Rollup of 8 pull requests

.mailmap

@@ -205,6 +205,10 @@ Gareth Daniel Smith <garethdanielsmith@gmail.com> gareth <gareth@gareth-N56VM.(n
 Gareth Daniel Smith <garethdanielsmith@gmail.com> Gareth Smith <garethdanielsmith@gmail.com>
 Gauri Kholkar <f2013002@goa.bits-pilani.ac.in>
 Georges Dubus <georges.dubus@gmail.com> <georges.dubus@compiletoi.net>
+Ghost <ghost> <jonasschievink@gmail.com>
+Ghost <ghost> <jonas.schievink@ferrous-systems.com>
+Ghost <ghost> <jonas@schievink.net>
+Ghost <ghost> <Jonas.Schievink@sony.com>
 Giles Cope <gilescope@gmail.com>
 Glen De Cauwsemaecker <decauwsemaecker.glen@gmail.com>
 Graham Fawcett <graham.fawcett@gmail.com> Graham Fawcett <fawcett@uwindsor.ca>

compiler/rustc_error_codes/src/error_codes/E0401.md

@@ -1,4 +1,4 @@
-Inner items do not inherit type or const parameters from the functions
+Inner items do not inherit the generic parameters from the items
 they are embedded in.
 
 Erroneous code example:
@@ -32,8 +32,8 @@ fn foo<T>(x: T) {
 }
 ```
 
-Items inside functions are basically just like top-level items, except
-that they can only be used from the function they are in.
+Items nested inside other items are basically just like top-level items, except
+that they can only be used from the item they are in.
 
 There are a couple of solutions for this.
 

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -523,7 +523,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                             Ty::new_misc_error(tcx).into()
                         }
                     }
-                    GenericParamDefKind::Const { has_default } => {
+                    GenericParamDefKind::Const { has_default, .. } => {
                         let ty = tcx
                             .at(self.span)
                             .type_of(param.def_id)

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -1255,7 +1255,7 @@ fn check_where_clauses<'tcx>(wfcx: &WfCheckingCtxt<'_, 'tcx>, span: Span, def_id
 
     let is_our_default = |def: &ty::GenericParamDef| match def.kind {
         GenericParamDefKind::Type { has_default, .. }
-        | GenericParamDefKind::Const { has_default } => {
+        | GenericParamDefKind::Const { has_default, .. } => {
             has_default && def.index >= generics.parent_count as u32
         }
         GenericParamDefKind::Lifetime => unreachable!(),

compiler/rustc_hir_analysis/src/collect/generics_of.rs

@@ -328,7 +328,10 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
                 name: param.name.ident().name,
                 def_id: param.def_id.to_def_id(),
                 pure_wrt_drop: param.pure_wrt_drop,
-                kind: ty::GenericParamDefKind::Const { has_default: default.is_some() },
+                kind: ty::GenericParamDefKind::Const {
+                    has_default: default.is_some(),
+                    is_host_effect: is_host_param,
+                },
             })
         }
     }));

compiler/rustc_hir_typeck/src/fallback.rs

@@ -4,6 +4,7 @@ use rustc_data_structures::{
     graph::{iterate::DepthFirstSearch, vec_graph::VecGraph},
     unord::{UnordBag, UnordMap, UnordSet},
 };
+use rustc_infer::infer::{DefineOpaqueTypes, InferOk};
 use rustc_middle::ty::{self, Ty};
 
 impl<'tcx> FnCtxt<'_, 'tcx> {
@@ -23,20 +24,10 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
             self.fulfillment_cx.borrow_mut().pending_obligations()
         );
 
-        // Check if we have any unsolved variables. If not, no need for fallback.
-        let unsolved_variables = self.unsolved_variables();
-        if unsolved_variables.is_empty() {
-            return;
-        }
+        let fallback_occured = self.fallback_types() || self.fallback_effects();
 
-        let diverging_fallback = self.calculate_diverging_fallback(&unsolved_variables);
-
-        // We do fallback in two passes, to try to generate
-        // better error messages.
-        // The first time, we do *not* replace opaque types.
-        for ty in unsolved_variables {
-            debug!("unsolved_variable = {:?}", ty);
-            self.fallback_if_possible(ty, &diverging_fallback);
+        if !fallback_occured {
+            return;
         }
 
         // We now see if we can make progress. This might cause us to
@@ -65,6 +56,53 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
         self.select_obligations_where_possible(|_| {});
     }
 
+    fn fallback_types(&self) -> bool {
+        // Check if we have any unsolved variables. If not, no need for fallback.
+        let unsolved_variables = self.unsolved_variables();
+
+        if unsolved_variables.is_empty() {
+            return false;
+        }
+
+        let diverging_fallback = self.calculate_diverging_fallback(&unsolved_variables);
+
+        // We do fallback in two passes, to try to generate
+        // better error messages.
+        // The first time, we do *not* replace opaque types.
