Re: DEVEL: Help with feature implementation

On 1/18/21 6:24 PM, Junio C Hamano wrote:

Antonio Russo [off-list ref] writes:

quoted

As a side note, would this list be willing to look at patches that remove
the need to use revs->limited?  Adding new features would be much easier if
we could restrict git to use streaming algorithms for these simplifications.

Do you mean you will write new implementations of operations like
"--simplify-merges", "--ancestory-path" and all its friends without
the need for the "limited" bit?

Yes.

Willing to look at?  I do not know about others, but sure, it would
make be extremely excited.

You may be able to rewrite some other operations that implicitly
require the limited bit into an incremental implementation, but I am
skeptical that you can do "simplify-merges" in a streaming fashion
in such a way that we'd dig a bit but not all the way down before
making decisions on which commits should be included in the output
and how their parenthood relationship should appear etc.  I and
Linus tried independently and we did not get that far in our
attempts (note: there wasn't commit-graph back then).

Yeah, it's a big task (but, it'd be useful work, rather than doing
another rewrite of my feature to make it work when revs->limited).
Each of the flags (simplify-merges, ancestry-path, etc.) is its own
little sub-project.

I haven't thought about any one flag specifically, but the fact that
two complete code paths exist right now just seem like a nightmare.
I'm not necessarily interested in making the implementations faster,
but rather getting rid of the duplicated code path.

It's also a long-term goal, but it's nice to hear that people would
be interested in it.

If you are talking about precomputed stuff like commit-graph, that
may change the equation, but we'd prefer to have the system work
without requiring these auxiliary data (in other words, it would be
fine to use them as optimization).

No, I understand that generation numbers can only be used as an
optimization (i.e., they might all be GENERATION_NUMBER_INFINITY).