freshen: resolve root vars

lcnr · lcnr · commit f392a870e9df · 2024-02-22T17:29:26.000+01:00
Without doing so we use the same candidate cache entry
for `?0: Trait&lt;?1&gt;` and `?0: Trait&lt;?0&gt;`. These goals are different
and we must not use the same entry for them.
diff --git a/compiler/rustc_infer/src/infer/freshen.rs b/compiler/rustc_infer/src/infer/freshen.rs
@@ -56,49 +56,46 @@ impl<'a, 'tcx> TypeFreshener<'a, 'tcx> {
         }
     }
 
-    fn freshen_ty<F>(&mut self, opt_ty: Option<Ty<'tcx>>, key: ty::InferTy, mk_fresh: F) -> Ty<'tcx>
+    fn freshen_ty<F>(&mut self, input: Result<Ty<'tcx>, ty::InferTy>, mk_fresh: F) -> Ty<'tcx>
     where
         F: FnOnce(u32) -> Ty<'tcx>,
     {
-        if let Some(ty) = opt_ty {
-            return ty.fold_with(self);
-        }
-
-        match self.ty_freshen_map.entry(key) {
-            Entry::Occupied(entry) => *entry.get(),
-            Entry::Vacant(entry) => {
-                let index = self.ty_freshen_count;
-                self.ty_freshen_count += 1;
-                let t = mk_fresh(index);
-                entry.insert(t);
-                t
-            }
+        match input {
+            Ok(ty) => ty.fold_with(self),
+            Err(key) => match self.ty_freshen_map.entry(key) {
+                Entry::Occupied(entry) => *entry.get(),
+                Entry::Vacant(entry) => {
+                    let index = self.ty_freshen_count;
+                    self.ty_freshen_count += 1;
+                    let t = mk_fresh(index);
+                    entry.insert(t);
+                    t
+                }
+            },
         }
     }
 
     fn freshen_const<F>(
         &mut self,
-        opt_ct: Option<ty::Const<'tcx>>,
-        key: ty::InferConst,
+        input: Result<ty::Const<'tcx>, ty::InferConst>,
         freshener: F,
         ty: Ty<'tcx>,
     ) -> ty::Const<'tcx>
     where
         F: FnOnce(u32) -> ty::InferConst,
     {
-        if let Some(ct) = opt_ct {
-            return ct.fold_with(self);
-        }
-
-        match self.const_freshen_map.entry(key) {
-            Entry::Occupied(entry) => *entry.get(),
-            Entry::Vacant(entry) => {
-                let index = self.const_freshen_count;
-                self.const_freshen_count += 1;
-                let ct = ty::Const::new_infer(self.infcx.tcx, freshener(index), ty);
-                entry.insert(ct);
-                ct
-            }
+        match input {
+            Ok(ct) => ct.fold_with(self),
+            Err(key) => match self.const_freshen_map.entry(key) {
+                Entry::Occupied(entry) => *entry.get(),
+                Entry::Vacant(entry) => {
+                    let index = self.const_freshen_count;
+                    self.const_freshen_count += 1;
+                    let ct = ty::Const::new_infer(self.infcx.tcx, freshener(index), ty);
+                    entry.insert(ct);
+                    ct
+                }
+            },
         }
     }
 }
@@ -146,19 +143,22 @@ impl<'a, 'tcx> TypeFolder<TyCtxt<'tcx>> for TypeFreshener<'a, 'tcx> {
     fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
         match ct.kind() {
             ty::ConstKind::Infer(ty::InferConst::Var(v)) => {
-                let opt_ct =
-                    self.infcx.inner.borrow_mut().const_unification_table().probe_value(v).known();
-                self.freshen_const(opt_ct, ty::InferConst::Var(v), ty::InferConst::Fresh, ct.ty())
+                let mut inner = self.infcx.inner.borrow_mut();
+                let input =
+                    inner.const_unification_table().probe_value(v).known().ok_or_else(|| {
+                        ty::InferConst::Var(inner.const_unification_table().find(v).vid)
+                    });
+                drop(inner);
+                self.freshen_const(input, ty::InferConst::Fresh, ct.ty())
             }
             ty::ConstKind::Infer(ty::InferConst::EffectVar(v)) => {
-                let opt_ct =
-                    self.infcx.inner.borrow_mut().effect_unification_table().probe_value(v).known();
-                self.freshen_const(
-                    opt_ct,
-                    ty::InferConst::EffectVar(v),
-                    ty::InferConst::Fresh,
-                    ct.ty(),
-                )
+                let mut inner = self.infcx.inner.borrow_mut();
+                let input =
+                    inner.effect_unification_table().probe_value(v).known().ok_or_else(|| {
+                        ty::InferConst::EffectVar(inner.effect_unification_table().find(v).vid)
+                    });
+                drop(inner);
+                self.freshen_const(input, ty::InferConst::Fresh, ct.ty())
             }
             ty::ConstKind::Infer(ty::InferConst::Fresh(i)) => {
                 if i >= self.const_freshen_count {
@@ -191,35 +191,37 @@ impl<'a, 'tcx> TypeFreshener<'a, 'tcx> {
     fn fold_infer_ty(&mut self, v: ty::InferTy) -> Option<Ty<'tcx>> {
         match v {
             ty::TyVar(v) => {
-                let opt_ty = self.infcx.inner.borrow_mut().type_variables().probe(v).known();
-                Some(self.freshen_ty(opt_ty, ty::TyVar(v), |n| Ty::new_fresh(self.infcx.tcx, n)))
+                let mut inner = self.infcx.inner.borrow_mut();
+                let input = inner
+                    .type_variables()
+                    .probe(v)
+                    .known()
+                    .ok_or_else(|| ty::TyVar(inner.type_variables().root_var(v)));
+                drop(inner);
+                Some(self.freshen_ty(input, |n| Ty::new_fresh(self.infcx.tcx, n)))
             }
 
