melange: repro of paths issues with include_subdirs (#9189)

Signed-off-by: Javier Chávarri <[email protected]>
Signed-off-by: Antonio Nuno Monteiro <[email protected]>

test/blackbox-tests/test-cases/melange/library-include-subdirs.t

@@ -0,0 +1,61 @@
+Test moving modules in a library with `(include_subdirs unqualified)`
+
+  $ cat > dune-project <<EOF
+  > (lang dune 3.8)
+  > (using melange 0.1)
+  > EOF
+
+  $ cat > dune <<EOF
+  > (melange.emit
+  >  (target output)
+  >  (alias mel)
+  >  (libraries foo)
+  >  (emit_stdlib false)
+  >  (preprocess (pps melange.ppx)))
+  > EOF
+
+  $ mkdir lib
+  $ cat > lib/dune <<EOF
+  > (include_subdirs unqualified)
+  > (library
+  >  (name foo)
+  >  (modes melange))
+  > EOF
+  $ cat > lib/foo.ml <<EOF
+  > let name = Bar.name
+  > EOF
+
+  $ mkdir lib/init
+  $ cat > lib/init/bar.ml <<EOF
+  > let name = "Zoe"
+  > EOF
+
+  $ dune build @mel
+
+Melange shows the proper path to `bar.js`
+
+  $ cat _build/default/output/lib/foo.js | grep bar.js
+  let Foo__Bar = require("./init/bar.js");
+
+  $ mv lib/init lib/end
+
+  $ dune build @mel
+
+The import in `foo.js` still shows the initial path to `bar.js`, but the file is not there anymore
+
+  $ cat _build/default/output/lib/foo.js | grep bar.js
+  let Foo__Bar = require("./init/bar.js");
+
+  $ test -f _build/default/output/lib/init/bar.js
+  [1]
+
+  $ test -f _build/default/output/lib/end/bar.js
+
+After removal of the js artifact, the path in `bar.js` import is correct
+
+  $ rm _build/default/output/lib/foo.js
+
+  $ dune build @mel
+
+  $ cat _build/default/output/lib/foo.js | grep bar.js
+  let Foo__Bar = require("./end/bar.js");