Auto merge of #96515 - lcnr:user-types-in-pat, r=nikomatsakis

correctly deal with user type ascriptions in pat

supersedes #93856

`thir::PatKind::AscribeUserType` previously resulted in `CanonicalUserTypeAnnotations` where the inferred type already had a subtyping relation according to `variance` to the `user_ty`.

The bug can pretty much be summarized as follows:

- during mir building
  - `user_ty -> inferred_ty`: considers variance
  - `StatementKind::AscribeUserType`: `inferred_ty` is the type of the place, so no variance needed
- during mir borrowck
  - `user_ty -> inferred_ty`: does not consider variance
  - `StatementKind::AscribeUserType`: applies variance

This mostly worked fine. The lifetimes in `inferred_ty` were only bound by its relation to `user_ty` and to the `place` of `StatementKind::AscribeUserType`, so it doesn't matter where exactly the subtyping happens.

It does however matter when having higher ranked subtying. At this point the place where the subtyping happens is forced, causing this mismatch between building and borrowck to result in unintended errors.

cc #96514 which is pretty much the same issue

r? `@nikomatsakis`

6 files changed, 65 insertions, 105 deletions

diff --git a/compiler/rustc_middle/src/mir/pretty.rs b/compiler/rustc_middle/src/mir/pretty.rs
index 8111409b8bc..eaa68bf1b38 100644
--- a/compiler/rustc_middle/src/mir/pretty.rs
+++ b/compiler/rustc_middle/src/mir/pretty.rs
@@ -1007,10 +1007,11 @@ fn write_user_type_annotations(
     for (index, annotation) in body.user_type_annotations.iter_enumerated() {
         writeln!(
             w,
-            "| {:?}: {:?} at {}",
+            "| {:?}: user_ty: {:?}, span: {}, inferred_ty: {:?}",
             index.index(),
             annotation.user_ty,
-            tcx.sess.source_map().span_to_embeddable_string(annotation.span)
+            tcx.sess.source_map().span_to_embeddable_string(annotation.span),
+            annotation.inferred_ty,
         )?;
     }
     if !body.user_type_annotations.is_empty() {
diff --git a/compiler/rustc_middle/src/thir.rs b/compiler/rustc_middle/src/thir.rs
index 26e070af764..b99e7573000 100644
--- a/compiler/rustc_middle/src/thir.rs
+++ b/compiler/rustc_middle/src/thir.rs
@@ -18,15 +18,11 @@ use rustc_index::vec::IndexVec;
 use rustc_middle::infer::canonical::Canonical;
 use rustc_middle::middle::region;
 use rustc_middle::mir::interpret::AllocId;
-use rustc_middle::mir::{
-    self, BinOp, BorrowKind, FakeReadCause, Field, Mutability, UnOp, UserTypeProjection,
-};
+use rustc_middle::mir::{self, BinOp, BorrowKind, FakeReadCause, Field, Mutability, UnOp};
 use rustc_middle::ty::adjustment::PointerCast;
 use rustc_middle::ty::subst::SubstsRef;
+use rustc_middle::ty::CanonicalUserTypeAnnotation;
 use rustc_middle::ty::{self, AdtDef, Ty, UpvarSubsts, UserType};
-use rustc_middle::ty::{
-    CanonicalUserType, CanonicalUserTypeAnnotation, CanonicalUserTypeAnnotations,
-};
 use rustc_span::{Span, Symbol, DUMMY_SP};
 use rustc_target::abi::VariantIdx;
 use rustc_target::asm::InlineAsmRegOrRegClass;
@@ -540,13 +536,13 @@ pub enum BindingMode {
     ByRef(BorrowKind),
 }
 
-#[derive(Clone, Debug, PartialEq, HashStable)]
+#[derive(Clone, Debug, HashStable)]
 pub struct FieldPat<'tcx> {
     pub field: Field,
     pub pattern: Pat<'tcx>,
 }
 
