Replaced constant fixed-length u8 vectors with byte strings (fixes #3257)

[thomas-daniels]

Replaced constant fixed-length u8 vectors in CodegenRust.py with byte strings (fixes #3257).

@jdm said that there is also an occurrence of a fixed-length vector in eventtarget.rs. I found this one, but when I tried to replace it, it gave errors (because it is not a u8 vector but a c_char vector). When I replaced it with b"...", it said:

dom/eventtarget.rs:182:46: 182:56 error: mismatched types: expected `&'static [i8]` but found `&'static [u8]` (expected i8 but found u8)

And when I did the same but with dropping the b (so, by changing it to "..."), it said:

dom/eventtarget.rs:182:46: 182:55 error: mismatched types: expected `&'static [i8]` but found `&'static str` (expected vector but found str)

I don't know whether there are other prefixes for the strings to make this work, but if there are, let me know and I'll use it there.

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[highfive]

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

[thomas-daniels]

Just saw that the Travis CI build failed. Pushed a new commit to fix this.

[Manishearth]

Nice to see you taking interest in Servo! :D

[thomas-daniels]

I put the parenthesis to fix the Travis CI build error at the wrong place; pushed a new commit to fix this.

[jdm]

With regards to the eventtarget error, you can just change the casts at http://mxr.mozilla.org/servo/source/components/script/dom/eventtarget.rs#182 and http://mxr.mozilla.org/servo/source/components/script/dom/eventtarget.rs#190 to be what you need.

[thomas-daniels]

With the help of Ms2ger and huon on IRC, I found a way to make the byte strings in eventtarget.rs work. I also fixed the latest Travis build error. Because the codegen apparently doesn't run automatically (and I have no idea how to run in manually), I could not check whether I still have got more errors, so I'll have to wait for the Travis CI build to see that.

[jdm]

Ah yes, this won't work since we can't call functions in constants. Maybe &%s_name[0] instead?

[huonw]

(It may hit rust-lang/rust#17233, depending on how s_name is created.)

[jdm]

Same deal here.

[jdm]

And here.

[jdm]

Aaaaand here.

[thomas-daniels]

@jdm I tried &%s_name[0], but that didn't work unfortunately. I got this error:

rustc: /home/larsberg/rust/src/llvm/include/llvm/Support/Casting.h:237: typename llvm::cast_retty<X, Y*>::ret_type llvm::cast(Y*) [with X = llvm::GlobalVariable; Y = llvm::Value; typename llvm::cast_retty<X, Y*>::ret_type = llvm::GlobalVariable*]: Assertion `isa<X>(Val) && "cast<Ty>() argument of incompatible type!"' failed.

I also tried to use functions instead of static variables, and creating a local non-static variable inside that function to perform the casting, but that didn't work; it said that function calls are only allowed in constructors, and I had to use it inside a static class.

[jdm]

Yeah, I think the LLVM problem is rust-lang/rust#17233, so we might be stuck until that gets fixed.

[thomas-daniels]

Alright, then I'll wait until that's fixed.

[Manishearth]

Does this work now?

[thomas-daniels]

@Manishearth The linked issue is still open, so I'd say it doesn't. (I would test it, but I don't know what exactly to test for -- I did many different things to try to make it work)