[manual] add --help-format option

Summary:
Allows one to dump the manuals in various formats:
- plain: plain text
- pager: default, display the man page in all its glory inside a pager
- groff: the source code of the man page
- auto: pager or plain

Reviewed By: mbouaziz

Differential Revision: D5027636

fbshipit-source-id: 3b97edc

infer/src/base/CommandLineOption.ml

@@ -816,7 +816,7 @@ let wrap_line indent_string wrap_length line0 =
     List.fold ~f:add_word_to_paragraph ~init:([], false, "", 0) words in
   List.rev (line::rev_lines)
 
-let show_manual ?internal_section default_doc command_opt =
+let show_manual ?internal_section format default_doc command_opt =
   let command_doc = match command_opt with
     | None ->
         default_doc
@@ -865,5 +865,5 @@ let show_manual ?internal_section default_doc command_opt =
           !sections hidden in
   let blocks = [`Blocks command_doc.manual_pre_options; `Blocks option_blocks;
                 `Blocks command_doc.manual_post_options] in
-  Cmdliner.Manpage.print `Auto Format.std_formatter (command_doc.title, blocks);
+  Cmdliner.Manpage.print format Format.std_formatter (command_doc.title, blocks);
   ()

infer/src/base/CommandLineOption.mli

@@ -227,6 +227,8 @@ val parse : ?config_file:string -> usage:Arg.usage_msg -> parse_mode -> command
 (** [is_env_var_set var] is true if $[var]=1 *)
 val is_env_var_set : string -> bool
 
-(** Display the manual of [command] to the user, or [command_doc] if [command] is None. If
-    [internal_section] is true, add a section about internal (hidden) options. *)
-val show_manual : ?internal_section:string -> command_doc -> command option -> unit
+(** Display the manual of [command] to the user, or [command_doc] if [command] is None. [format] is
+    used as for [Cmdliner.Manpage.print]. If [internal_section] is specified, add a section titled
+    [internal_section] about internal (hidden) options. *)
+val show_manual : ?internal_section:string -> Cmdliner.Manpage.format -> command_doc
+  -> command option -> unit

infer/src/base/Config.ml

@@ -978,6 +978,14 @@ and help =
     (Printf.sprintf "Show this manual with all internal options in the %s section" manual_internal);
   var
 
+and help_format =
+  CLOpt.mk_symbol ~long:"help-format"
+    ~symbols:[("auto", `Auto); ("groff", `Groff); ("pager", `Pager); ("plain", `Plain)]
+    ~eq:PVariant.(=) ~default:`Auto
+    ~in_help:(List.map CLOpt.all_commands ~f:(fun command -> command, manual_generic))
+    "Show this help in the specified format. $(b,auto) sets the format to $(b,plain) if the \
+     environment variable $(b,TERM) is \"dumb\" or undefined, and to $(b,pager) otherwise."
+
 and icfg_dotty_outfile =
   CLOpt.mk_path_opt ~long:"icfg-dotty-outfile" ~meta:"path"
     "If set, specifies path where .dot file should be written, it overrides the path for all \
@@ -1548,9 +1556,9 @@ let post_parsing_initialization command_opt =
   );
   (match !help with
    | `Help ->
-       CLOpt.show_manual CommandDoc.infer command_opt
+       CLOpt.show_manual !help_format CommandDoc.infer command_opt
    | `HelpFull ->
-       CLOpt.show_manual ~internal_section:manual_internal CommandDoc.infer command_opt
+       CLOpt.show_manual ~internal_section:manual_internal !help_format CommandDoc.infer command_opt
    | `None ->
        ()
   );