treat host effect params as erased generics in codegen

This fixes the changes brought to codegen tests when effect params are
added to libcore, by not attempting to monomorphize functions that get
the host param by being `const fn`.

compiler/rustc_codegen_gcc/src/callee.rs

@@ -100,7 +100,7 @@ pub fn get_fn<'gcc, 'tcx>(cx: &CodegenCx<'gcc, 'tcx>, instance: Instance<'tcx>)
             // whether we are sharing generics or not. The important thing here is
             // that the visibility we apply to the declaration is the same one that
             // has been applied to the definition (wherever that definition may be).
-            let is_generic = instance.args.non_erasable_generics().next().is_some();
+            let is_generic = instance.non_erasable_generics(tcx).next().is_some();
 
             if is_generic {
                 // This is a monomorphization. Its expected visibility depends

compiler/rustc_codegen_llvm/src/callee.rs

@@ -95,7 +95,8 @@ pub fn get_fn<'ll, 'tcx>(cx: &CodegenCx<'ll, 'tcx>, instance: Instance<'tcx>) ->
         unsafe {
             llvm::LLVMRustSetLinkage(llfn, llvm::Linkage::ExternalLinkage);
 
-            let is_generic = instance.args.non_erasable_generics().next().is_some();
+            let is_generic =
+                instance.args.non_erasable_generics(tcx, instance.def_id()).next().is_some();
 
             if is_generic {
                 // This is a monomorphization. Its expected visibility depends

compiler/rustc_codegen_llvm/src/debuginfo/mod.rs

@@ -349,6 +349,7 @@ impl<'ll, 'tcx> DebugInfoMethods<'tcx> for CodegenCx<'ll, 'tcx> {
         type_names::push_generic_params(
             tcx,
             tcx.normalize_erasing_regions(ty::ParamEnv::reveal_all(), args),
+            enclosing_fn_def_id,
             &mut name,
         );
 

compiler/rustc_codegen_ssa/src/back/symbol_export.rs

@@ -334,7 +334,7 @@ fn exported_symbols_provider_local(
 
             match *mono_item {
                 MonoItem::Fn(Instance { def: InstanceDef::Item(def), args }) => {
-                    if args.non_erasable_generics().next().is_some() {
+                    if args.non_erasable_generics(tcx, def).next().is_some() {
                         let symbol = ExportedSymbol::Generic(def, args);
                         symbols.push((
                             symbol,
@@ -346,10 +346,10 @@ fn exported_symbols_provider_local(
                         ));
                     }
                 }
-                MonoItem::Fn(Instance { def: InstanceDef::DropGlue(_, Some(ty)), args }) => {
+                MonoItem::Fn(Instance { def: InstanceDef::DropGlue(def_id, Some(ty)), args }) => {
                     // A little sanity-check
                     debug_assert_eq!(
-                        args.non_erasable_generics().next(),
+                        args.non_erasable_generics(tcx, def_id).next(),
                         Some(GenericArgKind::Type(ty))
                     );
                     symbols.push((

compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs

@@ -106,14 +106,14 @@ fn push_debuginfo_type_name<'tcx>(
                     ty_and_layout,
                     &|output, visited| {
                         push_item_name(tcx, def.did(), true, output);
-                        push_generic_params_internal(tcx, args, output, visited);
+                        push_generic_params_internal(tcx, args, def.did(), output, visited);
                     },
                     output,
                     visited,
                 );
             } else {
                 push_item_name(tcx, def.did(), qualified, output);
-                push_generic_params_internal(tcx, args, output, visited);
+                push_generic_params_internal(tcx, args, def.did(), output, visited);
             }
         }
         ty::Tuple(component_types) => {
@@ -237,8 +237,13 @@ fn push_debuginfo_type_name<'tcx>(
                 let principal =
                     tcx.normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), principal);
                 push_item_name(tcx, principal.def_id, qualified, output);
-                let principal_has_generic_params =
-                    push_generic_params_internal(tcx, principal.args, output, visited);
+                let principal_has_generic_params = push_generic_params_internal(
+                    tcx,
+                    principal.args,
+                    principal.def_id,
+                    output,
+                    visited,
+                );
 
