ensure correct treatment of colourisation re invisible characters

lib/processing.ml

@@ -7,6 +7,7 @@ type culr = {
   sz : int;
   mutable current : int;
   mutable first : bool;
+  mutable text_output : bool;
 }
 
 module Culriser = struct
@@ -25,28 +26,41 @@ module Culriser = struct
           [||] c
       else c
     in
-    { colours; sz = length colours; current = 0; first = true }
+    {
+      colours;
+      sz = length colours;
+      current = 0;
+      first = true;
+      text_output = false;
+    }
 
   let current t = t.colours.(t.current)
 
   let next t =
     t.current <- (t.current + 1) mod t.sz;
-    t.colours.(t.current)
+    current t
 
   let reset t =
     t.current <- 0;
-    t.first <- true
+    t.first <- true;
+    t.text_output <- false
 
   let serialise_with_colour t serialiser chunk =
     Emitter.serialise serialiser chunk;
-    (match chunk with
+    match chunk with
     | Separator _ ->
-        if not t.first then Emitter.serialise serialiser (Ansi [ Fg (next t) ])
+        if not t.first then
+          if t.text_output then (
+            Emitter.serialise serialiser (Ansi [ Fg (next t) ]);
+            t.text_output <- false)
+          else Emitter.serialise serialiser (Ansi [ Fg (current t) ])
     | Delimiter _ ->
         reset t;
-        Emitter.serialise serialiser (Ansi [ Fg (current t) ]);
-    | Text _ -> if t.first then t.first <- false
-    | _ -> ())
+        Emitter.serialise serialiser (Ansi [ Fg (current t) ])
+    | Text _ ->
+        if t.first then t.first <- false;
+        if not t.text_output then t.text_output <- true
+    | _ -> ()
 end
 
 let ansi_filter t s =