ocamllex: Check for matched parentheses in actions

[DemiMarie]

This checks that parentheses and curly braces are properly balenced in ocamllex actions.

Fixes #7455 for ocamllex (it was already fixed for ocamlyacc).

[shindere]

Thanks for this! How about using a (reference on a) mere list to implement the stack? It feels to me it would make the code slightly simpler. What do you think? Is it worth adding a test that verifies that incorrectly formed lexers are detected?

[xavierleroy]

+1 for a stack represented as a list. You don't even need a reference: the stack can be passed as argument to the action rule, as in (untested code):

and action stk = parse
    | '{'
        { action ('{' :: stk) lexbuf }
    | '}'
        { match stk with
          | [] -> Lexing.lexeme_start lexbuf
          | '{' :: stk' -> action stk' lexbuf
          |  c  :: _ -> raise_lexical_error lexbuf
                                 ("unmatched " ^ Char.escaped c)
        }

[DemiMarie]

+1 for a stack represented as a list. You don't even need a reference: the stack can be passed as argument to the action rule, as in (untested code):

and action stk = parse
    | '{'
        { action ('{' :: stk) lexbuf }
    | '}'
        { match stk with
          | [] -> Lexing.lexeme_start lexbuf
          | '{' :: stk' -> action stk' lexbuf
          |  c  :: _ -> raise_lexical_error lexbuf
                                 ("unmatched " ^ Char.escaped c)
        }

Nice trick! I mostly write C and Rust nowadays, and had already implemented this for ocamlyacc, so I went with the imperative approach I was familiar with. I switched to the approach you suggested, which required refactoring other code to use a functional style as well.

[damiendoligez]

Looks fine. I left a couple of suggestions that you're free to follow or ignore, my approval stands either way.

[damiendoligez]

@DemiMarie could you please rebase?

[DemiMarie]

@damiendoligez done

[shindere]

OK given the fact that the suggestions were minor I'm taking the responsibility of merging this. Suggestions can always be taken into acocunt later.

[shindere]

Sorry, no. This branch now has conflicts with trunk so a rebase is required. Gentle ping to @DemiMarie to do so and perhaps you could take this opportunity to take into account @damiendoligez's suggestions?

[DemiMarie]

Sorry, no. This branch now has conflicts with trunk so a rebase is required. Gentle ping to @DemiMarie to do so and perhaps you could take this opportunity to take into account @damiendoligez's suggestions?

I can do so but not immediately due to time constraints.

[damiendoligez]

@DemiMarie We can merge this whenever you have the time to fix the trivial conflict in Changes.

[DemiMarie]

@DemiMarie We can merge this whenever you have the time to fix the trivial conflict in Changes.

Done.

[damiendoligez]

Merged at last! Many thanks for your work and your patience.