rust/tests/ui/feature-gates/feature-gate-closure_track_caller.rs

#![feature(stmt_expr_attributes)]
#![feature(generators)]

fn main() {
    let _closure = #[track_caller] || {}; //~ `#[track_caller]` on closures
    let _generator = #[track_caller] || { yield; }; //~ `#[track_caller]` on closures
}
Support `#[track_caller]` on closures and generators This PR allows applying a `#[track_caller]` attribute to a closure/generator expression. The attribute as interpreted as applying to the compiler-generated implementation of the corresponding trait method (`FnOnce::call_once`, `FnMut::call_mut`, `Fn::call`, or `Generator::resume`). This feature does not have its own feature gate - however, it requires `#![feature(stmt_expr_attributes)]` in order to actually apply an attribute to a closure or generator. This is implemented in the same way as for functions - an extra location argument is appended to the end of the ABI. For closures, this argument is not part of the 'tupled' argument storing the parameters - the final closure argument for `#[track_caller]` closures is no longer a tuple. For direct (monomorphized) calls, the necessary support was already implemented - we just needeed to adjust some assertions around checking the ABI and argument count to take closures into account. For calls through a trait object, more work was needed. When creating a `ReifyShim`, we need to create a shim for the trait method (e.g. `FnOnce::call_mut`) - unlike normal functions, closures are never invoked directly, and always go through a trait method. Additional handling was needed for `InstanceDef::ClosureOnceShim`. In order to pass location information throgh a direct (monomorphized) call to `FnOnce::call_once` on an `FnMut` closure, we need to make `ClosureOnceShim` aware of `#[tracked_caller]`. A new field `track_caller` is added to `ClosureOnceShim` - this is used by `InstanceDef::requires_caller` location, allowing codegen to pass through the extra location argument. Since `ClosureOnceShim.track_caller` is only used by codegen, we end up generating two identical MIR shims - one for `track_caller == true`, and one for `track_caller == false`. However, these two shims are used by the entire crate (i.e. it's two shims total, not two shims per unique closure), so this shouldn't a big deal. 2021-06-27 14:01:11 -05:00			`#![feature(stmt_expr_attributes)]`
			`#![feature(generators)]`

			`fn main() {`
			let _closure = #[track_caller] \|\| {}; //~ `#[track_caller]` on closures
			let _generator = #[track_caller] \|\| { yield; }; //~ `#[track_caller]` on closures
			`}`