Dune reports warnings twice

[copy]

For example:

% cat dune
(executable
 (name test)
 (flags :standard -warn-error -26))
% cat test.ml
let () = let y = 6 in ()
% dune build test.exe          
File "test.ml", line 1, characters 13-14:
Warning 26: unused variable y.
File "test.ml", line 1, characters 13-14:
Warning 26: unused variable y.

[nojb]

The reason is that test.ml does not have a .mli which causes test.ml to be compiled twice; once with ocamlc (to produce the .cmi) and once with ocamlopt (to produce the .cmx) needed for test.exe.

[nojb]

Closing as this behaviour is expected.

[copy]

That's unfortunate. Couldn't dune add -w -a to the invocation of ocamlc?

[ghost]

This is a bit tedious, for instance if you only ask for the bytecode then we do need to display the warnings for the bytecode. Doing something different depending on what set of things are needed seems complicated to support and could hurt performance of incremental builds.

[ghost]

The best is to always have a .mli file