[Diagnostics] Add a tailored diagnostic for contextual lookup on protocols without Self requirement

Author: xedin

include/swift/AST/DiagnosticsSema.def

@@ -1902,6 +1902,10 @@ ERROR(type_does_not_conform_owner,none,
 ERROR(type_does_not_conform_in_decl_ref,none,
       "referencing %0 %1 on %2 requires that %3 conform to %4",
       (DescriptiveDeclKind, DeclName, Type, Type, Type))
+ERROR(contextual_member_ref_on_protocol_requires_self_requirement,none,
+      "contextual member reference to %0 %1 requires "
+      "'Self' constraint in the protocol extension",
+      (DescriptiveDeclKind, DeclName))
 NOTE(missing_sametype_requirement_on_self,none,
       "missing same-type requirement on 'Self'", ())
 ERROR(type_does_not_conform_anyobject_in_decl_ref,none,

lib/Sema/CSDiagnostics.cpp

@@ -7202,8 +7202,9 @@ bool InvalidMemberRefOnProtocolMetatype::diagnoseAsError() {
   auto *member = overload->choice.getDeclOrNull();
   assert(member);
 
-  emitDiagnostic(diag::cannot_infer_base_of_unresolved_member,
-                 DeclNameRef(member->getName()));
+  emitDiagnostic(
+      diag::contextual_member_ref_on_protocol_requires_self_requirement,
+      member->getDescriptiveKind(), member->getName());
 
   auto *extension = dyn_cast<ExtensionDecl>(member->getDeclContext());
 

lib/Sema/CSSimplify.cpp

@@ -6861,6 +6861,12 @@ performMemberLookup(ConstraintKind constraintKind, DeclNameRef memberName,
       // type via same-type requirement, otherwise it would be
       // impossible to find a witness for this member.
 
+      if (!isa<ExtensionDecl>(decl->getDeclContext())) {
+        result.addUnviable(candidate,
+                           MemberLookupResult::UR_TypeMemberOnInstance);
+        return;
+      }
+
       // Cannot instantiate a protocol or reference a member on
       // protocol composition type.
       if (isa<ConstructorDecl>(decl) ||

test/Constraints/static_members_on_protocol_in_generic_context.swift

@@ -227,43 +227,43 @@ _ = P[q: ""].other
 test(.doesntExist) // expected-error {{type 'P' has no member 'doesntExist'}}
 test(.doesnt.exist()) // expected-error {{type 'P' has no member 'doesnt'}}
 test(.invalidProp)
-// expected-error@-1 {{cannot infer contextual base in reference to member 'invalidProp'}}
+// expected-error@-1 {{contextual member reference to static property 'invalidProp' requires 'Self' constraint in the protocol extension}}
 test(.invalidProp.other)
-// expected-error@-1 {{cannot infer contextual base in reference to member 'invalidProp'}}
+// expected-error@-1 {{contextual member reference to static property 'invalidProp' requires 'Self' constraint in the protocol extension}}
 // expected-error@-2 {{value of type 'Int' has no member 'other'}}
 test(.invalidMethod())
-// expected-error@-1 {{cannot infer contextual base in reference to member 'invalidMethod()'}}
+// expected-error@-1 {{contextual member reference to static method 'invalidMethod()' requires 'Self' constraint in the protocol extension}}
 test(.invalidMethod().other)
-// expected-error@-1 {{cannot infer contextual base in reference to member 'invalidMethod()'}}
+// expected-error@-1 {{contextual member reference to static method 'invalidMethod()' requires 'Self' constraint in the protocol extension}}
 // expected-error@-2 {{value of type 'Int' has no member 'other'}}
 test(.generic(42))
-// expected-error@-1 {{cannot infer contextual base in reference to member 'generic'}}
+// expected-error@-1 {{contextual member reference to static method 'generic' requires 'Self' constraint in the protocol extension}}
 test(.generic(42).other)
-// expected-error@-1 {{cannot infer contextual base in reference to member 'generic'}}
+// expected-error@-1 {{contextual member reference to static method 'generic' requires 'Self' constraint in the protocol extension}}
 // expected-error@-2 {{value of type 'Int' has no member 'other'}}
-test(.generic(S())) // expected-error {{cannot infer contextual base in reference to member 'generic'}}
-test(.generic(G<Int>())) // expected-error {{cannot infer contextual base in reference to member 'generic'}}
-test(.genericWithReqs([S()])) // expected-error {{cannot infer contextual base in reference to member 'genericWithReqs'}}
+test(.generic(S())) // expected-error {{contextual member reference to static method 'generic' requires 'Self' constraint in the protocol extension}}
+test(.generic(G<Int>())) // expected-error {{contextual member reference to static method 'generic' requires 'Self' constraint in the protocol extension}}
+test(.genericWithReqs([S()])) // expected-error {{contextual member reference to static method 'genericWithReqs' requires 'Self' constraint in the protocol extension}}
 test(.genericWithReqs([42]))
-// expected-error@-1 {{cannot infer contextual base in reference to member 'genericWithReqs'}}
+// expected-error@-1 {{contextual member reference to static method 'genericWithReqs' requires 'Self' constraint in the protocol extension}}
 test(.genericWithReqs(()))
-// expected-error@-1 {{cannot infer contextual base in reference to member 'genericWithReqs'}}
+// expected-error@-1 {{contextual member reference to static method 'genericWithReqs' requires 'Self' constraint in the protocol extension}}
 
