Auto merge of #76269 - ayrtonm:function-reference-lint, r=oli-obk
added a lint against function references this lint suggests casting function references to `*const ()` closes #75239 r? `@RalfJung`
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155
src/test/ui/lint/function-item-references.rs
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155
src/test/ui/lint/function-item-references.rs
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// check-pass
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#![feature(c_variadic)]
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#![warn(function_item_references)]
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use std::fmt::Pointer;
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use std::fmt::Formatter;
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fn nop() { }
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fn foo() -> u32 { 42 }
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fn bar(x: u32) -> u32 { x }
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fn baz(x: u32, y: u32) -> u32 { x + y }
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unsafe fn unsafe_fn() { }
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extern "C" fn c_fn() { }
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unsafe extern "C" fn unsafe_c_fn() { }
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unsafe extern fn variadic(_x: u32, _args: ...) { }
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//function references passed to these functions should never lint
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fn call_fn(f: &dyn Fn(u32) -> u32, x: u32) { f(x); }
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fn parameterized_call_fn<F: Fn(u32) -> u32>(f: &F, x: u32) { f(x); }
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//function references passed to these functions should lint
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fn print_ptr<F: Pointer>(f: F) { println!("{:p}", f); }
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fn bound_by_ptr_trait<F: Pointer>(_f: F) { }
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fn bound_by_ptr_trait_tuple<F: Pointer, G: Pointer>(_t: (F, G)) { }
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fn implicit_ptr_trait<F>(f: &F) { println!("{:p}", f); }
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//case found in tinyvec that triggered a compiler error in an earlier version of the lint checker
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trait HasItem {
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type Item;
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fn assoc_item(&self) -> Self::Item;
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}
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fn _format_assoc_item<T: HasItem>(data: T, f: &mut Formatter) -> std::fmt::Result
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where T::Item: Pointer {
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//when the arg type bound by `Pointer` is an associated type, we shouldn't attempt to normalize
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Pointer::fmt(&data.assoc_item(), f)
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}
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//simple test to make sure that calls to `Pointer::fmt` aren't double counted
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fn _call_pointer_fmt(f: &mut Formatter) -> std::fmt::Result {
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let zst_ref = &foo;
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Pointer::fmt(&zst_ref, f)
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//~^ WARNING taking a reference to a function item does not give a function pointer
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}
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fn main() {
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//`let` bindings with function references shouldn't lint
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let _ = &foo;
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let _ = &mut foo;
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let zst_ref = &foo;
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let fn_item = foo;
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let indirect_ref = &fn_item;
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let _mut_zst_ref = &mut foo;
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let mut mut_fn_item = foo;
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let _mut_indirect_ref = &mut mut_fn_item;
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let cast_zst_ptr = &foo as *const _;
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let coerced_zst_ptr: *const _ = &foo;
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let _mut_cast_zst_ptr = &mut foo as *mut _;
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let _mut_coerced_zst_ptr: *mut _ = &mut foo;
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let _cast_zst_ref = &foo as &dyn Fn() -> u32;
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let _coerced_zst_ref: &dyn Fn() -> u32 = &foo;
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let _mut_cast_zst_ref = &mut foo as &mut dyn Fn() -> u32;
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let _mut_coerced_zst_ref: &mut dyn Fn() -> u32 = &mut foo;
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//the suggested way to cast to a function pointer
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let fn_ptr = foo as fn() -> u32;
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//correct ways to print function pointers
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println!("{:p}", foo as fn() -> u32);
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println!("{:p}", fn_ptr);
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//potential ways to incorrectly try printing function pointers
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println!("{:p}", &foo);
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//~^ WARNING taking a reference to a function item does not give a function pointer
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print!("{:p}", &foo);
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//~^ WARNING taking a reference to a function item does not give a function pointer
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format!("{:p}", &foo);
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//~^ WARNING taking a reference to a function item does not give a function pointer
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println!("{:p}", &foo as *const _);
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//~^ WARNING taking a reference to a function item does not give a function pointer
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println!("{:p}", zst_ref);
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//~^ WARNING taking a reference to a function item does not give a function pointer
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println!("{:p}", cast_zst_ptr);
