Describe the errno an error stores, not the current one

The description looked up the message of whatever errno was set when
the description was built, so an error printed later read
"Success (errno 28)".

Sources/CInotify/cinotify.h

@@ -5,6 +5,7 @@
 #include <sys/inotify.h>
 #include <unistd.h>
 #include <errno.h>
+#include <string.h>
 
 static inline int cinotify_deinit(int fd) {
 	return close(fd);
@@ -14,12 +15,8 @@ static inline int cinotify_get_errno(void) {
 	return errno;
 }
 
-static inline char* get_error_message() {
+static inline char* cinotify_error_message(int error_number) {
-	int error_number = errno;
+	return strerror(error_number);
-	errno = 0;
-	char* error_message = strerror(error_number);
-	if (errno > 0) return NULL;
-	return error_message;
 }
 
 #endif

Sources/Inotify/InotifyError.swift

@@ -17,9 +17,7 @@ public enum InotifyError: Error, Sendable, CustomStringConvertible {
 	}
 
 	private func readableErrno(_ code: Int32) -> String {
-		if let cStr = get_error_message() {
+		guard let message = cinotify_error_message(code) else { return "errno \(code)" }
-			return String(cString: cStr) + " (errno \(code))"
+		return String(cString: message) + " (errno \(code))"
-		}
-		return "errno \(code)"
 	}
 }

Tests/InotifyIntegrationTests/InotifyErrorTests.swift

@@ -0,0 +1,11 @@
+import Testing
+@testable import Inotify
+
+@Suite("Error Description")
+struct InotifyErrorTests {
+	@Test func describesTheStoredErrnoAndNotTheCurrentOne() {
+		let error = InotifyError.addWatchFailed(path: "/watched", errno: 28)
+
+		#expect(error.description == "inotify_add_watch failed for '/watched': No space left on device (errno 28)")
+	}
+}