-#[derive(Clone, Debug, PartialEq, HashStable)]
+#[derive(Clone, Debug, HashStable)]
 pub struct Pat<'tcx> {
     pub ty: Ty<'tcx>,
     pub span: Span,
@@ -559,37 +555,10 @@ impl<'tcx> Pat<'tcx> {
     }
 }
 
-#[derive(Copy, Clone, Debug, PartialEq, HashStable)]
-pub struct PatTyProj<'tcx> {
-    pub user_ty: CanonicalUserType<'tcx>,
-}
-
-impl<'tcx> PatTyProj<'tcx> {
-    pub fn from_user_type(user_annotation: CanonicalUserType<'tcx>) -> Self {
-        Self { user_ty: user_annotation }
-    }
-
-    pub fn user_ty(
-        self,
-        annotations: &mut CanonicalUserTypeAnnotations<'tcx>,
-        inferred_ty: Ty<'tcx>,
-        span: Span,
-    ) -> UserTypeProjection {
-        UserTypeProjection {
-            base: annotations.push(CanonicalUserTypeAnnotation {
-                span,
-                user_ty: self.user_ty,
-                inferred_ty,
-            }),
-            projs: Vec::new(),
-        }
-    }
-}
-
-#[derive(Copy, Clone, Debug, PartialEq, HashStable)]
+#[derive(Clone, Debug, HashStable)]
 pub struct Ascription<'tcx> {
-    pub user_ty: PatTyProj<'tcx>,
-    /// Variance to use when relating the type `user_ty` to the **type of the value being
+    pub annotation: CanonicalUserTypeAnnotation<'tcx>,
+    /// Variance to use when relating the `user_ty` to the **type of the value being
     /// matched**. Typically, this is `Variance::Covariant`, since the value being matched must
     /// have a type that is some subtype of the ascribed type.
     ///
@@ -608,12 +577,11 @@ pub struct Ascription<'tcx> {
     /// probably be checking for a `PartialEq` impl instead, but this preserves the behavior
     /// of the old type-check for now. See #57280 for details.
     pub variance: ty::Variance,
-    pub user_ty_span: Span,
 }
 
-#[derive(Clone, Debug, PartialEq, HashStable)]
+#[derive(Clone, Debug, HashStable)]
 pub enum PatKind<'tcx> {
-    /// A wildward pattern: `_`.
+    /// A wildcard pattern: `_`.
     Wild,
 
     AscribeUserType {
diff --git a/compiler/rustc_mir_build/src/build/matches/mod.rs b/compiler/rustc_mir_build/src/build/matches/mod.rs
index 83ecd185b3c..fbe08dd6f0e 100644
--- a/compiler/rustc_mir_build/src/build/matches/mod.rs
+++ b/compiler/rustc_mir_build/src/build/matches/mod.rs
@@ -523,8 +523,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                             },
                         ..
                     },
-                ascription:
-                    thir::Ascription { user_ty: pat_ascription_ty, variance: _, user_ty_span },
+                ascription: thir::Ascription { annotation, variance: _ },
             } => {
                 let place =
                     self.storage_live_binding(block, var, irrefutable_pat.span, OutsideGuard, true);
@@ -535,18 +534,15 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 let cause_let = FakeReadCause::ForLet(None);
                 self.cfg.push_fake_read(block, pattern_source_info, cause_let, place);
 