 test_combo(.doesntExist) // expected-error {{reference to member 'doesntExist' cannot be resolved without a contextual type}}
 test_combo(.doesnt.exist()) // expected-error {{reference to member 'doesnt' cannot be resolved without a contextual type}}
 test_combo(.invalidProp)
-// expected-error@-1 {{cannot infer contextual base in reference to member 'invalidProp'}}
+// expected-error@-1 {{contextual member reference to static property 'invalidProp' requires 'Self' constraint in the protocol extension}}
 test_combo(.invalidMethod())
-// expected-error@-1 {{cannot infer contextual base in reference to member 'invalidMethod()'}}
+// expected-error@-1 {{contextual member reference to static method 'invalidMethod()' requires 'Self' constraint in the protocol extension}}
 test_combo(.generic(42))
-// expected-error@-1 {{cannot infer contextual base in reference to member 'generic'}}
-test_combo(.generic(S())) // expected-error {{cannot infer contextual base in reference to member 'generic'}}
-test_combo(.generic(G<Int>())) // expected-error {{cannot infer contextual base in reference to member 'generic'}}
-test_combo(.genericWithReqs([S()])) // expected-error {{cannot infer contextual base in reference to member 'genericWithReqs'}}
+// expected-error@-1 {{contextual member reference to static method 'generic' requires 'Self' constraint in the protocol extension}}
+test_combo(.generic(S())) // expected-error {{contextual member reference to static method 'generic' requires 'Self' constraint in the protocol extension}}
+test_combo(.generic(G<Int>())) // expected-error {{contextual member reference to static method 'generic' requires 'Self' constraint in the protocol extension}}
+test_combo(.genericWithReqs([S()])) // expected-error {{contextual member reference to static method 'genericWithReqs' requires 'Self' constraint in the protocol extension}}
 test_combo(.genericWithReqs([42]))
-// expected-error@-1 {{cannot infer contextual base in reference to member 'genericWithReqs'}}
+// expected-error@-1 {{contextual member reference to static method 'genericWithReqs' requires 'Self' constraint in the protocol extension}}
 test_combo(.genericWithReqs(()))
-// expected-error@-1 {{cannot infer contextual base in reference to member 'genericWithReqs'}}
+// expected-error@-1 {{contextual member reference to static method 'genericWithReqs' requires 'Self' constraint in the protocol extension}}
 
 protocol Z {
   associatedtype T = Int
@@ -297,5 +297,5 @@ extension TestWithAssoc where U == Int { // expected-note {{missing same-type re
 
 func test_fixit_with_where_clause() {
   func test_assoc<T: TestWithAssoc>(_: T) {}
-  test_assoc(.intVar) // expected-error {{cannot infer contextual base in reference to member 'intVar'}}
+  test_assoc(.intVar) // expected-error {{contextual member reference to static property 'intVar' requires 'Self' constraint in the protocol extension}}
 }

test/expr/postfix/dot/optional_context_member.swift

@@ -82,7 +82,7 @@ protocol Horse {
 func rideAHorse(_ horse: Horse?) {}
 
 rideAHorse(.palomino)
-// expected-error@-1 {{cannot infer contextual base in reference to member 'palomino'}}
+// expected-error@-1 {{static member 'palomino' cannot be used on protocol metatype 'Horse.Protocol'}}
 
 // FIXME: This should work if the static member is part of a class though
 class Donkey {