[clang-tools-extra] [clang-tidy] Unsafe CRTP check (PR #82403)

[Piotr Zegar via cfe-commits]

================
@@ -0,0 +1,232 @@
+// RUN: %check_clang_tidy %s bugprone-unsafe-crtp %t
+
+namespace class_implicit_ctor {
+template <typename T>
+class CRTP {};
+// CHECK-MESSAGES: :[[@LINE-1]]:7: warning: the implicit default constructor of the CRTP is publicly accessible [bugprone-unsafe-crtp]
+// CHECK-MESSAGES: :[[@LINE-2]]:7: note: consider making it private
+// CHECK-FIXES: CRTP() = default;
+
+class A : CRTP<A> {};
+} // namespace class_implicit_ctor
+
+namespace class_uncostructible {
+template <typename T>
+class CRTP {
+// CHECK-MESSAGES: :[[@LINE-1]]:7: warning: the CRTP cannot be constructed from the derived class [bugprone-unsafe-crtp]
+// CHECK-MESSAGES: :[[@LINE-2]]:7: note: consider declaring the derived class as friend
+// CHECK-FIXES: friend T;
+    CRTP() = default;
+};
+
+class A : CRTP<A> {};
+} // namespace class_uncostructible 
+
+namespace class_public_default_ctor {
+template <typename T>
+class CRTP {
+public:
+    CRTP() = default;
+    // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: public contructor allows the CRTP to be constructed as a regular template class [bugprone-unsafe-crtp]
+    // CHECK-MESSAGES: :[[@LINE-2]]:5: note: consider making it private
+    // CHECK-FIXES: private:{{[[:space:]]*}}CRTP() = default;{{[[:space:]]*}}public:
+};
+
+class A : CRTP<A> {};
+} // namespace class_public_default_ctor
+
+namespace class_public_user_provided_ctor {
+template <typename T>
+class CRTP {
+public:
+    CRTP(int) {}
+    // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: public contructor allows the CRTP to be constructed as a regular template class [bugprone-unsafe-crtp]
+    // CHECK-MESSAGES: :[[@LINE-2]]:5: note: consider making it private
+    // CHECK-FIXES: private:{{[[:space:]]*}}CRTP(int) {}{{[[:space:]]*}}public:
+};
+
+class A : CRTP<A> {};
+} // namespace class_public_user_provided_ctor
+
+namespace class_public_multiple_user_provided_ctors {
+template <typename T>
+class CRTP {
+public:
+    CRTP(int) {}
+    // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: public contructor allows the CRTP to be constructed as a regular template class [bugprone-unsafe-crtp]
+    // CHECK-MESSAGES: :[[@LINE-2]]:5: note: consider making it private
+    // CHECK-FIXES: private:{{[[:space:]]*}}CRTP(int) {}{{[[:space:]]*}}public:
+    CRTP(float) {}
+    // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: public contructor allows the CRTP to be constructed as a regular template class [bugprone-unsafe-crtp]
+    // CHECK-MESSAGES: :[[@LINE-2]]:5: note: consider making it private
+    // CHECK-FIXES: private:{{[[:space:]]*}}CRTP(float) {}{{[[:space:]]*}}public:
+};
+
+class A : CRTP<A> {};
+} // namespace class_public_multiple_user_provided_ctors
+
+namespace class_protected_ctors {
+template <typename T>
+class CRTP {
+protected:
+    CRTP(int) {}
+    // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: protected contructor allows the CRTP to be inherited from as a regular template class [bugprone-unsafe-crtp]
+    // CHECK-MESSAGES: :[[@LINE-2]]:5: note: consider making it private
+    // CHECK-FIXES: private:{{[[:space:]]*}}CRTP(int) {}{{[[:space:]]*}}protected:
+    CRTP() = default;
+    // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: protected contructor allows the CRTP to be inherited from as a regular template class [bugprone-unsafe-crtp]
+    // CHECK-MESSAGES: :[[@LINE-2]]:5: note: consider making it private
+    // CHECK-FIXES: private:{{[[:space:]]*}}CRTP() = default;{{[[:space:]]*}}protected:
+    CRTP(float) {}
+    // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: protected contructor allows the CRTP to be inherited from as a regular template class [bugprone-unsafe-crtp]
+    // CHECK-MESSAGES: :[[@LINE-2]]:5: note: consider making it private
+    // CHECK-FIXES: private:{{[[:space:]]*}}CRTP(float) {}{{[[:space:]]*}}protected:
+};
+
+class A : CRTP<A> {};
+} // namespace class_protected_ctors
+
+namespace struct_implicit_ctor {
+template <typename T>
+struct CRTP {};
+// CHECK-MESSAGES: :[[@LINE-1]]:8: warning: the implicit default constructor of the CRTP is publicly accessible [bugprone-unsafe-crtp]
+// CHECK-MESSAGES: :[[@LINE-2]]:8: note: consider making it private
+// CHECK-FIXES: private:{{[[:space:]]*}}CRTP() = default;{{[[:space:]]*}}public:
+
+class A : CRTP<A> {};
+} // namespace struct_implicit_ctor
