[AppCheck] Force link categories (#13435)

Author: ncooke3

FirebaseAppCheck/Sources/Core/FIRApp+AppCheck.m

@@ -24,3 +24,7 @@ - (NSString *)resourceName {
 }
 
 @end
+
+/// Stub used to force the linker to include the categories in this file.
+void FIRInclude_FIRApp_AppCheck_Category(void) {
+}

FirebaseAppCheck/Sources/Core/FIRAppCheck.m

@@ -267,6 +267,20 @@ - (NSString *)resourceNameForApp:(FIRApp *)app {
       stringWithFormat:@"projects/%@/apps/%@", app.options.projectID, app.options.googleAppID];
 }
 
+#pragma mark - Force Category Linking
+
+extern void FIRInclude_FIRApp_AppCheck_Category(void);
+extern void FIRInclude_FIRHeartbeatLogger_AppCheck_Category(void);
+
+/// Does nothing when called, and not meant to be called.
+///
+/// This method forces the linker to include categories even if
+/// users do not include the '-ObjC' linker flag in their project.
++ (void)noop {
+  FIRInclude_FIRApp_AppCheck_Category();
+  FIRInclude_FIRHeartbeatLogger_AppCheck_Category();
+}
+
 @end
 
 NS_ASSUME_NONNULL_END

FirebaseAppCheck/Sources/Core/FIRHeartbeatLogger+AppCheck.m

@@ -31,3 +31,7 @@ - (GACAppCheckAPIRequestHook)requestHook {
 }
 
 @end
+
+/// Stub used to force the linker to include the categories in this file.
+void FIRInclude_FIRHeartbeatLogger_AppCheck_Category(void) {
+}