From 257b6719ed89104018f6a521f6141ecd3eec3fd9 Mon Sep 17 00:00:00 2001
From: Lexi Winter <lexi@le-fay.org>
Date: Wed, 25 Jun 2025 21:15:34 +0100
Subject: nihil: add an error type

---
 nihil.config/read.cc   | 13 ++++++++-----
 nihil.config/read.ccm  |  8 ++++++--
 nihil.config/write.cc  | 15 +++++++++++----
 nihil.config/write.ccm | 11 +++++++----
 4 files changed, 32 insertions(+), 15 deletions(-)

(limited to 'nihil.config')

diff --git a/nihil.config/read.cc b/nihil.config/read.cc
index d55703d..3c20566 100644
--- a/nihil.config/read.cc
+++ b/nihil.config/read.cc
@@ -4,6 +4,7 @@
 
 module;
 
+#include <expected>
 #include <filesystem>
 #include <format>
 #include <iterator>
@@ -16,7 +17,8 @@ module nihil.config;
 
 namespace nihil::config {
 
-auto read_from(std::filesystem::path const &filename) -> void
+auto read_from(std::filesystem::path const &filename)
+	-> std::expected<void, nihil::error>
 {
 	// TODO: nihil.ucl should have a way to load UCL from a filename.
 
@@ -26,10 +28,9 @@ auto read_from(std::filesystem::path const &filename) -> void
 		// Ignore ENOENT, it simply means we haven't created the
 		// config file yet, so default values will be used.
 		if (err.error() == std::errc::no_such_file_or_directory)
-			return;
-		throw error(std::format("{}: {}",
-			    filename.string(),
-			    err.error().message()));
+			return {};
+		auto errstr = std::format("cannot read {}", filename.string());
+		return std::unexpected(nihil::error(errstr, err.error()));
 	}
 
 	// Parse the UCL.
@@ -52,6 +53,8 @@ auto read_from(std::filesystem::path const &filename) -> void
 		throw error(std::format("{}: {}", filename.string(),
 					err.what()));
 	}
+
+	return {};
 }
 
 } // namespace nihil::config
diff --git a/nihil.config/read.ccm b/nihil.config/read.ccm
index 74b0bc0..18f7213 100644
--- a/nihil.config/read.ccm
+++ b/nihil.config/read.ccm
@@ -4,15 +4,19 @@
 
 module;
 
+#include <expected>
 #include <filesystem>
 
+import nihil;
+
 export module nihil.config:read;
 
 namespace nihil::config {
 
 /*
- * Load the configuration from a file.  Throws config::error on failure.
+ * Load the configuration from a file.
  */
-export auto read_from(std::filesystem::path const &filename) -> void;
+export [[nodiscard]] auto read_from(std::filesystem::path const &filename)
+	-> std::expected<void, nihil::error>;
 
 } // namespace nihil::config
diff --git a/nihil.config/write.cc b/nihil.config/write.cc
index 4b2a232..2b451bd 100644
--- a/nihil.config/write.cc
+++ b/nihil.config/write.cc
@@ -4,6 +4,7 @@
 
 module;
 
+#include <expected>
 #include <filesystem>
 #include <format>
 #include <utility>
@@ -15,7 +16,8 @@ module nihil.config;
 
 namespace nihil::config {
 
-auto write_to(std::filesystem::path const &filename) -> void
+auto write_to(std::filesystem::path const &filename)
+	-> std::expected<void, nihil::error>
 try {
 	auto uclconfig = ucl::map<ucl::object>();
 
@@ -30,10 +32,15 @@ try {
 	auto ucl_text = std::format("{:c}", uclconfig);
 	auto ret = safe_write_file(filename, ucl_text);
 	if (!ret)
-		throw error(std::format("{}: {}", filename.string(),
-					ret.error().message()));
+		return std::unexpected(nihil::error(
+			std::format("cannot write {}", filename.string()),
+			ret.error()));
+
+	return {};
 } catch (ucl::error const &exc) {
-	throw error(std::format("{}: {}", filename.string(), exc.what()));
+	return std::unexpected(nihil::error(
+			"failed to serialize configuration",
+			nihil::error(exc.what())));
 }
 
 };
diff --git a/nihil.config/write.ccm b/nihil.config/write.ccm
index 71cdbb3..1a07dd7 100644
--- a/nihil.config/write.ccm
+++ b/nihil.config/write.ccm
@@ -4,16 +4,19 @@
 
 module;
 
+#include <expected>
 #include <filesystem>
 
+import nihil;
+
 export module nihil.config:write;
 
-namespace nihil::config {
+export namespace nihil::config {
 
 /*
- * Write all config values (except defaults) to disk.  Throws config::error
- * on failure.
+ * Write all config values (except defaults) to disk.
  */
-auto write_to(std::filesystem::path const &filename) -> void;
+auto write_to(std::filesystem::path const &filename) ->
+	std::expected<void, nihil::error>;
 
 };
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