Original bug ID: 149
Reporter: administrator
Status: closed (set by @xavierleroy on 2006-06-17T09:20:15Z)
Resolution: fixed
Priority: normal
Severity: feature
Category: ~DO NOT USE (was: OCaml general)

Bug description

I might have found an bug in ocamlopt that I like to report. The
system where the bug can be observed is a i386 Linux 2.2.16 using
OCaml 3.0. The bug appears in an OCaml lex scanner in the following
situation:

let get = Lexing.lexeme

let digit = ['0'-'9']
let nat = digit+

and line = parse
eof { fun map l ->
error lexbuf map "unterminated line directive"
}
| ws+ { fun map l -> line lexbuf map l }
...
| nat { fun map l ->

                      (* inline the l' expression caused an
                      int_of_string failure with ocamlopt 
                      XXX *)
                      
                      let l' = int_of_string (get lexbuf)
                      in  line lexbuf map (int_of_string (get lexbuf))
                    }                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

...

The marked int_of_string function raises a Failure exception. This
does not happen when instead the let-bond value l' is used or the code
is translated to bytecode. I suspect that order of evaluation might
be a problem. Obviuosly int_of_string should only receive numbers
that it can convert because the scanner just matches these.

The scanner function line is used to scan cpp-like line directives:

    # 23 "file"

I have not broken down the problem to a very small program as you
might wish. But to lessen your pain I have created a tar file with
just the sources of the system and a very simple shell script to build
the system to observe the error. So although the system is quite large
it should be easy to build.

You can find it at:

    http://www.eecs.harvard.edu/~lindig/download/ocaml-bug.tar.gz

The tar archive contains a sh-script 'build' that builds the system (a
compiler) and runs it on a test file that should reproduce the bug.
The lexer code mentioned above is in line 345 in the file
src/scan.mll. The binary to run is:

    src/qc--.opt -lex bug.c--

The qc--.opt binary reports the tokens it scans to stdout. When it
reaches the first line directive in bug.c-- in the third line the
error should show:

./src/qc--.opt -lex bug.c--
bug.c-- 1 1 IMPORT
bug.c-- 1 8 BITSn(32)
bug.c-- 1 15 ID(printf)
bug.c-- 1 21 COMMA
bug.c-- 1 23 ID(sqrt)
bug.c-- 1 27 SEMI
bug.c-- 2 1 EXPORT
bug.c-- 2 8 ID(foo)
bug.c-- 2 11 COMMA
bug.c-- 2 13 ID(bar)
bug.c-- 2 16 SEMI
Uncaught exception: Failure("int_of_string")

It would be helpful when the Failure exception includes the offending
argument in case of xxx_of_string functions.

-- Christian

--
Christian Lindig Harvard University - EECS
lindig@eecs.harvard.edu 33 Oxford St, MD 242, Cambridge MA 02138
phone: (617) 496-7157 http://www.eecs.harvard.edu/~lindig/