bug! with a better error message for failing Instance::resolve

compiler/rustc_codegen_cranelift/src/abi/mod.rs

@@ -349,10 +349,9 @@ pub(crate) fn codegen_terminator_call<'tcx>(
 
     // Handle special calls like intrinsics and empty drop glue.
     let instance = if let ty::FnDef(def_id, substs) = *fn_ty.kind() {
-        let instance = ty::Instance::resolve(fx.tcx, ty::ParamEnv::reveal_all(), def_id, substs)
+        let instance =
-            .unwrap()
+            ty::Instance::expect_resolve(fx.tcx, ty::ParamEnv::reveal_all(), def_id, substs)
-            .unwrap()
+                .polymorphize(fx.tcx);
-            .polymorphize(fx.tcx);
 
         if fx.tcx.symbol_name(instance).name.starts_with("llvm.") {
             crate::intrinsics::codegen_llvm_intrinsic_call(

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -751,10 +751,13 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         let (instance, mut llfn) = match *callee.layout.ty.kind() {
             ty::FnDef(def_id, substs) => (
                 Some(
-                    ty::Instance::resolve(bx.tcx(), ty::ParamEnv::reveal_all(), def_id, substs)
+                    ty::Instance::expect_resolve(
-                        .unwrap()
+                        bx.tcx(),
-                        .unwrap()
+                        ty::ParamEnv::reveal_all(),
-                        .polymorphize(bx.tcx()),
+                        def_id,
+                        substs,
+                    )
+                    .polymorphize(bx.tcx()),
                 ),
                 None,
             ),

compiler/rustc_middle/src/ty/instance.rs

@@ -385,6 +385,21 @@ impl<'tcx> Instance<'tcx> {
         )
     }
 
+    pub fn expect_resolve(
+        tcx: TyCtxt<'tcx>,
+        param_env: ty::ParamEnv<'tcx>,
+        def_id: DefId,
+        substs: SubstsRef<'tcx>,
+    ) -> Instance<'tcx> {
+        match ty::Instance::resolve(tcx, param_env, def_id, substs) {
+            Ok(Some(instance)) => instance,
+            _ => bug!(
+                "failed to resolve instance for {}",
+                tcx.def_path_str_with_substs(def_id, substs)
+            ),
+        }
+    }
+
     // This should be kept up to date with `resolve`.
     pub fn resolve_opt_const_arg(
         tcx: TyCtxt<'tcx>,
@@ -525,7 +540,7 @@ impl<'tcx> Instance<'tcx> {
     pub fn resolve_drop_in_place(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> ty::Instance<'tcx> {
         let def_id = tcx.require_lang_item(LangItem::DropInPlace, None);
         let substs = tcx.intern_substs(&[ty.into()]);
-        Instance::resolve(tcx, ty::ParamEnv::reveal_all(), def_id, substs).unwrap().unwrap()
+        Instance::expect_resolve(tcx, ty::ParamEnv::reveal_all(), def_id, substs)
     }
 
     #[instrument(level = "debug", skip(tcx), ret)]

compiler/rustc_monomorphize/src/collector.rs

@@ -931,10 +931,13 @@ fn visit_fn_use<'tcx>(
 ) {
     if let ty::FnDef(def_id, substs) = *ty.kind() {
         let instance = if is_direct_call {
-            ty::Instance::resolve(tcx, ty::ParamEnv::reveal_all(), def_id, substs).unwrap().unwrap()
+            ty::Instance::expect_resolve(tcx, ty::ParamEnv::reveal_all(), def_id, substs)
         } else {
-            ty::Instance::resolve_for_fn_ptr(tcx, ty::ParamEnv::reveal_all(), def_id, substs)
+            match ty::Instance::resolve_for_fn_ptr(tcx, ty::ParamEnv::reveal_all(), def_id, substs)
-                .unwrap()
+            {
+                Some(instance) => instance,
+                _ => bug!("failed to resolve instance for {ty}"),
+            }
         };
         visit_instance_use(tcx, instance, is_direct_call, source, output);
     }
@@ -1369,9 +1372,8 @@ fn create_mono_items_for_default_impls<'tcx>(
                                 trait_ref.substs[param.index as usize]
                             }
                         });
-                    let instance = ty::Instance::resolve(tcx, param_env, method.def_id, substs)
+                    let instance =
-                        .unwrap()
+                        ty::Instance::expect_resolve(tcx, param_env, method.def_id, substs);
-                        .unwrap();
 
                     let mono_item = create_fn_mono_item(tcx, instance, DUMMY_SP);
                     if mono_item.node.is_instantiable(tcx) && should_codegen_locally(tcx, &instance)