Rollup merge of #101433 - jackh726:better-static-placeholder-error, r=compiler-errors

Emit a note that static bounds from HRTBs are a bug

This note isn't perfect, but opening this to either 1) land as is or 2) get some feedback on how to improve it

Let r? `@compiler-errors` and cc. `@nikomatsakis`

compiler/rustc_middle/src/infer/canonical.rs

@@ -22,6 +22,7 @@
 //! [c]: https://rust-lang.github.io/chalk/book/canonical_queries/canonicalization.html
 
 use crate::infer::MemberConstraint;
+use crate::mir::ConstraintCategory;
 use crate::ty::subst::GenericArg;
 use crate::ty::{self, BoundVar, List, Region, Ty, TyCtxt};
 use rustc_index::vec::IndexVec;
@@ -290,8 +291,10 @@ impl<'tcx, V> Canonical<'tcx, V> {
     }
 }
 
-pub type QueryOutlivesConstraint<'tcx> =
-    ty::Binder<'tcx, ty::OutlivesPredicate<GenericArg<'tcx>, Region<'tcx>>>;
+pub type QueryOutlivesConstraint<'tcx> = (
+    ty::Binder<'tcx, ty::OutlivesPredicate<GenericArg<'tcx>, Region<'tcx>>>,
+    ConstraintCategory<'tcx>,
+);
 
 TrivialTypeTraversalAndLiftImpls! {
     for <'tcx> {

compiler/rustc_middle/src/mir/query.rs

@@ -327,7 +327,7 @@ rustc_data_structures::static_assert_size!(ConstraintCategory<'_>, 16);
 ///
 /// See also `rustc_const_eval::borrow_check::constraints`.
 #[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord, Hash)]
-#[derive(TyEncodable, TyDecodable, HashStable)]
+#[derive(TyEncodable, TyDecodable, HashStable, Lift, TypeVisitable, TypeFoldable)]
 pub enum ConstraintCategory<'tcx> {
     Return(ReturnConstraint),
     Yield,
@@ -369,7 +369,7 @@ pub enum ConstraintCategory<'tcx> {
 }
 
 #[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord, Hash)]
-#[derive(TyEncodable, TyDecodable, HashStable)]
+#[derive(TyEncodable, TyDecodable, HashStable, TypeVisitable, TypeFoldable)]
 pub enum ReturnConstraint {
     Normal,
     ClosureUpvar(Field),

compiler/rustc_middle/src/traits/mod.rs

@@ -10,6 +10,7 @@ mod structural_impls;
 pub mod util;
 
 use crate::infer::canonical::Canonical;
+use crate::mir::ConstraintCategory;
 use crate::ty::abstract_const::NotConstEvaluatable;
 use crate::ty::subst::SubstsRef;
 use crate::ty::{self, AdtKind, Ty, TyCtxt};
@@ -183,6 +184,16 @@ impl<'tcx> ObligationCause<'tcx> {
             variant(DerivedObligationCause { parent_trait_pred, parent_code: self.code }).into();
         self
     }
+
+    pub fn to_constraint_category(&self) -> ConstraintCategory<'tcx> {
+        match self.code() {
+            MatchImpl(cause, _) => cause.to_constraint_category(),
+            AscribeUserTypeProvePredicate(predicate_span) => {
+                ConstraintCategory::Predicate(*predicate_span)
+            }
+            _ => ConstraintCategory::BoringNoLocation,
+        }
+    }
 }
 
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Lift)]
@@ -418,6 +429,8 @@ pub enum ObligationCauseCode<'tcx> {
         is_lit: bool,
         output_ty: Option<Ty<'tcx>>,
     },
+
+    AscribeUserTypeProvePredicate(Span),
 }
 
 /// The 'location' at which we try to perform HIR-based wf checking.

compiler/rustc_middle/src/ty/structural_impls.rs

@@ -3,7 +3,7 @@
 //! hand, though we've recently added some macros and proc-macros to help with the tedium.
 
 use crate::mir::interpret;
-use crate::mir::ProjectionKind;
+use crate::mir::{Field, ProjectionKind};
 use crate::ty::fold::{FallibleTypeFolder, TypeFoldable, TypeSuperFoldable};
 use crate::ty::print::{with_no_trimmed_paths, FmtPrinter, Printer};
 use crate::ty::visit::{TypeSuperVisitable, TypeVisitable, TypeVisitor};
@@ -648,6 +648,20 @@ impl<'a, 'tcx> Lift<'tcx> for ty::InstanceDef<'a> {
     }
 }
 
+impl<'tcx> Lift<'tcx> for Field {
+    type Lifted = Field;
+    fn lift_to_tcx(self, _tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
+        Some(self)
+    }
+}
+
+impl<'tcx> Lift<'tcx> for crate::mir::ReturnConstraint {
+    type Lifted = crate::mir::ReturnConstraint;
+    fn lift_to_tcx(self, _tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
+        Some(self)
+    }
+}
+
 ///////////////////////////////////////////////////////////////////////////
 // TypeFoldable implementations.