On Fri, 2025-02-28 at 18:05 +0100, Ben Boeckel via Gcc wrote: > Note that one thing that is missing is ninja's `restat = 1` feature. > This "restats" the output for the associated rule (probably spelled > `.RESTAT: output` in Make) and skips running dependent rules if the > output has not updated the mtime of the output(s) before the rule > (recipe) was executed. This can be used for modules to not have to > recompile sources that import the output modules it if they didn't > change
I've seen this statement a few times and I've read the description of restat in the Ninja docs and also the above, and I guess I'm just too dumb to understand it. Can someone explain with an example? In POSIX make, including GNU Make, if a command doesn't modify the modification time of the target then that target is not considered updated, and other targets which list it as a prerequisite are not invoked: $ cat Makefile MKTWO = touch one: two ; touch $@ two: three ; $(MKTWO) $@ When we change "three" and then allow the MKTWO recipe to update "two" then "one" is out-of-date and rebuilt: ~$ touch three; make touch two touch one ~$ touch three; make touch two touch one When we change "three" then cause the MKTWO recipe to NOT update "two", then "one" is not out-of-date and not rebuilt: ~$ touch three; make -f /tmp/x3.mk MKTWO=echo echo two two Can someone explain how the Ninja "restat" feature differs from this?
