ssa/mono: deduplicate type_has_metadata

The implementation of the `type_has_metadata` function is duplicated in
`rustc_codegen_ssa` and `rustc_monomorphize`, so move this to
`rustc_middle`.

Author: davidtwco

compiler/rustc_codegen_ssa/src/traits/type_.rs

@@ -1,7 +1,7 @@
 use rustc_abi::{AddressSpace, Float, Integer, Reg};
 use rustc_middle::bug;
+use rustc_middle::ty::Ty;
 use rustc_middle::ty::layout::{HasTyCtxt, HasTypingEnv, TyAndLayout};
-use rustc_middle::ty::{self, Ty};
 use rustc_target::callconv::{ArgAbi, CastTarget, FnAbi};
 
 use super::BackendTypes;
@@ -86,16 +86,7 @@ pub trait DerivedTypeCodegenMethods<'tcx>:
     }
 
     fn type_has_metadata(&self, ty: Ty<'tcx>) -> bool {
-        if ty.is_sized(self.tcx(), self.typing_env()) {
-            return false;
-        }
-
-        let tail = self.tcx().struct_tail_for_codegen(ty, self.typing_env());
-        match tail.kind() {
-            ty::Foreign(..) => false,
-            ty::Str | ty::Slice(..) | ty::Dynamic(..) => true,
-            _ => bug!("unexpected unsized tail: {:?}", tail),
-        }
+        self.tcx().type_has_metadata(ty, self.typing_env())
     }
 }
 

compiler/rustc_middle/src/ty/util.rs

@@ -208,6 +208,20 @@ impl<'tcx> TyCtxt<'tcx> {
         tcx.struct_tail_raw(ty, |ty| tcx.normalize_erasing_regions(typing_env, ty), || {})
     }
 
+    /// Returns true if a type has metadata.
+    pub fn type_has_metadata(self, ty: Ty<'tcx>, typing_env: ty::TypingEnv<'tcx>) -> bool {
+        if ty.is_sized(self, typing_env) {
+            return false;
+        }
+
+        let tail = self.struct_tail_for_codegen(ty, typing_env);
+        match tail.kind() {
+            ty::Foreign(..) => false,
+            ty::Str | ty::Slice(..) | ty::Dynamic(..) => true,
+            _ => bug!("unexpected unsized tail: {:?}", tail),
+        }
+    }
+
     /// Returns the deeply last field of nested structures, or the same type if
     /// not a structure at all. Corresponds to the only possible unsized field,
     /// and its type can be used to determine unsizing strategy.

compiler/rustc_monomorphize/src/collector.rs

@@ -1043,18 +1043,7 @@ fn find_vtable_types_for_unsizing<'tcx>(
 ) -> (Ty<'tcx>, Ty<'tcx>) {
     let ptr_vtable = |inner_source: Ty<'tcx>, inner_target: Ty<'tcx>| {
         let typing_env = ty::TypingEnv::fully_monomorphized();
-        let type_has_metadata = |ty: Ty<'tcx>| -> bool {
-            if ty.is_sized(tcx.tcx, typing_env) {
-                return false;
-            }
-            let tail = tcx.struct_tail_for_codegen(ty, typing_env);
-            match tail.kind() {
-                ty::Foreign(..) => false,
-                ty::Str | ty::Slice(..) | ty::Dynamic(..) => true,
-                _ => bug!("unexpected unsized tail: {:?}", tail),
-            }
-        };
-        if type_has_metadata(inner_source) {
+        if tcx.type_has_metadata(inner_source, typing_env) {
             (inner_source, inner_target)
         } else {
             tcx.struct_lockstep_tails_for_codegen(inner_source, inner_target, typing_env)