-                let ty_source_info = self.source_info(user_ty_span);
-                let user_ty = pat_ascription_ty.user_ty(
-                    &mut self.canonical_user_type_annotations,
-                    place.ty(&self.local_decls, self.tcx).ty,
-                    ty_source_info.span,
-                );
+                let ty_source_info = self.source_info(annotation.span);
+
+                let base = self.canonical_user_type_annotations.push(annotation);
                 self.cfg.push(
                     block,
                     Statement {
                         source_info: ty_source_info,
                         kind: StatementKind::AscribeUserType(
-                            Box::new((place, user_ty)),
+                            Box::new((place, UserTypeProjection { base, projs: Vec::new() })),
                             // We always use invariant as the variance here. This is because the
                             // variance field from the ascription refers to the variance to use
                             // when applying the type to the value being matched, but this
@@ -789,7 +785,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
             PatKind::AscribeUserType {
                 ref subpattern,
-                ascription: thir::Ascription { ref user_ty, user_ty_span, variance: _ },
+                ascription: thir::Ascription { ref annotation, variance: _ },
             } => {
                 // This corresponds to something like
                 //
@@ -799,16 +795,13 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 //
                 // Note that the variance doesn't apply here, as we are tracking the effect
                 // of `user_ty` on any bindings contained with subpattern.
-                let annotation = CanonicalUserTypeAnnotation {
-                    span: user_ty_span,
-                    user_ty: user_ty.user_ty,
-                    inferred_ty: subpattern.ty,
-                };
+
                 let projection = UserTypeProjection {
-                    base: self.canonical_user_type_annotations.push(annotation),
+                    base: self.canonical_user_type_annotations.push(annotation.clone()),
                     projs: Vec::new(),
                 };
-                let subpattern_user_ty = pattern_user_ty.push_projection(&projection, user_ty_span);
+                let subpattern_user_ty =
+                    pattern_user_ty.push_projection(&projection, annotation.span);
                 self.visit_primary_bindings(subpattern, subpattern_user_ty, f)
             }
 
@@ -932,9 +925,8 @@ struct Binding<'tcx> {
 /// influence region inference.
 #[derive(Clone, Debug)]
 struct Ascription<'tcx> {
-    span: Span,
     source: Place<'tcx>,
-    user_ty: PatTyProj<'tcx>,
+    annotation: CanonicalUserTypeAnnotation<'tcx>,
     variance: ty::Variance,
 }
 
@@ -1863,7 +1855,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             parent_bindings
                 .iter()
                 .flat_map(|(_, ascriptions)| ascriptions)
-                .chain(&candidate.ascriptions),
+                .cloned()
+                .chain(candidate.ascriptions),
         );
 
         // rust-lang/rust#27282: The `autoref` business deserves some
@@ -2067,32 +2060,24 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
     /// Append `AscribeUserType` statements onto the end of `block`
     /// for each ascription
-    fn ascribe_types<'b>(
+    fn ascribe_types(
         &mut self,
         block: BasicBlock,
-        ascriptions: impl IntoIterator<Item = &'b Ascription<'tcx>>,
-    ) where
-        'tcx: 'b,
-    {
+        ascriptions: impl IntoIterator<Item = Ascription<'tcx>>,
+    ) {
         for ascription in ascriptions {
-            let source_info = self.source_info(ascription.span);
+            let source_info = self.source_info(ascription.annotation.span);
 
