[musl] [C23 const 1/2] C23: change bsearch to a macro that respects the const contract

[Jens Gustedt <Jens.Gustedt@inria.fr>]

This adds a macro interface to stdlib that has an additional cast of
the return value to `void const*` for the case that the argument to
the call was also const-qualified. Nothing changes for the function
itself, only the identifier has to be protected with (), such that the
macro does not expand for the function declaration or definition.
---
 include/stdlib.h     | 12 +++++++++++-
 src/include/stdlib.h |  2 ++
 src/stdlib/bsearch.c |  2 +-
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/include/stdlib.h b/include/stdlib.h
index 68ccd467..f5281777 100644
--- a/include/stdlib.h
+++ b/include/stdlib.h
@@ -60,7 +60,17 @@ char *getenv (const char *);
 
 int system (const char *);
 
-void *bsearch (const void *, const void *, size_t, size_t, int (*)(const void *, const void *));
+void * (bsearch) (const void *, const void *, size_t, size_t, int (*)(const void *, const void *));
+#if __STDC_VERSION__ > 201112L
+# define bsearch(K, B, N, S, C)                                         \
+	_Generic(                                                       \
+		/* ensure conversion to a void pointer */               \
+		1 ? (B) : (void*)1,                                     \
+		void const*: (void const*)bsearch((K), (void const*)(B), (N), (S), (C)), \
+		/* volatile qualification of *B is an error for this call */ \
+		default:     bsearch((K), (B), (N), (S), (C))           \
+)
+#endif
 void qsort (void *, size_t, size_t, int (*)(const void *, const void *));
 
 int abs (int);
diff --git a/src/include/stdlib.h b/src/include/stdlib.h
index 812b04de..f0b03df9 100644
--- a/src/include/stdlib.h
+++ b/src/include/stdlib.h
@@ -16,4 +16,6 @@ hidden void *__libc_calloc(size_t, size_t);
 hidden void *__libc_realloc(void *, size_t);
 hidden void __libc_free(void *);
 
+#undef bsearch
+
 #endif
diff --git a/src/stdlib/bsearch.c b/src/stdlib/bsearch.c
index fe050ea3..4f62ea37 100644
--- a/src/stdlib/bsearch.c
+++ b/src/stdlib/bsearch.c
@@ -1,6 +1,6 @@
 #include <stdlib.h>
 
-void *bsearch(const void *key, const void *base, size_t nel, size_t width, int (*cmp)(const void *, const void *))
+void *(bsearch)(const void *key, const void *base, size_t nel, size_t width, int (*cmp)(const void *, const void *))
 {
 	void *try;
 	int sign;
-- 
2.34.1