fix: silence mismatches involving unresolved projections

crates/hir-ty/src/chalk_ext.rs

@@ -29,6 +29,7 @@ pub trait TyExt {
     fn contains_unknown(&self) -> bool;
     fn is_ty_var(&self) -> bool;
     fn is_union(&self) -> bool;
+    fn is_projection(&self) -> bool;
 
     fn as_adt(&self) -> Option<(hir_def::AdtId, &Substitution)>;
     fn as_builtin(&self) -> Option<BuiltinType>;
@@ -101,6 +102,13 @@ impl TyExt for Ty {
         matches!(self.adt_id(Interner), Some(AdtId(hir_def::AdtId::UnionId(_))))
     }
 
+    fn is_projection(&self) -> bool {
+        matches!(
+            self.kind(Interner),
+            TyKind::Alias(AliasTy::Projection(_)) | TyKind::AssociatedType(_, _)
+        )
+    }
+
     fn as_adt(&self) -> Option<(hir_def::AdtId, &Substitution)> {
         match self.kind(Interner) {
             TyKind::Adt(AdtId(adt), parameters) => Some((*adt, parameters)),

crates/hir-ty/src/infer.rs

@@ -429,6 +429,8 @@ pub struct InferenceResult {
     /// Type of the result of `.into_iter()` on the for. `ExprId` is the one of the whole for loop.
     pub type_of_for_iterator: FxHashMap<ExprId, Ty>,
     type_mismatches: FxHashMap<ExprOrPatId, TypeMismatch>,
+    /// Whether there are any type-mismatching errors in the result.
+    pub(crate) has_errors: bool,
     /// Interned common types to return references to.
     standard_types: InternedStandardTypes,
     /// Stores the types which were implicitly dereferenced in pattern binding modes.
@@ -654,6 +656,7 @@ impl<'a> InferenceContext<'a> {
             type_of_rpit,
             type_of_for_iterator,
             type_mismatches,
+            has_errors,
             standard_types: _,
             pat_adjustments,
             binding_modes: _,
@@ -695,16 +698,33 @@ impl<'a> InferenceContext<'a> {
         for ty in type_of_for_iterator.values_mut() {
             *ty = table.resolve_completely(ty.clone());
         }
+
+        *has_errors = !type_mismatches.is_empty();
+
         type_mismatches.retain(|_, mismatch| {
             mismatch.expected = table.resolve_completely(mismatch.expected.clone());
             mismatch.actual = table.resolve_completely(mismatch.actual.clone());
-            chalk_ir::zip::Zip::zip_with(
-                &mut UnknownMismatch(self.db),
-                Variance::Invariant,
-                &mismatch.expected,
-                &mismatch.actual,
-            )
-            .is_ok()
+            let unresolved_ty_mismatch = || {
+                chalk_ir::zip::Zip::zip_with(
+                    &mut UnknownMismatch(self.db, |ty| matches!(ty.kind(Interner), TyKind::Error)),
+                    Variance::Invariant,
+                    &mismatch.expected,
+                    &mismatch.actual,
+                )
+                .is_ok()
+            };
+
+            let unresolved_projections_mismatch = || {
+                chalk_ir::zip::Zip::zip_with(
+                    &mut UnknownMismatch(self.db, |ty| ty.contains_unknown() && ty.is_projection()),
+                    chalk_ir::Variance::Invariant,
+                    &mismatch.expected,
+                    &mismatch.actual,
+                )
+                .is_ok()
+            };
+
+            unresolved_ty_mismatch() && unresolved_projections_mismatch()
         });
         diagnostics.retain_mut(|diagnostic| {
             use InferenceDiagnostic::*;
@@ -1646,11 +1666,16 @@ impl std::ops::BitOrAssign for Diverges {
         *self = *self | other;
     }
 }
-/// A zipper that checks for unequal `{unknown}` occurrences in the two types. Used to filter out
-/// mismatch diagnostics that only differ in `{unknown}`. These mismatches are usually not helpful.
-/// As the cause is usually an underlying name resolution problem.
-struct UnknownMismatch<'db>(&'db dyn HirDatabase);
-impl chalk_ir::zip::Zipper<Interner> for UnknownMismatch<'_> {
+/// A zipper that checks for unequal `{unknown}` occurrences in the two types.
+/// Types that have different constructors are filtered out and tested by the
+/// provided closure `F`. Commonly used to filter out mismatch diagnostics that
+/// only differ in `{unknown}`. These mismatches are usually not helpful, as the
+/// cause is usually an underlying name resolution problem.
+///
+/// E.g. when F is `|ty| matches!(ty.kind(Interer), TyKind::Unknown)`, the zipper
+/// will skip over all mismatches that only differ in `{unknown}`.
+struct UnknownMismatch<'db, F: Fn(&Ty) -> bool>(&'db dyn HirDatabase, F);
+impl<F: Fn(&Ty) -> bool> chalk_ir::zip::Zipper<Interner> for UnknownMismatch<'_, F> {
     fn zip_tys(&mut self, variance: Variance, a: &Ty, b: &Ty) -> chalk_ir::Fallible<()> {
         let zip_substs = |this: &mut Self,
                           variances,
@@ -1721,7 +1746,7 @@ impl chalk_ir::zip::Zipper<Interner> for UnknownMismatch<'_> {
                 zip_substs(self, None, &fn_ptr_a.substitution.0, &fn_ptr_b.substitution.0)?
             }
             (TyKind::Error, TyKind::Error) => (),
-            (TyKind::Error, _) | (_, TyKind::Error) => return Err(chalk_ir::NoSolution),
+            _ if (self.1)(a) || (self.1)(b) => return Err(chalk_ir::NoSolution),
             _ => (),
         }
 

