MPR#5212: ocamlbuild does not warn for bad input

[damiendoligez]

PR transferred from https://caml.inria.fr/mantis/view.php?id=5212

I saw a parser example in the Genlex module. It took me HOURS to compile a similar example in ocamlbuild! This tool is fantastic for meany reasons, but is a bit weak for useability. Hopefully that can be improved, with better messaging :

(1) ocamlbuild -tags camlp4 example.byte does not work, but it does not tell that the camlp4 tag is not recognised or not usefull

(2) ocamlbuild -tags pp example.byte explains that pp waits for an argument, which is good, but :

(3) ocamlbuild -tags pp(camlp4o) example.byte gives the error bash: syntax error near unexpected token '(' which is not clear that it comes from ocamlbuild. a line such as ocamlbuild tag : bash : syntax error near unexpected token '(' would be better

(4) echo "example.ml:pp(camlp4o)" > _tags ; ocamlbuild example.byte gives the error Failure: lexing: empty token. where it is not clear that it comes from the _tags file, ant that it is due to ocamlbuild. One could think it comes from camlp4. A better localisation of the error would be appreciated. Example : File _tags, line 1, character 0-10 : bad syntax

(5) echo "<example.ml>:pp(camlp4o)" > _tags ; ocamlbuild example.byte eventually works. But why the -tags pp(camlp4o) option refuses it? It is not clear at all what to put on the tags option and what to put in the _tags file. At least, every line such as true : pp(camlp4o) should be equivalent to -tags pp(camlp4o) ?

Thanks,
William

---

file example.ml :

open Genlex
let _ = 
  let str = Stream.of_string "2 * (1 + 2)" in
  let lexer = Genlex.make_lexer [] in
  let rec parse_expr = parser
      [< 'Int n >] -> n
    | [< 'Kwd "("; n = parse_expr; 'Kwd ")" >] -> n
    | [< n1 = parse_expr; n2 = parse_remainder n1 >] -> n2
  and parse_remainder n1 = parser
      [< 'Kwd "+"; n2 = parse_expr >] -> n1+n2
  in
  Printf.printf "hello\n%!";
  parse_expr (lexer str)

---

See also the long discussion in the Mantis PR.

[gasche]

(1) is now solved:

$ ocamlbuild -tags camlp4 example.byte
Configuration "true: quiet, camlp4", line 1, characters 13-19:
Warning: the tag "camlp4" is not used in any flag or dependency declaration, so it will have no effect; it may be a typo. Otherwise you can use `mark_tag_used` in your myocamlbuild.ml to disable this warning.
+ /home/gasche/.opam/4.04.0/bin/ocamldep.opt -modules example.ml > example.ml.depends
File "example.ml", line 1, characters 8-10:
Error: Syntax error
Command exited with code 2.
Compilation unsuccessful after building 1 target (0 cached) in 00:00:00.

[gasche]

(4) is also now solved:

$ echo "example.ml:pp(camlp4o)" > _tags; ocamlbuild example.byte
File "_tags", line 1, characters 0-11:
Lexing error: Invalid globbing pattern "example.ml".
Compilation unsuccessful after building 0 targets (0 cached) in 00:00:00.

I'm actually proud of the usability improvements we made since this ticket was opened. The rest is a bash parsing issue that is not in our control: -tags pp(camlp4o) should be -tags "pp(camlp4)". The only thing we can do is to have the manual show example of these quotes, and it actually does (look for -tag "). Closing. Best issue of the day!