[PATCH] D42525: [clangd] Replace Optional in ScopeExitGuard (fix after r322838)

[Ilya Biryukov via Phabricator via cfe-commits]

ilya-biryukov created this revision.
ilya-biryukov added a reviewer: sammccall.
Herald added subscribers: ioeric, jkorous-apple, klimek.

r322838 changed semantics for llvm::Optional that removes the
guarantee of setting the value to empty after move.
This change creates a wrapper around Optional that gives this
guarantee, it is useful for code dealing with empty values that could
be moved.


Repository:
  rCTE Clang Tools Extra

https://reviews.llvm.org/D42525

Files:
  clangd/Function.h


Index: clangd/Function.h
===================================================================
--- clangd/Function.h
+++ clangd/Function.h
@@ -138,6 +138,33 @@
 }
 
 namespace detail {
+/// Optional-like type that sets its value to llvm::None when it was moved
+/// constructed from.
+template <class T> class CleaningOptional {
+public:
+  static_assert(std::is_same<typename std::decay<T>::type, T>::value,
+                "Implementation currently only supports decayed types");
+
+  CleaningOptional(T Value) : Value(std::move(Value)) {}
+
+  CleaningOptional(CleaningOptional &&Other) : Value(std::move(Other.Value)) {
+    Other.Value = llvm::None;
+  }
+
+  CleaningOptional &operator=(CleaningOptional &&Other) {
+    Value = std::move(Other.Value);
+    Other.Value = llvm::None;
+  }
+
+  explicit operator bool() const { return static_cast<bool>(Value); }
+
+  T &operator*() { return *Value; }
+  const T &operator*() const { return *Value; }
+
+private:
+  llvm::Optional<T> Value;
+};
+
 /// Runs provided callback in destructor. Use onScopeExit helper function to
 /// create this object.
 template <class Func> struct ScopeExitGuard {
@@ -159,7 +186,7 @@
   ScopeExitGuard &operator=(ScopeExitGuard &&Other) = default;
 
 private:
-  llvm::Optional<Func> F;
+  CleaningOptional<Func> F;
 };
 } // namespace detail
 


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