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//~^ WARNING taking a reference to a function item does not give a function pointer
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println!("{:p}", coerced_zst_ptr);
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//~^ WARNING taking a reference to a function item does not give a function pointer
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println!("{:p}", &fn_item);
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//~^ WARNING taking a reference to a function item does not give a function pointer
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println!("{:p}", indirect_ref);
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//~^ WARNING taking a reference to a function item does not give a function pointer
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println!("{:p}", &nop);
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//~^ WARNING taking a reference to a function item does not give a function pointer
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println!("{:p}", &bar);
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//~^ WARNING taking a reference to a function item does not give a function pointer
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println!("{:p}", &baz);
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//~^ WARNING taking a reference to a function item does not give a function pointer
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println!("{:p}", &unsafe_fn);
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//~^ WARNING taking a reference to a function item does not give a function pointer
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println!("{:p}", &c_fn);
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//~^ WARNING taking a reference to a function item does not give a function pointer
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println!("{:p}", &unsafe_c_fn);
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//~^ WARNING taking a reference to a function item does not give a function pointer
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println!("{:p}", &variadic);
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//~^ WARNING taking a reference to a function item does not give a function pointer
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println!("{:p}", &std::env::var::<String>);
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//~^ WARNING taking a reference to a function item does not give a function pointer
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println!("{:p} {:p} {:p}", &nop, &foo, &bar);
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//~^ WARNING taking a reference to a function item does not give a function pointer
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//~^^ WARNING taking a reference to a function item does not give a function pointer
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//~^^^ WARNING taking a reference to a function item does not give a function pointer
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//using a function reference to call a function shouldn't lint
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(&bar)(1);
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//passing a function reference to an arbitrary function shouldn't lint
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call_fn(&bar, 1);
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parameterized_call_fn(&bar, 1);
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std::mem::size_of_val(&foo);
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unsafe {
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//potential ways to incorrectly try transmuting function pointers
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std::mem::transmute::<_, usize>(&foo);
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//~^ WARNING taking a reference to a function item does not give a function pointer
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std::mem::transmute::<_, (usize, usize)>((&foo, &bar));
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//~^ WARNING taking a reference to a function item does not give a function pointer
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//~^^ WARNING taking a reference to a function item does not give a function pointer
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//the correct way to transmute function pointers
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std::mem::transmute::<_, usize>(foo as fn() -> u32);
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std::mem::transmute::<_, (usize, usize)>((foo as fn() -> u32, bar as fn(u32) -> u32));
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}
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//function references as arguments required to be bound by std::fmt::Pointer should lint
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print_ptr(&bar);
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//~^ WARNING taking a reference to a function item does not give a function pointer
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bound_by_ptr_trait(&bar);
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//~^ WARNING taking a reference to a function item does not give a function pointer
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bound_by_ptr_trait_tuple((&foo, &bar));
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//~^ WARNING taking a reference to a function item does not give a function pointer
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//~^^ WARNING taking a reference to a function item does not give a function pointer
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implicit_ptr_trait(&bar); // ignore
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//correct ways to pass function pointers as arguments bound by std::fmt::Pointer
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print_ptr(bar as fn(u32) -> u32);
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bound_by_ptr_trait(bar as fn(u32) -> u32);
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bound_by_ptr_trait_tuple((foo as fn() -> u32, bar as fn(u32) -> u32));
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}
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176
src/test/ui/lint/function-item-references.stderr
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src/test/ui/lint/function-item-references.stderr
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:40:18
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LL | Pointer::fmt(&zst_ref, f)
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| ^^^^^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
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note: the lint level is defined here
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--> $DIR/function-item-references.rs:3:9
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LL | #![warn(function_item_references)]
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| ^^^^^^^^^^^^^^^^^^^^^^^^
