Introduce InoutLifetimeDependence feature

Author: meg-gupta

include/swift/Basic/Features.def

@@ -416,6 +416,9 @@ EXPERIMENTAL_FEATURE(StructLetDestructuring, true)
 /// Enable returning non-escapable types from functions.
 EXPERIMENTAL_FEATURE(LifetimeDependence, true)
 
+/// Enable inout lifetime dependence - @lifetime(&arg)
+EXPERIMENTAL_FEATURE(InoutLifetimeDependence, true)
+
 /// Enable the `@_staticExclusiveOnly` attribute.
 EXPERIMENTAL_FEATURE(StaticExclusiveOnly, true)
 

lib/AST/FeatureSet.cpp

@@ -271,6 +271,18 @@ static bool usesFeatureLifetimeDependence(Decl *decl) {
   return false;
 }
 
+static bool usesFeatureInoutLifetimeDependence(Decl *decl) {
+  for (auto attr : decl->getAttrs().getAttributes<LifetimeAttr>()) {
+    for (auto source : attr->getLifetimeEntry()->getSources()) {
+      if (source.getParsedLifetimeDependenceKind() ==
+          ParsedLifetimeDependenceKind::Inout) {
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
 UNINTERESTING_FEATURE(DynamicActorIsolation)
 UNINTERESTING_FEATURE(NonfrozenEnumExhaustivity)
 UNINTERESTING_FEATURE(ClosureIsolation)

stdlib/cmake/modules/SwiftSource.cmake

@@ -631,6 +631,7 @@ function(_compile_swift_files
 
   list(APPEND swift_flags "-enable-experimental-feature" "NonescapableTypes")
   list(APPEND swift_flags "-enable-experimental-feature" "LifetimeDependence")
+  list(APPEND swift_flags "-enable-experimental-feature" "InoutLifetimeDependence")
 
   list(APPEND swift_flags "-enable-upcoming-feature" "MemberImportVisibility")