Print error lines and highlight error span

[jdm]

This isn't necessarily a request to pull, but more a request for feedback. This branch gives output like:

../src/test/compile-fail/forgot-ret.rs:8:19:12:1: note: In function f, not all control paths return a value ../src/test/compile-fail/forgot-ret.rs:8 fn f(int a) -> int { ../src/test/compile-fail/forgot-ret.rs:9 if (god_exists(a)) { ../src/test/compile-fail/forgot-ret.rs:10 ret 5; ...

../src/test/compile-fail/for-loop-decl.rs:13:40:13:44: error: mismatched types: expected @tup(uint,tup(uint,uint)) but found @tup(uint,var_info) (types differ) ../src/test/compile-fail/for-loop-decl.rs:13 for each (@tup(uint, tup(uint, uint)) p in enclosing.vars.items()) { ^~~~

The ^~~~ extends for the full width of the error span, so it's easier to see when spans are larger than they should be as well.

The downside here is that I took the easy route for obtaining the file contents and just read in the entire file on demand whenever we print an error. I fully acknowledge that that's an awful thing to do, but I was having trouble figuring out a better way to acquire the file contents from the lexer from all the different possible places we could be throwing errors.

[jdm]

Well, that turned out ugly. http://pastebin.mozilla.org/1269518 shows the output in full indented glory.

[marijnh]

The lexer already reads in the files in their entirety. You could extend the codemap to save these somewhere.

[brson]

This is cool. What happens when the span spans multiple lines?

I don't know how big of a concern it is to reread the file. This isn't critical path stuff since it only happens on failure, and the os is going to have the file cached (why should we cache it if the os does it for us?).

[brson]

OK. This is really cool. Integrated.