config: Make YAML/JSON modular and optional (#21)

src/configfmt.rs

@@ -0,0 +1,61 @@
+use serde::{de::DeserializeOwned, Serialize};
+use std::io::BufRead;
+
+pub enum ConfigFmt {
+    #[cfg(feature = "yaml-cfg")]
+    Yaml,
+    #[cfg(feature = "json-cfg")]
+    Json,
+}
+
+pub const CONFIG_NAMES: &'static [&'static str] = &[
+    #[cfg(feature = "yaml-cfg")]
+    "config.yaml",
+    #[cfg(feature = "json-cfg")]
+    "config.json",
+];
+
+impl ConfigFmt {
+    #[inline]
+    pub fn new(ext: &str) -> Option<Self> {
+        match ext {
+            #[cfg(feature = "yaml-cfg")]
+            "yaml" => Some(ConfigFmt::Yaml),
+            #[cfg(feature = "json-cfg")]
+            "json" => Some(ConfigFmt::Json),
+            _ => None,
+        }
+    }
+    #[inline]
+    pub fn from_reader<B: BufRead, T: DeserializeOwned>(&self, r: B) -> T {
+        match self {
+            #[cfg(feature = "yaml-cfg")]
+            ConfigFmt::Yaml => serde_yaml::from_reader(r).unwrap(),
+            #[cfg(feature = "json-cfg")]
+            ConfigFmt::Json => serde_json::from_reader(r).unwrap(),
+        }
+    }
+    #[inline]
+    pub fn to_string<T: Serialize + ?Sized>(&self, src: &T) -> String {
+        match self {
+            #[cfg(feature = "yaml-cfg")]
+            ConfigFmt::Yaml => serde_yaml::to_string(&src).unwrap(),
+            #[cfg(feature = "json-cfg")]
+            ConfigFmt::Json => serde_json::to_string_pretty(&src).unwrap(),
+        }
+    }
+}
+
+impl Default for ConfigFmt {
+    fn default() -> Self {
+        // attributes require curly braces to work
+        #[cfg(feature = "yaml-cfg")]
+        {
+            ConfigFmt::Yaml
+        }
+        #[cfg(all(feature = "json-cfg", not(feature = "yaml-cfg")))]
+        {
+            ConfigFmt::Json
+        }
+    }
+}