DefiniteInitialization: Error when noncopyable types are conditionally initialized.

include/swift/AST/DiagnosticsSIL.def

@@ -193,6 +193,11 @@ ERROR(ivar_not_initialized_by_init_accessor,none,
       "property %0 not initialized by init accessor",
       (DeclName))
 
+ERROR(noncopyable_dynamic_lifetime_unsupported,none,
+      "conditional initialization or destruction of noncopyable types is not "
+      "supported; this variable must be consistently in an initialized or "
+      "uninitialized state through every code path", ())
+
 ERROR(self_use_before_fully_init,none,
       "'self' used in %select{method call|property access}1 %0 before "
       "%select{all stored properties are initialized|"

lib/SILOptimizer/Mandatory/DefiniteInitialization.cpp

@@ -1220,6 +1220,11 @@ void LifetimeChecker::doIt() {
     } else if (auto *ABI = dyn_cast<AllocBoxInst>(memAddr)) {
       ABI->setDynamicLifetime();
     }
+    // We don't support noncopyable types with dynamic lifetimes currently.
+    if (TheMemory.getType().isMoveOnly()) {
+      diagnose(Module, TheMemory.getUninitializedValue()->getLoc(),
+               diag::noncopyable_dynamic_lifetime_unsupported);
+    }
   }
   if (!ConditionalDestroys.empty())
     handleConditionalDestroys(ControlVariable);

test/SILOptimizer/definite_init_disallow_move_only_dynamic.swift

@@ -0,0 +1,19 @@
+// RUN: %target-swift-frontend -emit-sil -verify %s
+
+enum E: Error { case err }
+
+struct NC: ~Copyable {
+  let x = 0
+
+  deinit { print("deinit") }
+}
+
+func chk(_ cond: Bool) throws {
+  let y: NC // expected-error{{not supported}} expected-warning{{never used}}
+  if cond {
+    y = NC()
+  }
+  throw E.err
+}
+
+try? chk(true)