init: add [[nodiscard]] to Result

It's better to either check these results or explicitly ignore them.
Only a few callers weren't already doing this, so it's relatively
trivial to enforce.

Test: build
Change-Id: I44cdc342e46128f66cac914aaa0b9b4559cacd8c

init/builtins.cpp

@@ -1018,7 +1018,11 @@ static Result<Success> ExecWithRebootOnFailure(const std::string& reboot_reason,
         if (siginfo.si_code != CLD_EXITED || siginfo.si_status != 0) {
             if (e4crypt_is_native()) {
                 LOG(ERROR) << "Rebooting into recovery, reason: " << reboot_reason;
-                reboot_into_recovery({"--prompt_and_wipe_data", "--reason="s + reboot_reason});
+                if (auto result = reboot_into_recovery(
+                            {"--prompt_and_wipe_data", "--reason="s + reboot_reason});
+                    !result) {
+                    LOG(FATAL) << "Could not reboot into recovery: " << result.error();
+                }
             } else {
                 LOG(ERROR) << "Failure (reboot suppressed): " << reboot_reason;
             }

init/keychords.cpp

@@ -41,7 +41,7 @@ Keychords::Keychords() : epoll_(nullptr), inotify_fd_(-1) {}
 
 Keychords::~Keychords() noexcept {
     if (inotify_fd_ >= 0) {
-        epoll_->UnregisterHandler(inotify_fd_);
+        epoll_->UnregisterHandler(inotify_fd_).IgnoreError();
         ::close(inotify_fd_);
     }
     while (!registration_.empty()) GeteventCloseDevice(registration_.begin()->first);
@@ -186,7 +186,11 @@ bool Keychords::GeteventEnable(int fd) {
         current_ |= mask & available & set;
         LambdaCheck();
     }
-    epoll_->RegisterHandler(fd, [this, fd]() { this->LambdaHandler(fd); });
+    if (auto result = epoll_->RegisterHandler(fd, [this, fd]() { this->LambdaHandler(fd); });
+        !result) {
+        LOG(WARNING) << "Could not register keychord epoll handler: " << result.error();
+        return false;
+    }
     return true;
 }
 
@@ -208,7 +212,7 @@ void Keychords::GeteventCloseDevice(const std::string& device) {
     auto it = registration_.find(device);
     if (it == registration_.end()) return;
     auto fd = (*it).second;
-    epoll_->UnregisterHandler(fd);
+    epoll_->UnregisterHandler(fd).IgnoreError();
     registration_.erase(it);
     ::close(fd);
 }
@@ -266,7 +270,11 @@ void Keychords::GeteventOpenDevice() {
     }
 
     if (inotify_fd_ >= 0) {
-        epoll_->RegisterHandler(inotify_fd_, [this]() { this->InotifyHandler(); });
+        if (auto result =
+                    epoll_->RegisterHandler(inotify_fd_, [this]() { this->InotifyHandler(); });
+            !result) {
+            LOG(WARNING) << "Could not register keychord epoll handler: " << result.error();
+        }
     }
 }
 

init/keychords_test.cpp

@@ -213,7 +213,7 @@ TestFrame::TestFrame(const std::vector<const std::vector<int>>& chords, EventHan
 }
 
 void TestFrame::RelaxForMs(std::chrono::milliseconds wait) {
-    epoll_.Wait(wait);
+    epoll_.Wait(wait).IgnoreError();
 }
 
 void TestFrame::SetChord(int key, bool value) {

init/reboot.cpp

@@ -142,7 +142,9 @@ static void TurnOffBacklight() {
         LOG(WARNING) << "cannot find blank_screen in TurnOffBacklight";
         return;
     }
-    service->Start();
+    if (auto result = service->Start(); !result) {
+        LOG(WARNING) << "Could not start blank_screen service: " << result.error();
+    }
 }
 
 static void ShutdownVold() {

init/result.h

@@ -151,7 +151,7 @@ inline Error ErrnoError() {
 }
 
 template <typename T>
-class Result {
+class [[nodiscard]] Result {
   public:
     Result() {}
 
@@ -170,6 +170,8 @@ class Result {
         : contents_(std::in_place_index_t<1>(), std::move(result_error.error_string),
                     result_error.error_errno) {}
 
+    void IgnoreError() const {}
+
     bool has_value() const { return contents_.index() == 0; }
 
     T& value() & { return std::get<0>(contents_); }

init/subcontext_benchmark.cpp

@@ -39,7 +39,7 @@ static void BenchmarkSuccess(benchmark::State& state) {
     free(context);
 
     while (state.KeepRunning()) {
-        subcontext.Execute(std::vector<std::string>{"return_success"});
+        subcontext.Execute(std::vector<std::string>{"return_success"}).IgnoreError();
     }
 
     if (subcontext.pid() > 0) {