+        for ty in unsolved_variables {
+            debug!("unsolved_variable = {:?}", ty);
+            self.fallback_if_possible(ty, &diverging_fallback);
+        }
+
+        true
+    }
+
+    fn fallback_effects(&self) -> bool {
+        let unsolved_effects = self.unsolved_effects();
+
+        if unsolved_effects.is_empty() {
+            return false;
+        }
+
+        // not setting `fallback_has_occured` here because that field is only used for type fallback
+        // diagnostics.
+
+        for effect in unsolved_effects {
+            let expected = self.tcx.consts.true_;
+            let cause = self.misc(rustc_span::DUMMY_SP);
+            match self.at(&cause, self.param_env).eq(DefineOpaqueTypes::Yes, expected, effect) {
+                Ok(InferOk { obligations, value: () }) => {
+                    self.register_predicates(obligations);
+                }
+                Err(e) => {
+                    bug!("cannot eq unsolved effect: {e:?}")
+                }
+            }
+        }
+
+        true
+    }
+
     // Tries to apply a fallback to `ty` if it is an unsolved variable.
     //
     // - Unconstrained ints are replaced with `i32`.

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -1295,17 +1295,25 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     (GenericParamDefKind::Type { .. }, GenericArg::Infer(inf)) => {
                         self.fcx.ty_infer(Some(param), inf.span).into()
                     }
-                    (GenericParamDefKind::Const { .. }, GenericArg::Infer(inf)) => {
+                    (
+                        &GenericParamDefKind::Const { has_default, is_host_effect },
+                        GenericArg::Infer(inf),
+                    ) => {
                         let tcx = self.fcx.tcx();
-                        self.fcx
-                            .ct_infer(
-                                tcx.type_of(param.def_id)
-                                    .no_bound_vars()
-                                    .expect("const parameter types cannot be generic"),
-                                Some(param),
-                                inf.span,
-                            )
-                            .into()
+
+                        if has_default && is_host_effect {
+                            self.fcx.var_for_effect(param)
+                        } else {
+                            self.fcx
+                                .ct_infer(
+                                    tcx.type_of(param.def_id)
+                                        .no_bound_vars()
+                                        .expect("const parameter types cannot be generic"),
+                                    Some(param),
+                                    inf.span,
+                                )
+                                .into()
+                        }
                     }
                     _ => unreachable!(),
                 }
@@ -1324,7 +1332,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     }
                     GenericParamDefKind::Type { has_default, .. } => {
                         if !infer_args && has_default {
-                            // If we have a default, then we it doesn't matter that we're not
+                            // If we have a default, then it doesn't matter that we're not
                             // inferring the type arguments: we provide the default where any
                             // is missing.
                             tcx.type_of(param.def_id).instantiate(tcx, args.unwrap()).into()
@@ -1336,17 +1344,28 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             self.fcx.var_for_def(self.span, param)
                         }
                     }
-                    GenericParamDefKind::Const { has_default } => {
-                        if !infer_args
-                            && has_default
-                            && !tcx.has_attr(param.def_id, sym::rustc_host)
-                        {
-                            tcx.const_param_default(param.def_id)
-                                .instantiate(tcx, args.unwrap())
-                                .into()
-                        } else {
-                            self.fcx.var_for_def(self.span, param)
+                    GenericParamDefKind::Const { has_default, is_host_effect } => {
+                        if has_default {
+                            // N.B. this is a bit of a hack. `infer_args` is passed depending on
+                            // whether the user has provided generic args. E.g. for `Vec::new`
+                            // we would have to infer the generic types. However, for `Vec::<T>::new`
+                            // where the allocator param `A` has a default we will *not* infer. But
