Disallow stored properties to have uninhabited types

Reword comment

Add tuple test case

Author: Azoy

include/swift/AST/DiagnosticsSema.def

@@ -1367,6 +1367,10 @@ ERROR(pattern_binds_no_variables,none,
       "variables",
       (unsigned))
 
+ERROR(stored_property_no_uninhabited_type,none,
+      "stored property %0 cannot have uninhabited type %1",
+      (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 +2461,15 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
       }
     }
 
+    // Reject variable if it is a stored property with a structurally
+    // uninhabited type
+    if (VD->isInstanceMember() && VD->hasStorage() && 
+        VD->getInterfaceType()->isStructurallyUninhabited()) {
+      TC.diagnose(VD->getLoc(), diag::stored_property_no_uninhabited_type,
+                  VD->getName(), VD->getInterfaceType());
+      VD->markInvalid();
+    }
+
     if (!checkOverrides(VD)) {
       // If a property has an override attribute but does not override
       // anything, complain.

test/decl/var/properties.swift

@@ -1267,3 +1267,12 @@ 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 uninhabited type 'Never'}}
+  
+  var y: (Int, Never, Bool) // expected-error {{stored property 'y' cannot have uninhabited type '(Int, Never, Bool)'}}
+}