Escape block-end sequence if contained in the error-block

lib/block.ml

@@ -171,7 +171,7 @@ let pp_error ?syntax ?delim ppf outputs =
       Fmt.pf ppf "]%a[\n{err@mdx-error[\n%a\n]err}"
         Fmt.(option string)
         delim
-        Fmt.(list ~sep:(any "\n") Output.pp)
+        Fmt.(list ~sep:(any "\n") Output.(pp ~escape_strings:[ "]err}" ]))
         outputs
   | _ -> ()
 

lib/output.ml

@@ -20,8 +20,10 @@ let dump ppf = function
   | `Output s -> Fmt.pf ppf "`Output %S" s
   | `Ellipsis -> Fmt.pf ppf "`Ellipsis"
 
-let pp ?(pad = 0) ppf = function
-  | `Output s -> Fmt.pf ppf "%a%s" Pp.pp_pad pad s
+let pp ?(pad = 0) ?(escape_strings = []) ppf = function
+  | `Output s ->
+      let s = Util.String.escape ~escape_strings s in
+      Fmt.pf ppf "%a%s" Pp.pp_pad pad s
   | `Ellipsis -> Fmt.pf ppf "%a..." Pp.pp_pad pad
 
 let equals_sub l r start length =

lib/output.mli

@@ -28,7 +28,7 @@ val merge : [ `Output of string ] list -> t list -> t list
 (** [merge output test] merges any [`Ellipsis] items from [test] into
    [output]. *)
 
-val pp : ?pad:int -> t Fmt.t
+val pp : ?pad:int -> ?escape_strings:string list -> t Fmt.t
 (** [pp] is the pretty-printer for test outputs. [pad] is the size of
    the optional whitespace left-padding (by default it is 0). *)
 

lib/util.ml

@@ -105,6 +105,14 @@ module String = struct
 
   let english_conjonction words = english_concat ~last_sep:"and" words
   let all_blank = Astring.String.for_all Astring.Char.Ascii.is_white
+
+  let replace ~before ~after s =
+    s |> Astring.String.cuts ~sep:before |> Astring.String.concat ~sep:after
+
+  let escape ~escape_strings s =
+    List.fold_left
+      (fun acc seq -> replace ~before:seq ~after:("\\" ^ seq) acc)
+      s escape_strings
 end
 
 module List = struct

lib/util.mli

@@ -66,6 +66,9 @@ module String : sig
 
   val all_blank : string -> bool
   (** [all_blank s] is true if every character of s is a whitespace *)
+
+  val escape : escape_strings:string list -> string -> string
+  (** [escape ~escape_strings s] escape all occurrences in [s] of each string listed in [escape_strings]. *)
 end
 
 module Sexp : sig