fix(posix): guard Windows shims with _WIN32 instead of #error

clang-tidy's Linux pre-merge check parses these headers via the global
include path, sees the #error guard, and reports clang-diagnostic-error
on every PR. Wrap the Windows-only bodies in #ifdef _WIN32 / #endif so
the shims are silent no-ops on non-Windows toolchains while still being
correctness-sized on the targets that actually compile against MinGW or
MSVC. Also covers libgen.h / time.h / sys/types.h whose static inlines
referenced MS-specific identifiers (gmtime_s family, basename
redeclaration, quad_t typedef redefinition) and px4_windows_internal.h
which is consumed only by the Windows backend.

Signed-off-by: Nuno Marques <n.marques21@hotmail.com>

platforms/posix/include/windows_shim/afunix.h

@@ -43,9 +43,7 @@
  */
 #pragma once
 
-#ifndef _WIN32
-#  error "afunix.h shim only valid on Windows"
-#endif
+#ifdef _WIN32
 
 #include <stddef.h>
 #include <string.h>
@@ -114,3 +112,5 @@ typedef struct sockaddr_un sockaddr_un;
 #ifdef __cplusplus
 }
 #endif
+
+#endif /* _WIN32 */

platforms/posix/include/windows_shim/arpa/inet.h

@@ -40,9 +40,7 @@
  */
 #pragma once
 
-#ifndef _WIN32
-#  error "arpa/inet.h shim only valid on Windows"
-#endif
+#ifdef _WIN32
 
 #include <stddef.h>
 
@@ -73,3 +71,5 @@ struct in_addr inet_makeaddr(in_addr_t net, in_addr_t host);
 #ifdef __cplusplus
 }
 #endif
+
+#endif /* _WIN32 */

platforms/posix/include/windows_shim/libgen.h

@@ -38,6 +38,8 @@
 
 #pragma once
 
+#ifdef _WIN32
+
 #include <string.h>
 
 #ifdef __cplusplus
@@ -79,7 +81,7 @@ static inline char *dirname(char *path)
 		return (char *)".";
 	}
 
-	char *last = NULL;
+	char *last = nullptr;
 
 	for (char *p = path; *p; ++p) {
 		if (*p == '/' || *p == '\\') {
@@ -103,3 +105,5 @@ static inline char *dirname(char *path)
 #ifdef __cplusplus
 }
 #endif
+
+#endif /* _WIN32 */

platforms/posix/include/windows_shim/net/if.h

@@ -41,9 +41,7 @@
  */
 #pragma once
 
-#ifndef _WIN32
-#  error "net/if.h shim only valid on Windows"
-#endif
+#ifdef _WIN32
 
 #ifndef WIN32_LEAN_AND_MEAN
 #define WIN32_LEAN_AND_MEAN
@@ -241,3 +239,5 @@ void                 if_freenameindex(struct if_nameindex *ptr);
 #ifdef __cplusplus
 }
 #endif
+
+#endif /* _WIN32 */

platforms/posix/include/windows_shim/netdb.h

@@ -42,9 +42,7 @@
  */
 #pragma once
 
-#ifndef _WIN32
-#  error "netdb.h shim only valid on Windows"
-#endif
+#ifdef _WIN32
 
 #include <stdint.h>
 
@@ -164,3 +162,5 @@ struct servent *getservent(void);
 #ifdef __cplusplus
 }
 #endif
+
+#endif /* _WIN32 */

platforms/posix/include/windows_shim/netinet/in.h

@@ -40,9 +40,7 @@
  */
 #pragma once
 
-#ifndef _WIN32
-#  error "netinet/in.h shim only valid on Windows"
-#endif
+#ifdef _WIN32
 
 #include <stdint.h>
 
@@ -91,3 +89,5 @@ typedef uint16_t in_port_t;
 #ifndef IN6_ARE_ADDR_EQUAL
 #define IN6_ARE_ADDR_EQUAL(a, b) IN6_ADDR_EQUAL((a), (b))
 #endif
+
+#endif /* _WIN32 */

platforms/posix/include/windows_shim/netinet/tcp.h

@@ -39,9 +39,7 @@
  */
 #pragma once
 
-#ifndef _WIN32
-#  error "netinet/tcp.h shim only valid on Windows"
-#endif
+#ifdef _WIN32
 
 #include <netinet/in.h>
 #include <winsock2.h>
@@ -70,3 +68,5 @@
 #ifndef TCP_USER_TIMEOUT
 #define TCP_USER_TIMEOUT 18
 #endif
+
+#endif /* _WIN32 */

platforms/posix/include/windows_shim/netinet/udp.h

@@ -38,12 +38,12 @@
  */
 #pragma once
 
-#ifndef _WIN32
-#  error "netinet/udp.h shim only valid on Windows"
-#endif
+#ifdef _WIN32
 
