app: improve config loading and merging

crates/app/src/config.rs

@@ -1,6 +1,10 @@
 use clap::Parser;
 
-use self::{cli::Args, config_file::Configs};
+use self::{
+    cli::Args,
+    config_file::{find_config_file, Configs},
+    error::ConfigError,
+};
 
 mod cli;
 mod config_file;
@@ -11,14 +15,49 @@ pub struct Config {
 }
 
 impl Config {
-    pub fn read() -> Self {
+    pub fn read() -> Result<Self, ConfigError> {
         let args = Args::parse();
-        let cfg = Configs::read(args.config_file);
+        let config_path = if let Some(config_path) = args.config_path {
+            config_path
+        } else {
+            find_config_file()?
+        };
+        let file_config = Configs::read(config_path)?;
 
-        Self {
+        Ok(Self {
             // this is negated because to an outward api, the negative is more intuitive,
             // while in the source the other way around is more intuitive
-            startup_msg: !(args.no_startup_message || cfg.no_startup_message),
+            startup_msg: !(args.no_startup_message || file_config.no_startup_message),
+        })
+    }
+}
+
+pub mod error {
+    #[derive(Debug)]
+    pub enum ConfigError {
+        NoConfigDir,
+        NoConfigFileFound,
+        IoError(std::io::Error),
+        UnknownExtension(Option<String>),
+        SerdeJsonError(serde_json::Error),
+        SerdeRonError(ron::error::SpannedError),
+    }
+
+    impl From<std::io::Error> for ConfigError {
+        fn from(value: std::io::Error) -> Self {
+            Self::IoError(value)
+        }
+    }
+
+    impl From<serde_json::Error> for ConfigError {
+        fn from(value: serde_json::Error) -> Self {
+            Self::SerdeJsonError(value)
+        }
+    }
+
+    impl From<ron::error::SpannedError> for ConfigError {
+        fn from(value: ron::error::SpannedError) -> Self {
+            Self::SerdeRonError(value)
         }
     }
 }