-            debug!(
-                "adding user ascription at span {:?} of place {:?} and {:?}",
-                source_info.span, ascription.source, ascription.user_ty,
-            );
-
-            let user_ty = ascription.user_ty.user_ty(
-                &mut self.canonical_user_type_annotations,
-                ascription.source.ty(&self.local_decls, self.tcx).ty,
-                source_info.span,
-            );
+            let base = self.canonical_user_type_annotations.push(ascription.annotation);
             self.cfg.push(
                 block,
                 Statement {
                     source_info,
                     kind: StatementKind::AscribeUserType(
-                        Box::new((ascription.source, user_ty)),
+                        Box::new((
+                            ascription.source,
+                            UserTypeProjection { base, projs: Vec::new() },
+                        )),
                         ascription.variance,
                     ),
                 },
diff --git a/compiler/rustc_mir_build/src/build/matches/simplify.rs b/compiler/rustc_mir_build/src/build/matches/simplify.rs
index 895df5808db..b4a0c965d6b 100644
--- a/compiler/rustc_mir_build/src/build/matches/simplify.rs
+++ b/compiler/rustc_mir_build/src/build/matches/simplify.rs
@@ -152,15 +152,14 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         match *match_pair.pattern.kind {
             PatKind::AscribeUserType {
                 ref subpattern,
-                ascription: thir::Ascription { variance, user_ty, user_ty_span },
+                ascription: thir::Ascription { ref annotation, variance },
             } => {
                 // Apply the type ascription to the value at `match_pair.place`, which is the
                 if let Ok(place_resolved) =
                     match_pair.place.clone().try_upvars_resolved(self.tcx, self.typeck_results)
                 {
                     candidate.ascriptions.push(Ascription {
-                        span: user_ty_span,
-                        user_ty,
+                        annotation: annotation.clone(),
                         source: place_resolved.into_place(self.tcx, self.typeck_results),
                         variance,
                     });
diff --git a/compiler/rustc_mir_build/src/thir/cx/block.rs b/compiler/rustc_mir_build/src/thir/cx/block.rs
index 72ce8c24cdd..d0b18ce67c6 100644
--- a/compiler/rustc_mir_build/src/thir/cx/block.rs
+++ b/compiler/rustc_mir_build/src/thir/cx/block.rs
@@ -6,6 +6,7 @@ use rustc_middle::thir::*;
 use rustc_middle::ty;
 
 use rustc_index::vec::Idx;
+use rustc_middle::ty::CanonicalUserTypeAnnotation;
 
 impl<'tcx> Cx<'tcx> {
     pub(crate) fn mirror_block(&mut self, block: &'tcx hir::Block<'tcx>) -> Block {
@@ -80,13 +81,17 @@ impl<'tcx> Cx<'tcx> {
                                 self.typeck_results.user_provided_types().get(ty.hir_id)
                             {
                                 debug!("mirror_stmts: user_ty={:?}", user_ty);
+                                let annotation = CanonicalUserTypeAnnotation {
+                                    user_ty,
+                                    span: ty.span,
+                                    inferred_ty: self.typeck_results.node_type(ty.hir_id),
+                                };
                                 pattern = Pat {
                                     ty: pattern.ty,
                                     span: pattern.span,
                                     kind: Box::new(PatKind::AscribeUserType {
                                         ascription: Ascription {
-                                            user_ty: PatTyProj::from_user_type(user_ty),
-                                            user_ty_span: ty.span,
+                                            annotation,
                                             variance: ty::Variance::Covariant,
                                         },
                                         subpattern: pattern,
diff --git a/compiler/rustc_mir_build/src/thir/pattern/mod.rs b/compiler/rustc_mir_build/src/thir/pattern/mod.rs
index 1f152549a63..e0dec1daf63 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/mod.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/mod.rs
@@ -19,8 +19,9 @@ use rustc_middle::mir::interpret::{get_slice_bytes, ConstValue};
 use rustc_middle::mir::interpret::{ErrorHandled, LitToConstError, LitToConstInput};
 use rustc_middle::mir::{self, UserTypeProjection};
 use rustc_middle::mir::{BorrowKind, Field, Mutability};
-use rustc_middle::thir::{Ascription, BindingMode, FieldPat, Pat, PatKind, PatRange, PatTyProj};
+use rustc_middle::thir::{Ascription, BindingMode, FieldPat, Pat, PatKind, PatRange};
 use rustc_middle::ty::subst::{GenericArg, SubstsRef};
+use rustc_middle::ty::CanonicalUserTypeAnnotation;
 use rustc_middle::ty::{self, AdtDef, ConstKind, DefIdTree, Region, Ty, TyCtxt, UserType};
 use rustc_span::{Span, Symbol};
 
@@ -227,7 +228,8 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
                 for end in &[lo, hi] {
                     if let Some((_, Some(ascription))) = end {
                         let subpattern = Pat { span: pat.span, ty, kind: Box::new(kind) };
-                        kind = PatKind::AscribeUserType { ascription: *ascription, subpattern };
+                        kind =
+                            PatKind::AscribeUserType { ascription: ascription.clone(), subpattern };
                     }
                 }
 