 #include <netinet/in.h>
 
 #ifndef SOL_UDP
 #define SOL_UDP IPPROTO_UDP
 #endif
+
+#endif /* _WIN32 */

platforms/posix/include/windows_shim/sys/types.h

@@ -78,6 +78,7 @@ typedef unsigned int useconds_t;
 #include_next <sys/types.h>
 #endif
 
+#ifdef _WIN32
 #ifndef _PX4_SYS_TYPES_ALIASES_DEFINED
 #define _PX4_SYS_TYPES_ALIASES_DEFINED
 /** @name BSD/GNU scalar aliases
@@ -99,3 +100,4 @@ typedef long long      quad_t;
 typedef unsigned long long u_quad_t;
 /** @} */
 #endif
+#endif /* _WIN32 */

platforms/posix/include/windows_shim/sys/un.h

@@ -42,9 +42,7 @@
  */
 #pragma once
 
-#ifndef _WIN32
-#  error "sys/un.h shim only valid on Windows"
-#endif
+#ifdef _WIN32
 
 #include <stddef.h>
 #include <string.h>
@@ -64,3 +62,5 @@ typedef struct sockaddr_un sockaddr_un;
 /* afunix.h already provides struct sockaddr_un. Re-export sun_path/sun_family
  * aliases if any translation unit expects them. afunix.h on Windows already
  * names them that way, so no further work is needed. */
+
+#endif /* _WIN32 */

platforms/posix/include/windows_shim/time.h

@@ -40,6 +40,8 @@
  */
 #pragma once
 
+#ifdef _WIN32
+
 #if defined(_MSC_VER) && !defined(__clang__)
 #if defined(__has_include)
 #  if __has_include(<../ucrt/time.h>)
@@ -104,30 +106,30 @@ int nanosleep(const struct timespec *req, struct timespec *rem);
 /** @brief Thread-safe UTC conversion using the Windows gmtime_s() order. */
 static inline struct tm *gmtime_r(const time_t *timep, struct tm *result)
 {
-	if (!timep || !result) { return NULL; }
-	return (gmtime_s(result, timep) == 0) ? result : NULL;
+	if (!timep || !result) { return nullptr; }
+	return (gmtime_s(result, timep) == 0) ? result : nullptr;
 }
 
 /** @brief Thread-safe local-time conversion using the Windows localtime_s(). */
 static inline struct tm *localtime_r(const time_t *timep, struct tm *result)
 {
-	if (!timep || !result) { return NULL; }
-	return (localtime_s(result, timep) == 0) ? result : NULL;
+	if (!timep || !result) { return nullptr; }
+	return (localtime_s(result, timep) == 0) ? result : nullptr;
 }
 
 /** @brief Thread-safe asctime() wrapper; @p buf must hold at least 26 bytes. */
 static inline char *asctime_r(const struct tm *tm, char *buf)
 {
-	if (!tm || !buf) { return NULL; }
+	if (!tm || !buf) { return nullptr; }
 	/* POSIX requires a 26-byte buffer; match that to asctime_s. */
-	return (asctime_s(buf, 26, tm) == 0) ? buf : NULL;
+	return (asctime_s(buf, 26, tm) == 0) ? buf : nullptr;
 }
 
 /** @brief Thread-safe ctime() wrapper; @p buf must hold at least 26 bytes. */
 static inline char *ctime_r(const time_t *timep, char *buf)
 {
-	if (!timep || !buf) { return NULL; }
-	return (ctime_s(buf, 26, timep) == 0) ? buf : NULL;
+	if (!timep || !buf) { return nullptr; }
+	return (ctime_s(buf, 26, timep) == 0) ? buf : nullptr;
 }
 
 #ifndef timerisset
@@ -167,3 +169,5 @@ static inline char *ctime_r(const time_t *timep, char *buf)
 #endif
 
 #endif /* _PX4_TIME_R_SHIM_DEFINED */
+
+#endif /* _WIN32 */

platforms/posix/src/px4/windows/include/px4_windows_internal.h

@@ -49,9 +49,7 @@
  */
 #pragma once
 
-#ifndef _WIN32
-#  error "px4_windows_internal.h is Windows-only"
-#endif
+#ifdef _WIN32
 
 #define _WIN32_WINNT 0x0A00
 #include <string.h>
@@ -110,3 +108,5 @@ int px4_wsa_error_to_errno(int err);
  * @return Static, human-readable error string.
  */
 const char *px4_hstrerror_text(int err);
+
+#endif /* _WIN32 */