-            ty::IntVar(v) => Some(
-                self.freshen_ty(
-                    self.infcx
-                        .inner
-                        .borrow_mut()
-                        .int_unification_table()
-                        .probe_value(v)
-                        .map(|v| v.to_type(self.infcx.tcx)),
-                    ty::IntVar(v),
-                    |n| Ty::new_fresh_int(self.infcx.tcx, n),
-                ),
-            ),
-
-            ty::FloatVar(v) => Some(
-                self.freshen_ty(
-                    self.infcx
-                        .inner
-                        .borrow_mut()
-                        .float_unification_table()
-                        .probe_value(v)
-                        .map(|v| v.to_type(self.infcx.tcx)),
-                    ty::FloatVar(v),
-                    |n| Ty::new_fresh_float(self.infcx.tcx, n),
-                ),
-            ),
+            ty::IntVar(v) => {
+                let mut inner = self.infcx.inner.borrow_mut();
+                let input = inner
+                    .int_unification_table()
+                    .probe_value(v)
+                    .map(|v| v.to_type(self.infcx.tcx))
+                    .ok_or_else(|| ty::IntVar(inner.int_unification_table().find(v)));
+                drop(inner);
+                Some(self.freshen_ty(input, |n| Ty::new_fresh_int(self.infcx.tcx, n)))
+            }
+
+            ty::FloatVar(v) => {
+                let mut inner = self.infcx.inner.borrow_mut();
+                let input = inner
+                    .float_unification_table()
+                    .probe_value(v)
+                    .map(|v| v.to_type(self.infcx.tcx))
+                    .ok_or_else(|| ty::FloatVar(inner.float_unification_table().find(v)));
+                drop(inner);
+                Some(self.freshen_ty(input, |n| Ty::new_fresh_float(self.infcx.tcx, n)))
+            }
 
             ty::FreshTy(ct) | ty::FreshIntTy(ct) | ty::FreshFloatTy(ct) => {
                 if ct >= self.ty_freshen_count {
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -40,7 +40,6 @@ use rustc_middle::dep_graph::DepNodeIndex;
 use rustc_middle::mir::interpret::ErrorHandled;
 use rustc_middle::ty::_match::MatchAgainstFreshVars;
 use rustc_middle::ty::abstract_const::NotConstEvaluatable;
-use rustc_middle::ty::fold::BottomUpFolder;
 use rustc_middle::ty::relate::TypeRelation;
 use rustc_middle::ty::GenericArgsRef;
 use rustc_middle::ty::{self, EarlyBinder, PolyProjectionPredicate, ToPolyTraitRef, ToPredicate};
@@ -2435,28 +2434,8 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
         match self.match_impl(impl_def_id, impl_trait_header, obligation) {
             Ok(args) => args,
             Err(()) => {
-                // FIXME: A rematch may fail when a candidate cache hit occurs
-                // on the freshened form of the trait predicate, but the match
-                // fails for some reason that is not captured in the freshened
-                // cache key. For example, equating an impl trait ref against
-                // the placeholder trait ref may fail due the Generalizer relation
-                // raising a CyclicalTy error due to a sub_root_var relation
-                // for a variable being generalized...
-                let guar = self.infcx.dcx().span_delayed_bug(
-                    obligation.cause.span,
-                    format!(
-                        "Impl {impl_def_id:?} was matchable against {obligation:?} but now is not"
-                    ),
-                );
-                let value = self.infcx.fresh_args_for_item(obligation.cause.span, impl_def_id);
-                let err = Ty::new_error(self.tcx(), guar);
-                let value = value.fold_with(&mut BottomUpFolder {
-                    tcx: self.tcx(),
-                    ty_op: |_| err,
-                    lt_op: |l| l,
-                    ct_op: |c| c,
-                });
-                Normalized { value, obligations: vec![] }
+                let predicate = self.infcx.resolve_vars_if_possible(obligation.predicate);
+                bug!("impl {impl_def_id:?} was matchable against {predicate:?} but now is not")
             }
         }
     }
diff --git a/tests/ui/impl-trait/issues/issue-62742.rs b/tests/ui/impl-trait/issues/issue-62742.rs
@@ -3,6 +3,8 @@ use std::marker::PhantomData;
 fn _alias_check() {
     WrongImpl::foo(0i32);
     //~^ ERROR the trait bound `RawImpl<_>: Raw<_>` is not satisfied
+    //~| ERROR the trait bound `RawImpl<_>: Raw<_>` is not satisfied
+    //~| ERROR the trait bound `RawImpl<_>: Raw<_>` is not satisfied
     WrongImpl::<()>::foo(0i32);
     //~^ ERROR the trait bound `RawImpl<()>: Raw<()>` is not satisfied
     //~| ERROR trait bounds were not satisfied
diff --git a/tests/ui/impl-trait/issues/issue-62742.stderr b/tests/ui/impl-trait/issues/issue-62742.stderr
@@ -1,3 +1,18 @@
+error[E0277]: the trait bound `RawImpl<_>: Raw<_>` is not satisfied
+  --> $DIR/issue-62742.rs:4:5
+   |
+LL |     WrongImpl::foo(0i32);
+   |     ^^^^^^^^^^^^^^ the trait `Raw<_>` is not implemented for `RawImpl<_>`
+   |
+   = help: the trait `Raw<[_]>` is implemented for `RawImpl<_>`
+note: required by a bound in `SafeImpl::<T, A>::foo`
+  --> $DIR/issue-62742.rs:30:20
+   |
+LL | impl<T: ?Sized, A: Raw<T>> SafeImpl<T, A> {
+   |                    ^^^^^^ required by this bound in `SafeImpl::<T, A>::foo`
+LL |     pub fn foo(value: A::Value) {}
+   |            --- required by a bound in this associated function
+
 error[E0277]: the trait bound `RawImpl<_>: Raw<_>` is not satisfied
   --> $DIR/issue-62742.rs:4:5
    |
@@ -6,13 +21,21 @@ LL |     WrongImpl::foo(0i32);
    |
    = help: the trait `Raw<[_]>` is implemented for `RawImpl<_>`
 note: required by a bound in `SafeImpl`
-  --> $DIR/issue-62742.rs:26:35
+  --> $DIR/issue-62742.rs:28:35
    |
 LL | pub struct SafeImpl<T: ?Sized, A: Raw<T>>(PhantomData<(A, T)>);
    |                                   ^^^^^^ required by this bound in `SafeImpl`
 
