Re: [PATCH 1/2] revision: Denote root commits with '#'

On 1/18/21 3:33 PM, Junio C Hamano wrote:

Junio C Hamano [off-list ref] writes:

quoted

[Footnote]

*1* Stepping back a bit, I think concentrating too much on "is it
     root?" is a wrong way to think about the problem.  Suppose you
     have two histories, e.g. (time flows from left to right; A and X
     are roots)

A shorter and more concrete example.  Start from an empty repository:

	$ git init
	$ git commit --allow-empty -m Aroot
	$ git checkout --orphan side
	$ git commit --allow-empty -m Xroot
	$ git log --all --graph --oneline
         * a1f7cb2 (HEAD -> side) Xroot
         * b6fb655 (master) Aroot

These depict two root commits, Aroot and Xroot, and no other
commits.  We do want to show that these two commits do not have
parent-child relationship at all, and your (and a few proposals made
by other in the past) solution was to show them both with "#".

Continuing in the same repository:

	$ git checkout --orphan another
	$ git commit --allow-empty -m Oroot
	$ git commit --allow-empty -m A
	$ git log --graph --oneline ^another^ another side
         * eddf116 (HEAD -> another) A
         * a1f7cb2 (side) Xroot

These depict two commits, A and Xroot, and no other commits.  We
also want to show that these two commits do not have parent-child
relationship at all, but if we paint Xroot with "#", it still makes
it appear that A is a child of Xroot.

quoted

     And the right way to look at it is "does A have any parent in
     the part of the history being shown?", not "does A have any
     parent?"  Then 'A' will get exactly the same treatment in the
     two examples, and the visual problem that makes A appear as if
     it has parent-child relationship with unrelated commit X goes
     away.

So the condition we saw in your patches, !commit->parents, which
attempted to see if it was root, needs to be replaced with a helper
function that checks if there is any parent that is shown in the
output.  Perhaps

	int no_interesting_parents(struct commit *commit)
	{
		struct commit_list *parents = commit->parents;

		while (parents) {
			if (!(parents->object.flags & UNINTERESTING))
				return 0;
			parents = parents->next;
		}
		return 1;
	}

or something like that should serve as a replacement, i.e.

	return !commit->parents ? "#" : "*";

would become

	return no_interesting_parents(commit) ? "#" : "*";

Hmm?

Okay, I see what you mean. Fixing --graph to avoid implying ancestry sounds like a better approach to me.

That being said, I spoke to Jason recently, and he expressed interest in optionally marking root commits so they are easy to search for in a graph with something like /# in `less`. I see value in this, too.

So would you be open to my modifying of the patch in question (patch 1+2 squashed, I guess) to instead use "--mark-roots=<mark>" to optionally mark root commits with a string <mark>, and pursue fixing the --graph rendering issue in another series?

If so, what would you like to see out of the --left-right issue? Maybe "--mark-left-root=<mark>" and "--mark-right-root=<mark>", so multi-byte strings may be used? Can there be more than one root on either side? (so the option would use a plural "roots" instead of "root"?)

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