Enforce that android::base::expected, i.e. Result return values are handled

Ignoring failures can hide errors.

Existing noncompliant uses are marked with a TODO comment.

This is currently reported as a warning at `bazel build` time, and a
clang-tidy failure at `bazel test` time. As far as I can tell, clang
compiler warnings automatically are converted into `clang-diagnostic-*`
failures in clang-tidy, which we convert to errors in our clang-tidy
tests.

Properties of this approach:

- Applies only to our GitHub repository, and not the google-internal
  downstream. This avoids us blocking submission of other changes
  Google's internal source tree.
- Doesn't break `bazel build`, `bazel run`, or `debuild` at the time of
  compiler updates or active development of new code.
- Validated at PR submission time on GitHub by the `run-cvd-unit-tests`
  action which runs clang-tidy and blocks submission.
- Possible to reproduce failures with `bazel test`.

Bug: b/471073085

Author: Databean

base/cvd/build_variables.bzl

@@ -2,4 +2,5 @@ COPTS = [
     "-std=c++17",
     # https://cs.android.com/android/platform/superproject/main/+/main:build/soong/cc/config/global.go;l=428;drc=27f57506c28cc8e4f6a0c0b8ac22c85aa9140688
     "-ftrivial-auto-var-init=zero",
+    "-DNODISCARD_EXPECTED",
 ]

base/cvd/cuttlefish/common/libs/utils/files.cpp

@@ -148,15 +148,18 @@ bool FileHasContent(const std::string& path) {
 Result<void> HardLinkDirecoryContentsRecursively(
     const std::string& source, const std::string& destination) {
   CF_EXPECTF(IsDirectory(source), "Source '{}' is not a directory", source);
-  EnsureDirectoryExists(destination, 0755);
+
+  // TODO: b/471069557 - diagnose need
+  Result<void> unused = EnsureDirectoryExists(destination, 0755);
 
   const std::function<bool(const std::string&)> linker =
       [&source, &destination](const std::string& filepath) mutable {
         std::string src_path = filepath;
         std::string dst_path =
             destination + "/" + filepath.substr(source.size() + 1);
         if (IsDirectory(src_path)) {
-          EnsureDirectoryExists(dst_path);
+          // TODO: b/471069557 - diagnose need
+          Result<void> unused = EnsureDirectoryExists(dst_path);
           return true;
         }
         bool overwrite_existing = true;

base/cvd/cuttlefish/host/commands/casimir_control_server/casimir_controller.cpp

@@ -233,7 +233,9 @@ CasimirController::SendBroadcast(std::vector<uint8_t> data, std::string type,
   CF_EXPECT(Write(poll_command), "Failed to send broadcast frame");
 
   if (timeout != 0) {
-    ReadRfPacket(std::chrono::microseconds(timeout));
+    // TODO: b/471069557 - diagnose unused
+    Result<std::shared_ptr<std::vector<uint8_t>>> unused =
+        ReadRfPacket(std::chrono::microseconds(timeout));
   }
 
   return std::make_tuple(data, type, crc, bits, bitrate, timeout, power);

base/cvd/cuttlefish/host/commands/cvd/cli/commands/create.cpp

@@ -327,7 +327,8 @@ Result<void> CvdCreateCommandHandler::Handle(const CommandRequest& request) {
 
   group.SetAllStates(cvd::INSTANCE_STATE_STOPPED);
   group.SetStartTime(CvdServerClock::now());
-  instance_manager_.UpdateInstanceGroup(group);
+  // TODO: b/471069557 - diagnose unused
+  Result<void> unused = instance_manager_.UpdateInstanceGroup(group);
 
   GatherVmInstantiationMetrics(group);
 

base/cvd/cuttlefish/host/commands/cvd/cli/commands/load_configs.cpp

@@ -160,7 +160,8 @@ class LoadConfigsCommand : public CvdCommandHandler {
         EnsureDirectoryExists(group.HomeDir(), 0775, /* group_name */ "");
     if (!mkdir_res.ok()) {
       group.SetAllStates(cvd::INSTANCE_STATE_PREPARE_FAILED);
-      instance_manager_.UpdateInstanceGroup(group);
+      // TODO: b/471069557 - diagnose unused
+      Result<void> unused = instance_manager_.UpdateInstanceGroup(group);
     }
     CF_EXPECT(std::move(mkdir_res));
 
