dune doesn't reset DUNE_CACHE_ROOT inside cram tests

[davesnx]

Opening this issue to see if there's an alternative I'm missing but running dune inside a cram tests makes warnings/hints appear about cache (and most probably any global setup for dune)

If DUNE_CACHE_ROOT is /path/that/does/not/exist/temp this output pops out:

   $ dune build @melange
+  Warning: Cache directories could not be created: Read-only file system;
+  disabling cache
+  Hint: Make sure the directory /path/that/does/not/exist/temp can be created

Reference issue from reasonml/reason-react#870 (comment)

Is there any cache, or set of env variables that should be set on cram tests by users or by default?

[davesnx]

I found this #6138 to be related to the dune's test itself, and @emillon didn't want to disable cache inside cram tests for dune itself.

[Alizter]

@davesnx I apologise that this question went unnoticed. Looking at the original issues it was not apparent what it was you wanted.

Do you want the cache to be disabled in that specific cram test or do you want the cache root to point somewhere controlled?

DUNE_CACHE=disabled might be something that helps here.

[vbgl]

I think the issue is more general than cache issues.

When calling dune as part of a cram test, e.g., with $ dune exec example.exe, the cram file asserts what is the output of the execution of the whole command, which involves both dune and the system under test. However, the aim of the test case is to test the system under test, not to test dune.

So, irrespective of the (mis)configuration of caches, is it possible to turn off the output of dune to avoid polluting the cram test with irrelevant things?

[Alizter]

So, irrespective of the (mis)configuration of caches, is it possible to turn off the output of dune to avoid polluting the cram test with irrelevant things?

Not entirely.

We don't use warnings very often in dune but this seems to be one of the rare (sensible?) cases. I've checked and --display quiet does not affect dune warnings or errors.

In the tests for dune itself we use the env var INSIDE_DUNE, but this disables cache and doesn't seem to be what you are asking for.

I can introduce a silent display option that would output nothing for any reason but that seems like overkill for the case of a warning that is only emitted by dune cache. My solution here would be to stop using dune cache, or point it to somewhere inside the test.

In dune, we routinely pipe stderr to /dev/null, but this won't address your dune exec.

Another thing that might be worth expanding on, how often is it that a user would like to test dune itself in a cram test? The dune repo is the only one I am aware of with such a need.

[vbgl]

Warning about weird cache configuration is indeed sensible, but it is a pity that such a warning makes tests fail.

[Alizter]

The specific test mentioned above can be rewritten like:

dune build @melange 2> /dev/null

If that actually fails the cram test will report its exit code anyway.

[vbgl]

Yes. This is the fix I had suggested: reasonml/reason-react#870 (comment)