crates/hir-ty/src/mir/lower.rs

@@ -90,7 +90,7 @@ pub enum MirLowerError {
     UnresolvedField,
     UnsizedTemporary(Ty),
     MissingFunctionDefinition(DefWithBodyId, ExprId),
-    TypeMismatch(TypeMismatch),
+    TypeMismatch(Option<TypeMismatch>),
     /// This should never happen. Type mismatch should catch everything.
     TypeError(&'static str),
     NotSupported(String),
@@ -170,14 +170,15 @@ impl MirLowerError {
                     body.pretty_print_expr(db.upcast(), *owner, *it)
                 )?;
             }
-            MirLowerError::TypeMismatch(e) => {
-                writeln!(
+            MirLowerError::TypeMismatch(e) => match e {
+                Some(e) => writeln!(
                     f,
                     "Type mismatch: Expected {}, found {}",
                     e.expected.display(db),
                     e.actual.display(db),
-                )?;
-            }
+                )?,
+                None => writeln!(f, "Type mismatch: types mismatch with {{unknown}}",)?,
+            },
             MirLowerError::GenericArgNotProvided(id, subst) => {
                 let parent = id.parent;
                 let param = &db.generic_params(parent).type_or_consts[id.local_id];
@@ -2152,8 +2153,10 @@ pub fn lower_to_mir(
     // need to take this input explicitly.
     root_expr: ExprId,
 ) -> Result<MirBody> {
-    if let Some((_, it)) = infer.type_mismatches().next() {
-        return Err(MirLowerError::TypeMismatch(it.clone()));
+    if infer.has_errors {
+        return Err(MirLowerError::TypeMismatch(
+            infer.type_mismatches().next().map(|(_, it)| it.clone()),
+        ));
     }
     let mut ctx = MirLowerCtx::new(db, owner, body, infer);
     // 0 is return local

crates/hir-ty/src/tests/diagnostics.rs

@@ -136,3 +136,20 @@ impl Trait for () {
 "#,
     );
 }
+
+#[test]
+fn no_mismatches_with_unresolved_projections() {
+    check_no_mismatches(
+        r#"
+// Thing is {unknown}
+fn create() -> Option<(i32, Thing)> {
+    Some((69420, Thing))
+}
+
+fn consume() -> Option<()> {
+    let (number, thing) = create()?;
+    Some(())
+}
+"#,
+    );
+}

crates/hir/src/lib.rs

@@ -1678,6 +1678,7 @@ impl DefWithBody {
         for d in &infer.diagnostics {
             acc.extend(AnyDiagnostic::inference_diagnostic(db, self.into(), d, &source_map));
         }
+
         for (pat_or_expr, mismatch) in infer.type_mismatches() {
             let expr_or_pat = match pat_or_expr {
                 ExprOrPatId::ExprId(expr) => source_map.expr_syntax(expr).map(Either::Left),