[PATCH 1 of 2 v8] graft: support grafting across move/copy (issue4028)

[Yuya Nishihara]

On Fri, 26 Aug 2016 11:16:31 -0500, Gábor Stefanik wrote:
> # HG changeset patch
> # User Gábor Stefanik <gabor.stefanik at nng.com>
> # Date 1472225958 -7200
> #      Fri Aug 26 17:39:18 2016 +0200
> # Node ID f32aa28298164aa38830e83369c57c9553c6ff08
> # Parent  318e2b600b80e4ed3c6f37df46ec7544f60d4c0b
> graft: support grafting across move/copy (issue4028)

Sorry for late reply, and I don't fully understand how this patch handles
reverse copy tracking correctly yet. But weekend is over, so I just wrote
random comments.

> +    # In certain scenarios (e.g. graft, update or rebase), ca can be overridden
> +    # We still need to know a real common ancestor in this case
> +    # We can't just compute _c1.ancestor(_c2) and compare it to ca, because
> +    # there can be multiple common ancestors, e.g. in case of bidmerge.
> +    cta = ca
> +    # ca.descendant(wc) and ca.descendant(ca) are False, work around that
> +    _c1 = c1.p1() if c1.rev() is None else c1
> +    _c2 = c2.p1() if c2.rev() is None else c2
> +    dirty_c1 = not (ca == _c1 or ca.descendant(_c1))
> +    dirty_c2 = not (ca == _c2 or ca.descendant(_c2))
> +    graft = dirty_c1 or dirty_c2
> +    if graft:
> +        cta = _c1.ancestor(_c2)

Can we know if we're doing graft-type merge beforehand? I think ca.descendant()
isn't fast so it should be avoided for normal merges.

>      # find interesting file sets from manifests
> +    if graft:
> +        repo.ui.debug("  computing unmatched files in rotated DAG\n")
>      addedinm1 = m1.filesnotin(ma)
>      addedinm2 = m2.filesnotin(ma)
> -    u1, u2 = _computenonoverlap(repo, c1, c2, addedinm1, addedinm2)
> +    _u1, _u2 = _computenonoverlap(repo, c1, c2, addedinm1, addedinm2)
> +    if not graft:
> +        u1, u2 = _u1, _u2
> +    else: # need to recompute this for directory move handling when grafting
> +        repo.ui.debug("  computing unmatched files in unrotated DAG\n")
> +        u1, u2 = _computenonoverlap(repo, c1, c2, m1.filesnotin(mta),
> +                                                  m2.filesnotin(mta))
> +
>      bothnew = sorted(addedinm1 & addedinm2)
>  
>      for f in u1:
> -        checkcopies(c1, f, m1, m2, ca, limit, diverge, copy1, fullcopy1)
> +        checkcopies(c1, f, m1, m2, ca, cta, dirty_c1, limit, diverge, copy1,
> +                    fullcopy1, incomplete1, incompletediverge)
>  
>      for f in u2:
> -        checkcopies(c2, f, m2, m1, ca, limit, diverge, copy2, fullcopy2)
> +        checkcopies(c2, f, m2, m1, ca, cta, dirty_c2, limit, diverge, copy2,
> +                    fullcopy2, incomplete2, incompletediverge)

[snip]

> +    # combine partial copy paths discovered in the previous step
> +    copyfrom, copyto = incomplete1, incomplete2
> +    if dirty_c1:
> +        copyfrom, copyto = incomplete2, incomplete1
> +    for f in copyfrom:
> +        if f in copyto:
> +            copy[copyto[f]] = copyfrom[f]
> +            del copyto[f]
> +    for f in incompletediverge:
> +        assert f not in diverge
> +        ic = incompletediverge[f]
> +        if ic[0] in copyto:
> +            diverge[f] = [copyto[ic[0]], ic[1]]

According to Matt's comment, we need two copy traces split at 'ca', but we use
ones split at 'cta' (and somewhat 'ca' is taken into account?), because it
wouldn't be easy to track copies backwards.

https://www.mercurial-scm.org/pipermail/mercurial-devel/2016-August/086915.html

I guess that are addressed these "incomplete" dicts and "if"s in checkcopies(),
but I wonder if there are unhandled cases such as non-linear DAG to be rotated,
which might include "ypoc". I'm not sure, though.