RE: Using Format/export-subst Howto.

> -----Original Message-----
> From: Michael J Gruber [mailto:git@drmicha.warpmail.net] 
> Sent: Monday, September 17, 2012 8:17 AM
> To: Junio C Hamano
> Cc: Johannes Sixt; Mestnik, Michael J - Eagan, MN - 
> Contractor; git@vger.kernel.org
> Subject: Re: Using Format/export-subst Howto.
> 
> 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
>