[libc++][ranges] Reject non-class types in ranges::to

[Yuzhiy05]

This patch adds static_assert using is_class_v and is_union_v to reject no-class type template parameters.

Fixes #132133

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@llvm/pr-subscribers-libcxx

Author: Yuzhiy (Yuzhiy05)

Changes

add static_assert using is_class_v and is_union_v to reject no-class type template parameter and test for this
Close #132133
@frederick-vs-ja
Sorry for the delayed response on the previous PR —I spent some time learning how to build libc++ and run its tests. I’ve written a test referencing the to.static_assert.verify.cpp file in the same directory, but it fails to compile. I have two questions:

Why does a test expecting a failed static assertion pass in lit?
What might be wrong with my test implementation?

---

Full diff: https://github.com/llvm/llvm-project/pull/135802.diff

2 Files Affected:

• (modified) libcxx/include/__ranges/to.h (+4-2)
• (added) libcxx/test/libcxx/ranges/range.utility/range.utility.conv/to.verfiy.cpp (+17)

diff --git a/libcxx/include/__ranges/to.h b/libcxx/include/__ranges/to.h
index c937b0656de87..2adae5e0edbfb 100644
--- a/libcxx/include/__ranges/to.h
+++ b/libcxx/include/__ranges/to.h
@@ -28,6 +28,8 @@
 #include <__type_traits/add_pointer.h>
 #include <__type_traits/is_const.h>
 #include <__type_traits/is_volatile.h>
+#include <__type_traits/is_class.h>
+#include <__type_traits/is_union.h>
 #include <__type_traits/type_identity.h>
 #include <__utility/declval.h>
 #include <__utility/forward.h>
@@ -81,7 +83,7 @@ template <class _Container, input_range _Range, class... _Args>
   static_assert(!is_const_v<_Container>, "The target container cannot be const-qualified, please remove the const");
   static_assert(
       !is_volatile_v<_Container>, "The target container cannot be volatile-qualified, please remove the volatile");
-
+  static_assert(is_class_v<_Container>||is_union_v<_Container>, "The target must be a class type");
   // First see if the non-recursive case applies -- the conversion target is either:
   // - a range with a convertible value type;
   // - a non-range type which might support being created from the input argument(s) (e.g. an `optional`).
@@ -208,7 +210,7 @@ template <class _Container, class... _Args>
   static_assert(!is_const_v<_Container>, "The target container cannot be const-qualified, please remove the const");
   static_assert(
       !is_volatile_v<_Container>, "The target container cannot be volatile-qualified, please remove the volatile");
-
+  static_assert(is_class_v<_Container>||is_union_v<_Container>, "The target must be a class type");
   auto __to_func = []<input_range _Range, class... _Tail>(_Range&& __range, _Tail&&... __tail) static
     requires requires { //
       /**/ ranges::to<_Container>(std::forward<_Range>(__range), std::forward<_Tail>(__tail)...);
diff --git a/libcxx/test/libcxx/ranges/range.utility/range.utility.conv/to.verfiy.cpp b/libcxx/test/libcxx/ranges/range.utility/range.utility.conv/to.verfiy.cpp
new file mode 100644
index 0000000000000..9ff01b10a759d
--- /dev/null
+++ b/libcxx/test/libcxx/ranges/range.utility/range.utility.conv/to.verfiy.cpp
@@ -0,0 +1,17 @@
+#include <ranges>
+
+
+
+void test(){
+    struct R {
+        int* begin() const{reurn nullptr;};
+        int* end() const{return nullptr;};
+    
+        operator int() const { return 0; }
+      };
+      (void)std::ranges::to<int>(R{});
+        //expected-error-re@*:* {{static assertion failed{{.*}}The target must be a class type}}
+      (void)(R{} | std::ranges::to<int>());
+        //expected-error-re@*:* {{static assertion failed{{.*}}The target must be a class type}}
+    
+}
\ No newline at end of file

[frederick-vs-ja]

I’ve written a test referencing the to.static_assert.verify.cpp file in the same directory, but it fails to compile.

Compilation failure is exactly expected. Just go ahead.

Why does a test expecting a failed static assertion pass in lit?

We want to verify that static_assert (usually corresponding to Mandates in the standard wording) works.

What might be wrong with my test implementation?

See other review comments. Also, perhaps we want to verify that const types, volatile types, other arithmetic types, pointer types, pointer-to-member types, enumeration types, cv void, reference types, and function types are also rejected.

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[Yuzhiy05]

I’ve written a test referencing the to.static_assert.verify.cpp file in the same directory, but it fails to compile.

Compilation failure is exactly expected. Just go ahead.

sorry,my previous statement was unclear， I meant to say is that in my LLVM LIT tests, the results show failures (test failures), even expect compilation errors.but the to.static_assert.verify.cpp is passed and this expect failures

[Yuzhiy05]

What might be wrong with my test implementation?

See other review comments. Also, perhaps we want to verify that const types, volatile types, other arithmetic types, pointer types, pointer-to-member types, enumeration types, cv void, reference types, and function types are also rejected.

I understand now. but the tests for const and volatile type qualifications are in a separate test file (to.static_assert.verify.cpp). perhaps I should consolidate these tests into a unified file ?

[frederick-vs-ja]

What might be wrong with my test implementation?

See other review comments. Also, perhaps we want to verify that const types, volatile types, other arithmetic types, pointer types, pointer-to-member types, enumeration types, cv void, reference types, and function types are also rejected.

I understand now. but the tests for const and volatile type qualifications are in a separate test file (to.static_assert.verify.cpp). perhaps I should consolidate these tests into a unified file ?

I think adding to the existing to.static_assert.verify.cpp would be better.

[frederick-vs-ja]

LGTM. Although I'd wait for @philnik777.

[philnik777]

LGTM with formatting change.

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