Re: Content-based dependencies

[Mike Shal]

On 5/6/09, Yang Zhang <address@hidden> wrote:
> Is there a way to have GNU make cache copies of source files, so that when
> rules are triggered by timestamp comparisons between targets and sources, it
> will also compare the current source with the cached source to make sure
> that it actually changed before executing the actions (only executing if
> they differ)?

This sounded familiar - I found some older threads on the issue:

http://www.mail-archive.com/address@hidden/msg05559.html
http://www.mail-archive.com/address@hidden/msg04985.html

Also the solution here may work for you:
http://www.kolpackov.net/pipermail/notes/2004-September.txt

Ultimately what is your goal here? Are you trying to avoid the "change
a comment in a header rebuilds everything" issue, or do you have some
other timestamp problems? Keep in mind that doing a diff or using a
checksum to determine out-of-dateness isn't exactly cheap - you may be
trying to optimize a corner case to the detriment of the general case.

-Mike