                 let projection_bounds: SmallVec<[_; 4]> = trait_data
                     .projection_bounds()
@@ -516,7 +521,13 @@ pub fn compute_debuginfo_vtable_name<'tcx>(
             tcx.normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), trait_ref);
         push_item_name(tcx, trait_ref.def_id, true, &mut vtable_name);
         visited.clear();
-        push_generic_params_internal(tcx, trait_ref.args, &mut vtable_name, &mut visited);
+        push_generic_params_internal(
+            tcx,
+            trait_ref.args,
+            trait_ref.def_id,
+            &mut vtable_name,
+            &mut visited,
+        );
     } else {
         vtable_name.push('_');
     }
@@ -610,20 +621,20 @@ fn push_unqualified_item_name(
 fn push_generic_params_internal<'tcx>(
     tcx: TyCtxt<'tcx>,
     args: GenericArgsRef<'tcx>,
+    def_id: DefId,
     output: &mut String,
     visited: &mut FxHashSet<Ty<'tcx>>,
 ) -> bool {
-    if args.non_erasable_generics().next().is_none() {
+    debug_assert_eq!(args, tcx.normalize_erasing_regions(ty::ParamEnv::reveal_all(), args));
+    let mut args = args.non_erasable_generics(tcx, def_id).peekable();
+    if args.peek().is_none() {
         return false;
     }
-
-    debug_assert_eq!(args, tcx.normalize_erasing_regions(ty::ParamEnv::reveal_all(), args));
-
     let cpp_like_debuginfo = cpp_like_debuginfo(tcx);
 
     output.push('<');
 
-    for type_parameter in args.non_erasable_generics() {
+    for type_parameter in args {
         match type_parameter {
             GenericArgKind::Type(type_parameter) => {
                 push_debuginfo_type_name(tcx, type_parameter, true, output, visited);
@@ -691,11 +702,12 @@ fn push_const_param<'tcx>(tcx: TyCtxt<'tcx>, ct: ty::Const<'tcx>, output: &mut S
 pub fn push_generic_params<'tcx>(
     tcx: TyCtxt<'tcx>,
     args: GenericArgsRef<'tcx>,
+    def_id: DefId,
     output: &mut String,
 ) {
     let _prof = tcx.prof.generic_activity("compute_debuginfo_type_name");
     let mut visited = FxHashSet::default();
-    push_generic_params_internal(tcx, args, output, &mut visited);
+    push_generic_params_internal(tcx, args, def_id, output, &mut visited);
 }
 
 fn push_closure_or_generator_name<'tcx>(
@@ -738,7 +750,7 @@ fn push_closure_or_generator_name<'tcx>(
     // Truncate the args to the length of the above generics. This will cut off
     // anything closure- or generator-specific.
     let args = args.truncate_to(tcx, generics);
-    push_generic_params_internal(tcx, args, output, visited);
+    push_generic_params_internal(tcx, args, enclosing_fn_def_id, output, visited);
 }
 
 fn push_close_angle_bracket(cpp_like_debuginfo: bool, output: &mut String) {

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -1642,8 +1642,8 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     ValuePairs::Terms(infer::ExpectedFound { expected, found }) => {
                         match (expected.unpack(), found.unpack()) {
                             (ty::TermKind::Ty(expected), ty::TermKind::Ty(found)) => {
-                                let is_simple_err =
-                                    expected.is_simple_text() && found.is_simple_text();
+                                let is_simple_err = expected.is_simple_text(self.tcx)
+                                    && found.is_simple_text(self.tcx);
                                 OpaqueTypesVisitor::visit_expected_found(
                                     self.tcx, expected, found, span,
                                 )
@@ -1885,7 +1885,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                         }
                         s
                     };
-                    if !(values.expected.is_simple_text() && values.found.is_simple_text())
+                    if !(values.expected.is_simple_text(self.tcx) && values.found.is_simple_text(self.tcx))
                         || (exp_found.is_some_and(|ef| {
                             // This happens when the type error is a subset of the expectation,
                             // like when you have two references but one is `usize` and the other

compiler/rustc_middle/src/mir/mono.rs

@@ -78,9 +78,11 @@ impl<'tcx> MonoItem<'tcx> {
         }
     }
 
-    pub fn is_generic_fn(&self) -> bool {
-        match *self {
-            MonoItem::Fn(ref instance) => instance.args.non_erasable_generics().next().is_some(),
+    pub fn is_generic_fn(&self, tcx: TyCtxt<'tcx>) -> bool {
+        match self {
+            MonoItem::Fn(instance) => {
+                instance.args.non_erasable_generics(tcx, instance.def_id()).next().is_some()
+            }
             MonoItem::Static(..) | MonoItem::GlobalAsm(..) => false,
         }
     }

