SwiftRemoteMirror: Add convenience API for demangling

rdar://problem/26060031

Author: bitjammer

include/swift/SwiftRemoteMirror/SwiftRemoteMirror.h

@@ -23,6 +23,8 @@
 #include "MemoryReaderInterface.h"
 #include "SwiftRemoteMirrorTypes.h"
 
+#include <stdlib.h>
+
 /// Major version changes when there are ABI or source incompatible changes.
 #define SWIFT_REFLECTION_VERSION_MAJOR 3
 
@@ -159,6 +161,18 @@ void swift_reflection_dumpInfoForMetadata(SwiftReflectionContextRef ContextRef,
 void swift_reflection_dumpInfoForInstance(SwiftReflectionContextRef ContextRef,
                                           uintptr_t Object);
 
+/// Demangle a type name.
+///
+/// Copies at most `MaxLength` bytes from the demangled name string into
+/// `OutDemangledName`.
+///
+/// Returns the length of the demangled string this function tried to copy
+/// into `OutDemangledName`.
+size_t swift_reflection_demangle(const char *MangledName,
+                                 size_t Length,
+                                 char *OutDemangledName,
+                                 size_t MaxLength);
+
 #ifdef __cplusplus
 } // extern "C"
 #endif

stdlib/public/SwiftRemoteMirror/SwiftRemoteMirror.cpp

@@ -287,3 +287,14 @@ void swift_reflection_dumpInfoForInstance(SwiftReflectionContextRef ContextRef,
     TI->dump();
   }
 }
+
+size_t swift_reflection_demangle(const char *MangledName, size_t Length,
+                                 char *OutDemangledName, size_t MaxLength) {
+  if (MangledName == NULL || Length == 0)
+    return 0;
+
+  std::string Mangled(MangledName, Length);
+  auto Demangled = Demangle::demangleTypeAsString(Mangled);
+  strncpy(OutDemangledName, Demangled.c_str(), MaxLength);
+  return Demangled.size();
+}