+
+namespace struct_default_ctor {
+template <typename T>
+struct CRTP {
+    CRTP() = default;
+    // CHECK-MESSAGES: :[[@LINE-1]]:5: warning: public contructor allows the CRTP to be constructed as a regular template class [bugprone-unsafe-crtp]
+    // CHECK-MESSAGES: :[[@LINE-2]]:5: note: consider making it private
+    // CHECK-FIXES: private:{{[[:space:]]*}}CRTP() = default;{{[[:space:]]*}}public:
+};
+
+class A : CRTP<A> {};
+} // namespace struct_default_ctor
+
+namespace same_class_multiple_crtps {
+template <typename T>
+struct CRTP {};
+// CHECK-MESSAGES: :[[@LINE-1]]:8: warning: the implicit default constructor of the CRTP is publicly accessible [bugprone-unsafe-crtp]
+// CHECK-MESSAGES: :[[@LINE-2]]:8: note: consider making it private
+// CHECK-FIXES: private:{{[[:space:]]*}}CRTP() = default;{{[[:space:]]*}}public:
+
+template <typename T>
+struct CRTP2 {};
+// CHECK-MESSAGES: :[[@LINE-1]]:8: warning: the implicit default constructor of the CRTP is publicly accessible [bugprone-unsafe-crtp]
+// CHECK-MESSAGES: :[[@LINE-2]]:8: note: consider making it private
+// CHECK-FIXES: private:{{[[:space:]]*}}CRTP2() = default;{{[[:space:]]*}}public:
+
+class A : CRTP<A>, CRTP2<A> {};
+} // namespace same_class_multiple_crtps
+
+namespace same_crtp_multiple_classes {
+template <typename T>
+class CRTP {
+// CHECK-MESSAGES: :[[@LINE-1]]:7: warning: the CRTP cannot be constructed from the derived class [bugprone-unsafe-crtp]
+// CHECK-MESSAGES: :[[@LINE-2]]:7: note: consider declaring the derived class as friend
+// CHECK-FIXES: friend T;
+    CRTP() = default;
+};
+
+class A : CRTP<A> {};
+class B : CRTP<B> {};
+} // namespace same_crtp_multiple_classes
+
+namespace crtp_template {
+template <typename T, typename U>
+class CRTP {
+// CHECK-MESSAGES: :[[@LINE-1]]:7: warning: the CRTP cannot be constructed from the derived class [bugprone-unsafe-crtp]
+// CHECK-MESSAGES: :[[@LINE-2]]:7: note: consider declaring the derived class as friend
+// CHECK-FIXES: friend U;
+    CRTP() = default;
+};
+
+class A : CRTP<int, A> {};
+} // namespace crtp_template
+
+namespace crtp_template2 {
+template <typename T, typename U>
+class CRTP {
+// CHECK-MESSAGES: :[[@LINE-1]]:7: warning: the CRTP cannot be constructed from the derived class [bugprone-unsafe-crtp]
+// CHECK-MESSAGES: :[[@LINE-2]]:7: note: consider declaring the derived class as friend
+// CHECK-FIXES: friend T;
+    CRTP() = default;
+};
+
+class A : CRTP<A, A> {};
+} // namespace crtp_template2
+
+namespace template_derived {
+template <typename T>
+class CRTP {};
+// CHECK-MESSAGES: :[[@LINE-1]]:7: warning: the implicit default constructor of the CRTP is publicly accessible [bugprone-unsafe-crtp]
+// CHECK-MESSAGES: :[[@LINE-2]]:7: note: consider making it private
+// CHECK-FIXES: CRTP() = default;
+
+template<typename T>
+class A : CRTP<A<T>> {};
+
+// FIXME: Ideally the warning should be triggered without instantiation.
+void foo() {
+  A<int> A;
+  (void) A;
+}
+} // namespace template_derived
+
+namespace template_derived_explicit_specialization {
+template <typename T>
+class CRTP {};
+// CHECK-MESSAGES: :[[@LINE-1]]:7: warning: the implicit default constructor of the CRTP is publicly accessible [bugprone-unsafe-crtp]
+// CHECK-MESSAGES: :[[@LINE-2]]:7: note: consider making it private
+// CHECK-FIXES: CRTP() = default;
+
+template<typename T>
+class A : CRTP<A<T>> {};
+
+template<>
+class A<int> : CRTP<A<int>> {};
+} // namespace template_derived_explicit_specialization
+
+namespace explicit_derived_friend {
+class A;
+
+template <typename T>
+class CRTP {
+    CRTP() = default;
+    friend A;
+};
+
+class A : CRTP<A> {};
+} // namespace explicit_derived_friend
+
+namespace explicit_derived_friend_multiple {
+class A;
+
+template <typename T>
+class CRTP {
+// CHECK-MESSAGES: :[[@LINE-1]]:7: warning: the CRTP cannot be constructed from the derived class [bugprone-unsafe-crtp]
+// CHECK-MESSAGES: :[[@LINE-2]]:7: note: consider declaring the derived class as friend
+// CHECK-FIXES: friend T;
+    CRTP() = default;
+    friend A;
+};
+
+class A : CRTP<A> {};
+class B : CRTP<B> {};
+} // namespace explicit_derived_friend_multiple
+
+namespace no_warning {
+template <typename T>
+class CRTP
+{
+    CRTP() = default;
+    friend T;
+};
+
+class A : CRTP<A> {};
+} // namespace no_warning
----------------
PiotrZSL wrote:

It shouldn't, just exclude such classes.

https://github.com/llvm/llvm-project/pull/82403