rust-lang-ci
diff --git a/‎crates/hir-def/src/attr.rs
+27-15 b/‎crates/hir-def/src/attr.rs
+27-15
diff --git a/‎crates/hir-ty/src/infer.rs
+1-1 b/‎crates/hir-ty/src/infer.rs
+1-1
diff --git a/‎crates/hir-ty/src/infer/unify.rs
+64-19 b/‎crates/hir-ty/src/infer/unify.rs
+64-19
diff --git a/‎crates/hir-ty/src/lib.rs
+2-2 b/‎crates/hir-ty/src/lib.rs
+2-2
@@ -377,27 +377,39 @@ impl AttrsWithOwner {
             AttrDefId::GenericParamId(it) => match it {
                 GenericParamId::ConstParamId(it) => {
                     let src = it.parent().child_source(db);
-                    RawAttrs::from_attrs_owner(
-                        db.upcast(),
-                        src.with_value(&src.value[it.local_id()]),
-                        db.span_map(src.file_id).as_ref(),
-                    )
+                    // FIXME: We should be never getting `None` here.
+                    match src.value.get(it.local_id()) {
+                        Some(val) => RawAttrs::from_attrs_owner(
+                            db.upcast(),
+                            src.with_value(val),
+                            db.span_map(src.file_id).as_ref(),
+                        ),
+                        None => RawAttrs::EMPTY,
+                    }
                 }
                 GenericParamId::TypeParamId(it) => {
                     let src = it.parent().child_source(db);
-                    RawAttrs::from_attrs_owner(
-                        db.upcast(),
-                        src.with_value(&src.value[it.local_id()]),
-                        db.span_map(src.file_id).as_ref(),
-                    )
+                    // FIXME: We should be never getting `None` here.
+                    match src.value.get(it.local_id()) {
+                        Some(val) => RawAttrs::from_attrs_owner(
+                            db.upcast(),
+                            src.with_value(val),
+                            db.span_map(src.file_id).as_ref(),
+                        ),
+                        None => RawAttrs::EMPTY,
+                    }
                 }
                 GenericParamId::LifetimeParamId(it) => {
                     let src = it.parent.child_source(db);
-                    RawAttrs::from_attrs_owner(
-                        db.upcast(),
-                        src.with_value(&src.value[it.local_id]),
-                        db.span_map(src.file_id).as_ref(),
-                    )
+                    // FIXME: We should be never getting `None` here.
+                    match src.value.get(it.local_id) {
+                        Some(val) => RawAttrs::from_attrs_owner(
+                            db.upcast(),
+                            src.with_value(val),
+                            db.span_map(src.file_id).as_ref(),
+                        ),
+                        None => RawAttrs::EMPTY,
+                    }
                 }
             },
             AttrDefId::ExternBlockId(it) => attrs_from_item_tree_loc(db, it),
 
@@ -68,7 +68,7 @@ use crate::{
 #[allow(unreachable_pub)]
 pub use coerce::could_coerce;
 #[allow(unreachable_pub)]
-pub use unify::could_unify;
+pub use unify::{could_unify, could_unify_deeply};
 
 use cast::CastCheck;
 pub(crate) use closure::{CaptureKind, CapturedItem, CapturedItemWithoutTy};
 
@@ -74,6 +74,12 @@ impl<T: HasInterner<Interner = Interner>> Canonicalized<T> {
     }
 }
 
+/// Check if types unify.
+///
+/// Note that we consider placeholder types to unify with everything.
+/// This means that there may be some unresolved goals that actually set bounds for the placeholder
+/// type for the types to unify. For example `Option<T>` and `Option<U>` unify although there is
+/// unresolved goal `T = U`.
 pub fn could_unify(
     db: &dyn HirDatabase,
     env: Arc<TraitEnvironment>,
@@ -82,21 +88,35 @@ pub fn could_unify(
     unify(db, env, tys).is_some()
 }
 
+/// Check if types unify eagerly making sure there are no unresolved goals.
+///
+/// This means that placeholder types are not considered to unify if there are any bounds set on
+/// them. For example `Option<T>` and `Option<U>` do not unify as we cannot show that `T = U`
+pub fn could_unify_deeply(
+    db: &dyn HirDatabase,
+    env: Arc<TraitEnvironment>,
+    tys: &Canonical<(Ty, Ty)>,
+) -> bool {
+    let mut table = InferenceTable::new(db, env);
+    let vars = make_substitutions(tys, &mut table);
+    let ty1_with_vars = vars.apply(tys.value.0.clone(), Interner);
+    let ty2_with_vars = vars.apply(tys.value.1.clone(), Interner);
+    let ty1_with_vars = table.normalize_associated_types_in(ty1_with_vars);
+    let ty2_with_vars = table.normalize_associated_types_in(ty2_with_vars);
+    table.resolve_obligations_as_possible();
+    table.propagate_diverging_flag();
+    let ty1_with_vars = table.resolve_completely(ty1_with_vars);
+    let ty2_with_vars = table.resolve_completely(ty2_with_vars);
+    table.unify_deeply(&ty1_with_vars, &ty2_with_vars)
+}
+
 pub(crate) fn unify(
     db: &dyn HirDatabase,
     env: Arc<TraitEnvironment>,
     tys: &Canonical<(Ty, Ty)>,
 ) -> Option<Substitution> {
     let mut table = InferenceTable::new(db, env);
-    let vars = Substitution::from_iter(
-        Interner,
-        tys.binders.iter(Interner).map(|it| match &it.kind {
-            chalk_ir::VariableKind::Ty(_) => table.new_type_var().cast(Interner),
-            // FIXME: maybe wrong?
-            chalk_ir::VariableKind::Lifetime => table.new_type_var().cast(Interner),
-            chalk_ir::VariableKind::Const(ty) => table.new_const_var(ty.clone()).cast(Interner),
-        }),
-    );
+    let vars = make_substitutions(tys, &mut table);
     let ty1_with_vars = vars.apply(tys.value.0.clone(), Interner);
     let ty2_with_vars = vars.apply(tys.value.1.clone(), Interner);
     if !table.unify(&ty1_with_vars, &ty2_with_vars) {
@@ -125,6 +145,21 @@ pub(crate) fn unify(
     ))
 }
 
