Add support for parsing @lifetime attribute to specify lifetime dependencies on declarations

include/swift/AST/Attr.h

@@ -24,6 +24,7 @@
 #include "swift/AST/DeclNameLoc.h"
 #include "swift/AST/Identifier.h"
 #include "swift/AST/KnownProtocols.h"
+#include "swift/AST/LifetimeDependence.h"
 #include "swift/AST/MacroDeclaration.h"
 #include "swift/AST/Ownership.h"
 #include "swift/AST/PlatformKind.h"
@@ -2627,6 +2628,27 @@ public:
   }
 };
 
+class LifetimeAttr final
+    : public DeclAttribute,
+      private llvm::TrailingObjects<LifetimeAttr, LifetimeDependenceSpecifier> {
+
+  friend TrailingObjects;
+
+  unsigned NumEntries = 0;
+
+  explicit LifetimeAttr(SourceLoc atLoc, SourceRange baseRange, bool implicit,
+                        ArrayRef<LifetimeDependenceSpecifier> entries);
+
+public:
+  static LifetimeAttr *create(ASTContext &context, SourceLoc atLoc,
+                              SourceRange baseRange, bool implicit,
+                              ArrayRef<LifetimeDependenceSpecifier> entries);
+
+  static bool classof(const DeclAttribute *DA) {
+    return DA->getKind() == DeclAttrKind::Lifetime;
+  }
+};
+
 /// Predicate used to filter MatchingAttributeRange.
 template <typename ATTR, bool AllowInvalid> struct ToAttributeKind {
   ToAttributeKind() {}

include/swift/AST/DeclAttr.def

@@ -506,6 +506,10 @@ SIMPLE_DECL_ATTR(unsafe, Unsafe,
   ABIStableToAdd | ABIStableToRemove | APIBreakingToAdd | APIStableToRemove,
   160)
 
+DECL_ATTR(lifetime, Lifetime,
+  OnAccessor | OnConstructor | OnFunc | OnSubscript | LongAttribute | ABIBreakingToAdd | ABIStableToRemove | APIBreakingToAdd | APIStableToRemove,
+  161)
+
 LAST_DECL_ATTR(Unsafe)
 
 #undef DECL_ATTR_ALIAS

include/swift/AST/LifetimeDependence.h

@@ -74,7 +74,9 @@ private:
 
 public:
   static LifetimeDependenceSpecifier getNamedLifetimeDependenceSpecifier(
-      SourceLoc loc, ParsedLifetimeDependenceKind kind, Identifier name) {
+      SourceLoc loc, Identifier name,
+      ParsedLifetimeDependenceKind kind =
+          ParsedLifetimeDependenceKind::Default) {
     return {loc, SpecifierKind::Named, kind, name};
   }
 
@@ -84,13 +86,15 @@ public:
   }
 
   static LifetimeDependenceSpecifier getOrderedLifetimeDependenceSpecifier(
-      SourceLoc loc, ParsedLifetimeDependenceKind kind, unsigned index) {
+      SourceLoc loc, unsigned index,
+      ParsedLifetimeDependenceKind kind =
+          ParsedLifetimeDependenceKind::Default) {
     return {loc, SpecifierKind::Ordered, kind, index};
   }
 
-  static LifetimeDependenceSpecifier
-  getSelfLifetimeDependenceSpecifier(SourceLoc loc,
-                                     ParsedLifetimeDependenceKind kind) {
+  static LifetimeDependenceSpecifier getSelfLifetimeDependenceSpecifier(
+      SourceLoc loc, ParsedLifetimeDependenceKind kind =
+                         ParsedLifetimeDependenceKind::Default) {
     return {loc, SpecifierKind::Self, kind, {}};
   }