Re: [PATCH v2 02/18] Add a new builtin: branch-diff

On Mon, May 7, 2018 at 3:05 PM, Igor Djordjevic
[off-list ref] wrote:

List, rename, delete -- all these seem more as basic CRUD operations,
where comparison is a more complex one. And not to get me wrong - I
could see "branch diff" being part of "branch", but not really when
"diff" already exists as a separate thing, already doing quite some
(but still diff related, and configurable) stuff.

If we go with "branch --diff", because it has the CRUD operations already
there for branches, I might ask for "remote --diff" to diff two remotes. ;)
(That command "remote --diff" would not make any sense, would it?)

Basically, what you (conceptually) call "two versions of the same
branch", I simply call "two branches" (from usage standpoint).

If I diff 2 (topic) branches, which are based on a different version
from upstream, then I see changes from commits that I don't care
about, but this tool explicitly excludes them. Instead it includes
the ordering of the commits as well as its commit messages to
the diff.

So I would not say this tool "diffs two branches", as that is understood
as "diffing the trees, where each of the two branches points two",
whereas this tool diffs a patch series, or if you give Git-ranges,
then it would produce such a patch series in memory.

And you may have a branch that got split, or more of them that got
unified, so defining "previous branch version" may not be that
straightforward - it`s really just "two commit ranges" (as man page
defines it in general), with "two versions of a patch series" only
being the most common/expected use case of the former.

Finally, if user picks two totally unrelated "branches" to compare,
he won`t get a really useful diff - but it`s the same as if he would
compare two totally unrelated commits (where tree state massively
changed in between, or having unrelated histories, even).

I used just that, but narrowed down the comparison to one file
instead of the whole tree.

With something like `git diff --branch <commit1>...<commit2>` you
would get yet another "diff look", useful for use case in question
here.

Personally I think this patch series should neither extend git-diff
nor git-branch.

It should not extend git-diff, because currently git-diff can diff
tree-ishs (and does that very well) and comparing to
worktree/index.

It should also not extend git-branch, as that command is for
CRUD operations that you hinted at earlier (Earlier I proposed
git-remote --diff for diffing two remote, which makes no sense,
another one might be git-worktree, which also just does CRUD
for worktrees. It would be a bad idea to have "git worktree --diff")

Hence I propose "git range-diff", similar to topic-diff, that
was proposed earlier.

* it "diffs ranges" of commits.
* it can also deal with out-of-git things like patch series,
  but that is a mere by product and may not be desired.
  Just like git-diff can also compare two files outside a git
  repo, that would not be a good use case.
  Keep the name Git-centric!
* it autocompletes well.

Stefan