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I recently noticed that some of my blog posts, most notably my Templates in YARPP 3 article, was producing a PHP error:

Warning: preg_match() [function.preg-match]: Compilation failed: unrecognized character after (?< at offset 3 in /…/html/blog/wp-content/plugins/wp-syntax/geshi/geshi.php on line 2132

This seemed to be coming from the version 1.0.8.4 version of Geshi I had installed. A quick google search for “geshi line 2132” gives you over a thousand errors, so this seems to be common issue. Geshi is a fabulous and popular syntax highlighter and is the core component of the WP-Syntax plugin for WordPress.

I did some digging around and realized that the issue was with the compilation of this monstrosity of a regular expression, used (as far as I can tell) to identify PHP code snippets, for example the <?php … ?> keywords:

/(?<start><\\?(?>php\b)?)(?:
(?>[^\"'?\\/<]+)|
\\?(?!>)|
(?>'(?>[^'\\\\]|\\\\'|\\\\\\\|\\\\)*')|
(?>\"(?>[^\"\\\\]|\\\\\"|\\\\\\\\|\\\\)*\")|
(?>\\/\\*(?>[^\\*]|(?!\\*\\/)\\*)*\\*\\/)|
\\/\\/(?>.*?$)|
\\/(?=[^*\\/])|
<(?!<<)|
<<<(?<phpdoc>\w+)\s.*?\s\k<phpdoc>
)*(?<end>\\?>|\Z)/sm

Not knowing exactly where to start in diagnosing this crazy expression, I simply disabled those “script delimiters” in the geshi/php.php file. The sections I commented out are lines 1080-1101. Now the script delimiters like <?php don’t get highlighted nicely, but I feel that’s a small price to pay for eliminating these errors. Another solution for the WP-Syntax users seems to be to downgrade to 0.9.4. Hopefully in the near future an update to Geshi will come out which fixes this issue once and for all.

I still have yet to find a fix to the dvipng discoloration mystery I ran into back at The Academic Approach, even with the latest MacTeX version, so I’m going to repost the problem here.

In May 2007, I wrote the following to the OS X TeX listhost:¹

Hi all,

I’ve recently run into what I believe is a rare bug in dvipng: here’s the setup. (To play along, you can get my test files: http://mitcho.com/discolor.zip .) I am using MacTeX… in fact, it’s today’s release.

The LaTeX source file (discolored.tex) loads just two packages: color and graphicx. The body does two things: an \includegraphics with a local PNG file (with the bb option to specify the BoundingBox explicitly) and a \textcolor command introducing some green text, using the green defined there.

pdflatex produces the expected result: the figure and the green text.

But when you run the following commands…

latex discolored.tex

dvipng -D 200 discolored.dvi

you get a PNG (discolored1.png) which shows the text in a brownish color… the green is gone!!

There are two quick ways to fix this that I’ve found: one is to not include the image… if you comment the \includegraphics command out, the color comes out fine. The second is to not specify a -D (output resolution) parameter in the dvipng… this also gives you the expected output. However, in my current project, neither of these are available options…

I am frankly not very familiar with the inner workings of dvipng… does anyone have any thoughts? Can this bug be reproduced?

Any hints or suggestions are welcome!

Ditto.