[sourcekit] Merge SourceKit into the Swift repo.

The code goes into its own sub-tree under 'tools' but tests go under 'test',
so that running 'check-swift' will also run all the SourceKit tests.

SourceKit is disabled on non-darwin platforms.

tools/SourceKit/lib/Support/UIDRegistry.cpp

@@ -0,0 +1,106 @@
+#include "SourceKit/Support/UIdent.h"
+#include "SourceKit/Support/Concurrency.h"
+#include "llvm/ADT/StringMap.h"
+#include "llvm/Support/raw_ostream.h"
+#include <mutex>
+#include <vector>
+
+using namespace SourceKit;
+using llvm::StringRef;
+
+namespace {
+class UIDRegistryImpl {
+  typedef llvm::StringMap<void *, llvm::BumpPtrAllocator> HashTableTy;
+  typedef llvm::StringMapEntry<void *> EntryTy;
+  HashTableTy HashTable;
+  WorkQueue Queue{ WorkQueue::Dequeuing::Concurrent, "UIDRegistryImpl" };
+
+public:
+
+  void *get(StringRef Str);
+  static StringRef getName(void *Ptr);
+  static void setTag(void *Ptr, void *Tag);
+  static void *getTag(void *Ptr);
+};
+}
+
+static UIDRegistryImpl *getGlobalRegistry() {
+  static UIDRegistryImpl *GlobalRegistry = 0;
+  if (!GlobalRegistry) {
+    static std::once_flag flag;
+    std::call_once(flag, [](){ GlobalRegistry = new UIDRegistryImpl(); });
+  }
+  return GlobalRegistry;
+}
+
+UIdent::UIdent(llvm::StringRef Str) {
+  Ptr = getGlobalRegistry()->get(Str);
+}
+
+llvm::StringRef UIdent::getName() const {
+  if (isInvalid())
+    return StringRef();
+  return UIDRegistryImpl::getName(Ptr);
+}
+
+const char *UIdent::c_str() const {
+  if (isInvalid())
+    return "";
+  return getName().begin();
+}
+
+void UIdent::setTag(void *Tag) {
+  assert(isValid());
+  UIDRegistryImpl::setTag(Ptr, Tag);
+}
+
+void *UIdent::getTag() const {
+  assert(isValid());
+  return UIDRegistryImpl::getTag(Ptr);
+}
+
+void UIdent::dump() const {
+  print(llvm::errs());
+}
+
+void UIdent::print(llvm::raw_ostream &OS) const {
+  if (isInvalid())
+    OS << "<<INVALID>>";
+  else
+    OS << getName();
+}
+
+void *UIDRegistryImpl::get(StringRef Str) {
+  assert(!Str.empty());
+  assert(Str.find(' ') == StringRef::npos);
+  EntryTy *Ptr = 0;
+  Queue.dispatchSync([&]{
+    HashTableTy::iterator It = HashTable.find(Str);
+    if (It != HashTable.end())
+      Ptr = &(*It);
+  });
+
+  if (Ptr == 0) {
+    Queue.dispatchBarrierSync([&]{
+      EntryTy &Entry = *HashTable.insert(std::make_pair(Str, nullptr)).first;
+      Ptr = &Entry;
+    });
+  }
+
+  return Ptr;
+}
+
+StringRef UIDRegistryImpl::getName(void *Ptr) {
+  EntryTy *Entry = static_cast<EntryTy*>(Ptr);
+  return Entry->getKey();
+}
+
+void UIDRegistryImpl::setTag(void *Ptr, void *Tag) {
+  EntryTy *Entry = static_cast<EntryTy*>(Ptr);
+  Entry->setValue(Tag);
+}
+
+void *UIDRegistryImpl::getTag(void *Ptr) {
+  EntryTy *Entry = static_cast<EntryTy*>(Ptr);
+  return Entry->getValue();
+}