Fix multilines for OCaml block in .mli file

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/dune.inc

@@ -275,6 +275,18 @@
  (alias runtest)
  (action (diff multilines/test-case.md multilines.actual)))
 
+(rule
+ (target multilines-mli.actual)
+ (deps (package mdx) (source_tree multilines-mli))
+ (action
+  (with-stdout-to %{target}
+   (chdir multilines-mli
+    (run ocaml-mdx test --output - test-case.mli)))))
+
+(rule
+ (alias runtest)
+ (action (diff multilines-mli/test-case.mli multilines-mli.actual)))
+
 (rule
  (target non-det.actual)
  (deps (package mdx) (source_tree non-det))

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

@@ -0,0 +1,45 @@
+(**
+
+In OCaml docstring everything is indented with two spaces
+
+Test multi-lines shell commands:
+
+{@sh[
+  $ for i in `seq 1 10`; do \
+  >   echo $i; \
+  > done
+  1
+  ...
+  10
+]}
+
+This works for normal OCaml fragments:
+
+{[
+  let rec fact = function
+  | 1 -> 1
+  | n -> n * fact (n-1)
+]}
+
+The formatting for multilines in .mli files is the following:
+- 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
+  ]}
+
+But it does not work fine for toplevel (see [multilines/test-case.md] for the
+correct definition of [fact], which get erased by [mdx]):
+
+{[
+  # let rec fact = function;;
+  Line 1, characters 24-26:
+  Error: Syntax error
+]}
+*)