CXX-2745 Define and use BSONCXX_PRIVATE_INLINE_CXX17 for inline variables (#1468)

Author: eramongodb

src/bsoncxx/include/bsoncxx/v1/detail/compare.hpp

@@ -93,23 +93,22 @@ class strong_ordering {
 #pragma pop_macro("DEFOP")
 
     // nonstd: Swap greater/less values
-    constexpr strong_ordering inverted() const noexcept {
-        return *this < nullptr ? greater : *this > nullptr ? less : *this;
-    }
+    constexpr strong_ordering inverted() const noexcept;
 };
 
-#pragma push_macro("INLINE_VAR")
-#undef INLINE_VAR
-#define INLINE_VAR                             \
-    BSONCXX_PRIVATE_IF_GNU_LIKE([[gnu::weak]]) \
-    BSONCXX_PRIVATE_IF_MSVC(__declspec(selectany))
-
-INLINE_VAR const strong_ordering strong_ordering::less = strong_ordering(strong_ordering::_construct{}, -1);
-INLINE_VAR const strong_ordering strong_ordering::greater = strong_ordering(strong_ordering::_construct{}, 1);
-INLINE_VAR const strong_ordering strong_ordering::equivalent = strong_ordering(strong_ordering::_construct{}, 0);
-INLINE_VAR const strong_ordering strong_ordering::equal = strong_ordering(strong_ordering::_construct{}, 0);
-
-#pragma pop_macro("INLINE_VAR")
+BSONCXX_PRIVATE_INLINE_CXX17 strong_ordering const strong_ordering::less =
+    strong_ordering(strong_ordering::_construct{}, -1);
+BSONCXX_PRIVATE_INLINE_CXX17 strong_ordering const strong_ordering::greater =
+    strong_ordering(strong_ordering::_construct{}, 1);
+BSONCXX_PRIVATE_INLINE_CXX17 strong_ordering const strong_ordering::equivalent =
+    strong_ordering(strong_ordering::_construct{}, 0);
+BSONCXX_PRIVATE_INLINE_CXX17 strong_ordering const strong_ordering::equal =
+    strong_ordering(strong_ordering::_construct{}, 0);
+
+// Define out-of-line to avoid GCC error: ‘bsoncxx::detail::strong_ordering::*’ declared weak after being used
+inline constexpr strong_ordering strong_ordering::inverted() const noexcept {
+    return *this < nullptr ? greater : *this > nullptr ? less : *this;
+}
 
 // Implements a three-way comparison between two objects. That is, in
 // a single operation, determine whether the left operand is less-than, greater-than,

src/bsoncxx/include/bsoncxx/v1/detail/macros.hpp

@@ -107,6 +107,31 @@
 #endif
 // clang-format on
 
+// Use this on variables that can only be inline in C++17 or newer, such as static constexpr data members.
+//
+// GCC does not allow __inline__ (even with __extension__) given -std=c++11 and -pedantic-errors (unconditional
+// compilation error until GCC 12 which added -Wc++17-extensions suppression), but supports [[gnu::weak]] even with
+// constant-evaluation and constant-folding on all currently-supported GCC versions (GCC 4.8.x and newer).
+//
+// Clang: does not allow using [[gnu::weak]] with constexpr, but supports __inline__ as a language extension even with
+// -std=c++11 and -pedantic-errors via diagnostic suppression on all currently-supported Clang versions
+// (-Wc++1z-extensions suppression since Clang 3.9 and -Wc++17-extensions suppression since Clang 5.0).
+//
+// MSVC: supports inline variables since 19.12 (with /std:c++latest), but behavior is broken for static data members
+// (multiple definitions) until 19.20 even when __cpp_inline_variables is defined.
+#if (                                                                                                      \
+    !defined(_MSC_VER) &&                                                                                  \
+    (__cplusplus >= 201703L || (defined(__cpp_inline_variables) && __cpp_inline_variables >= 201606L))) || \
+    (defined(_MSC_VER) && _MSC_VER >= 1920 && defined(_MSVC_LANG) && _MSVC_LANG >= 201703L)
+#define BSONCXX_PRIVATE_INLINE_CXX17 inline
+#else
+#define BSONCXX_PRIVATE_INLINE_CXX17                                                                   \
+    BSONCXX_PRIVATE_IF_GCC([[gnu::weak]])                                                              \
+    BSONCXX_PRIVATE_IF_CLANG(_Pragma("clang diagnostic push") _Pragma(                                 \
+        "clang diagnostic ignored \"-Wc++17-extensions\"") __inline__ _Pragma("clang diagnostic pop")) \
+    BSONCXX_PRIVATE_IF_MSVC(__declspec(selectany))
+#endif
+
 // Disable a warning for a particular compiler.
 //
 // The argument should be of the form:

src/bsoncxx/include/bsoncxx/v1/detail/postlude.hpp

@@ -51,6 +51,7 @@
 #pragma pop_macro("BSONCXX_PRIVATE_IF_GCC")
 #pragma pop_macro("BSONCXX_PRIVATE_IF_GNU_LIKE")
 #pragma pop_macro("BSONCXX_PRIVATE_IF_MSVC")
+#pragma pop_macro("BSONCXX_PRIVATE_INLINE_CXX17")
 #pragma pop_macro("BSONCXX_PRIVATE_PRAGMA_IMPL")
 #pragma pop_macro("BSONCXX_PRIVATE_PRAGMA")
 #pragma pop_macro("BSONCXX_PRIVATE_RETURNS")

src/bsoncxx/include/bsoncxx/v1/detail/prelude.hpp

@@ -76,6 +76,8 @@
 #undef BSONCXX_PRIVATE_IF_GNU_LIKE
 #pragma push_macro("BSONCXX_PRIVATE_IF_MSVC")
 #undef BSONCXX_PRIVATE_IF_MSVC
+#pragma push_macro("BSONCXX_PRIVATE_INLINE_CXX17")
+#undef BSONCXX_PRIVATE_INLINE_CXX17
 #pragma push_macro("BSONCXX_PRIVATE_PRAGMA")
 #undef BSONCXX_PRIVATE_PRAGMA
 #pragma push_macro("BSONCXX_PRIVATE_PRAGMA_IMPL")

src/bsoncxx/include/bsoncxx/v1/oid.hpp

@@ -43,7 +43,7 @@ class oid {
     ///
     /// The number of bytes required to represent an ObjectID.
     ///
-    static constexpr BSONCXX_ABI_EXPORT std::size_t k_oid_length = 12;
+    static constexpr std::size_t k_oid_length = 12;
 
    private:
     std::array<std::uint8_t, k_oid_length> _bytes;
@@ -198,6 +198,8 @@ class oid {
     /* explicit(false) */ oid(for_overwrite_tag) : _bytes{} {}
 };
 
+BSONCXX_PRIVATE_INLINE_CXX17 constexpr std::size_t oid::k_oid_length;
+
 } // namespace v1
 } // namespace bsoncxx
 

src/bsoncxx/include/bsoncxx/v1/types/view.hpp

@@ -49,7 +49,7 @@ struct b_double {
     ///
     /// The type represented by this BSON type value.
     ///
-    static constexpr BSONCXX_ABI_EXPORT id type_id = id::k_double;
+    static constexpr id type_id = id::k_double;
 
     ///
     /// The represented value.
@@ -100,7 +100,7 @@ struct b_string {
     ///
     /// The type represented by this BSON type value.
     ///
-    static constexpr BSONCXX_ABI_EXPORT id type_id = id::k_string;
+    static constexpr id type_id = id::k_string;
 
     ///
     /// The represented value.
@@ -148,7 +148,7 @@ struct b_document {
     ///
     /// The type represented by this BSON type value.
     ///
-    static constexpr BSONCXX_ABI_EXPORT id type_id = id::k_document;
+    static constexpr id type_id = id::k_document;
 
     ///
     /// The represented value.
@@ -200,7 +200,7 @@ struct b_array {
     ///
     /// The type represented by this BSON type value.
     ///
-    static constexpr BSONCXX_ABI_EXPORT id type_id = id::k_array;
+    static constexpr id type_id = id::k_array;
 
     ///
     /// The represented value.
@@ -248,7 +248,7 @@ struct b_binary {
     ///
     /// The type represented by this BSON type value.
     ///
-    static constexpr BSONCXX_ABI_EXPORT id type_id = id::k_binary;
+    static constexpr id type_id = id::k_binary;
 
     ///
     /// The represented value's binary subtype component.
@@ -317,7 +317,7 @@ struct b_undefined {
     ///
     /// The type represented by this BSON type value.
     ///
-    static constexpr BSONCXX_ABI_EXPORT id type_id = id::k_undefined;
+    static constexpr id type_id = id::k_undefined;
 
     ///
     /// Return true.
@@ -343,7 +343,7 @@ struct b_oid {
     ///
     /// The type represented by this BSON type value.
     ///
-    static constexpr BSONCXX_ABI_EXPORT id type_id = id::k_oid;
+    static constexpr id type_id = id::k_oid;
 
     ///
     /// The represented value.
@@ -391,7 +391,7 @@ struct b_bool {
     ///
     /// The type represented by this BSON type value.
     ///
-    static constexpr BSONCXX_ABI_EXPORT id type_id = id::k_bool;
+    static constexpr id type_id = id::k_bool;
 
     ///
     /// The represented value.
@@ -439,7 +439,7 @@ struct b_date {
     ///
     /// The type represented by this BSON type value.
     ///
-    static constexpr BSONCXX_ABI_EXPORT id type_id = id::k_date;
+    static constexpr id type_id = id::k_date;
 
     ///
     /// The represented value (milliseconds relative to the Unix epoch).
@@ -498,7 +498,7 @@ struct b_null {
     ///
     /// The type represented by this BSON type value.
     ///
-    static constexpr BSONCXX_ABI_EXPORT id type_id = id::k_null;
+    static constexpr id type_id = id::k_null;
 
