[CMake] How to build only when file contents are actually changed?

[Michael Wild]

On 08/14/2012 01:18 PM, Peng Yu wrote:
>> CMake really leaves the decision when to recompile something to the
>> backend, i.e. GNU Make, Xcode, Visual Studio, ninja etc. It merely
>> defines dependencies and then lets the actual build tool handle the
>> rest, and most of them choose to use simple time-stamps instead of
> 
> Although GNU Make natively does not support build on content change,
> it can be hijacked using the trick in the link that I mentioned. I
> think that it is not impossible to do so in cmake at the language
> level. But it is better if cmake can support this natively.

Again, using ccache solves this much more elegantly. And calling md5sum
twice is also not very nice...

> 
> Yes this is a feature request not a bug report. (To J Decker)

Well, if you have the time, I'm pretty sure that the CMake developers
would happily review your patch implementing this feature.

> 
> This feature is available to scons. And I think it is reasonable to
> expect cmake also have it. I seems that people here did think about it
> seriously before, which is a surprise to me.

Yes, but scons is monolithic. It doesn't have the backend build-system
from the front end and hence doesn't have to ensure that GNU Make
behaves consistently with what Xcode, Visual Studio, ninja etc. do.

Michael