build(vim-patch.sh): include commit subject

[wookayin]

Problem: vim-patch commits lack an informative title and summary in the
very first line of the commit message when the vim-revision is a Git SHA
hash, unlike when is a Vim version. This makes it difficult to discern
at a glance what changes are introduced by such vim-patch commits (in
git log, PR title, changelog generated by git-cliff, etc.).

e.g. Before:

vim-patch:abcdef123456

runtime(vim): improve performance

<some details>
...

Solution: Repeat the title of the upstream commit message, to improve
the clarity and visibility of the commit message.

e.g. After:

vim-patch:abcdef123456: runtime(vim): improve performance

<some details>
...

Note: the vim-patch:<hash> token is still needed by vim-patch.sh
(but not necessarily in the very first line of the commit message) to
determine which vim patches have been applied.

[wookayin]

We could possibly consider the 'new' commit message style starting from 11.0-dev cycle, if I may propose this. Though we might discuss first to have a consensus on which format would be the best for devs.

Since the prefix might be a bit too lengthy, we could also consider some other alternatives like:

1. More abbreviated SHA hash: e.g. vim-patch:abcdef01: runtime(vim): improve performance

• con: we might want lengthy enough SHA hashes (8+ or 12 chars), normalization might be an issue

2. Or do not include the SHA in the first-line title: e.g. vim-patch: runtime(vim): improve performance

• Since the SHA hash itself is not very useful for human other than the internal purposes for vim-patch.sh
• Note: Tokens like vim-patch:abcdef012345 are still needed in the commit message body.

[zeertzjq]

Actually the token only needs to have 7 hex digits:

  # Use sed…{7,7} to normalize (internal) Git hashes (for tokens caches).
  git -C "${NVIM_SOURCE_DIR}" log -E --grep='vim-patch:[^ ,{]{7,}' \
    | grep -oE 'vim-patch:[^ ,{:]{7,}' \
    | sort \
    | uniq \
    | sed -nEe 's/^(vim-patch:([0-9]+\.[^ ]+|[0-9a-z]{7,7})).*/\1/p'

    # Check for vim-patch:<commit_hash> (usually runtime updates).
    token="vim-patch:${line:0:7}"
    if [[ "${tokens[$token]-}" ]]; then
      continue
    fi

[wookayin]

For this PR I've drafted with not changing the number of hex digits, but I will leave to other core dev's decision whether to use 12 hex digits (current, since 03a0417), 7 digits, or other number of digits (say 8) --- if we think the title can be too length. I personally think being a bit lengthy for vim-patches is fine.

[justinmk]

will leave to other core dev's decision whether to use 12 hex digits (current, since 03a0417), 7 digits, or other

I generally recommend 12 digits, but for vim-patch it's low risk.