Bad signature for `main` asserts

[ben0x539]

Given an invalid definition of main, like fn main(a: int) {}, rustc complains, and suggests:

foo.rs:1:0: 1:18 error: Wrong type in main function: found `fn(int)`, expected `extern fn(++v: ~[~str]) -> ()` or `extern fn() -> ()`

Naively, I went and put extern fn main() {} or even extern fn main(++args: ~[~str]) {} in my code, including the spurious extern, and now rustc chokes on it:

rustc: [...]/rust/src/llvm/lib/VMCore/Instructions.cpp:275: void llvm::CallInst::init(llvm::Value*, llvm::ArrayRef<llvm::Value*>, const llvm::Twine&): Assertion `(Args.size() == FTy->getNumParams() || (FTy->isVarArg() && Args.size() > FTy->getNumParams())) && "Calling a function with bad signature!"' failed.
Aborted

Neither of these messages should happen quite like that. :)

This is on commit b68d287 on the incoming branch.

[graydon]

Short term fix for you is just not to have args in your main function; we only support one non-empty variant (takes an owned vector of owned strings) and we're removing that in favour of a runtime call to fetch the command line args.

Of course, this is also a terrible error message. Tagging as diagnostic-related.

[brson]

The bad error message is fixed now. Assert is not.

[catamorphism]

Not critical for 0.6. De-milestoning.

[bstrie]

Since the original bug is fixed, closing this in favor of #6451.