Re: Moved files and merges

On Sat, Sep 03, 2005 at 01:25:50AM -0700, Junio C Hamano wrote:

Junio C Hamano [off-list ref] writes:

quoted

"H. Peter Anvin" [off-list ref] writes:

quoted

I currently have two klibc trees,

I cloned them to take a look.  You_do_ seem to have a lot of
renames.

Well, I think I understand how your trees ancestry looks like,
but still haven't come up with a good problem definition.  I am
sorry that this message is not a solution for your problem but
would end up to be just my rambling and thinking aloud.

The ancestry looks like this:

       ----#4-#5---#7   #0: 1.0.14 released, next version is 1.0.15
      /      /              5691e96ebfccd21a1f75d3518dd55a96b311d1aa
     /---#1-#3---#6     #1: Explain why execvpe/execlpe work the way they do.
    //     /                1d774a8cbd8e8b90759491591987cb509122bd78
  #0-----#2             #2: 1.1 released, next version is 1.1.1
                            3a41b60f6730077db3f04cf2874c96a0e53da453
                        #3: Merge of #2 into #1
                            7ab38d71de2964129cf1d5bc4e071d103e807a0d
                        #4: socketcalls aren't always *.S files; they can...
                            f52be163e684fc3840e557ecf242270926136b67
                        #5: Merge of #3 into #4
                            2e2a79d62a96b6b0d4bc93697fe77cd3030cdfd9
                        #6: Warnings cleanup
                            f5260f8737517f19a03ee906cd64dfc9930221cd
                        #7: Remove obsoleted files from merge
                            59709a172ee58c9d529a8c4b6f5cf53460629cb3

and you are trying to merge #6 into #7 (or #7 into #6).  #6 does
not have usr/kinit and nfsmount at the top; #7 has nfsmount
under usr/kinit/.

The merge base of #6 and #7 is #3.  #3->#7 involves many renames
like nfsmount/sunrpc.h -> usr/kinit/nfsmount/sunrpc.h, while
#3->#6 involves no renames.  This can be seen by 

       $ git-diff-tree -M --diff-filter=R -r '#3' '#7' | wc -l

These renames are introduced by #5 merge, whose immediate
ancestors are #3 and #4.

Now, there is a question.  When you merge #6 and #7, development
between #3 and #7 have a lot of renames, while #3 and #6 do not.
What should this merge do?  Should it follow the rename, and if
so why?

Maybe I am missing something... but why should the merge operation
ignore renames? Is there a merge case when ignoring renames is the
Right Thing to do?

Lets say the branches A and B has the common ancestor C which contains
a file named "foo". If A has renamed "foo" to "foobar" and B has made
some content changes to "foo" shouldn't the result be a file named
"foobar" with the content changes B made to "foo" in it?

As I see it when we rename 'foo' to 'foobar' we say that "this file
should from now on be named 'foobar'". Furthermore, when we make some
content changes to some file we say "this file should have this new
content instead of its old content". In particular I do not think the
user expresses an intent to keep the name of a file just because she
makes some changes to its contents. So IMHO the merge of "this file
should from now on be named 'foobar'" and "this file should have this
new content instead of its old content" should be "this file should
from now on be named 'foobar' and have this new content".

I think it is feasible to teach the merge machinery about those rename
cases, it probably isn't trivial to implement but I certainly think it
is possible. It may be the case that the user should be warned when
such automatic merges involving renames are performed though.


- Fredrik