test(melange): incorrect path when public lib depends on private lib

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

test/blackbox-tests/test-cases/melange/private-lib-dep.t

@@ -0,0 +1,83 @@
+Melange public library depends on private library
+
+  $ cat > dune-project <<EOF
+  > (lang dune 3.8)
+  > (package (name foo))
+  > (using melange 0.1)
+  > EOF
+
+  $ mkdir -p priv
+  $ cat > priv/dune <<EOF
+  > (library
+  >  (name priv)
+  >  (package foo)
+  >  (modes melange))
+  > EOF
+  $ cat > priv/priv.ml <<EOF
+  > let x = "private"
+  > EOF
+
+  $ mkdir -p lib
+  $ cat > lib/dune <<EOF
+  > (library
+  >  (public_name foo)
+  >  (modes melange)
+  >  (libraries priv))
+  > EOF
+  $ cat > lib/foo.ml <<EOF
+  > let x = "public lib uses " ^ Priv.x
+  > EOF
+
+  $ cat > dune <<EOF
+  > (melange.emit
+  >  (target output)
+  >  (libraries foo)
+  >  (emit_stdlib false))
+  > EOF
+
+  $ cat > entry.ml <<EOF
+  > let () = Js.log Foo.x
+  > EOF
+
+  $ dune build @melange
+
+  $ node _build/default/output/entry.js
+  node:internal/modules/cjs/loader:1078
+    throw err;
+    ^
+  
+  Error: Cannot find module 'priv/priv.js'
+  Require stack:
+  - $TESTCASE_ROOT/_build/default/output/node_modules/foo/foo.js
+  - $TESTCASE_ROOT/_build/default/output/entry.js
+      at Module._resolveFilename (node:internal/modules/cjs/loader:1075:15)
+      at Module._load (node:internal/modules/cjs/loader:920:27)
+      at Module.require (node:internal/modules/cjs/loader:1141:19)
+      at require (node:internal/modules/cjs/helpers:110:18)
+      at Object.<anonymous> ($TESTCASE_ROOT/_build/default/output/node_modules/foo/foo.js:4:12)
+      at Module._compile (node:internal/modules/cjs/loader:1254:14)
+      at Module._extensions..js (node:internal/modules/cjs/loader:1308:10)
+      at Module.load (node:internal/modules/cjs/loader:1117:32)
+      at Module._load (node:internal/modules/cjs/loader:958:12)
+      at Module.require (node:internal/modules/cjs/loader:1141:19) {
+    code: 'MODULE_NOT_FOUND',
+    requireStack: [
+      '$TESTCASE_ROOT/_build/default/output/node_modules/foo/foo.js',
+      '$TESTCASE_ROOT/_build/default/output/entry.js'
+    ]
+  }
+  
+  Node.js v18.15.0
+  [1]
+
+  $ cat _build/default/output/node_modules/foo/foo.js
+  // Generated by Melange
+  'use strict';
+  
+  var Priv = require("priv/priv.js");
+  
+  var x = "public lib uses " + Priv.x;
+  
+  exports.x = x;
+  /* No side effect */
+