[cmake-developers] slow regex implementation in RegularExpression

[Alexander Neundorf]

On Thursday 17 November 2011, Alexandru Ciobanu wrote:
> On 2011-11-17, at 3:26 PM, Alexander Neundorf wrote:
> >> [ Regular expressions syntax ]
> >> In terms of regular expressions syntax, the only difference that I've
> >> seen is that TRE treats the curly brackets "{" and "}" as special
> >> characters, because it uses them for its "approximate matching". 
> >> Details here: http://laurikari.net/tre/documentation/regex-syntax/
> >> 
> >> The only CMake component that uses curly brackets in a regexp is:
> >>    Modules/FindJNI.cmake
> >> 
> >> but it was trivial to fix because they were used as mere delimiters.
> > 
> > Well, but there are cmake files out there (i.e. all existing cmake-based
> > projects) which also must behave basically exactly the same as before,
> > otherwise their builds might break.
> > 
> > Not sure how to achieve this.
> > A policy ?
> 
> Actually it is very easy to make it transparent and thus not need to modify
> any .cmake files.
> 
> We just need to escape the curly brackets:
>    {   ->   \{
>    }   ->   \}
> in the regular expression before compiling it.
> 
> This way we'll have full compatibility with previous regexp syntax.

Hmm, I think there are more differences:
http://laurikari.net/tre/documentation/regex-syntax/

Currently AFAIK cmake doesn't support all that, e.g. [[:digit:]] or \\d.
So, currently a regex could contain "[[:digit:]]", which matches something 
right now, and something else then.
There are more.

It is nice that this implementation supports more, but it potentially 
introduces changes in behaviour i.e. incompatibilities.

Alex