add hook to retrieve config file path

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "clappconfig"
-version = "0.1.0"
+version = "0.2.0"
 authors = ["Ondřej Hruška <ondra@ondrovo.com>"]
 edition = "2018"
 license = "MIT"

src/lib.rs

@@ -48,6 +48,12 @@ pub trait AppConfig: Sized + Serialize + DeserializeOwned + Debug + Default {
         clap
     }
 
+    /// Called when the config file is resolved, e.g. to store it in Config
+    /// for later relative path resolution
+    fn on_config_file_found(&mut self, _path : &PathBuf) {
+        //
+    }
+
     /// Configure the config object using args.
     /// Logging has already been inited and configured.
     fn configure<'a>(self, _clap: &clap::ArgMatches<'a>) -> Fallible<Self::Init>;
@@ -119,15 +125,32 @@ pub trait AppConfig: Sized + Serialize + DeserializeOwned + Debug + Default {
 
         let filepath = PathBuf::from_str(cfg_file)?;
 
-        let config: Self = if filepath.is_file() {
-            let path = filepath.canonicalize()?;
-            Self::pre_log_println(format!("Loading config from: {}", path.display()));
+        let config = if filepath.exists() {
+            let mut path = filepath.canonicalize()?;
+
+            if path.is_dir() {
+                path = path.join(cfg_file_name);
+            }
+
+            if path.exists() {
+                Self::pre_log_println(format!("Loading config from: {}", path.display()));
+
+                let buf = read_file(&path)?;
 
-            let buf = read_file(path)?;
-            json5::from_str(&buf)?
+                let mut config: Self = json5::from_str(&buf)?;
+                config.on_config_file_found(&path);
+                config
+            } else {
+                Self::pre_log_println(format!(
+                    "Config file \"{}\" does not exist, using defaults.",
+                    path.display()
+                ));
+
+                Self::default()
+            }
         } else {
             Self::pre_log_println(format!(
-                "Config file \"{}\" does not exist, using defaults.",
+                "Config path \"{}\" does not exist, using defaults.",
                 cfg_file
             ));