Merge pull request #19992 from Azoy/sr-8811

[Sema] Disallow stored properties to have uninhabited types

Author: jrose-apple

include/swift/AST/DiagnosticsSema.def

@@ -1367,6 +1367,15 @@ ERROR(pattern_binds_no_variables,none,
       "variables",
       (unsigned))
 
+ERROR(pattern_no_uninhabited_type,none,
+      "%select{%select{variable|constant}0|stored property}1 %2 cannot have "
+      "enum type %3 with no cases",
+      (bool, bool, Identifier, Type))
+ERROR(pattern_no_uninhabited_tuple_type,none,
+      "%select{%select{variable|constant}0|stored property}1 %2 cannot have "
+      "tuple type %3 containing enum with no cases",
+      (bool, bool, Identifier, Type))
+
 ERROR(nscoding_unstable_mangled_name,none,
       "%select{private|fileprivate|nested|local}0 class %1 has an "
       "unstable name when archiving via 'NSCoding'",

lib/Sema/TypeCheckDecl.cpp

@@ -2461,6 +2461,25 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
       }
     }
 
+    // Reject variable if it is a stored property with an uninhabited type
+    if (VD->hasStorage() && 
+        VD->getInterfaceType()->isStructurallyUninhabited()) {
+      auto uninhabitedTypeDiag = diag::pattern_no_uninhabited_type;
+      
+      if (VD->getInterfaceType()->is<TupleType>()) {
+        uninhabitedTypeDiag = diag::pattern_no_uninhabited_tuple_type;
+      } else {
+        assert((VD->getInterfaceType()->is<EnumType>() || 
+                VD->getInterfaceType()->is<BoundGenericEnumType>()) && 
+          "unknown structurally uninhabited type");
+      }
+          
+      TC.diagnose(VD->getLoc(), uninhabitedTypeDiag, VD->isLet(),
+                  VD->isInstanceMember(), VD->getName(),
+                  VD->getInterfaceType());
+      VD->markInvalid();
+    }
+
     if (!checkOverrides(VD)) {
       // If a property has an override attribute but does not override
       // anything, complain.

test/IRGen/generic_enums.swift

@@ -6,4 +6,5 @@ struct Bar<A1, A2> {
 }
 
 enum Foo<A>{
+  case bar
 }

test/Reflection/Inputs/TypeLowering.swift

@@ -144,8 +144,14 @@ public struct MetatypeStruct {
   public let abstractMetatype: MetadataHolder<BasicStruct.Type, BasicStruct>
 }
 
+// We don't allow stored properties to have uninhabited types now, but make a
+// wrapper over one to continue testing this 
 public enum EmptyEnum {}
 
+public struct EmptyEnumWrapper<T> {
+  public var value: T
+}
+
 public enum NoPayloadEnum {
   case A
   case B
@@ -194,7 +200,7 @@ public enum MultiPayloadGenericDynamic<T, U> {
 }
 
 public struct EnumStruct {
-  public let empty: EmptyEnum
+  public let empty: EmptyEnumWrapper<EmptyEnum>
   public let noPayload: NoPayloadEnum
   public let sillyNoPayload: SillyNoPayloadEnum
   public let singleton: SingletonEnum

test/Reflection/typeref_lowering.swift

@@ -926,7 +926,9 @@
 // CHECK-64: (struct TypeLowering.EnumStruct)
 // CHECK-64-NEXT: (struct size=81 alignment=8 stride=88 num_extra_inhabitants=[[PTR_XI]]
 // CHECK-64-NEXT:   (field name=empty offset=0
-// CHECK-64-NEXT:     (no_payload_enum size=0 alignment=1 stride=1 num_extra_inhabitants=0))
+// CHECK-64-NEXT:     (struct size=0 alignment=1 stride=1 num_extra_inhabitants=0
+// CHECK-64-NEXT:       (field name=value offset=0
+// CHECK-64-NEXT:         (no_payload_enum size=0 alignment=1 stride=1 num_extra_inhabitants=0))))
 // CHECK-64-NEXT:   (field name=noPayload offset=0
 // CHECK-64-NEXT:     (no_payload_enum size=1 alignment=1 stride=1 num_extra_inhabitants=0))
 // CHECK-64-NEXT:   (field name=sillyNoPayload offset=1

test/attr/attr_noreturn.swift

@@ -34,7 +34,8 @@ func noReturn3(_: Int)
 // expected-error@-2 {{'@noreturn' has been removed; functions that never return should have a return type of 'Never' instead}}{{1-11=}}{{53-56=Never}}
 
