[Lldb-commits] [lldb] [lldb] Eliminate SupportFileSP nullptr derefs (PR #168624)

[Jonas Devlieghere via lldb-commits]

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@@ -0,0 +1,96 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLDB_UTILITY_NONNULLSHAREDPTR_H
+#define LLDB_UTILITY_NONNULLSHAREDPTR_H
+
+#include <memory>
+#include <utility>
+
+namespace lldb_private {
+
+/// A non-nullable shared pointer that always holds a valid object.
+///
+/// NonNullSharedPtr is a smart pointer wrapper around std::shared_ptr that
+/// guarantees the pointer is never null. If default-constructed, it creates
+/// a default-constructed instance of T.
+///
+/// This class is used for enforcing invariants at the type level and
+/// eliminating entire classes of null pointer bugs.
+///
+/// @tparam T The type of object to manage. Must be default-constructible.
+template <typename T> class NonNullSharedPtr : private std::shared_ptr<T> {
+  using Base = std::shared_ptr<T>;
+
+public:
+  NonNullSharedPtr() : Base(std::make_shared<T>()) {}
+
+  NonNullSharedPtr(const std::shared_ptr<T> &t)
+      : Base(t ? t : std::make_shared<T>()) {
+    assert(t && "NonNullSharedPtr initialized from NULL shared_ptr");
+  }
+
+  NonNullSharedPtr(std::shared_ptr<T> &&t)
+      : Base(t ? std::move(t) : std::make_shared<T>()) {
+    // Can't assert on t as it's been moved-from.
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JDevlieghere wrote:

Yes, but that could only happen if `make_shared` failed, and then we're in the scenario described in the previous comment.

https://github.com/llvm/llvm-project/pull/168624