Merge pull request #66766 from amritpan/key-path-backward-diag

[ConstraintSystem] Fix keyPath diagnostic error for value convert to contextual types

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -12202,7 +12202,7 @@ ConstraintSystem::simplifyKeyPathConstraint(
              (definitelyKeyPathType && capability == ReadOnly)) {
     auto resolvedKPTy =
       BoundGenericType::get(kpDecl, nullptr, {rootTy, valueTy});
-    return matchTypes(keyPathTy, resolvedKPTy, ConstraintKind::Bind, subflags,
+    return matchTypes(resolvedKPTy, keyPathTy, ConstraintKind::Bind, subflags,
                       loc);
   } else {
     addUnsolvedConstraint(Constraint::create(*this, ConstraintKind::KeyPath,

test/Constraints/keypath.swift

@@ -206,3 +206,19 @@ func rdar85458997() {
   _ = S(\.name)
   // expected-error@-1 {{cannot infer key path type from context; consider explicitly specifying a root type}} {{10-10=<#Root#>}}
 }
+
+// https://github.com/apple/swift/issues/65965 - failed to produce correct types for key path capability mismatch
+func issue_65965() {
+  struct S {
+	  var s: String
+	  let v: String
+  }
+	
+  let refKP: ReferenceWritableKeyPath<S, String>
+  refKP = \.s
+  // expected-error@-1 {{key path value type 'WritableKeyPath<S, String>' cannot be converted to contextual type 'ReferenceWritableKeyPath<S, String>'}}
+	
+  let writeKP: WritableKeyPath<S, String>
+  writeKP = \.v
+  // expected-error@-1 {{key path value type 'KeyPath<S, String>' cannot be converted to contextual type 'WritableKeyPath<S, String>'}}
+}