Michael J Gruber <g...@drmicha.warpmail.net> writes:
> ... but wondering
> whether we could and should support concatenating filters by either
>
> - making it easy to request it (say by setting
> "filter.gpgtopdftotext.textconvpipe" to a list of textconv filter names
> which are to be applied in sequence)
>
> or
>
> - doing it automatically (remove the pattern which triggered the filter,
> and apply attributes again to the resulting pathspec)
I think what you are getting at is to start from something like this:
= .gitattributes =
*.gpg diff=gpg
*.pdf diff=pdf
and have "git cat-file --textconv frotz.pdf.gpg" (and other textconv
users) notice that:
(1) The path matches "*.gpg" pattern, and calls for
diff.gpg.textconv conversion. This already happens in the
current system.
(2) After stripping the "*.gpg" pattern (i.e. look at the part of
the path that matched the wildcard part * in the attribute
selector), notice that the remainder, "frotz.pdf", could match
the "*.pdf" pattern. The output from the previous filter could
be treated as if it were a blob that is stored in that path.
A few issues that need to be addressed while designing this feature
that come to my mind at random are:
* This seems to call for a new concept, but what exactly is that
concept? Your RFD sounds as if you desire a "cascadable
textconv", but it may be of a somewhat larger scope, "virtual
blob at a virtual path", which the last sentence in (2) above
seems to suggest.
* What is this new concept an attribute to? If we express this as
"the textconv conversion result of any path with attribute
diff=gpg can be treated as the contents of a virtual blob", then
we are making it an attribute of the gpg "type", i.e.
= .git/config =
[diff "gpg"]
textconv = gpg -v
textconvProducesVirtualBlob = yes
To me, that seems sufficient for this particular application at
the first glance, but are there other attributes that may want to
produce such virtual blob for further processing? Is limiting
this to textconv too restrictive? I do not know.
* What is the rule to come up with the "virtual path" to base the
attribute look-up on for the "virtual blob contents"? In the
above example, the pattern was a simple "*.gpg", and we used a
naïve "what did the asterisk match?", but imagine a case where
you have some documents that you want to do "gpg -v" and some you
don't. You express this by having the former class of files
named with "conv-" prefix, or some convention that is convenient
for you.
Your .gitattributes may say something like:
= .gitattributes =
conv-*.gpg diff=gpg
When deciding what attributes to use to further process the
result of conversion (i.e. "virtual blob contents") for
conv-frotz.pdf.gpg, what virtual path should we use? Should we
use "conv-frotz.pdf", or just "frotz.pdf"?
"The difference does not matter--either would work" is not a
satisfactory answer, once you consider that you may want to have
two or more classes of pdf files that you may want to treat
differently, just like you did for gpg encrypted files in this
example setting. It seems to suggest that we want to use
conv-frotz.pdf as the virtual path, but how would we derive that
from the pattern "conv-*.gpg" and path "conv-frotz.pdf.gpg"? It
appears to me that you would need a way to say between the two
literal parts in the pattern, "conv-" part needs to be kept but
".gpg" part needs to be stripped when forming the result.
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