split out NULL from stddef header

include/stddef.h

@@ -14,8 +14,7 @@
 #endif // _WCHAR_T
 
 #include <bits/size-t.h>
-
-#define NULL 0
+#include <bits/null.h>
 
 #ifndef __PTRDIFF_TYPE__
 #define __PTRDIFF_TYPE__ long int

src/header/bits_null/cbindgen.toml

@@ -0,0 +1,11 @@
+# POSIX header spec: https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/stddef.h.html
+#
+# This type is split out to prevent importing all of stddef.h into other headers.
+#
+# POSIX headers that require NULL (without the rest of stddef.h):
+# - locale.h
+# - stddef.h (where it should be defined)
+# - time.h
+include_guard = "_RELIBC_BITS_NULL_T_H"
+language = "C"
+no_includes = true

src/header/bits_null/mod.rs

@@ -0,0 +1,5 @@
+use crate::platform::types::c_void;
+
+/// Null pointer constant.
+#[expect(clippy::zero_ptr)]
+pub const NULL: *mut c_void = 0 as *mut c_void;

src/header/locale/cbindgen.toml

@@ -2,10 +2,10 @@
 #
 # Spec quotations relating to includes:
 # - "The <locale.h> header shall define NULL (as described in <stddef.h>) and at least the following as macros:"
-sys_includes = ["stddef.h"]
 include_guard = "_RELIBC_LOCALE_H"
 after_includes = """
 #include <bits/locale-t.h> // for locale_t
+#include <bits/null.h>     // for NULL from stddef.h
 """
 language = "C"
 style = "Tag"

src/header/mod.rs

@@ -26,6 +26,7 @@ pub mod bits_locale_t;
 pub mod bits_mode_t;
 #[path = "bits_nlink-t/mod.rs"]
 pub mod bits_nlink_t;
+pub mod bits_null;
 #[path = "bits_off-t/mod.rs"]
 pub mod bits_off_t;
 #[path = "bits_pid-t/mod.rs"]

src/header/time/cbindgen.toml

@@ -9,16 +9,17 @@
 # - "NULL As described in <stddef.h>."
 # - "Inclusion of the <time.h> header may make visible all symbols from the <signal.h> header."
 #
-# stddef.h brings in size_t and NULL
 # bits/timespec.h brings in time_t
 # features.h included for deprecated annotations
-sys_includes = ["stddef.h", "features.h"]
+sys_includes = ["features.h"]
 include_guard = "_RELIBC_TIME_H"
 language = "C"
 style = "Tag"
 no_includes = true
 cpp_compat = true
 after_includes = """
+#include <bits/null.h>      // for NULL from stddef.h
+#include <bits/size-t.h>    // for size_t from sys/types.h
 #include <bits/clock-t.h>   // for clock_t from sys/types.h
 #include <bits/clockid-t.h> // for clockid_t from sys/types.h
 #include <bits/pid-t.h>     // for pid_t from sys/types.h