Avoid type inference panic on bitslice methods

Should fix #10090, #10046, #10179.
This is only a workaround, but the proper fix requires some bigger
refactoring (also related to fixing #10058), and this at least prevents
the crash.

crates/hir/src/lib.rs

@@ -2612,7 +2612,7 @@ impl Type {
             None,
             name,
             method_resolution::LookupMode::MethodCall,
-            callback,
+            &mut |ty, id| callback(&ty.value, id),
         );
     }
 
@@ -2664,7 +2664,7 @@ impl Type {
             None,
             name,
             method_resolution::LookupMode::Path,
-            callback,
+            &mut |ty, id| callback(&ty.value, id),
         );
     }
 

crates/hir_ty/src/infer/coerce.rs

@@ -277,7 +277,7 @@ impl<'a> InferenceContext<'a> {
                 continue;
             }
 
-            let referent_ty = canonicalized.decanonicalize_ty(referent_ty.value);
+            let referent_ty = canonicalized.decanonicalize_ty(&mut self.table, referent_ty);
 
             // At this point, we have deref'd `a` to `referent_ty`.  So
             // imagine we are coercing from `&'a mut Vec<T>` to `&'b mut [T]`.

crates/hir_ty/src/infer/expr.rs

@@ -328,10 +328,8 @@ impl<'a> InferenceContext<'a> {
                     },
                 );
                 let res = derefs.by_ref().find_map(|(callee_deref_ty, _)| {
-                    self.callable_sig(
+                    let ty = &canonicalized.decanonicalize_ty(&mut self.table, callee_deref_ty);
-                        &canonicalized.decanonicalize_ty(callee_deref_ty.value),
+                    self.callable_sig(ty, args.len())
-                        args.len(),
-                    )
                 });
                 let (param_tys, ret_ty): (Vec<Ty>, Ty) = match res {
                     Some(res) => {
@@ -510,17 +508,20 @@ impl<'a> InferenceContext<'a> {
                     },
                 );
                 let ty = autoderef.by_ref().find_map(|(derefed_ty, _)| {
-                    let def_db = self.db.upcast();
                     let module = self.resolver.module();
+                    let db = self.db;
                     let is_visible = |field_id: &FieldId| {
                         module
                             .map(|mod_id| {
-                                self.db.field_visibilities(field_id.parent)[field_id.local_id]
+                                db.field_visibilities(field_id.parent)[field_id.local_id]
-                                    .is_visible_from(def_db, mod_id)
+                                    .is_visible_from(db.upcast(), mod_id)
                             })
                             .unwrap_or(true)
                     };
-                    match canonicalized.decanonicalize_ty(derefed_ty.value).kind(&Interner) {
+                    match canonicalized
+                        .decanonicalize_ty(&mut self.table, derefed_ty)
+                        .kind(&Interner)
+                    {
                         TyKind::Tuple(_, substs) => name.as_tuple_index().and_then(|idx| {
                             substs
                                 .as_slice(&Interner)
@@ -637,7 +638,7 @@ impl<'a> InferenceContext<'a> {
                                 },
                             ) {
                                 Some(derefed_ty) => {
-                                    canonicalized.decanonicalize_ty(derefed_ty.value)
+                                    canonicalized.decanonicalize_ty(&mut self.table, derefed_ty)
                                 }
                                 None => self.err_ty(),
                             }
@@ -740,8 +741,9 @@ impl<'a> InferenceContext<'a> {
                         krate,
                         index_trait,
                     );
-                    let self_ty =
+                    let self_ty = self_ty.map_or(self.err_ty(), |t| {
-                        self_ty.map_or(self.err_ty(), |t| canonicalized.decanonicalize_ty(t.value));
+                        canonicalized.decanonicalize_ty(&mut self.table, t)
+                    });
                     self.resolve_associated_type_with_params(
                         self_ty,
                         self.resolve_ops_index_output(),
@@ -987,7 +989,7 @@ impl<'a> InferenceContext<'a> {
         });
         let (receiver_ty, method_ty, substs) = match resolved {
             Some((ty, func)) => {
-                let ty = canonicalized_receiver.decanonicalize_ty(ty);
+                let ty = canonicalized_receiver.decanonicalize_ty(&mut self.table, ty);
                 let generics = generics(self.db.upcast(), func.into());
                 let substs = self.substs_for_method_call(generics, generic_args, &ty);
                 self.write_method_resolution(tgt_expr, func, substs.clone());

crates/hir_ty/src/infer/unify.rs

@@ -41,8 +41,13 @@ where
 }
 
 impl<T: HasInterner<Interner = Interner>> Canonicalized<T> {
-    pub(super) fn decanonicalize_ty(&self, ty: Ty) -> Ty {
+    /// this method is wrong and shouldn't exist
-        chalk_ir::Substitute::apply(&self.free_vars, ty, &Interner)
+    pub(super) fn decanonicalize_ty(&self, table: &mut InferenceTable, ty: Canonical<Ty>) -> Ty {
+        let mut vars = self.free_vars.clone();
+        while ty.binders.len(&Interner) > vars.len() {
+            vars.push(table.new_type_var().cast(&Interner));
+        }
+        chalk_ir::Substitute::apply(&vars, ty.value, &Interner)
     }
 