+fn make_substitutions(
+    tys: &chalk_ir::Canonical<(chalk_ir::Ty<Interner>, chalk_ir::Ty<Interner>)>,
+    table: &mut InferenceTable<'_>,
+) -> chalk_ir::Substitution<Interner> {
+    Substitution::from_iter(
+        Interner,
+        tys.binders.iter(Interner).map(|it| match &it.kind {
+            chalk_ir::VariableKind::Ty(_) => table.new_type_var().cast(Interner),
+            // FIXME: maybe wrong?
+            chalk_ir::VariableKind::Lifetime => table.new_type_var().cast(Interner),
+            chalk_ir::VariableKind::Const(ty) => table.new_const_var(ty.clone()).cast(Interner),
+        }),
+    )
+}
+
 bitflags::bitflags! {
     #[derive(Default, Clone, Copy)]
     pub(crate) struct TypeVariableFlags: u8 {
@@ -431,6 +466,18 @@ impl<'a> InferenceTable<'a> {
         true
     }
 
+    /// Unify two relatable values (e.g. `Ty`) and check whether trait goals which arise from that could be fulfilled
+    pub(crate) fn unify_deeply<T: ?Sized + Zip<Interner>>(&mut self, ty1: &T, ty2: &T) -> bool {
+        let result = match self.try_unify(ty1, ty2) {
+            Ok(r) => r,
+            Err(_) => return false,
+        };
+        result.goals.iter().all(|goal| {
+            let canonicalized = self.canonicalize(goal.clone());
+            self.try_resolve_obligation(&canonicalized).is_some()
+        })
+    }
+
     /// Unify two relatable values (e.g. `Ty`) and return new trait goals arising from it, so the
     /// caller needs to deal with them.
     pub(crate) fn try_unify<T: ?Sized + Zip<Interner>>(
@@ -501,7 +548,8 @@ impl<'a> InferenceTable<'a> {
 
     fn register_obligation_in_env(&mut self, goal: InEnvironment<Goal>) {
         let canonicalized = self.canonicalize(goal);
-        if !self.try_resolve_obligation(&canonicalized) {
+        let solution = self.try_resolve_obligation(&canonicalized);
+        if matches!(solution, Some(Solution::Ambig(_))) {
             self.pending_obligations.push(canonicalized);
         }
     }
@@ -627,38 +675,35 @@ impl<'a> InferenceTable<'a> {
     fn try_resolve_obligation(
         &mut self,
         canonicalized: &Canonicalized<InEnvironment<Goal>>,
-    ) -> bool {
+    ) -> Option<chalk_solve::Solution<Interner>> {
         let solution = self.db.trait_solve(
             self.trait_env.krate,
             self.trait_env.block,
             canonicalized.value.clone(),
         );
 
-        match solution {
+        match &solution {
             Some(Solution::Unique(canonical_subst)) => {
                 canonicalized.apply_solution(
                     self,
                     Canonical {
-                        binders: canonical_subst.binders,
+                        binders: canonical_subst.binders.clone(),
                         // FIXME: handle constraints
-                        value: canonical_subst.value.subst,
+                        value: canonical_subst.value.subst.clone(),
                     },
                 );
-                true
             }
             Some(Solution::Ambig(Guidance::Definite(substs))) => {
-                canonicalized.apply_solution(self, substs);
-                false
+                canonicalized.apply_solution(self, substs.clone());
             }
             Some(_) => {
                 // FIXME use this when trying to resolve everything at the end
-                false
             }
             None => {
                 // FIXME obligation cannot be fulfilled => diagnostic
-                true
             }
         }
+        solution
     }
 
     pub(crate) fn callable_sig(
 
@@ -79,8 +79,8 @@ pub use builder::{ParamKind, TyBuilder};
 pub use chalk_ext::*;
 pub use infer::{
     closure::{CaptureKind, CapturedItem},
-    could_coerce, could_unify, Adjust, Adjustment, AutoBorrow, BindingMode, InferenceDiagnostic,
-    InferenceResult, OverloadedDeref, PointerCast,
+    could_coerce, could_unify, could_unify_deeply, Adjust, Adjustment, AutoBorrow, BindingMode,
+    InferenceDiagnostic, InferenceResult, OverloadedDeref, PointerCast,
 };
 pub use interner::Interner;
 pub use lower::{