[libc++] Assert that lengths fit in difference_type

[davidben]

Summary

This can help flag accidentally passing in negative values into the string_view constructor. This aligns with a similar check in absl::string_view.

Fixes https://github.com/llvm/llvm-project/issues/61100

[davidben]

(This is my first time contributing here or using this tool, so let me know if I got something wrong!)

[Mordante]

Thanks for your contribution, a few comments.

libcxx/test/libcxx/strings/string.view/assert.ctor.length.pass.cpp

11–13

Why is this not supported in these language versions? We have enabled string_view in older language versions.

16

Please add the function's synopsis here, best look for other tests for examples.

[davidben]

Updates the test per review.

[davidben]

libcxx/test/libcxx/strings/string.view/assert.ctor.length.pass.cpp

11–13

I just copied that from assert.ctor.pointer.pass.cpp. :-) Removed.

16

Something like this?

[davidben]

libcxx/test/libcxx/strings/string.view/assert.ctor.length.pass.cpp

11–13

Looks like that didn't work because the assertion is only allowed in constexpr starting C++14. I'll make this match the other assert and disable the test in C++11.

[davidben]

Hopefully fix C++11 test failures.

[Mordante]

LGTM, but can you reupload this revision to see that it passes the Windows CI, these errors look odd so I like to have a rerun. It seems the exception issue is unrelated.

Can you provide "your name" <[e-mail]> then we can commit on your behalf when the CI is happy.

libcxx/test/libcxx/strings/string.view/assert.ctor.length.pass.cpp

11–13

Oke sounds good.

16

Yes thanks!

[davidben]

Reuploading

[davidben]

In D145981#4199900, @Mordante wrote:

LGTM, but can you reupload this revision to see that it passes the Windows CI, these errors look odd so I like to have a rerun. It seems the exception issue is unrelated.

Done.

Can you provide "your name" <[e-mail]> then we can commit on your behalf when the CI is happy.

"David Benjamin" <[e-mail]>

[Mordante]

In D145981#4200694, @davidben wrote:

In D145981#4199900, @Mordante wrote:

Can you provide "your name" <[e-mail]> then we can commit on your behalf when the CI is happy.

"David Benjamin" <[e-mail]>

Thanks I just committed this patch on your behalf, feel free to close the bug report.

libcxx/include/string_view

#endif
     _LIBCPP_INLINE_VISIBILITY
     basic_string_view& operator=(const basic_string_view&) _NOEXCEPT = default;
 
     _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
     basic_string_view(const _CharT* __s, size_type __len) _NOEXCEPT
         : __data_(__s), __size_(__len)
     {
 #if _LIBCPP_STD_VER >= 14
+    _LIBCPP_ASSERT(__len <= static_cast<size_type>(numeric_limits<difference_type>::max()), "string_view::string_view(_CharT *, size_t): length does not fit in difference_type");
     _LIBCPP_ASSERT(__len == 0 || __s != nullptr, "string_view::string_view(_CharT *, size_t): received nullptr");
 #endif
     }
 
 #if _LIBCPP_STD_VER >= 20
     template <contiguous_iterator _It, sized_sentinel_for<_It> _End>
       requires (is_same_v<iter_value_t<_It>, _CharT> && !is_convertible_v<_End, size_type>)
     constexpr _LIBCPP_HIDE_FROM_ABI basic_string_view(_It __begin, _End __end)

libcxx/test/libcxx/strings/string.view/assert.ctor.length.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: has-unix-headers
+
+// UNSUPPORTED: c++03, c++11
+// XFAIL: use_system_cxx_lib && target={{.+}}-apple-macosx{{10.9|10.10|10.11|10.12|10.13|10.14|10.15|11.0|12.0}}
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ENABLE_ASSERTIONS=1
+
+// Construct a string_view from an invalid length
+// constexpr basic_string_view( const _CharT* s, size_type len )
+
+#include <string_view>
+
+#include "check_assertion.h"
+
+int main(int, char**) {
+  char c = 0;
+  TEST_LIBCPP_ASSERT_FAILURE(
+      std::string_view(&c, -1), "string_view::string_view(_CharT *, size_t): length does not fit in difference_type");
+  return 0;
+}