Re: Using Format/export-subst Howto.

[Michael J Gruber <git@drmicha.warpmail.net>]

Junio C Hamano venit, vidit, dixit 14.09.2012 23:23:
> Michael J Gruber <git@drmicha.warpmail.net> writes:
> 
>> you need to "rm file && git checkout file"). If the user has to
>> update $Id$ to match the current sha1 (by remembering to do a more
>> forceful checkout than checkout -f) then one half of that feature
>> is useless.
> 
> As if there is any value in "$Id$" _feature_.  It's a checkbox item, 
> nothing more ;-).

It's your favorite feature^Wcheckbox item, I know ;)

I wouldn't mind dropping it or making it export-only, but the current
state of that item is quite confusing. I seem to remember this has been
brought up before.

Junio C Hamano venit, vidit, dixit 15.09.2012 00:26:
> Junio C Hamano <gitster@pobox.com> writes:
> 
>> Michael J Gruber <git@drmicha.warpmail.net> writes:
>> 
>>> you need to "rm file && git checkout file"). If the user has to
>>> update $Id$ to match the current sha1 (by remembering to do a
>>> more forceful checkout than checkout -f) then one half of that
>>> feature is useless.
>> 
>> As if there is any value in "$Id$" _feature_.  It's a checkbox
>> item, nothing more ;-).
> 
> Having said that, I think you could do something along this line (I 
> am thinking aloud, so there may be leaps in the logic below).
> 
> * Introduce a new on-disk flag in the index.  Call it X.  After 
> entry.c:write_entry() writes it out to the working tree, this flag is
> cleared.  And this codepath is the only place that clears this flag.
> 
> * When applying a clean filter (from here on, everything that breaks
> byte-for-byte identity between the copy on the working tree and the
> contents that is hashed and stored in the object store are considered
> "clean filter", including CRLF->LF and ident), internally apply the
> corresponding smudge filter to the cleaned result and compare it with
> the original input we obtained from the working tree.  If they
> differ, flip the X bit on for the path in the index.
> 
> * When "checkout" and any potential callers of write_entry() decide 
> whether it is worth calling write_entry() [*1*], consider any path
> with the X bit on as "dirty" and call write_entry().
> 
> You have to be very careful when designing the third point, though. 
> There will now be two kinds of "the working tree file is different 
> from the version registerd in the index" once you do the above. 
> Different only because of "clean->smudge" roundtrip comparison, and 
> different because it does have a real local modification.  The former
> must be considered "no local modification" for the purpose of merges
> and branch switching (otherwise you will get "cannot merge, you have
> local modifications" error).
> 
> 
> [Footnote]
> 
> *1* This currently is done primarily with ie_match_stat(), that 
> essentially is "Does the result of applying 'clean' to the working 
> tree contents match what is registered to the index?  Do not bother 
> doing this check over and over again once you checked this until the
> file in the working tree is modified again".
> 

You've convinced me not to try this in-core...

Maybe a post-commit hook is enough for Id. It's just that we also have
no in-core way of doing a forceful enough checkout on those files. But I
wouldn't mind making Id export-only (export-subst). Really, most people
who look at Id really want something like VERSION_GEN (without having to
use a build script/make/...).

Michael