     ///
     /// Return true.
@@ -524,7 +524,7 @@ struct b_regex {
     ///
     /// The type represented by this BSON type value.
     ///
-    static constexpr BSONCXX_ABI_EXPORT id type_id = id::k_regex;
+    static constexpr id type_id = id::k_regex;
 
     ///
     /// The represented value's "pattern" component.
@@ -577,7 +577,7 @@ struct b_dbpointer {
     ///
     /// The type represented by this BSON type value.
     ///
-    static constexpr BSONCXX_ABI_EXPORT id type_id = id::k_dbpointer;
+    static constexpr id type_id = id::k_dbpointer;
 
     ///
     /// The represented value's "$ref" (namespace) component.
@@ -623,7 +623,7 @@ struct b_code {
     ///
     /// The type represented by this BSON type value.
     ///
-    static constexpr BSONCXX_ABI_EXPORT id type_id = id::k_code;
+    static constexpr id type_id = id::k_code;
 
     ///
     /// The represented value.
@@ -673,7 +673,7 @@ struct b_symbol {
     ///
     /// The type represented by this BSON type value.
     ///
-    static constexpr BSONCXX_ABI_EXPORT id type_id = id::k_symbol;
+    static constexpr id type_id = id::k_symbol;
 
     ///
     /// The represented value.
@@ -723,7 +723,7 @@ struct b_codewscope {
     ///
     /// The type represented by this BSON type value.
     ///
-    static constexpr BSONCXX_ABI_EXPORT id type_id = id::k_codewscope;
+    static constexpr id type_id = id::k_codewscope;
 
     ///
     /// The represented value's "$code" component.
@@ -769,7 +769,7 @@ struct b_int32 {
     ///
     /// The type represented by this BSON type value.
     ///
-    static constexpr BSONCXX_ABI_EXPORT id type_id = id::k_int32;
+    static constexpr id type_id = id::k_int32;
 
     ///
     /// The represented value.
@@ -817,7 +817,7 @@ struct b_timestamp {
     ///
     /// The type represented by this BSON type value.
     ///
-    static constexpr BSONCXX_ABI_EXPORT id type_id = id::k_timestamp;
+    static constexpr id type_id = id::k_timestamp;
 
     ///
     /// The represented value's "i" component.
@@ -863,7 +863,7 @@ struct b_int64 {
     ///
     /// The type represented by this BSON type value.
     ///
-    static constexpr BSONCXX_ABI_EXPORT id type_id = id::k_int64;
+    static constexpr id type_id = id::k_int64;
 
     ///
     /// The represented value.
@@ -911,7 +911,7 @@ struct b_decimal128 {
     ///
     /// The type represented by this BSON type value.
     ///
-    static constexpr BSONCXX_ABI_EXPORT id type_id = id::k_decimal128;
+    static constexpr id type_id = id::k_decimal128;
 
     ///
     /// The represented value.
@@ -959,7 +959,7 @@ struct b_maxkey {
     ///
     /// The type represented by this BSON type value.
     ///
-    static constexpr BSONCXX_ABI_EXPORT id type_id = id::k_maxkey;
+    static constexpr id type_id = id::k_maxkey;
 
     ///
     /// Return true.
@@ -985,7 +985,7 @@ struct b_minkey {
     ///
     /// The type represented by this BSON type value.
     ///
-    static constexpr BSONCXX_ABI_EXPORT id type_id = id::k_minkey;
+    static constexpr id type_id = id::k_minkey;
 
     ///
     /// Return true.
@@ -1004,6 +1004,12 @@ struct b_minkey {
 
 // BSONCXX_V1_TYPES_XMACRO: update above.
 
+#pragma push_macro("X")
+#undef X
+#define X(_name, _val) BSONCXX_PRIVATE_INLINE_CXX17 constexpr id b_##_name::type_id;
+BSONCXX_V1_TYPES_XMACRO(X)
+#pragma pop_macro("X")
+
 ///
 /// A non-owning, read-only union of BSON type values.
 ///

src/bsoncxx/include/bsoncxx/v_noabi/bsoncxx/oid.hpp

@@ -43,7 +43,7 @@ class oid {
     v1::oid _oid;
 
    public:
-    static constexpr BSONCXX_ABI_EXPORT std::size_t k_oid_length = v1::oid::k_oid_length;
+    static constexpr std::size_t k_oid_length = v1::oid::k_oid_length;
 
     ///
     /// Constructs an oid and initializes it to a newly generated ObjectId.
@@ -165,6 +165,8 @@ class oid {
     friend BSONCXX_ABI_EXPORT_CDECL(int) oid_compare(oid const& lhs, oid const& rhs);
 };
 
+BSONCXX_PRIVATE_INLINE_CXX17 constexpr std::size_t oid::k_oid_length;
+
 ///
 /// Convert to the @ref bsoncxx::v_noabi equivalent of `v`.
 ///