5 files changed, 23 insertions, 22 deletions
diff --git a/src/buildtool/common/TARGETS b/src/buildtool/common/TARGETS
index c20ea4e5..dd8fdbd8 100644
--- a/src/buildtool/common/TARGETS
+++ b/src/buildtool/common/TARGETS
@@ -150,7 +150,7 @@
   , "name": ["location"]
   , "hdrs": ["location.hpp"]
   , "srcs": ["location.cpp"]
-  , "deps": [["@", "json", "", "json"]]
+  , "deps": [["@", "json", "", "json"], ["src/utils/cpp", "expected"]]
   , "stage": ["src", "buildtool", "common"]
   , "private-deps":
     [ ["@", "fmt", "", "fmt"]
diff --git a/src/buildtool/common/location.cpp b/src/buildtool/common/location.cpp
index bc3a57dc..a266069d 100644
--- a/src/buildtool/common/location.cpp
+++ b/src/buildtool/common/location.cpp
@@ -22,9 +22,10 @@
 
 auto ReadLocationObject(nlohmann::json const& location,
                         std::optional<std::filesystem::path> const& ws_root)
-    -> std::variant<std::string, std::optional<location_res_t>> {
+    -> expected<std::optional<location_res_t>, std::string> {
     if (not location.contains("path") or not location.contains("root")) {
-        return fmt::format("Malformed location object: {}", location.dump(-1));
+        return unexpected(
+            fmt::format("Malformed location object: {}", location.dump(-1)));
     }
     auto root = location["root"].get<std::string>();
     auto path = location["path"].get<std::string>();
@@ -37,7 +38,7 @@ auto ReadLocationObject(nlohmann::json const& location,
             Logger::Log(LogLevel::Warning,
                         "Not in workspace root, ignoring location {}.",
                         location.dump(-1));
-            return std::nullopt;
+            return std::optional<location_res_t>{std::nullopt};
         }
         root_path = *ws_root;
     }
@@ -47,8 +48,9 @@ auto ReadLocationObject(nlohmann::json const& location,
     if (root == "system") {
         root_path = FileSystemManager::GetCurrentDirectory().root_path();
     }
-    return std::make_pair(std::filesystem::weakly_canonical(
-                              std::filesystem::absolute(root_path / path)),
-                          std::filesystem::weakly_canonical(
-                              std::filesystem::absolute(root_path / base)));
+    return std::optional<location_res_t>{
+        std::make_pair(std::filesystem::weakly_canonical(
+                           std::filesystem::absolute(root_path / path)),
+                       std::filesystem::weakly_canonical(
+                           std::filesystem::absolute(root_path / base)))};
 }
diff --git a/src/buildtool/common/location.hpp b/src/buildtool/common/location.hpp
index 2e9d3841..c3788339 100644
--- a/src/buildtool/common/location.hpp
+++ b/src/buildtool/common/location.hpp
@@ -17,17 +17,16 @@
 #include <string>
 #include <unordered_set>
 #include <utility>
-#include <variant>
 
 #include "nlohmann/json.hpp"
+#include "src/utils/cpp/expected.hpp"
 
 using location_res_t = std::pair<std::filesystem::path, std::filesystem::path>;
 
 /// \brief Parse a location object stored in a JSON object.
-/// \returns An error + data union, where at index 0 is the string message on
-/// fatal failure, and at index 1 is an optional parsed location (nullopt if
-/// location should be ignored) on success.
+/// \returns optional parsed location (nullopt if location should be ignored) on
+/// success or unexpected error as string.
 [[nodiscard]] auto ReadLocationObject(
     nlohmann::json const& location,
     std::optional<std::filesystem::path> const& ws_root)
-    -> std::variant<std::string, std::optional<location_res_t>>;
+    -> expected<std::optional<location_res_t>, std::string>;
diff --git a/src/buildtool/main/serve.cpp b/src/buildtool/main/serve.cpp
index 0eaf174e..e21eac0f 100644
--- a/src/buildtool/main/serve.cpp
+++ b/src/buildtool/main/serve.cpp
@@ -45,11 +45,11 @@ namespace {
     -> std::optional<std::pair<std::filesystem::path, std::filesystem::path>> {
     if (location.IsNotNull()) {
         auto res = ReadLocationObject(location->ToJson(), std::nullopt);
-        if (res.index() == 0) {
-            Logger::Log(LogLevel::Error, std::get<0>(res));
+        if (not res) {
+            Logger::Log(LogLevel::Error, res.error());
             std::exit(kExitFailure);
         }
-        return std::get<1>(res);
+        return *res;
     }
     return std::nullopt;
 }
diff --git a/src/other_tools/just_mr/rc.cpp b/src/other_tools/just_mr/rc.cpp
index 89fb8ef2..0a5a171a 100644
--- a/src/other_tools/just_mr/rc.cpp
+++ b/src/other_tools/just_mr/rc.cpp
@@ -37,11 +37,11 @@ namespace {
     -> std::optional<std::pair<std::filesystem::path, std::filesystem::path>> {
     if (location.IsNotNull()) {
         auto res = ReadLocationObject(location->ToJson(), ws_root);
-        if (res.index() == 0) {
-            Logger::Log(LogLevel::Error, std::get<0>(res));
+        if (not res) {
+            Logger::Log(LogLevel::Error, res.error());
             std::exit(kExitConfigError);
         }
-        return std::get<1>(res);
+        return *res;
     }
     return std::nullopt;
 }
@@ -52,11 +52,11 @@ namespace {
     std::optional<std::filesystem::path> const& ws_root)
     -> std::optional<std::pair<std::filesystem::path, std::filesystem::path>> {
     auto res = ReadLocationObject(location, ws_root);
-    if (res.index() == 0) {
-        Logger::Log(LogLevel::Error, std::get<0>(res));
+    if (not res) {
+        Logger::Log(LogLevel::Error, res.error());
         std::exit(kExitConfigError);
     }
-    return std::get<1>(res);
+    return *res;
 }
 
 [[nodiscard]] auto ReadOptionalLocationList(