Use C++17's [[nodiscard]] instead of WARN_UNUSED_RESULT

No functionality change. Also remove some header guards along the way.

Test: m
Change-Id: I1afdcaea95a3dd56f392c4e61d7670f43615792a
diff --git a/server/RouteController.h b/server/RouteController.h
index d40288b..e36320f 100644
--- a/server/RouteController.h
+++ b/server/RouteController.h
@@ -14,10 +14,9 @@
  * limitations under the License.
  */
 
-#ifndef NETD_SERVER_ROUTE_CONTROLLER_H
-#define NETD_SERVER_ROUTE_CONTROLLER_H
+#pragma once
 
-#include "NetdConstants.h"
+#include "NetdConstants.h"  // IptablesTarget
 #include "Permission.h"
 
 #include <android-base/thread_annotations.h>
@@ -27,8 +26,7 @@
 #include <map>
 #include <mutex>
 
-namespace android {
-namespace net {
+namespace android::net {
 
 class UidRanges;
 
@@ -46,7 +44,7 @@
 
     static const char* const LOCAL_MANGLE_INPUT;
 
-    static int Init(unsigned localNetId) WARN_UNUSED_RESULT;
+    [[nodiscard]] static int Init(unsigned localNetId);
 
     // Returns an ifindex given the interface name, by looking up in sInterfaceToTable.
     // This is currently only used by NetworkController::addInterfaceToNetwork
@@ -57,55 +55,56 @@
     // used to add them.
     static uint32_t getIfIndex(const char* interface) EXCLUDES(sInterfaceToTableLock);
 
-    static int addInterfaceToLocalNetwork(unsigned netId, const char* interface) WARN_UNUSED_RESULT;
-    static int removeInterfaceFromLocalNetwork(unsigned netId,
-                                               const char* interface) WARN_UNUSED_RESULT;
+    [[nodiscard]] static int addInterfaceToLocalNetwork(unsigned netId, const char* interface);
+    [[nodiscard]] static int removeInterfaceFromLocalNetwork(unsigned netId, const char* interface);
 
-    static int addInterfaceToPhysicalNetwork(unsigned netId, const char* interface,
-                                             Permission permission) WARN_UNUSED_RESULT;
-    static int removeInterfaceFromPhysicalNetwork(unsigned netId, const char* interface,
-                                                  Permission permission) WARN_UNUSED_RESULT;
+    [[nodiscard]] static int addInterfaceToPhysicalNetwork(unsigned netId, const char* interface,
+                                                           Permission permission);
+    [[nodiscard]] static int removeInterfaceFromPhysicalNetwork(unsigned netId,
+                                                                const char* interface,
+                                                                Permission permission);
 
-    static int addInterfaceToVirtualNetwork(unsigned netId, const char* interface, bool secure,
-                                            const UidRanges& uidRanges) WARN_UNUSED_RESULT;
-    static int removeInterfaceFromVirtualNetwork(unsigned netId, const char* interface, bool secure,
-                                                 const UidRanges& uidRanges) WARN_UNUSED_RESULT;
+    [[nodiscard]] static int addInterfaceToVirtualNetwork(unsigned netId, const char* interface,
+                                                          bool secure, const UidRanges& uidRanges);
+    [[nodiscard]] static int removeInterfaceFromVirtualNetwork(unsigned netId,
+                                                               const char* interface, bool secure,
+                                                               const UidRanges& uidRanges);
 
-    static int modifyPhysicalNetworkPermission(unsigned netId, const char* interface,
-                                               Permission oldPermission,
-                                               Permission newPermission) WARN_UNUSED_RESULT;
+    [[nodiscard]] static int modifyPhysicalNetworkPermission(unsigned netId, const char* interface,
+                                                             Permission oldPermission,
+                                                             Permission newPermission);
 
-    static int addUsersToVirtualNetwork(unsigned netId, const char* interface, bool secure,
-                                        const UidRanges& uidRanges) WARN_UNUSED_RESULT;
-    static int removeUsersFromVirtualNetwork(unsigned netId, const char* interface, bool secure,
-                                             const UidRanges& uidRanges) WARN_UNUSED_RESULT;
+    [[nodiscard]] static int addUsersToVirtualNetwork(unsigned netId, const char* interface,
+                                                      bool secure, const UidRanges& uidRanges);
+    [[nodiscard]] static int removeUsersFromVirtualNetwork(unsigned netId, const char* interface,
+                                                           bool secure, const UidRanges& uidRanges);
 
-    static int addUsersToRejectNonSecureNetworkRule(const UidRanges& uidRanges)
-                                                    WARN_UNUSED_RESULT;
-    static int removeUsersFromRejectNonSecureNetworkRule(const UidRanges& uidRanges)
-                                                         WARN_UNUSED_RESULT;
+    [[nodiscard]] static int addUsersToRejectNonSecureNetworkRule(const UidRanges& uidRanges);
+    [[nodiscard]] static int removeUsersFromRejectNonSecureNetworkRule(const UidRanges& uidRanges);
 
