test(single-context): install conditional sources

test/blackbox-tests/test-cases/melange/conditional-sources-dune-package.t

@@ -0,0 +1,53 @@
+  $ mkdir a app
+  $ cat > a/dune-project <<EOF
+  > (lang dune 3.8)
+  > (package (name a))
+  > (using melange 0.1)
+  > EOF
+  $ cat > a/dune <<EOF
+  > (library
+  >  (modes melange :standard)
+  >  (name a)
+  >  (public_name a.sub))
+  > EOF
+
+  $ cat > a/foo.ml <<EOF
+  > let x = "foo"
+  > EOF
+  $ cat > a/melange_only.melange.ml <<EOF
+  > let x = "melange"
+  > EOF
+
+  $ dune build --root a
+  $ dune install --root a --prefix $PWD/prefix > /dev/null
+
+  $ grep -E "melange_modules|a__Melange_only|sub/melange_only.ml" prefix/lib/a/dune-package
+     sub/melange/a__Melange_only.cmi
+     sub/melange/a__Melange_only.cmj
+     sub/melange/a__Melange_only.cmt
+   (melange_modules
+        (obj_name a__Melange_only)
+        (source (path Melange_only) (impl (path sub/melange_only.ml))))))
+
+  $ cat > app/dune-project <<EOF
+  > (lang dune 3.8)
+  > (using melange 0.1)
+  > EOF
+  $ cat > app/dune <<EOF
+  > (melange.emit
+  >  (target dist)
+  >  (alias dist)
+  >  (emit_stdlib false)
+  >  (libraries a.sub))
+  > EOF
+  $ cat > app/bar.ml <<EOF
+  > let () = Js.log A.Melange_only.x
+  > EOF
+
+  $ OCAMLPATH=$PWD/prefix/lib/:$OCAMLPATH dune build --root app @dist
+  $ find app/_build/default/dist/node_modules/a.sub -type f | sort
+  app/_build/default/dist/node_modules/a.sub/a.js
+  app/_build/default/dist/node_modules/a.sub/foo.js
+  app/_build/default/dist/node_modules/a.sub/melange_only.js
+  $ node app/_build/default/dist/bar.js
+  melange