Subject: Re: [PATCH] userdiff: add built-in pattern for CSS

From: Junio C Hamano <[email-masked]>
Date: Fri, 20 May 2016 15:37:26 -0700

William Duclot <[email-masked]> writes:

> CSS is widely used, motivating it being included as a built-in pattern.
>
> It must be noted that the word_regex for CSS (i.e. the regex defining
> what is a word in the language) does not consider '.' and '#' characters
> (in CSS selectors) to be part of the word. This behavior is documented
> by the test t/t4018/css-rule.
> The logic behind this behavior is the following: identifiers in CSS
> selectors are identifiers in a HTML/XML document. Therefore, the '.'/'#'
> character are not part of the identifier, but an indicator of the nature
> of the identifier in HTML/XML (class or id). Diffing ".class1" and
> ".class2" must show that the class name is changed, but we still are
> selecting a class.

In other words, if "div#foo" changed to "span#bar", word-diff would
say that "div changed to span, # didn't change and foo changed to
bar".

Which makes sense to me.

The above is not a request to change anything; just me thinking
aloud to see if I agree with the reasoning.

> diff --git a/userdiff.c b/userdiff.c
> index 6bf2505..0f9cfbe 100644
> --- a/userdiff.c
> +++ b/userdiff.c
> @@ -148,6 +148,14 @@ PATTERNS("csharp",
>  	 "[a-zA-Z_][a-zA-Z0-9_]*"
>  	 "|[-+0-9.e]+[fFlL]?|0[xXbB]?[0-9a-fA-F]+[lL]?"
>  	 "|[-+*/<>%&^|=!]=|--|\\+\\+|<<=?|>>=?|&&|\\|\\||::|->"),
> +PATTERNS("css",
> +	 "^([^,{}]+)((,[^}]*\\{)|([ \t]*\\{))$",
> +	 /* -- */
> +	 /* This regex comes from W3C CSS specs. Should theoretically also allow ISO 10646 characters U+00A0 and higher,
> +	  * this not handled in this regex. */
> +	 "-?[_a-zA-F][-_a-zA-F0-9]*" /* identifiers */
> +	 "|-?[0-9]+|\\#[0-9a-fA-F]+" /* numbers */
> +),

Style:

	/*
         * This regex comes from ...
         * ...
         * but they are not handled with this regex.
         */

I wonder if IPATTERN() may make it easier to express the above.

Also, a-zA-F (twice seen in "identifiers" section) looks somewhat
suspicious.  a-fA-F or a-zA-Z I would understand, and I suspect this
is a misspelled form of the latter.