@vbgl: shouldn't liblapack and blas be listed in propagatedBuildInputs instead?

Don’t know. Do you have a test case?

I have a private nixpkgs with a package depending on lacaml, and I had to manually add -lblas in order to build it, or the build would fail with "-lblas: cannot find blas library". I then read a bit about propagatedBuildInputs, changed my local version of lacaml like this:

     sha256 = "1aflg07cc9ak9mg1cr0qr368c9s141glwlarl5nhalf6hhq7ibcb";
   };
 
-  buildInputs =
-    [ ocaml findlib dune base stdio liblapack blas ] ++
+  buildInputs = [ ocaml findlib dune base stdio ];
+  propagatedBuildInputs = [ liblapack blas ] ++
     stdenv.lib.optionals stdenv.isDarwin
       [ darwin.apple_sdk.frameworks.Accelerate ];

and it worked.
Note that my understanding of propagatedBuildInputs, esp. in the context of OCaml, is very limited.

Initially, I though the full path to the blas library would be recorded in the lacaml cmxa, but ocamlobjinfo reveals that only -cclib -lblas is recorded there, which prevent nix to automatically record the dependency, I guess.

Other packages (including zmq) seems to use propagatedBuildInputs, I guess for this reason.

Shall I open a PR for that change to lacaml?