@@ -169,7 +170,8 @@ class LoadConfigsCommand : public CvdCommandHandler {
       auto fetch_res = executor_.ExecuteOne(fetch_cmd, std::cerr);
       if (!fetch_res.ok()) {
         group.SetAllStates(cvd::INSTANCE_STATE_PREPARE_FAILED);
-        instance_manager_.UpdateInstanceGroup(group);
+        // TODO: b/471069557 - diagnose unused
+        Result<void> unused = instance_manager_.UpdateInstanceGroup(group);
       }
       CF_EXPECTF(std::move(fetch_res),
                  "Failed to fetch build artifacts, check '{}' for details",

base/cvd/cuttlefish/host/commands/cvd/cli/commands/status.cpp

@@ -166,7 +166,8 @@ Result<void> CvdStatusCommandHandler::Handle(const CommandRequest& request) {
         CF_EXPECT(selector::SelectGroup(instance_manager_, request));
     status_array = CF_EXPECT(group.FetchStatus(
         std::chrono::seconds(flags.wait_for_launcher_seconds)));
-    instance_manager_.UpdateInstanceGroup(group);
+    // TODO: b/471069557 - diagnose unused
+    Result<void> unused = instance_manager_.UpdateInstanceGroup(group);
   } else {
     std::pair<LocalInstance, LocalInstanceGroup> pair =
         flags.instance_name.empty()
@@ -178,7 +179,8 @@ Result<void> CvdStatusCommandHandler::Handle(const CommandRequest& request) {
     LocalInstanceGroup group = pair.second;
     status_array.append(CF_EXPECT(instance.FetchStatus(
         std::chrono::seconds(flags.wait_for_launcher_seconds))));
-    instance_manager_.UpdateInstanceGroup(group);
+    // TODO: b/471069557 - diagnose unused
+    Result<void> unused = instance_manager_.UpdateInstanceGroup(group);
   }
 
   if (flags.print) {

base/cvd/cuttlefish/host/commands/cvd/fetch/extract_image_contents.cc

@@ -52,7 +52,8 @@ Result<std::vector<std::string>> ExtractImageContents(
   } else {
     CF_EXPECT(MoveDirectoryContents(image_filepath, target_dir));
     // Ignore even if removing directory fails - harmless.
-    RecursivelyRemoveDirectory(image_filepath);
+    // TODO: b/471069557 - diagnose unused
+    Result<void> unused = RecursivelyRemoveDirectory(image_filepath);
   }
   return files;
 }

base/cvd/cuttlefish/host/commands/cvd/fetch/fetch_context.cc

@@ -145,7 +145,8 @@ Result<void> FetchArtifact::ExtractOneTo(const std::string& member_name,
   fetch_build_context_.trace_.CompletePhase(std::move(phase),
                                             FileSize(extract_path));
 
-  fetch_build_context_.DesparseFiles({local_path});
+  // TODO: b/471069557 - diagnose unused
+  Result<void> unused = fetch_build_context_.DesparseFiles({local_path});
 
   return {};
 }

base/cvd/cuttlefish/host/commands/cvd/instances/instance_database_helper.cpp

@@ -73,7 +73,8 @@ CvdInstanceDatabaseTest::~CvdInstanceDatabaseTest() {
 
 void CvdInstanceDatabaseTest::ClearWorkspace() {
   if (!workspace_dir_.empty()) {
-    RecursivelyRemoveDirectory(workspace_dir_);
+    // TODO: b/471069557 - diagnose unused
+    Result<void> unused = RecursivelyRemoveDirectory(workspace_dir_);
   }
 }
 

base/cvd/cuttlefish/host/commands/cvd/instances/instance_manager.cpp

@@ -228,7 +228,8 @@ Result<void> InstanceManager::StopInstanceGroup(
                "\".\nThis can happen if instances are already stopped.\n";
   }
   group.SetAllStates(cvd::INSTANCE_STATE_STOPPED);
-  instance_db_.UpdateInstanceGroup(group);
+  // TODO: b/471069557 - diagnose unused
+  Result<void> unused = instance_db_.UpdateInstanceGroup(group);
   return {};
 }
 
@@ -264,7 +265,8 @@ Result<void> InstanceManager::Clear() {
     if (Result<void> res = RemoveFile(config_link);!res.ok()) {
       LOG(ERROR) << res.error().FormatForEnv();
     }
-    RemoveGroupDirectory(group);
+    // TODO: b/471069557 - diagnose unused
+    Result<void> unused = RemoveGroupDirectory(group);
   }
   std::cerr << "Stopped all known instances\n";
   return {};