fix: disallow absolute paths in dune ocaml top-module

Signed-off-by: Ali Caglayan <alizter@gmail.com>

CHANGES.md

@@ -3,6 +3,9 @@ Unreleased
 
 - Add `dune show rules` as alias of the `dune rules` command. (#8000, @Alizter)
 
+- Fix `dune ocaml top-module` to correctly reject absolute paths. (#8249, fixes
+  #7370, @Alizter)
+
 - Add `dune show installed-libraries` as an alias of the `dune
   installed-libraries` command. (#8135, @Alizter)
 

bin/ocaml/top.ml

@@ -207,7 +207,11 @@ module Module = struct
   let term =
     let+ common = Common.term
     and+ module_path =
-      Arg.(required & pos 0 (some string) None & Arg.info [] ~docv:"MODULE")
+      let doc =
+        "Relative path to an OCaml module. (File extension not necessary)."
+      in
+      Arg.(
+        required & pos 0 (some string) None & Arg.info [] ~docv:"MODULE" ~doc)
     and+ ctx_name =
       Common.context_arg ~doc:{|Select context where to build/run utop.|}
     in
@@ -223,12 +227,12 @@ module Module = struct
               |> Option.value_exn
             in
             let+ directives =
-              let module_path =
+              if Filename.is_relative module_path then
                 let root = Common.root common in
-                Path.Source.relative Path.Source.root
-                  (root.reach_from_root_prefix ^ module_path)
-              in
-              module_directives sctx module_path
+                module_directives sctx
+                  (Path.Source.relative Path.Source.root
+                     (Filename.concat root.reach_from_root_prefix module_path))
+              else User_error.raise [ Pp.text "Module path must be relative." ]
             in
             Dune_rules.Toplevel.print_toplevel_init_file directives))
 end

test/blackbox-tests/test-cases/top-module/load-from-lib.t

@@ -57,11 +57,6 @@ We try to load a module defined in a library with a dependnecy
   $ ls _build/default/mydummylib/*.cma
   _build/default/mydummylib/mydummylib.cma
 
-  $ dune ocaml top-module $PWD/foo/foo.ml 2>&1 | head -n7
-  Internal error, please report upstream including the contents of _build/log.
-  Description:
-    ("Local.relative: received absolute path",
-    { t = "."
-    ; path =
-        "$TESTCASE_ROOT/foo/foo.ml"
-    })
+  $ dune ocaml top-module $PWD/foo/foo.ml
+  Error: Module path must be relative.
+  [1]