abi: Display bound on TyAbiInterface

The `fmt::Debug` impl for `TyAndLayout<'a, Ty>'` requires `fmt::Display`
on the `Ty` parameter. In `ArgAbi`, `TyAndLayout`'s Ty` is instantiated
with a parameter that implements `TyAbiInterface`. `TyAbiInterface`
only required `fmt::Debug` be implemented on `Self`, not `fmt::Display`,
which meant that it wasn't actually possible to debug print `ArgAbi`.

Author: davidtwco

compiler/rustc_abi/src/callconv.rs

@@ -60,6 +60,7 @@ impl<'a, Ty> TyAndLayout<'a, Ty> {
     /// This is public so that it can be used in unit tests, but
     /// should generally only be relevant to the ABI details of
     /// specific targets.
+    #[tracing::instrument(skip(cx), level = "debug")]
     pub fn homogeneous_aggregate<C>(&self, cx: &C) -> Result<HomogeneousAggregate, Heterogeneous>
     where
         Ty: TyAbiInterface<'a, C> + Copy,

compiler/rustc_abi/src/layout/ty.rs

@@ -155,7 +155,7 @@ impl<'a, Ty> AsRef<LayoutData<FieldIdx, VariantIdx>> for TyAndLayout<'a, Ty> {
 
 /// Trait that needs to be implemented by the higher-level type representation
 /// (e.g. `rustc_middle::ty::Ty`), to provide `rustc_target::abi` functionality.
-pub trait TyAbiInterface<'a, C>: Sized + std::fmt::Debug {
+pub trait TyAbiInterface<'a, C>: Sized + std::fmt::Debug + std::fmt::Display {
     fn ty_and_layout_for_variant(
         this: TyAndLayout<'a, Self>,
         cx: &C,

compiler/rustc_target/src/callconv/aarch64.rs

@@ -9,13 +9,14 @@ use crate::spec::{Abi, HasTargetSpec, Target};
 /// Used to accommodate Apple and Microsoft's deviations from the usual AAPCS ABI.
 ///
 /// Corresponds to Clang's `AArch64ABIInfo::ABIKind`.
-#[derive(Copy, Clone, PartialEq)]
+#[derive(Copy, Clone, Debug, PartialEq)]
 pub(crate) enum AbiKind {
     AAPCS,
     DarwinPCS,
     Win64,
 }
 
+#[tracing::instrument(skip(cx), level = "debug")]
 fn is_homogeneous_aggregate<'a, Ty, C>(cx: &C, arg: &mut ArgAbi<'a, Ty>) -> Option<Uniform>
 where
     Ty: TyAbiInterface<'a, C> + Copy,
@@ -73,6 +74,7 @@ fn softfloat_float_abi<Ty>(target: &Target, arg: &mut ArgAbi<'_, Ty>) {
     }
 }
 
+#[tracing::instrument(skip(cx), level = "debug")]
 fn classify_ret<'a, Ty, C>(cx: &C, ret: &mut ArgAbi<'a, Ty>, kind: AbiKind)
 where
     Ty: TyAbiInterface<'a, C> + Copy,
@@ -105,6 +107,7 @@ where
     ret.make_indirect();
 }
 
+#[tracing::instrument(skip(cx), level = "debug")]
 fn classify_arg<'a, Ty, C>(cx: &C, arg: &mut ArgAbi<'a, Ty>, kind: AbiKind)
 where
     Ty: TyAbiInterface<'a, C> + Copy,