Diagnose @_lifetime on targets that are Escapable

Lifetime dependencies can be attached to ~Escapable types only

Author: meg-gupta

include/swift/AST/DiagnosticsSema.def

@@ -8334,6 +8334,8 @@ ERROR(lifetime_dependence_duplicate_target, none,
       "invalid duplicate target lifetime dependencies on function", ())
 ERROR(lifetime_parameter_requires_inout, none,
       "lifetime-dependent parameter '%0' must be 'inout'", (StringRef))
+ERROR(lifetime_target_requires_nonescapable, none,
+      "invalid lifetime dependence on an Escapable %0", (StringRef))
 
 //------------------------------------------------------------------------------
 // MARK: Lifetime Dependence Requirements

lib/AST/LifetimeDependence.cpp

@@ -227,6 +227,13 @@ static bool isDiagnosedNonEscapable(Type type) {
   return !type->isEscapable();
 }
 
+static bool isDiagnosedEscapable(Type type) {
+  if (type->hasError()) {
+    return false;
+  }
+  return type->isEscapable();
+}
+
 void LifetimeDependenceInfo::getConcatenatedData(
     SmallVectorImpl<bool> &concatenatedData) const {
   auto pushData = [&](IndexSubset *paramIndices) {
@@ -893,8 +900,16 @@ class LifetimeDependenceChecker {
                  diag::lifetime_parameter_requires_inout,
                  targetDescriptor->getString());
       }
+      if (isDiagnosedEscapable(targetDeclAndIndex->first->getTypeInContext())) {
+        diagnose(targetDescriptor->getLoc(),
+                 diag::lifetime_target_requires_nonescapable, "target");
+      }
       targetIndex = targetDeclAndIndex->second;
     } else {
+      if (isDiagnosedEscapable(getResultOrYield())) {
+        diagnose(entry->getLoc(), diag::lifetime_target_requires_nonescapable,
+                 "result");
+      }
       targetIndex = afd->hasImplicitSelfDecl()
         ? afd->getParameters()->size() + 1
         : afd->getParameters()->size();

stdlib/private/StdlibUnittest/StdlibUnittest.swift

@@ -754,7 +754,6 @@ public func expectNil<T>(
   }
 }
 
-@_lifetime(copy value)
 public func expectNil<T: ~Copyable & ~Escapable>(
   _ value: borrowing T?,
   _ message: @autoclosure () -> String = "",

test/Sema/lifetime_attr.swift

@@ -142,3 +142,33 @@ struct Wrapper : ~Escapable {
   }
 }
 
+@_lifetime(inValue) // expected-error{{invalid lifetime dependence on an Escapable result}}
+func getInt(_ inValue: Int) -> Int {
+  return inValue
+}
+
+@_lifetime(_outValue: borrow inValue) // expected-error{{invalid lifetime dependence on an Escapable target}}
+func getInt(_outValue: inout Int, _ inValue: Int)  {
+  _outValue = inValue
+}
+
+@_lifetime(inValue) // expected-error{{invalid lifetime dependence on an Escapable result}}
+func getGeneric<T>(_ inValue: T) -> T {
+  return inValue
+}
+
+@_lifetime(_outValue: borrow inValue) // expected-error{{invalid lifetime dependence on an Escapable target}}
+func getGeneric<T>(_outValue: inout T, _ inValue: T)  {
+  _outValue = inValue
+}
+
+@_lifetime(borrow inValue)
+func getGeneric<T : ~Escapable>(_ inValue: T) -> T {
+  return inValue
+}
+
+@_lifetime(_outValue: borrow inValue)
+func getGeneric<T : ~Escapable>(_outValue: inout T, _ inValue: T)  {
+  _outValue = inValue
+}
+