std.regex character consumption

[Jonathan M Davis]

On Friday, October 08, 2010 14:13:36 petevik38 at yahoo.com.au wrote:
> I've been running into a few problems with regular expressions in D. One
> of the issues I've had recently is matching strings with non ascii
> characters. As an example:
> 
>     auto re = regex( `(.*)\.txt`, "i" );
>     re.printProgram();
>     auto m = match( "bà.txt", re );
>     writefln( "'%s'", m.captures[1] );
> 
> When I run this I get the following error:
> 
> dchar decode(in char[], ref size_t): Invalid UTF-8 sequence [160 46 116
> 120] around index 0
> printProgram()
>   0: 	REparen len=1 n=0, pc=>10
>   9: 	REanystar
>  10: 	REistring x4, '.txt'
>  19: 	REend
> 
> While investigating the cause, I noticed that during execution of many
> of the regex instructions (e.g. REanystar), the source is advanced with:
> 
>                 src++;
> 
> However in other cases (REanychar), it is advanced with:
> 
>                 src += std.utf.stride(input, src);
> 
> I found that by replacing the code REanystar with stride, the code
> worked as expected. Although I can't claim to have a solid understanding
> of the code, it seems to me that most of the cases of src++ should be
> using stride instead.
> 
> Is this correct, or have I made some silly mistake and got completely
> the wrong end of the stick?

Well, without looking at the code, I can't say for certain what's going on, but 
using ++ with chars or wchars is definitely wrong in virtually all cases. 
stride() will actually go to the next code point, while ++ will just go to the 
next code unit, which could be in the middle of a code point.

- Jonathan M Davis