-    static int addInterfaceToDefaultNetwork(const char* interface,
-                                            Permission permission) WARN_UNUSED_RESULT;
-    static int removeInterfaceFromDefaultNetwork(const char* interface,
-                                                 Permission permission) WARN_UNUSED_RESULT;
+    [[nodiscard]] static int addInterfaceToDefaultNetwork(const char* interface,
+                                                          Permission permission);
+    [[nodiscard]] static int removeInterfaceFromDefaultNetwork(const char* interface,
+                                                               Permission permission);
 
     // |nexthop| can be NULL (to indicate a directly-connected route), "unreachable" (to indicate a
     // route that's blocked), "throw" (to indicate the lack of a match), or a regular IP address.
-    static int addRoute(const char* interface, const char* destination, const char* nexthop,
-                        TableType tableType) WARN_UNUSED_RESULT;
-    static int removeRoute(const char* interface, const char* destination, const char* nexthop,
-                           TableType tableType) WARN_UNUSED_RESULT;
+    [[nodiscard]] static int addRoute(const char* interface, const char* destination,
+                                      const char* nexthop, TableType tableType);
+    [[nodiscard]] static int removeRoute(const char* interface, const char* destination,
+                                         const char* nexthop, TableType tableType);
 
-    static int enableTethering(const char* inputInterface,
-                               const char* outputInterface) WARN_UNUSED_RESULT;
-    static int disableTethering(const char* inputInterface,
-                                const char* outputInterface) WARN_UNUSED_RESULT;
+    [[nodiscard]] static int enableTethering(const char* inputInterface,
+                                             const char* outputInterface);
+    [[nodiscard]] static int disableTethering(const char* inputInterface,
+                                              const char* outputInterface);
 
-    static int addVirtualNetworkFallthrough(unsigned vpnNetId, const char* physicalInterface,
-                                            Permission permission) WARN_UNUSED_RESULT;
-    static int removeVirtualNetworkFallthrough(unsigned vpnNetId, const char* physicalInterface,
-                                               Permission permission) WARN_UNUSED_RESULT;
+    [[nodiscard]] static int addVirtualNetworkFallthrough(unsigned vpnNetId,
+                                                          const char* physicalInterface,
+                                                          Permission permission);
+    [[nodiscard]] static int removeVirtualNetworkFallthrough(unsigned vpnNetId,
+                                                             const char* physicalInterface,
+                                                             Permission permission);
 
     // For testing.
     static int (*iptablesRestoreCommandFunction)(IptablesTarget, const std::string&,
@@ -118,9 +117,9 @@
     static std::map<std::string, uint32_t> sInterfaceToTable GUARDED_BY(sInterfaceToTableLock);
 
     static int configureDummyNetwork();
-    static int flushRoutes(const char* interface) EXCLUDES(sInterfaceToTableLock);
-    static int flushRoutes(uint32_t table);
-    static uint32_t getRouteTableForInterfaceLocked(const char *interface)
+    [[nodiscard]] static int flushRoutes(const char* interface) EXCLUDES(sInterfaceToTableLock);
+    [[nodiscard]] static int flushRoutes(uint32_t table);
+    static uint32_t getRouteTableForInterfaceLocked(const char* interface)
             REQUIRES(sInterfaceToTableLock);
     static uint32_t getRouteTableForInterface(const char *interface) EXCLUDES(sInterfaceToTableLock);
     static int modifyDefaultNetwork(uint16_t action, const char* interface, Permission permission);
@@ -141,14 +140,10 @@
 // Public because they are called by by RouteControllerTest.cpp.
 // TODO: come up with a scheme of unit testing this code that does not rely on making all its
 // functions public.
-int modifyIpRoute(uint16_t action, uint32_t table, const char* interface, const char* destination,
-                  const char* nexthop) WARN_UNUSED_RESULT;
-int flushRoutes(uint32_t table) WARN_UNUSED_RESULT;
+[[nodiscard]] int modifyIpRoute(uint16_t action, uint32_t table, const char* interface,
+                                const char* destination, const char* nexthop);
 uint32_t getRulePriority(const nlmsghdr *nlh);
-WARN_UNUSED_RESULT int modifyIncomingPacketMark(unsigned netId, const char* interface,
-                                                Permission permission, bool add);
+[[nodiscard]] int modifyIncomingPacketMark(unsigned netId, const char* interface,
+                                           Permission permission, bool add);
 
-}  // namespace net
-}  // namespace android
-
-#endif  // NETD_SERVER_ROUTE_CONTROLLER_H
+}  // namespace android::net