Andreas Schwab venit, vidit, dixit 18.11.2015 18:49:
> Lars Schneider <[email protected]> writes:
>
>> git diff branchA...branchB
>> --> gives me the diff between (the common ancestor of A and B) and B. That
>> means I never see changes on branchA.
>>
>> git log branchA...branchB
>> --> gives me the commits reachable from A and B. That includes changes from
>> branchA.
>>
>> Is this because of a design decision that I do not (yet) understand or is
>> this inconsistent for historical reasons?
>
> git diff operates on two revisions. That is inherently incompatible
> with the usual meaning of A...B and A..B, which are set operations on
> the revision history. That git diff accepts this syntax is only for
> convenience.
That convenience can be a bit misleading, though, as the OP points out.
Just to spell this out because the other response (not the one I'm
replying to) could be misunderstood:
git diff A..B is the diff between (the trees in commits) A and B. It
will show you the "changes" that are only in A with "-", the changes
that are only in B with "+" - that is, if you want to think about diffs
as "positive changes" to a "virtual common base tree".
[ If p are the plus lines and m the minus lines, the diff says
B = A + p - m = (A-m) + p
<=> A = B - p + m = (B-p) + m
<=> B-p = A-m (virtual common base tree) ]
git log A..B will show you all commits that are in (=reachable from) B
but not in A. That is, it will show you all commits between the "most
recent" common ancestor (let's call it C) and B (including B), but not
those between C and A (and not A either).
git log A...B will show you all commits "specific to A and B", i.e.
those between C and B and those between C and A (including A and B,
excluding C).
git diff A...B will show you the diff between C and B.
So, both "diff A..B" and "log A...B" show changes/commits introduced by
A only or B only.
"diff A...B" and "log A..B" show changes/commits introduced by B only.
Maybe there's a way to think about these that makes them actually look
consistent - the only one that I can think of is the actual
implementation (we need to compute the merge base for both "..."
commands), but that's a really bad argument for a user facing notation.
Michael
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