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:77:22
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LL | println!("{:p}", &foo);
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| ^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:79:20
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LL | print!("{:p}", &foo);
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| ^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:81:21
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LL | format!("{:p}", &foo);
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| ^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:84:22
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LL | println!("{:p}", &foo as *const _);
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| ^^^^^^^^^^^^^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:86:22
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LL | println!("{:p}", zst_ref);
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| ^^^^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:88:22
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LL | println!("{:p}", cast_zst_ptr);
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| ^^^^^^^^^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:90:22
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LL | println!("{:p}", coerced_zst_ptr);
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| ^^^^^^^^^^^^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:93:22
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LL | println!("{:p}", &fn_item);
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| ^^^^^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:95:22
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LL | println!("{:p}", indirect_ref);
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| ^^^^^^^^^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:98:22
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LL | println!("{:p}", &nop);
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| ^^^^ help: cast `nop` to obtain a function pointer: `nop as fn()`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:100:22
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LL | println!("{:p}", &bar);
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| ^^^^ help: cast `bar` to obtain a function pointer: `bar as fn(_) -> _`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:102:22
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LL | println!("{:p}", &baz);
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| ^^^^ help: cast `baz` to obtain a function pointer: `baz as fn(_, _) -> _`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:104:22
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LL | println!("{:p}", &unsafe_fn);
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| ^^^^^^^^^^ help: cast `unsafe_fn` to obtain a function pointer: `unsafe_fn as unsafe fn()`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:106:22
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LL | println!("{:p}", &c_fn);
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| ^^^^^ help: cast `c_fn` to obtain a function pointer: `c_fn as extern "C" fn()`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:108:22
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LL | println!("{:p}", &unsafe_c_fn);
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| ^^^^^^^^^^^^ help: cast `unsafe_c_fn` to obtain a function pointer: `unsafe_c_fn as unsafe extern "C" fn()`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:110:22
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LL | println!("{:p}", &variadic);
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| ^^^^^^^^^ help: cast `variadic` to obtain a function pointer: `variadic as unsafe extern "C" fn(_, ...)`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:112:22
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LL | println!("{:p}", &std::env::var::<String>);
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| ^^^^^^^^^^^^^^^^^^^^^^^^ help: cast `var` to obtain a function pointer: `var as fn(_) -> _`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:115:32
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LL | println!("{:p} {:p} {:p}", &nop, &foo, &bar);
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| ^^^^ help: cast `nop` to obtain a function pointer: `nop as fn()`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:115:38
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LL | println!("{:p} {:p} {:p}", &nop, &foo, &bar);
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| ^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:115:44
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LL | println!("{:p} {:p} {:p}", &nop, &foo, &bar);
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| ^^^^ help: cast `bar` to obtain a function pointer: `bar as fn(_) -> _`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:130:41
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LL | std::mem::transmute::<_, usize>(&foo);
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| ^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:132:50
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LL | std::mem::transmute::<_, (usize, usize)>((&foo, &bar));
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| ^^^^^^^^^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:132:50
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LL | std::mem::transmute::<_, (usize, usize)>((&foo, &bar));
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| ^^^^^^^^^^^^ help: cast `bar` to obtain a function pointer: `bar as fn(_) -> _`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:142:15
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LL | print_ptr(&bar);
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| ^^^^ help: cast `bar` to obtain a function pointer: `bar as fn(_) -> _`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:144:24
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LL | bound_by_ptr_trait(&bar);
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| ^^^^ help: cast `bar` to obtain a function pointer: `bar as fn(_) -> _`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:146:30
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LL | bound_by_ptr_trait_tuple((&foo, &bar));
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| ^^^^^^^^^^^^ help: cast `bar` to obtain a function pointer: `bar as fn(_) -> _`
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warning: taking a reference to a function item does not give a function pointer
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--> $DIR/function-item-references.rs:146:30
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LL | bound_by_ptr_trait_tuple((&foo, &bar));
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| ^^^^^^^^^^^^ help: cast `foo` to obtain a function pointer: `foo as fn() -> _`
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warning: 28 warnings emitted
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