Re: Extending "extended SHA1" syntax to traverse through gitlinks?

On Sun, Aug 21, 2016 at 03:46:36PM +0200, Jakub Narębski wrote:

W dniu 21.08.2016 o 00:50, Josh Triplett pisze:

quoted

Currently, if you have a branch "somebranch" that contains a gitlink
"somecommit", you can write "somebranch:somecommit" to refer to the
commit, just like a tree or blob.  ("man git-rev-parse" defines this
syntax in the "SPECIFYING REVISIONS" section.)  You can use this
anywhere you can use a committish, including "git show
somebranch:somecommit", "git log somebranch:somecommit..anotherbranch",
or even "git format-patch -1 somebranch:somecommit".

However, you cannot traverse *through* the gitlink to look at files
inside its own tree, or to look at other commits relative to that
commit.  For instance, "somebranch:somecommit:somefile" and
"somebranch:somecommit~3" do not work.

Note that there is the same problem traversing through trees:
while 'git cat-file -p HEAD:subdir/file' works, the 'HEAD:subdir:file'
doesn't:

  $ git cat-file -p HEAD:subdir:file
  fatal: Not a valid object name HEAD:subdir:file

Interesting point; if extending this syntax anyway, any treeish ought to
work, not just a committish.

Though you can do resolve step manually

  $ git cat-file -p $(git rev-parse HEAD:subdir):file

This works.

True, but that seems quite inconvenient.

quoted

I'd love to have a syntax that allows traversing through the gitlink to
other files or commits.  Ideally, I'd suggest the syntax above, as a
natural extension of the existing extended syntax.

And with the above manual resolving, you can see the problem with
implementing it: the git-cat-file (in submodule) and git-rev-parse
(in supermodule) are across repository boundary.

Only if the gitlink points to a commit that doesn't exist in the same
repository.  A gitlink can point to a commit you already have.

Also the problem with proposed syntax is that is not very visible.
But perhaps it is all right.  Maybe :/ as separator would be better,
or using parentheses or braces?

It seems as visible as the standard commit:path syntax; the second colon
seems just as visible as the first.  :/ already has a different meaning
(text search), so that would introduce inconsistency.

quoted

(That syntax would potentially introduce ambiguity if you had a file
named "somecommit:somefile" or "somecommit~3".  That doesn't seem like a
problem, though; the existing syntax already doesn't support accessing a
file named "x..y" or "x...y", so scripts already can't expect to access
arbitrary filenames with that syntax without some kind of quoting, which
we also don't have.)

Errr... what?

  $ echo A..B >A..B
  $ git add A..B
  $ git commit -m 'A..B added'
  [master 2d69af9] A..B added
   1 file changed, 1 insertion(+), 1 deletion(-)
   create mode 100644 A..B
  $ git show HEAD:A..B
  A..B

I stand corrected; I didn't find that.  I thought rev parsing worked
independently from the repository, and didn't have any automagic
detection based on the contents of the repository?

This seems ambiguous, and (AFAICT) not documented.  If HEAD:A and B both
refer to a commit, in addition to the blob A..B, which will HEAD:A..B
refer to?  I did test the HEAD:gitlink..anotherbranch case, and it does
parse as a range.