[Gnu-arch-users] FEATURE PLANS: selected commit

[Tom Lord]

Selections name subsets of a tree, coloring elements of that subset as
interesting for "names only", "contents", or "both".

Given an ORIG and MOD tree, along with a SELECTIONS, we (usually) know how
to make a third tree, TARGET, which is a good answer to the question
"what does `like ORIG but with the changes from MOD that occur within
SELECTION' mean?"

The answer is:

        TARGET = The overlay within SELECTION of MOD onto ORIG.

using the definition of "overlay" from the previous message.

Semantically, selected commit is very easy, therefore:

        ORIG := the immediate ancestor of the commit

        MOD := the user's working dir

        SELECTION := the user's specified selection

        TARGET := overlay (SELECTION, MOD, ORIG)

        commit TARGET

        replace patch-log of MOD with patch-log of post-commit TARGET

        replace auto-changelogs of MOD with patch-logs from TARGET

Implementation-wise, I believe we can compute the contents of TARGET 
in-core, prior to invoking the normal `commit' logic, and then fairly
trivially use the `vu_' layer to fake out `commit' into thinking that
TARGET actually exists on disk.

I realize that the post with the "overlay" algorithm is tediously
detailed but let me point out one nice feature of it for selective
commit: it can give very clear error messages about why a proposed
selective commit doesn't make sense (e.g,. for half-included renames).


-t

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