type-check lang items

[thestinger]

These aren't currently well-defined by the language. If you define anything with a somewhat matching LLVM signature, it will compile. Not only does it not care about the type signatures matching what it expects, there is no handling for these being defined on the wrong types of AST nodes.

[thestinger]

I don't think this is milestone-worthy, because these are already implementation details.

[emberian]

This leads to craziness like:

#[no_std];

#[main]
#[lang="start"]
fn start() { }

[2:21:07]/tmp> rustc foo.rs
task 'rustc' has overflowed its stack
zsh: illegal hardware instruction (core dumped) rustc foo.rs

or, more benignly:

#[no_std];

#[lang="start"]
fn start() { }

#[main]
fn main() { }

which just plain asserts:

rustc: /build/rust-git/src/rust/src/llvm/lib/IR/Instructions.cpp:276: 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.

or, more crazily:

#[no_std];

#[lang="start"]
mod a { }

#[main]
fn main() { }

which "just" ICEs:

error: internal compiler error: node_id_to_type: no type for node `mod a (id=2)`
This message reflects a bug in the Rust compiler. 
We would appreciate a bug report: https://github.com/mozilla/rust/wiki/HOWTO-submit-a-Rust-bug-report
task 'rustc' failed at 'explicit failure', /build/rust-git/src/rust/src/libsyntax/diagnostic.rs:102
task '<main>' failed at 'explicit failure', /build/rust-git/src/rust/src/librustc/lib.rs:395

Language items are the interface between the compiler and the language. They need to be well-defined and verified for correctness, IMO.

[emberian]

(Nominating)

[pnkfelix]

This should not block 1.0. Assigning P-low.

[nagisa]

Still asserts with

#![no_std]
#![feature(no_std,core,lang_items)]

extern crate core;

#[lang="start"]
fn main() {
}

#[lang = "stack_exhausted"] extern fn stack_exhausted() {}
#[lang = "eh_personality"] extern fn eh_personality() {}
#[lang = "panic_fmt"] fn panic_fmt() -> ! { loop{} }

[steveklabnik]

Triage: no changes

[steveklabnik]

Triage; not aware of any changes here