fix multiline indentation for ocaml blocks in .mli files

Signed-off-by: Paul-Elliot <peada@free.fr>

lib/block.ml

@@ -158,15 +158,20 @@ let pp_lines syntax t =
   in
   Fmt.(list ~sep:(any "\n") pp)
 
-let lstrip string =
-  let hpad = Misc.hpad_of_lines [ string ] in
-  Astring.String.with_index_range string ~first:hpad
+let lstrip strings =
+  let hpad = Misc.hpad_of_lines strings in
+  List.map
+    (fun string ->
+      let min a b = if a < b then a else b in
+      let first = min (Misc.hpad_of_lines [ string ]) hpad in
+      Astring.String.with_index_range string ~first)
+    strings
 
 let pp_contents ?syntax ppf t =
   match (syntax, t.contents) with
   | Some Syntax.Mli, [ line ] -> Fmt.pf ppf "%s" line
   | Some Syntax.Mli, lines ->
-      Fmt.pf ppf "@\n%a@\n" (pp_lines syntax t) (List.map lstrip lines)
+      Fmt.pf ppf "@\n%a@\n" (pp_lines syntax t) (lstrip lines)
   | (Some Cram | Some Normal | None), [] -> ()
   | (Some Cram | Some Normal | None), _ ->
       Fmt.pf ppf "%a\n" (pp_lines syntax t) t.contents

test/bin/mdx-test/expect/multilines-mli/test-case.mli

@@ -22,19 +22,20 @@ This works for normal OCaml fragments:
 ]}
 
 The formatting for multilines in .mli files is the following:
-- Everything is indented with two spaces after the column of the opening code
-  block.
+- The first line is indented two spaces after the comment opening
+- The other lines are indented to keep the original indentation relative to the
+  first line
 
   {[
     match None with
     | None -> ()
     | Some a -> match a with
-    | None -> ()
-    | Some b -> b
+      | None -> ()
+      | Some b -> b
   ]}
 
 But it does not work fine for toplevel (see [multilines/test-case.md] for the
-correct definition of [fact]):
+correct definition of [fact], which get erased by [mdx]):
 
 {[
   # let rec fact = function;;