compiler/rustc_middle/src/ty/diagnostics.rs

@@ -70,10 +70,10 @@ impl<'tcx> Ty<'tcx> {
     /// description in error messages. This is used in the primary span label. Beyond what
     /// `is_simple_ty` includes, it also accepts ADTs with no type arguments and references to
     /// ADTs with no type arguments.
-    pub fn is_simple_text(self) -> bool {
+    pub fn is_simple_text(self, tcx: TyCtxt<'tcx>) -> bool {
         match self.kind() {
-            Adt(_, args) => args.non_erasable_generics().next().is_none(),
-            Ref(_, ty, _) => ty.is_simple_text(),
+            Adt(def, args) => args.non_erasable_generics(tcx, def.did()).next().is_none(),
+            Ref(_, ty, _) => ty.is_simple_text(tcx),
             _ => self.is_simple_ty(),
         }
     }

compiler/rustc_middle/src/ty/generic_args.rs

@@ -379,12 +379,17 @@ impl<'tcx> GenericArgs<'tcx> {
         self.iter().filter_map(|k| k.as_const())
     }
 
+    /// Returns generic arguments that are not lifetimes or host effect params.
     #[inline]
     pub fn non_erasable_generics(
         &'tcx self,
+        tcx: TyCtxt<'tcx>,
+        def_id: DefId,
     ) -> impl DoubleEndedIterator<Item = GenericArgKind<'tcx>> + 'tcx {
-        self.iter().filter_map(|k| match k.unpack() {
-            GenericArgKind::Lifetime(_) => None,
+        let generics = tcx.generics_of(def_id);
+        self.iter().enumerate().filter_map(|(i, k)| match k.unpack() {
+            _ if Some(i) == generics.host_effect_index => None,
+            ty::GenericArgKind::Lifetime(_) => None,
             generic => Some(generic),
         })
     }

compiler/rustc_middle/src/ty/generics.rs

@@ -212,10 +212,12 @@ impl<'tcx> Generics {
     pub fn own_requires_monomorphization(&self) -> bool {
         for param in &self.params {
             match param.kind {
-                GenericParamDefKind::Type { .. } | GenericParamDefKind::Const { .. } => {
+                GenericParamDefKind::Type { .. }
+                | GenericParamDefKind::Const { is_host_effect: false, .. } => {
                     return true;
                 }
-                GenericParamDefKind::Lifetime => {}
+                GenericParamDefKind::Lifetime
+                | GenericParamDefKind::Const { is_host_effect: true, .. } => {}
             }
         }
         false

compiler/rustc_middle/src/ty/instance.rs

@@ -139,7 +139,7 @@ impl<'tcx> Instance<'tcx> {
         }
 
         // If this a non-generic instance, it cannot be a shared monomorphization.
-        self.args.non_erasable_generics().next()?;
+        self.args.non_erasable_generics(tcx, self.def_id()).next()?;
 
         match self.def {
             InstanceDef::Item(def) => tcx
@@ -344,6 +344,7 @@ impl<'tcx> Instance<'tcx> {
     pub fn mono(tcx: TyCtxt<'tcx>, def_id: DefId) -> Instance<'tcx> {
         let args = GenericArgs::for_item(tcx, def_id, |param, _| match param.kind {
             ty::GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(),
+            ty::GenericParamDefKind::Const { is_host_effect: true, .. } => tcx.consts.true_.into(),
             ty::GenericParamDefKind::Type { .. } => {
                 bug!("Instance::mono: {:?} has type parameters", def_id)
             }

compiler/rustc_mir_transform/src/inline.rs

@@ -390,7 +390,12 @@ impl<'tcx> Inliner<'tcx> {
 
         // Reachability pass defines which functions are eligible for inlining. Generally inlining
         // other functions is incorrect because they could reference symbols that aren't exported.
-        let is_generic = callsite.callee.args.non_erasable_generics().next().is_some();
+        let is_generic = callsite
+            .callee
+            .args
+            .non_erasable_generics(self.tcx, callsite.callee.def_id())
+            .next()
+            .is_some();
         if !is_generic && !callee_attrs.requests_inline() {
             return Err("not exported");
         }

