Fix url opened by "dune ocaml doc"

Prior to this change, "dune ocaml doc" would attempt to open an
incorrect url in browsers: "file://_build/default/_doc/_html/index.html".
This is incorrect because it appears to be a path relative to the
project root, but browsers interpret "file://foo/some/path" as the
path "/some/path" on the host referred to by "foo". In my experiments
however, the "foo" component is ignored and the browser redirects to
"file:///some/path" instead. Indeed, when I run "dune ocaml doc" I end
up at "file:///default/_doc/_html/index.html", with the "_build"
component of the path being ignored, and the remainder of the path
treated as an absolute path (which obviously doesn't refer to the
correct file).

It seems like droppping the "file://" prefix of the url is enough to
get browers to accept the relative path and correctly navigate to
"file:///absolute/path/to/index.html". Alternatively we could fix the
logic for computing an absolute path to index.html and keep the
"file://" prefix of the url, but that seems more complicated. I've
updated a variable name from "absolute_toplevel_index_pathh" to
"relative_toplevel_index_path" to reflect that it is in fact a path
relative to the project root and not an absolute path.

Signed-off-by: Stephen Sherratt <stephen@sherra.tt>

bin/ocaml/doc.ml

@@ -23,7 +23,7 @@ let term =
       Alias.in_dir ~name:Dune_rules.Alias.doc ~recursive:true ~contexts:setup.contexts dir
       |> Alias.request
     in
-    let absolute_toplevel_index_path =
+    let relative_toplevel_index_path =
       let toplevel_index_path =
         let is_default ctx = ctx |> Context.name |> Dune_engine.Context_name.is_default in
         let doc_ctx = List.find_exn setup.contexts ~f:is_default in
@@ -32,7 +32,7 @@ let term =
       Path.(toplevel_index_path |> build |> to_string_maybe_quoted)
     in
     Console.print
-      [ Pp.textf "Docs built. Index can be found here: %s" absolute_toplevel_index_path ];
+      [ Pp.textf "Docs built. Index can be found here: %s" relative_toplevel_index_path ];
     match
       let open Option.O in
       let* cmd_name, args =
@@ -47,8 +47,7 @@ let term =
       in
       ( open_command
       , (* First element of argv is the name of the command. *)
-        let url = "file://" ^ absolute_toplevel_index_path in
-        (cmd_name :: args) @ [ url ] )
+        (cmd_name :: args) @ [ relative_toplevel_index_path ] )
     with
     | Some (cmd, args) ->
       Proc.restore_cwd_and_execve (Path.to_absolute_filename cmd) args ~env:Env.initial

doc/changes/10897.md

@@ -0,0 +1 @@
+- Fix the URL opened by the command `dune ocaml doc`. (#10897, @gridbugs)

test/blackbox-tests/test-cases/odoc/doc-browser.t/run.t

@@ -1,8 +1,8 @@
 This tests shows how to use the `dune ocaml doc` command to open the
 documentation index to a browser.
   $ if [ "$(uname)" = Darwin ]; then mv xdg-open open; fi
-  $ export PATH=.:$PATH 
-  $ dune ocaml doc | sed -e 's|^-u *||'
+  $ export PATH=.:$PATH
+  $ dune ocaml doc
   Docs built. Index can be found here: _build/default/_doc/_html/index.html
   open command received args:
-  file://_build/default/_doc/_html/index.html
+  _build/default/_doc/_html/index.html