[ccache] Bug with clang

Anders Björklund anders at itension.se
Sat Mar 12 17:15:37 UTC 2016

Eric Chamberland wrote:

> We are happy using ccache with clang but I just discovered today that
> ccache hides documentation warnings!
> My CC* environment variables:
> CCACHE_SLOPPINESS=include_file_mtime
> CCACHE_DIR=/home/ccache/cmpbib/ccache
> How can I retrieve the documentation warnings with ccache?  Do I do
> something wrong?

Hmm, since you are using CCACHE_CPP2=1 you *should* be getting
source-level warnings too. However, if you cached the previous
result without using that setting (CCACHE_CPP2) you could still
get the cached results, i.e. the one without the extra warnings.

But it is strange because CCACHE_CPP2 should be in the hash now.
Could be a bug with direct mode perhaps, that it never runs cpp.
It only looks at the (unchanged) files, and returns the cache...
If you clear the cache (or CCACHE_NODIRECT=1), does it remain ?

I can reproduce your problem without CCACHE_CPP2 (due to the .ii)
but I cannot reproduce it with CCACHE_CPP2 (when using the .cc) ?
Your suggestion to use -C with the -E is interesting, though you
would still get your macros expanded in warnings - and such*.

* http://peter.eisentraut.org/blog/2014/12/01/ccache-and-clang-part-3/

So maybe only keeping comments is not enough, full source is needed ?

And maybe how to use ccache with clang should be better documented ?

It was only recently that the clang tests were fixed (396df7e), so it
seems like most developers are using gcc - and thus that is assumed.
I think we will see more things like this with GCC 5 (and later) too,
so some extra lines about source-level warnings are probably needed...

For now, the best workaround here is the "run_second_cpp" config.


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