https://bugs.gentoo.org/981862
https://github.com/nonstd-lite/span-lite/pull/88
https://github.com/nonstd-lite/span-lite/commit/5ac676ad861
--- a/src/libs/3rdparty/span/span.hpp
+++ b/src/libs/3rdparty/span/span.hpp
@@ -47,4 +47,20 @@
 #endif
 
+#ifndef  span_CONFIG_CONTRACT_LEVEL_ON
+# define span_CONFIG_CONTRACT_LEVEL_ON  1
+#endif
+
+#ifndef  span_CONFIG_CONTRACT_VIOLATION_THROWS
+# define span_CONFIG_CONTRACT_VIOLATION_THROWS  0
+#endif
+
+#ifndef   span_CONFIG_CONTRACT_VIOLATION_TERMINATES
+# if      span_CONFIG_CONTRACT_VIOLATION_THROWS
+#  define span_CONFIG_CONTRACT_VIOLATION_TERMINATES  0
+# else
+#  define span_CONFIG_CONTRACT_VIOLATION_TERMINATES  1
+# endif
+#endif
+
 #ifndef  span_CONFIG_EXTENT_TYPE
 # define span_CONFIG_EXTENT_TYPE  std::size_t
@@ -171,6 +187,6 @@
 #endif
 
-#if    defined( span_CONFIG_CONTRACT_VIOLATION_THROWS     ) && span_CONFIG_CONTRACT_VIOLATION_THROWS && \
-       defined( span_CONFIG_CONTRACT_VIOLATION_TERMINATES ) && span_CONFIG_CONTRACT_VIOLATION_TERMINATES
+#if    span_CONFIG_CONTRACT_VIOLATION_THROWS && \
+       span_CONFIG_CONTRACT_VIOLATION_TERMINATES
 # error Please define none or one of span_CONFIG_CONTRACT_VIOLATION_THROWS and span_CONFIG_CONTRACT_VIOLATION_TERMINATES to 1, but not both.
 #endif
@@ -497,4 +513,8 @@
 #endif
 
+#if span_CONFIG( CONTRACT_VIOLATION_TERMINATES )
+# include <exception>
+#endif
+
 // Contract violation