Expressions like 3#0;; are ignored by the toplevel and the compiler

[vicuna]

Original bug ID: 6604
Reporter: rdicosmo
Assigned to: @gasche
Status: resolved (set by @gasche on 2017-10-04T09:07:17Z)
Resolution: fixed
Priority: normal
Severity: minor
Target version: 4.06.0 +dev/beta1/beta2/rc1
Fixed in version: 4.07.0+dev/beta2/rc1/rc2
Category: lexing and parsing
Tags: junior_job

Bug description

The very simple syntactically incorrect expression 3#0;; is simply ignored both by the toplevel and the compiler. On the other hand, 3#foo;; is handled properly

Steps to reproduce

Just type 3#0;; in any toplevel (tested 3.12 , 4.00, 4.01 and 4.02)

$ ocaml
OCaml version 4.01.0

3#0;;

^CInterrupted.

3#foo;;

Error: This expression has type int
It has no method foo

Or try to compile a file containing the single line

3#0;;

Additional information

The interpreter executed via js_of_ocaml (see try.ocamlpro.org, for example) does not exhibit this behaviour.

Welcome to TryOCaml (v. 4.01.0)

3#0;;

File "", line 1, characters 2-3:
Error: Syntax error
File "", line 1, characters 3-5:
Error: Syntax error

[vicuna]

Comment author: @yallop

The '#0' is a way of setting the line number for error messages; it's used in tools like ocamlyacc.

$ cat lines1.ml
let x = 2 + 3#0
in x + "four"
$ ocamlc lines1.ml
File "lines1.ml", line 0, characters 8-14:
Error: This expression has type string but an expression was expected of type
int
$ cat lines2.ml
let x = 2 + 3
in x + "four"
$ ocamlc lines2.ml
File "lines2.ml", line 2, characters 8-14:
Error: This expression has type string but an expression was expected of type
int

[vicuna]

Comment author: @damiendoligez

If possible, we should find a way to disable it in the toplevel.

Also, make it more robust by making the filename string mandatory.

Even better, only accept it at the beginning of a line (simply make the \n part of the token).

[vicuna]

Comment author: @xavierleroy

The '# lineno filename' directive is handled directly within the lexer, so it is not particularly natural to turn it off in the toplevel.

I agree with making the filename string mandatory. The filename is always there in '# lineno filename' directives generated by ocamllex, ocamlyacc, gcc -E and clang -E.

Recognizing '#' only at beginning of line would make things more robust too. However, it's not good enough to just recognize "\n#", because it doesn't work for the first line. gcc -E and clang -E will gladly generate '# lineno filename' as the first line of output.

[vicuna]

Comment author: @xavierleroy

See ongoing work in #931

[vicuna]

Comment author: @gasche

Fixed in trunk (will not be in 4.06) by the aforementioned PR from Tadeu Zagallo.