Add a Pygments lexer for MIR output, and fix HTML escaping.

[birkenfeld]

Also fixes the problem of insufficient HTML escaping of MIR output
by neither highlighting nor escaping it.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @nikomatsakis (or someone else) soon.

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[jonas-schievink]

This is going to be... interesting to rewrite in Rust for #187

[birkenfeld]

Well, as it happens I was just beginning to port parts of Pygments to Rust. I could probably have a version with the three lexers in question ready pretty soon.

[birkenfeld]

Regardless, could the escaping bug be fixed now at least? It is actively hurting readability of the MIR output.

[jonas-schievink]

Oh, please don't hold back features because of the rewrite. I'm fine with either waiting for your Pygments port or writing a temporary highlighter for #187.

[alexcrichton]

Thanks @birkenfeld! Sounds reasonable to merge for now and tackle in the rewrite in #187 later.

@jonas-schievink also I still hope to get around to taking a closer look soon, sorry it's taking awhile :(

[alexcrichton]

Ah unfortunately it looks like this breaks the MIR button as it also requires some JS changes, perhaps those could be prep'd as well?

[birkenfeld]

Sorry - looks like I'll have to set up a local instance after all. Stand by...

[NotaseCretagen]

(Side note: Thanks Alex for restarting play-pen, I've been waiting for that feature when you press Esc key after clicking Run button, to kick in for a while now :D EDIT: confirmed working on both firefox(46.0) and chromium(52.0.2716.0))

[alexcrichton]

@NotaseCretagen oh oops! Feel free to ping me if it ever needs a restart and I'm not getting around to it