+                            // for effect params this is a different story: if the user has not written
+                            // anything explicit for the effect param, we always need to try to infer
+                            // it before falling back to default, such that a `const fn` such as
+                            // `needs_drop::<()>` can still be called in const contexts. (if we defaulted
+                            // instead of inferred, typeck would error)
+                            if is_host_effect {
+                                return self.fcx.var_for_effect(param);
+                            } else if !infer_args {
+                                return tcx
+                                    .const_param_default(param.def_id)
+                                    .instantiate(tcx, args.unwrap())
+                                    .into();
+                            }
                         }
+
+                        self.fcx.var_for_def(self.span, param)
                     }
                 }
             }

compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs

@@ -266,7 +266,14 @@ impl<'a, 'tcx> AstConv<'tcx> for FnCtxt<'a, 'tcx> {
         param: Option<&ty::GenericParamDef>,
         span: Span,
     ) -> Const<'tcx> {
+        // FIXME ideally this shouldn't use unwrap
         match param {
+            Some(
+                param @ ty::GenericParamDef {
+                    kind: ty::GenericParamDefKind::Const { is_host_effect: true, .. },
+                    ..
+                },
+            ) => self.var_for_effect(param).as_const().unwrap(),
             Some(param) => self.var_for_def(span, param).as_const().unwrap(),
             None => self.next_const_var(
                 ty,

compiler/rustc_hir_typeck/src/generator_interior/mod.rs

@@ -643,17 +643,14 @@ fn check_must_not_suspend_ty<'tcx>(
         }
         ty::Array(ty, len) => {
             let descr_pre = &format!("{}array{} of ", data.descr_pre, plural_suffix);
+            let target_usize =
+                len.try_eval_target_usize(fcx.tcx, fcx.param_env).unwrap_or(0) as usize;
+            let plural_len = target_usize.saturating_add(1);
             check_must_not_suspend_ty(
                 fcx,
                 ty,
                 hir_id,
-                SuspendCheckData {
-                    descr_pre,
-                    plural_len: len.try_eval_target_usize(fcx.tcx, fcx.param_env).unwrap_or(0)
-                        as usize
-                        + 1,
-                    ..data
-                },
+                SuspendCheckData { descr_pre, plural_len, ..data },
             )
         }
         // If drop tracking is enabled, we want to look through references, since the referent

compiler/rustc_infer/src/infer/canonical/canonicalizer.rs

@@ -522,6 +522,17 @@ impl<'cx, 'tcx> TypeFolder<TyCtxt<'tcx>> for Canonicalizer<'cx, 'tcx> {
                     }
                 }
             }
+            ty::ConstKind::Infer(InferConst::EffectVar(vid)) => {
+                match self.infcx.probe_effect_var(vid) {
+                    Some(value) => return self.fold_const(value.as_const(self.infcx.tcx)),
+                    None => {
+                        return self.canonicalize_const_var(
+                            CanonicalVarInfo { kind: CanonicalVarKind::Effect },
+                            ct,
+                        );
+                    }
+                }
+            }
             ty::ConstKind::Infer(InferConst::Fresh(_)) => {
                 bug!("encountered a fresh const during canonicalization")
             }
@@ -690,7 +701,8 @@ impl<'cx, 'tcx> Canonicalizer<'cx, 'tcx> {
             .iter()
             .map(|v| CanonicalVarInfo {
                 kind: match v.kind {
-                    CanonicalVarKind::Ty(CanonicalTyVarKind::Int | CanonicalTyVarKind::Float) => {
+                    CanonicalVarKind::Ty(CanonicalTyVarKind::Int | CanonicalTyVarKind::Float)
+                    | CanonicalVarKind::Effect => {
                         return *v;
                     }
                     CanonicalVarKind::Ty(CanonicalTyVarKind::General(u)) => {

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

@@ -151,7 +151,11 @@ impl<'tcx> InferCtxt<'tcx> {
                     universe_map(ui),
                 )
                 .into(),
-
+            CanonicalVarKind::Effect => {
+                let vid = self.inner.borrow_mut().effect_unification_table().new_key(None);
+                ty::Const::new_infer(self.tcx, ty::InferConst::EffectVar(vid), self.tcx.types.bool)
+                    .into()
+            }
             CanonicalVarKind::PlaceholderConst(ty::PlaceholderConst { universe, bound }, ty) => {
                 let universe_mapped = universe_map(universe);
                 let placeholder_mapped = ty::PlaceholderConst { universe: universe_mapped, bound };