@@ -432,13 +434,14 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
 
         if let Some(user_ty) = self.user_substs_applied_to_ty_of_hir_id(hir_id) {
             debug!("lower_variant_or_leaf: kind={:?} user_ty={:?} span={:?}", kind, user_ty, span);
+            let annotation = CanonicalUserTypeAnnotation {
+                user_ty,
+                span,
+                inferred_ty: self.typeck_results.node_type(hir_id),
+            };
             kind = PatKind::AscribeUserType {
                 subpattern: Pat { span, ty, kind: Box::new(kind) },
-                ascription: Ascription {
-                    user_ty: PatTyProj::from_user_type(user_ty),
-                    user_ty_span: span,
-                    variance: ty::Variance::Covariant,
-                },
+                ascription: Ascription { annotation, variance: ty::Variance::Covariant },
             };
         }
 
@@ -499,18 +502,21 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
                 }
 
                 let user_provided_types = self.typeck_results().user_provided_types();
-                if let Some(u_ty) = user_provided_types.get(id) {
-                    let user_ty = PatTyProj::from_user_type(*u_ty);
+                if let Some(&user_ty) = user_provided_types.get(id) {
+                    let annotation = CanonicalUserTypeAnnotation {
+                        user_ty,
+                        span,
+                        inferred_ty: self.typeck_results().node_type(id),
+                    };
                     Pat {
                         span,
                         kind: Box::new(PatKind::AscribeUserType {
                             subpattern: pattern,
                             ascription: Ascription {
+                                annotation,
                                 /// Note that use `Contravariant` here. See the
                                 /// `variance` field documentation for details.
                                 variance: ty::Variance::Contravariant,
-                                user_ty,
-                                user_ty_span: span,
                             },
                         }),
                         ty: const_.ty(),
@@ -645,7 +651,7 @@ impl<'tcx, T: PatternFoldable<'tcx>> PatternFoldable<'tcx> for Option<T> {
     }
 }
 
-macro_rules! CloneImpls {
+macro_rules! ClonePatternFoldableImpls {
     (<$lt_tcx:tt> $($ty:ty),+) => {
         $(
             impl<$lt_tcx> PatternFoldable<$lt_tcx> for $ty {
@@ -657,11 +663,11 @@ macro_rules! CloneImpls {
     }
 }
 
-CloneImpls! { <'tcx>
+ClonePatternFoldableImpls! { <'tcx>
     Span, Field, Mutability, Symbol, hir::HirId, usize, ty::Const<'tcx>,
     Region<'tcx>, Ty<'tcx>, BindingMode, AdtDef<'tcx>,
     SubstsRef<'tcx>, &'tcx GenericArg<'tcx>, UserType<'tcx>,
-    UserTypeProjection, PatTyProj<'tcx>
+    UserTypeProjection, CanonicalUserTypeAnnotation<'tcx>
 }
 
 impl<'tcx> PatternFoldable<'tcx> for FieldPat<'tcx> {
@@ -694,14 +700,10 @@ impl<'tcx> PatternFoldable<'tcx> for PatKind<'tcx> {
             PatKind::Wild => PatKind::Wild,
             PatKind::AscribeUserType {
                 ref subpattern,
-                ascription: Ascription { variance, ref user_ty, user_ty_span },
+                ascription: Ascription { ref annotation, variance },
             } => PatKind::AscribeUserType {
                 subpattern: subpattern.fold_with(folder),
-                ascription: Ascription {
-                    user_ty: user_ty.fold_with(folder),
-                    variance,
-                    user_ty_span,
-                },
+                ascription: Ascription { annotation: annotation.fold_with(folder), variance },
             },
             PatKind::Binding { mutability, name, mode, var, ty, ref subpattern, is_primary } => {
                 PatKind::Binding {