     pub(super) fn apply_solution(

crates/hir_ty/src/method_resolution.rs

@@ -380,7 +380,7 @@ pub(crate) fn lookup_method(
     traits_in_scope: &FxHashSet<TraitId>,
     visible_from_module: Option<ModuleId>,
     name: &Name,
-) -> Option<(Ty, FunctionId)> {
+) -> Option<(Canonical<Ty>, FunctionId)> {
     iterate_method_candidates(
         ty,
         db,
@@ -421,7 +421,7 @@ pub fn iterate_method_candidates<T>(
     visible_from_module: Option<ModuleId>,
     name: Option<&Name>,
     mode: LookupMode,
-    mut callback: impl FnMut(&Ty, AssocItemId) -> Option<T>,
+    mut callback: impl FnMut(&Canonical<Ty>, AssocItemId) -> Option<T>,
 ) -> Option<T> {
     let mut slot = None;
     iterate_method_candidates_dyn(
@@ -454,7 +454,7 @@ pub fn iterate_method_candidates_dyn(
     visible_from_module: Option<ModuleId>,
     name: Option<&Name>,
     mode: LookupMode,
-    callback: &mut dyn FnMut(&Ty, AssocItemId) -> ControlFlow<()>,
+    callback: &mut dyn FnMut(&Canonical<Ty>, AssocItemId) -> ControlFlow<()>,
 ) -> ControlFlow<()> {
     match mode {
         LookupMode::MethodCall => {
@@ -520,7 +520,7 @@ fn iterate_method_candidates_with_autoref(
     traits_in_scope: &FxHashSet<TraitId>,
     visible_from_module: Option<ModuleId>,
     name: Option<&Name>,
-    mut callback: &mut dyn FnMut(&Ty, AssocItemId) -> ControlFlow<()>,
+    mut callback: &mut dyn FnMut(&Canonical<Ty>, AssocItemId) -> ControlFlow<()>,
 ) -> ControlFlow<()> {
     iterate_method_candidates_by_receiver(
         &deref_chain[0],
@@ -580,7 +580,7 @@ fn iterate_method_candidates_by_receiver(
     traits_in_scope: &FxHashSet<TraitId>,
     visible_from_module: Option<ModuleId>,
     name: Option<&Name>,
-    mut callback: &mut dyn FnMut(&Ty, AssocItemId) -> ControlFlow<()>,
+    mut callback: &mut dyn FnMut(&Canonical<Ty>, AssocItemId) -> ControlFlow<()>,
 ) -> ControlFlow<()> {
     // We're looking for methods with *receiver* type receiver_ty. These could
     // be found in any of the derefs of receiver_ty, so we have to go through
@@ -622,7 +622,7 @@ fn iterate_method_candidates_for_self_ty(
     traits_in_scope: &FxHashSet<TraitId>,
     visible_from_module: Option<ModuleId>,
     name: Option<&Name>,
-    mut callback: &mut dyn FnMut(&Ty, AssocItemId) -> ControlFlow<()>,
+    mut callback: &mut dyn FnMut(&Canonical<Ty>, AssocItemId) -> ControlFlow<()>,
 ) -> ControlFlow<()> {
     iterate_inherent_methods(
         self_ty,
@@ -645,7 +645,7 @@ fn iterate_trait_method_candidates(
     traits_in_scope: &FxHashSet<TraitId>,
     name: Option<&Name>,
     receiver_ty: Option<&Canonical<Ty>>,
-    callback: &mut dyn FnMut(&Ty, AssocItemId) -> ControlFlow<()>,
+    callback: &mut dyn FnMut(&Canonical<Ty>, AssocItemId) -> ControlFlow<()>,
 ) -> ControlFlow<()> {
     let receiver_is_array = matches!(self_ty.value.kind(&Interner), chalk_ir::TyKind::Array(..));
     // if ty is `dyn Trait`, the trait doesn't need to be in scope
@@ -697,7 +697,7 @@ fn iterate_trait_method_candidates(
             }
             known_implemented = true;
             // FIXME: we shouldn't be ignoring the binders here
-            callback(&self_ty.value, *item)?
+            callback(&self_ty, *item)?
         }
     }
     ControlFlow::Continue(())
@@ -738,7 +738,7 @@ fn iterate_inherent_methods(
     receiver_ty: Option<&Canonical<Ty>>,
     krate: CrateId,
     visible_from_module: Option<ModuleId>,
-    callback: &mut dyn FnMut(&Ty, AssocItemId) -> ControlFlow<()>,
+    callback: &mut dyn FnMut(&Canonical<Ty>, AssocItemId) -> ControlFlow<()>,
 ) -> ControlFlow<()> {
     let def_crates = match def_crates(db, &self_ty.value, krate) {
         Some(k) => k,
@@ -773,7 +773,7 @@ fn iterate_inherent_methods(
                     cov_mark::hit!(impl_self_type_match_without_receiver);
                     continue;
                 }
-                let receiver_ty = receiver_ty.map(|x| &x.value).unwrap_or(&self_ty.value);
+                let receiver_ty = receiver_ty.unwrap_or(&self_ty);
                 callback(receiver_ty, item)?;
             }
         }

crates/hir_ty/src/tests/regression.rs

@@ -1145,3 +1145,35 @@ impl<'a, T, DB: TypeMetadata> Output<'a, T, DB> {
         "#,
     );
 }
+
+#[test]
+fn bitslice_panic() {
+    check_no_mismatches(
+        r#"
+//- minicore: option, deref
+
+pub trait BitView {
+    type Store;
+}
+
+pub struct Lsb0;
+
+pub struct BitArray<V: BitView> { }
+
+pub struct BitSlice<T> { }
+
+impl<V: BitView> core::ops::Deref for BitArray<V> {
+    type Target = BitSlice<V::Store>;
+}
+
+impl<T> BitSlice<T> {
+    pub fn split_first(&self) -> Option<(T, &Self)> { loop {} }
+}
+
+fn multiexp_inner() {
+    let exp: &BitArray<Foo>;
+    exp.split_first();
+}
+        "#,
+    );
+}