Re: [PATCH] avoid exponential regex match for java and objc function names

[Junio C Hamano <gitster@pobox.com>]

Paolo Bonzini <bonzini@gnu.org> writes:

> In the old regex
>
> ^[ \t]*(([ \t]*[A-Za-z_][A-Za-z_0-9]*){2,}[ \t]*\([^;]*)$
>         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> you can backtrack arbitrarily from [A-Za-z_0-9]* into [A-Za-z_], thus
> causing an exponential number of backtracks.  Ironically it also causes
> the regex not to work as intended; for example "catch" can match the
> underlined part of the regex, the first repetition matching "c" and
> the second matching "atch".
>
> The replacement regex avoids this problem, because it makes sure that
> at least a space/tab is eaten on each repetition.  In other words,
> a suffix of a repetition can never be a prefix of the next repetition.

Thanks; nicely done.

Should I remove the "/* -- */" or is it for better readability I should
keep?

> Signed-off-by: Paolo Bonzini <bonzini@gnu.org>
> ---
>  userdiff.c |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/userdiff.c b/userdiff.c
> index d556da9..57529ae 100644
> --- a/userdiff.c
> +++ b/userdiff.c
> @@ -13,7 +13,8 @@ PATTERNS("html", "^[ \t]*(<[Hh][1-6][ \t].*>.*)$",
>  	 "[^<>= \t]+|[^[:space:]]|[\x80-\xff]+"),
>  PATTERNS("java",
>  	 "!^[ \t]*(catch|do|for|if|instanceof|new|return|switch|throw|while)\n"
> -	 "^[ \t]*(([ \t]*[A-Za-z_][A-Za-z_0-9]*){2,}[ \t]*\\([^;]*)$",
> +	 "^[ \t]*(([A-Za-z_][A-Za-z_0-9]*[ \t]+)+[A-Za-z_][A-Za-z_0-9]*[ \t]*\\([^;]*)$",
> +	 /* -- */
>  	 "[a-zA-Z_][a-zA-Z0-9_]*"
>  	 "|[-+0-9.e]+[fFlL]?|0[xXbB]?[0-9a-fA-F]+[lL]?"
>  	 "|[-+*/<>%&^|=!]="
> @@ -25,7 +26,7 @@ PATTERNS("objc",
>  	 /* Objective-C methods */
>  	 "^[ \t]*([-+][ \t]*\\([ \t]*[A-Za-z_][A-Za-z_0-9* \t]*\\)[ \t]*[A-Za-z_].*)$\n"
>  	 /* C functions */
> -	 "^[ \t]*(([ \t]*[A-Za-z_][A-Za-z_0-9]*){2,}[ \t]*\\([^;]*)$\n"
> +	 "^[ \t]*(([A-Za-z_][A-Za-z_0-9]*[ \t]+)+[A-Za-z_][A-Za-z_0-9]*[ \t]*\\([^;]*)$\n"
>  	 /* Objective-C class/protocol definitions */
>  	 "^(@(implementation|interface|protocol)[ \t].*)$",
>  	 /* -- */
> -- 
> 1.6.0.3