[CSDiagnostics] Add a diagnostic for superclass requirement failure in opaque return type

Author: xedin

include/swift/AST/DiagnosticsSema.def

@@ -2690,6 +2690,9 @@ ERROR(type_does_not_conform_in_opaque_return,none,
 ERROR(type_is_not_equal_in_opaque_return,none,
       "return type of %kind0 requires the types %1 and %2 be equivalent",
       (const ValueDecl *, Type, Type))
+ERROR(types_not_inherited_in_opaque_return,none,
+      "return type of %kind0 requires that %1 inherit from %2",
+      (const ValueDecl *, Type, Type))
 ERROR(types_not_equal_decl,none,
       "%kind0 requires the types %1 and %2 be equivalent",
       (const ValueDecl *, Type, Type))

lib/Sema/CSDiagnostics.cpp

@@ -457,12 +457,25 @@ bool RequirementFailure::diagnoseAsError() {
     auto *namingDecl = OTD->getNamingDecl();
 
     auto &req = getRequirement();
-    if (req.getKind() == RequirementKind::SameType) {
-      emitDiagnostic(diag::type_is_not_equal_in_opaque_return, namingDecl, lhs,
-                     rhs);
-    } else {
+    switch (req.getKind()) {
+    case RequirementKind::Conformance:
+    case RequirementKind::Layout:
       emitDiagnostic(diag::type_does_not_conform_in_opaque_return, namingDecl,
                      lhs, rhs, rhs->isAnyObject());
+      break;
+
+    case RequirementKind::Superclass:
+      emitDiagnostic(diag::types_not_inherited_in_opaque_return, namingDecl,
+                    lhs, rhs);
+      break;
+
+    case RequirementKind::SameType:
+      emitDiagnostic(diag::type_is_not_equal_in_opaque_return, namingDecl, lhs,
+                     rhs);
+      break;
+
+    case RequirementKind::SameShape:
+      return false;
     }
 
     if (auto *repr = namingDecl->getOpaqueResultTypeRepr()) {

test/type/opaque.swift

@@ -601,6 +601,8 @@ do {
 
   struct S: P1 {}
 
+  class A {}
+
   func test1() -> some P3<Int> { // expected-note {{opaque return type declared here}}
     return G<S>()
     // expected-error@-1 {{return type of local function 'test1()' requires the types 'S' and 'Int' be equivalent}}
@@ -610,4 +612,9 @@ do {
     return G<S>()
     // expected-error@-1 {{return type of local function 'test2()' requires the types 'S' and 'G<S>' be equivalent}}
   }
+
+  func test3() -> some P1 & A { // expected-note {{opaque return type declared here}}
+    S()
+    // expected-error@-1 {{return type of local function 'test3()' requires that 'S' inherit from 'A'}}
+  }
 }