compiler/rustc_monomorphize/src/collector.rs

@@ -459,7 +459,7 @@ fn collect_items_rec<'tcx>(
     // Check for PMEs and emit a diagnostic if one happened. To try to show relevant edges of the
     // mono item graph.
     if tcx.sess.diagnostic().err_count() > error_count
-        && starting_item.node.is_generic_fn()
+        && starting_item.node.is_generic_fn(tcx)
         && starting_item.node.is_user_defined()
     {
         let formatted_item = with_no_trimmed_paths!(starting_item.node.to_string());
@@ -1315,6 +1315,7 @@ fn create_mono_items_for_default_impls<'tcx>(
     // it, to validate whether or not the impl is legal to instantiate at all.
     let only_region_params = |param: &ty::GenericParamDef, _: &_| match param.kind {
         GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(),
+        GenericParamDefKind::Const { is_host_effect: true, .. } => tcx.consts.true_.into(),
         GenericParamDefKind::Type { .. } | GenericParamDefKind::Const { .. } => {
             unreachable!(
                 "`own_requires_monomorphization` check means that \

compiler/rustc_monomorphize/src/partitioning.rs

@@ -221,7 +221,7 @@ where
         }
 
         let characteristic_def_id = characteristic_def_id_of_mono_item(cx.tcx, mono_item);
-        let is_volatile = is_incremental_build && mono_item.is_generic_fn();
+        let is_volatile = is_incremental_build && mono_item.is_generic_fn(cx.tcx);
 
         let cgu_name = match characteristic_def_id {
             Some(def_id) => compute_codegen_unit_name(
@@ -801,7 +801,7 @@ fn mono_item_visibility<'tcx>(
         return Visibility::Hidden;
     }
 
-    let is_generic = instance.args.non_erasable_generics().next().is_some();
+    let is_generic = instance.args.non_erasable_generics(tcx, def_id).next().is_some();
 
     // Upstream `DefId` instances get different handling than local ones.
     let Some(def_id) = def_id.as_local() else {

compiler/rustc_symbol_mangling/src/lib.rs

@@ -108,7 +108,6 @@ use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
 use rustc_middle::mir::mono::{InstantiationMode, MonoItem};
 use rustc_middle::query::Providers;
-use rustc_middle::ty::GenericArgsRef;
 use rustc_middle::ty::{self, Instance, TyCtxt};
 use rustc_session::config::SymbolManglingVersion;
 
@@ -144,7 +143,7 @@ fn symbol_name_provider<'tcx>(tcx: TyCtxt<'tcx>, instance: Instance<'tcx>) -> ty
         // This closure determines the instantiating crate for instances that
         // need an instantiating-crate-suffix for their symbol name, in order
         // to differentiate between local copies.
-        if is_generic(instance.args) {
+        if is_generic(instance, tcx) {
             // For generics we might find re-usable upstream instances. If there
             // is one, we rely on the symbol being instantiated locally.
             instance.upstream_monomorphization(tcx).unwrap_or(LOCAL_CRATE)
@@ -246,7 +245,7 @@ fn compute_symbol_name<'tcx>(
     // the ID of the instantiating crate. This avoids symbol conflicts
     // in case the same instances is emitted in two crates of the same
     // project.
-    let avoid_cross_crate_conflicts = is_generic(args) || is_globally_shared_function;
+    let avoid_cross_crate_conflicts = is_generic(instance, tcx) || is_globally_shared_function;
 
     let instantiating_crate = avoid_cross_crate_conflicts.then(compute_instantiating_crate);
 
@@ -278,6 +277,6 @@ fn compute_symbol_name<'tcx>(
     symbol
 }
 
-fn is_generic(args: GenericArgsRef<'_>) -> bool {
-    args.non_erasable_generics().next().is_some()
+fn is_generic<'tcx>(instance: Instance<'tcx>, tcx: TyCtxt<'tcx>) -> bool {
+    instance.args.non_erasable_generics(tcx, instance.def_id()).next().is_some()
 }

compiler/rustc_ty_utils/src/instance.rs

@@ -55,6 +55,7 @@ fn resolve_instance<'tcx>(
             }
         } else {
             debug!(" => free item");
+            // FIXME(effects): we may want to erase the effect param if that is present on this item.
             ty::InstanceDef::Item(def_id)
         };