clang 17 compatibility fixes (#4767)

* Copy clang 17 compatibility fixes from PR #4762 to a separate PR.

* Add gcc:13 C++20

* Add silkeh/clang:16-bullseye C++20

Author: rwgk

.github/workflows/ci.yml

@@ -302,6 +302,9 @@ jobs:
           - clang: 15
             std: 20
             container_suffix: "-bullseye"
+          - clang: 16
+            std: 20
+            container_suffix: "-bullseye"
 
     name: "🐍 3 • Clang ${{ matrix.clang }} • C++${{ matrix.std }} • x64"
     container: "silkeh/clang:${{ matrix.clang }}${{ matrix.container_suffix }}"
@@ -465,6 +468,7 @@ jobs:
           - { gcc: 10, std: 17 }
           - { gcc: 11, std: 20 }
           - { gcc: 12, std: 20 }
+          - { gcc: 13, std: 20 }
 
     name: "🐍 3 • GCC ${{ matrix.gcc }} • C++${{ matrix.std }}• x64"
     container: "gcc:${{ matrix.gcc }}"

include/pybind11/cast.h

@@ -1377,7 +1377,15 @@ inline namespace literals {
 /** \rst
     String literal version of `arg`
  \endrst */
-constexpr arg operator"" _a(const char *name, size_t) { return arg(name); }
+constexpr arg
+#if !defined(__clang__) && defined(__GNUC__) && __GNUC__ < 5
+operator"" _a // gcc 4.8.5 insists on having a space (hard error).
+#else
+operator""_a // clang 17 generates a deprecation warning if there is a space.
+#endif
+    (const char *name, size_t) {
+    return arg(name);
+}
 } // namespace literals
 
 PYBIND11_NAMESPACE_BEGIN(detail)

include/pybind11/pytypes.h

@@ -1612,7 +1612,15 @@ inline namespace literals {
 /** \rst
     String literal version of `str`
  \endrst */
-inline str operator"" _s(const char *s, size_t size) { return {s, size}; }
+inline str
+#if !defined(__clang__) && defined(__GNUC__) && __GNUC__ < 5
+operator"" _s // gcc 4.8.5 insists on having a space (hard error).
+#else
+operator""_s // clang 17 generates a deprecation warning if there is a space.
+#endif
+    (const char *s, size_t size) {
+    return {s, size};
+}
 } // namespace literals
 
 /// \addtogroup pytypes