better layout documentation string

Author: bobzhang

jscomp/bsb/bsb_arg.ml

@@ -73,7 +73,25 @@
        buf +> "  ";
        buf +> key ; 
        buf +> (String.make (!max_col - String.length key + 2 ) ' ');
-       buf +> doc;
+       let cur = ref 0 in 
+       let doc_length = String.length doc in 
+       while !cur < doc_length do 
+         match String.index_from_opt doc !cur '\n' with 
+         | None -> 
+           if !cur <> 0 then begin 
+             buf +>  "\n";
+             buf +> String.make (!max_col + 4) ' ' ;
+           end;
+           buf +> String.sub doc !cur (String.length doc - !cur );
+           cur := doc_length
+         | Some new_line_pos -> 
+           if !cur <> 0 then begin 
+             buf +>  "\n";
+             buf +> String.make (!max_col + 4) ' ' ;
+           end;
+           buf +> String.sub doc !cur (new_line_pos - !cur );
+           cur := new_line_pos + 1
+       done ;
        buf +> "\n"
      )
  ;;

jscomp/main/bsb_main.ml

@@ -62,9 +62,13 @@ let bsb_main_flags : (string * spec * string) list=
     "-install", unit_set_spec do_install,
     "Install public interface files into lib/ocaml";
     "-init", String (String_call (fun path -> generate_theme_with_path := Some path)),
-    "Init sample project to get started. Note (`bsb -init sample` will create a sample project while `bsb -init .` will reuse current directory)";
+    "Init sample project to get started. \n\
+    Note (`bsb -init sample` will create a sample project while \n\
+    `bsb -init .` will reuse current directory)";
     "-theme", String (String_set current_theme),
-    "The theme for project initialization, default is basic(https://github.com/bucklescript/bucklescript/tree/master/jscomp/bsb/templates)";
+    "The theme for project initialization. \n\
+    default is basic:\n\
+    https://github.com/bucklescript/bucklescript/tree/master/jscomp/bsb/templates";
 
     "-regen", unit_set_spec force_regenerate,
     "(internal) Always regenerate build.ninja no matter bsconfig.json is changed or not (for debugging purpose)";
@@ -78,7 +82,10 @@ let bsb_main_flags : (string * spec * string) list=
   we make it at this time to make `bsb -help` easier
 *)
     "-ws", call_spec ignore, 
-    "[host:]port specify a websocket number (and optionally, a host). When a build finishes, we send a message to that port. For tools that listen on build completion." ;
+    "[host:]port \n\
+    specify a websocket number (and optionally, a host). \n\
+    When a build finishes, we send a message to that port. \n\
+    For tools that listen on build completion." ;
 #if BS_NATIVE then
     "-backend", String (String_call (fun s -> 
         match s with