 // Test that error recovery gives us the 'Never' return type
-let x: Never = noReturn1(0) // No error
+let x: Never = noReturn1(0)
+// expected-error@-1 {{constant 'x' cannot have enum type 'Never' with no cases}}
 
 // @noreturn in function type declarations
 let valueNoReturn: @noreturn () -> ()

test/attr/attr_objc.swift

@@ -941,11 +941,12 @@ class infer_instanceVar1 {
   // expected-note@-2 {{Swift structs cannot be represented in Objective-C}}
 
   var var_PlainEnum: PlainEnum
-// CHECK-LABEL: {{^}}  var var_PlainEnum: PlainEnum
+  // expected-error@-1 {{stored property 'var_PlainEnum' cannot have enum type 'PlainEnum' with no cases}}
 
   @objc var var_PlainEnum_: PlainEnum
   // expected-error@-1 {{property cannot be marked @objc because its type cannot be represented in Objective-C}}
   // expected-note@-2 {{non-'@objc' enums cannot be represented in Objective-C}}
+  // expected-error@-3 {{stored property 'var_PlainEnum_' cannot have enum type 'PlainEnum' with no cases}}
 
   var var_PlainProtocol: PlainProtocol
 // CHECK-LABEL: {{^}}  var var_PlainProtocol: PlainProtocol
@@ -1271,6 +1272,7 @@ class infer_instanceVar1 {
   // expected-error@-1 {{'unowned' may only be applied to class and class-bound protocol types, not 'PlainStruct'}}
   unowned var var_Unowned_bad3: PlainEnum
   // expected-error@-1 {{'unowned' may only be applied to class and class-bound protocol types, not 'PlainEnum'}}
+  // expected-error@-2 {{stored property 'var_Unowned_bad3' cannot have enum type 'PlainEnum' with no cases}}
   unowned var var_Unowned_bad4: String
   // expected-error@-1 {{'unowned' may only be applied to class and class-bound protocol types, not 'String'}}
 // CHECK-NOT: @objc{{.*}}Unowned_fail

test/decl/var/properties.swift

@@ -1267,3 +1267,25 @@ class WeakFixItTest {
   // expected-error @+1 {{'weak' variable should have optional type '(WFI_P1 & WFI_P2)?'}} {{18-18=(}} {{33-33=)?}}
   weak var bar : WFI_P1 & WFI_P2
 }
+
+// SR-8811
+// Stored properties cannot have uninhabited types
+
+struct SR8811 {
+  var x: Never // expected-error {{stored property 'x' cannot have enum type 'Never' with no cases}}
+  
+  var y: (Int, Never, Bool) // expected-error {{stored property 'y' cannot have tuple type '(Int, Never, Bool)' containing enum with no cases}}
+}
+
+let sr8811x: Never // expected-error {{constant 'sr8811x' cannot have enum type 'Never' with no cases}}
+
+var sr8811y: (Int, Never) // expected-error {{variable 'sr8811y' cannot have tuple type '(Int, Never)' containing enum with no cases}}
+
+// Ok
+var sr8811z: Never {
+  return fatalError()
+}
+
+enum SR8811EmptyGenericEnum<A> {}
+
+let sr8811z: SR8811EmptyGenericEnum<Int> // expected-error {{constant 'sr8811z' cannot have enum type 'SR8811EmptyGenericEnum<Int>' with no cases}}

test/expr/expressions.swift

@@ -584,9 +584,9 @@ func conversionTest(_ a: inout Double, b: inout Int) {
   var pi_f3 = float.init(getPi()) // expected-error {{ambiguous use of 'init(_:)'}}
   var pi_f4 = float.init(pi_f)
 
-  var e = Empty(f)
+  var e = Empty(f) // expected-error {{variable 'e' cannot have enum type 'Empty' with no cases}}
   var e2 = Empty(d) // expected-error{{cannot convert value of type 'Double' to expected argument type 'Float'}}
-  var e3 = Empty(Float(d))
+  var e3 = Empty(Float(d)) // expected-error {{variable 'e3' cannot have enum type 'Empty' with no cases}}
 }
 
 struct Rule { // expected-note {{'init(target:dependencies:)' declared here}}