+error[E0277]: the trait bound `RawImpl<_>: Raw<_>` is not satisfied
+  --> $DIR/issue-62742.rs:4:5
+   |
+LL |     WrongImpl::foo(0i32);
+   |     ^^^^^^^^^^^^^^^^^^^^ the trait `Raw<_>` is not implemented for `RawImpl<_>`
+   |
+   = help: the trait `Raw<[_]>` is implemented for `RawImpl<_>`
+
 error[E0599]: the function or associated item `foo` exists for struct `SafeImpl<(), RawImpl<()>>`, but its trait bounds were not satisfied
-  --> $DIR/issue-62742.rs:6:22
+  --> $DIR/issue-62742.rs:8:22
    |
 LL |     WrongImpl::<()>::foo(0i32);
    |                      ^^^ function or associated item cannot be called on `SafeImpl<(), RawImpl<()>>` due to unsatisfied trait bounds
@@ -24,33 +47,33 @@ LL | pub struct SafeImpl<T: ?Sized, A: Raw<T>>(PhantomData<(A, T)>);
    | ----------------------------------------- function or associated item `foo` not found for this struct
    |
 note: trait bound `RawImpl<()>: Raw<()>` was not satisfied
-  --> $DIR/issue-62742.rs:28:20
+  --> $DIR/issue-62742.rs:30:20
    |
 LL | impl<T: ?Sized, A: Raw<T>> SafeImpl<T, A> {
    |                    ^^^^^^  --------------
    |                    |
    |                    unsatisfied trait bound introduced here
 note: the trait `Raw` must be implemented
-  --> $DIR/issue-62742.rs:12:1
+  --> $DIR/issue-62742.rs:14:1
    |
 LL | pub trait Raw<T: ?Sized> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0277]: the trait bound `RawImpl<()>: Raw<()>` is not satisfied
-  --> $DIR/issue-62742.rs:6:5
+  --> $DIR/issue-62742.rs:8:5
    |
 LL |     WrongImpl::<()>::foo(0i32);
    |     ^^^^^^^^^^^^^^^ the trait `Raw<()>` is not implemented for `RawImpl<()>`
    |
    = help: the trait `Raw<[()]>` is implemented for `RawImpl<()>`
    = help: for that trait implementation, expected `[()]`, found `()`
 note: required by a bound in `SafeImpl`
-  --> $DIR/issue-62742.rs:26:35
+  --> $DIR/issue-62742.rs:28:35
    |
 LL | pub struct SafeImpl<T: ?Sized, A: Raw<T>>(PhantomData<(A, T)>);
    |                                   ^^^^^^ required by this bound in `SafeImpl`
 
-error: aborting due to 3 previous errors
+error: aborting due to 5 previous errors
 
 Some errors have detailed explanations: E0277, E0599.
 For more information about an error, try `rustc --explain E0277`.
