rust complains about "const fn" which was never declared as such

[matthiaskrgr]

Given the following code:

fn f() { dbg!(); }
static A: fn() = f;
static B: () = A();

fn main() {
    println!("Hello, world!");
    B
}

The current output is:

error: function pointers are not allowed in const fn
 --> src/main.rs:3:16
  |
3 | static B: () = A();
  |                ^^^

error: could not compile `f` due to previous error

IMO it's a bit weird that rust tells me about a "const fn" since there is none in the code snippet...? 😅

[mbartlett21]

@rustbot claim

Here's the relevant code:

rust/compiler/rustc_const_eval/src/transform/check_consts/ops.rs

Lines 85 to 94 in f001f93

	pub struct FnCallIndirect;
	impl<'tcx> NonConstOp<'tcx> for FnCallIndirect {
	fn build_error(
	&self,
	ccx: &ConstCx<'_, 'tcx>,
	span: Span,
	) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
	ccx.tcx.sess.struct_span_err(span, "function pointers are not allowed in const fn")
	}
	}

But then saying that function pointers aren't allowed in statics is just false, since there is a function pointer assigned to A.

[mbartlett21]

Note: The error message is now "function pointer calls are not allowed in statics"