KeyPaths: Put an override shim on swift_getKeyPath.

This will let future compilers that support new key path features backward-deploy logic for interpreting new kinds of key path patterns.

Author: jckarter

include/swift/Runtime/Metadata.h

@@ -766,6 +766,10 @@ void verifyMangledNameRoundtrip(const Metadata *metadata);
 SWIFT_CC(swift) SWIFT_RUNTIME_STDLIB_API
 const TypeContextDescriptor *swift_getTypeContextDescriptor(const Metadata *type);
 
+// Defined in KeyPath.swift in the standard library.
+SWIFT_RUNTIME_EXPORT
+const HeapObject *swift_getKeyPath(const void *pattern, const void *arguments);
+
 } // end namespace swift
 
 #endif // SWIFT_RUNTIME_METADATA_H

stdlib/public/core/KeyPath.swift

@@ -2069,7 +2069,10 @@ internal var keyPathObjectHeaderSize: Int {
 }
 
 // Runtime entry point to instantiate a key path object.
-@_cdecl("swift_getKeyPath")
+// Note that this has a compatibility override shim in the runtime so that
+// future compilers can backward-deploy support for instantiating new key path
+// pattern features.
+@_cdecl("swift_getKeyPathImpl")
 public func _swift_getKeyPath(pattern: UnsafeMutableRawPointer,
                               arguments: UnsafeRawPointer)
     -> UnsafeRawPointer {

stdlib/public/runtime/CompatibilityOverride.def

@@ -17,16 +17,21 @@
 
 /// #define OVERRIDE(name, ret, attrs, namespace, typedArgs, namedArgs)
 ///   Provides information about an overridable function.
-///   - name is the name of the function, without any leading swift_ or namespace.
+///   - name is the name of the function, without any leading swift_ or
+///     namespace.
 ///   - ret is the return type of the function.
 ///   - attrs is the attributes, if any, applied to the function definition.
-///   - namespace is the namespace, if any, the function is in, including a trailing ::
-///   - typedArgs is the argument list, including types, surrounded by parentheses
-///   - namedArgs is the list of argument names, with no types, surrounded by parentheses
+///   - namespace is the namespace, if any, the function is in, including a
+///     trailing ::
+///   - typedArgs is the argument list, including types, surrounded by
+///     parentheses
+///   - namedArgs is the list of argument names, with no types, surrounded by
+///     parentheses
 ///
-/// The entries are organized by group. A user may define OVERRIDE to get all entries,
-/// or define one or more of OVERRIDE_METADATALOOKUP, OVERRIDE_CASTING, OVERRIDE_OBJC,
-/// OVERRIDE_FOREIGN, or OVERRIDE_PROTOCOLCONFORMANCE to get only those entries.
+/// The entries are organized by group. A user may define OVERRIDE to get all
+/// entries, or define one or more of OVERRIDE_METADATALOOKUP, OVERRIDE_CASTING,
+/// OVERRIDE_OBJC, OVERRIDE_FOREIGN, OVERRIDE_PROTOCOLCONFORMANCE,
+/// and OVERRIDE_KEYPATH to get only those entries.
 
 // NOTE: this file is used to build the definition of OverrideSection in
 // CompatibilityOverride.cpp, which is part of the ABI. Do not move or remove entries
@@ -38,6 +43,7 @@
 #  define OVERRIDE_OBJC OVERRIDE
 #  define OVERRIDE_FOREIGN OVERRIDE
 #  define OVERRIDE_PROTOCOLCONFORMANCE OVERRIDE
+#  define OVERRIDE_KEYPATH OVERRIDE
 #else
 #  ifndef OVERRIDE_METADATALOOKUP
 #    define OVERRIDE_METADATALOOKUP(...)
@@ -54,6 +60,9 @@
 #  ifndef OVERRIDE_PROTOCOLCONFORMANCE
 #    define OVERRIDE_PROTOCOLCONFORMANCE(...)
 #  endif
+#  ifndef OVERRIDE_KEYPATH
+#    define OVERRIDE_KEYPATH(...)
+#  endif
 #endif
 
 OVERRIDE_METADATALOOKUP(getTypeByMangledName, const Metadata *,
@@ -127,6 +136,10 @@ OVERRIDE_PROTOCOLCONFORMANCE(conformsToProtocol, const WitnessTable *, , swift::
                               const ProtocolDescriptor *protocol),
                              (type, protocol))
 
+OVERRIDE_KEYPATH(getKeyPath, const HeapObject *, , swift::,
+                 (const void *pattern, const void *arguments),
+                 (pattern, arguments))
+
 #if SWIFT_OBJC_INTEROP
 
 OVERRIDE_OBJC(dynamicCastObjCClass, const void *, , swift::,
@@ -169,3 +182,4 @@ OVERRIDE_FOREIGN(dynamicCastForeignClassUnconditional, const void *, , swift::,
 #undef OVERRIDE_OBJC
 #undef OVERRIDE_FOREIGN
 #undef OVERRIDE_PROTOCOLCONFORMANCE
+#undef OVERRIDE_KEYPATH

stdlib/public/runtime/Metadata.cpp

@@ -46,6 +46,7 @@
 #endif
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/Hashing.h"
+#include "CompatibilityOverride.h"
 #include "ErrorObject.h"
 #include "ExistentialMetadataImpl.h"
 #include "swift/Runtime/Debug.h"
@@ -4239,3 +4240,14 @@ void swift::verifyMangledNameRoundtrip(const Metadata *metadata) {
 const TypeContextDescriptor *swift::swift_getTypeContextDescriptor(const Metadata *type) {
     return type->getTypeContextDescriptor();
 }
+
+// Emit compatibility override shims for keypath runtime functionality. The
+// implementation of these functions is in the standard library in
+// KeyPath.swift.
+
+SWIFT_RUNTIME_STDLIB_SPI
+const HeapObject *swift_getKeyPathImpl(const void *pattern,
+                                       const void *arguments);
+
+#define OVERRIDE_KEYPATH COMPATIBILITY_OVERRIDE
+#include "CompatibilityOverride.def"