebase merged branches
  branch: add --squashed to find squash merged branches

 Documentation/git-branch.adoc |  26 ++-
 builtin/branch.c              | 345 ++++++++++++++++++++++++++++++++--
 t/t3200-branch.sh             | 192 +++++++++++++++++++
 3 files changed, 537 insertions(+), 26 deletions(-)

base-commit: 47fdf2208c5b94c8cc01c106b8f7c85efb91c926

Submitted-As: https://lore.kernel.org/git/pull.2425.v3.git.git.1792585717.gitgitgadget@gmail.com
In-Reply-To: https://lore.kernel.org/git/pull.2425.git.git.1790667030497.gitgitgadget@gmail.com
In-Reply-To: https://lore.kernel.org/git/pull.2425.v2.git.git.1791711665.gitgitgadget@gmail.com