[3.17]backport #11248 fix(melange): use output of virtual library when compiling its source…

doc/changes/11248.md

@@ -0,0 +1,3 @@
+- Fix a crash in the Melange rules that would prevent compiling public library
+  implementations of virtual libraries. (@amonteiro, #11248)
+

src/dune_rules/melange/melange_rules.ml

@@ -598,6 +598,7 @@ let setup_js_rules_libraries =
             in
             cmj_includes ~requires_link ~scope lib_config
           in
+          let output = output_of_lib ~target_dir vlib in
           parallel_build_source_modules
             ~sctx
             ~scope

test/blackbox-tests/test-cases/melange/virtual-lib-public-impl.t

@@ -0,0 +1,50 @@
+Test virtual libraries where the virtual implementation is a public library
+
+  $ mkdir -p vlib js_impl test
+  $ cat > dune-project <<EOF
+  > (lang dune 3.13)
+  > (using melange 0.1)
+  > (package (name the_lib))
+  > (package (name concrete_lib))
+  > EOF
+  $ cat > vlib/dune <<EOF
+  > (library
+  >  (name the_lib)
+  >  (modes melange native)
+  >  (public_name the_lib)
+  >  (virtual_modules virt))
+  > EOF
+  $ cat > vlib/the_lib.mli <<EOF
+  > module Time : sig
+  >   val gettimeofday : unit -> float
+  > end
+  > EOF
+  $ cat > vlib/the_lib.ml <<EOF
+  > module Time = struct
+  >   let gettimeofday () = Virt.gettimeofday ()
+  > end
+  > EOF
+  $ cat > vlib/virt.mli <<EOF
+  > val gettimeofday : unit -> float
+  > EOF
+
+  $ cat > js_impl/dune <<EOF
+  > (library
+  >  (name timeJs)
+  >  (public_name concrete_lib)
+  >  (implements the_lib)
+  >  (modes melange)
+  >  (preprocess (pps melange.ppx)))
+  > EOF
+  $ cat > js_impl/virt.ml <<EOF
+  > let gettimeofday : unit -> float = fun () -> 42.
+  > EOF
+
+  $ cat > test/dune <<EOF
+  > (melange.emit
+  >  (target output)
+  >  (libraries the_lib concrete_lib)
+  >  (emit_stdlib false))
+  > EOF
+
+  $ dune build @melange