[clang-tools-extra] [clang-tidy] introduce a unused local non trival variable check (PR #76101)

[Tyler Rockwood via cfe-commits]

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@@ -0,0 +1,79 @@
+// RUN: %check_clang_tidy %s bugprone-unused-local-non-trivial-variable %t -- \
+// RUN:       -config="{CheckOptions: {bugprone-unused-local-non-trivial-variable.IncludeTypeRegex: '::async::Future'}}"
+
+
+namespace async {
+template <typename T>
+class Ptr {
+  public:
+  explicit Ptr(T Arg) : Underlying(new T(Arg)) {}
+  T& operator->() {
+    return Underlying;
+  }
+  ~Ptr() {
+    delete Underlying;
+  }
+  private:
+    T* Underlying;
+};
+
+template<typename T>
+class Future {
+public:    
+    T get() {
+        return Pending;
+    }
+    ~Future();
+private:
+    T Pending;
+};
+
+
+} // namespace async
+
+// Warning is still emitted if there are type aliases.
+namespace a {
+template<typename T>
+using Future = async::Future<T>;
+} // namespace a
+
+void releaseUnits();
+struct Units {
+  ~Units() {
+    releaseUnits();
+  }
+};
+a::Future<Units> acquireUnits();
+
+template<typename T>
+T qux(T Generic) {
+    async::Future<Units> PendingA = acquireUnits();
+    auto PendingB = acquireUnits();
+    // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: unused local variable 'PendingB' of type 'a::Future<Units>' (aka 'Future<Units>') [bugprone-unused-local-non-trivial-variable]
+    async::Future<Units> MustBeUsed;
+    // CHECK-MESSAGES: :[[@LINE-1]]:26: warning: unused local variable 'MustBeUsed' of type 'async::Future<Units>' [bugprone-unused-local-non-trivial-variable]
+    PendingA.get();
+    return Generic;
+}
+
+async::Future<int> Global;
+
+int bar(int Num) {
+    a::Future<Units> PendingA = acquireUnits();
+    a::Future<Units> PendingB = acquireUnits(); // not used at all, unused variable not fired because of destructor side effect
+    // CHECK-MESSAGES: :[[@LINE-1]]:22: warning: unused local variable 'PendingB' of type 'a::Future<Units>' (aka 'Future<Units>') [bugprone-unused-local-non-trivial-variable]
+    auto Num2 = PendingA.get();
+    auto Num3 = qux(Num);
+    async::Ptr<a::Future<Units>> Shared = async::Ptr<a::Future<Units>>(acquireUnits());
+    static auto UnusedStatic = async::Future<Units>();
+    thread_local async::Future<Units> UnusedThreadLocal;
+    auto Captured = acquireUnits();
+    Num3 += [Captured]() {
+      return 1;
+    }();
+    a::Future<Units> Referenced = acquireUnits();
+    a::Future<Units>* Pointer = &Referenced;
+    a::Future<Units>& Reference = Referenced;
+    const a::Future<Units>& ConstReference = Referenced;
+    return Num * Num3;
+}
----------------
rockwotj wrote:

Done.

https://github.com/llvm/llvm-project/pull/76101