Went back and simplified Config to be a smart wrapper around toml::Table

src/config.rs

@@ -1,26 +1,19 @@
-use std::collections::BTreeMap;
 use std::path::{Path, PathBuf};
 use std::fs::File;
 use std::io::Read;
 use toml::{self, Value};
-use serde::Deserialize;
+use toml::value::Table;
+use serde::{Deserialize, Deserializer};
 
 use errors::*;
 
 
 /// The overall configuration object for MDBook.
-#[derive(Debug, Clone, Default, PartialEq, Serialize, Deserialize)]
-#[serde(default)]
+#[derive(Debug, Clone, Default, PartialEq)]
 pub struct Config {
     /// Metadata about the book.
     pub book: BookConfig,
-    /// Arbitrary information which renderers can use during the rendering
-    /// stage.
-    pub output: BTreeMap<String, Value>,
-    /// Information for use by preprocessors.
-    pub preprocess: BTreeMap<String, Value>,
-    /// Information for use by postprocessors.
-    pub postprocess: BTreeMap<String, Value>,
+    rest: Table,
 }
 
 impl Config {
@@ -39,6 +32,22 @@ impl Config {
         Config::from_str(&buffer)
     }
 
+    /// Fetch an arbitrary item from the `Config` as a `toml::Value`.
+    ///
+    /// You can use dotted indices to access nested items (e.g.
+    /// `output.html.playpen` will fetch the "playpen" out of the html output
+    /// table).
+    pub fn get(&self, key: &str) -> Option<&Value> {
+        let pieces: Vec<_> = key.split(".").collect();
+        recursive_get(&pieces, &self.rest)
+    }
+
+    /// Fetch a value from the `Config` so you can mutate it.
+    pub fn get_mut<'a>(&'a mut self, key: &str) -> Option<&'a mut Value> {
+        let pieces: Vec<_> = key.split(".").collect();
+        recursive_get_mut(&pieces, &mut self.rest)
+    }
+
     /// Convenience method for getting the html renderer's configuration.
     ///
     /// # Note
@@ -46,44 +55,74 @@ impl Config {
     /// This is for compatibility only. It will be removed completely once the
     /// rendering and plugin system is established.
     pub fn html_config(&self) -> Option<HtmlConfig> {
-        self.try_get_output("html").ok()
+        self.get_deserialized("output.html").ok()
     }
 
-    /// Try to get an output and deserialize it as a `T`.
-    pub fn try_get_output<'de, T: Deserialize<'de>, S: AsRef<str>>(&self, name: S) -> Result<T> {
-        get_deserialized(name, &self.output)
-    }
+    /// Convenience function to fetch a value from the config and deserialize it
+    /// into some arbitrary type.
+    pub fn get_deserialized<'de, T: Deserialize<'de>, S: AsRef<str>>(&self, name: S) -> Result<T> {
+        let name = name.as_ref();
 
-    /// Try to get the configuration for a preprocessor, deserializing it as a
-    /// `T`.
-    pub fn try_get_preprocessor<'de, T: Deserialize<'de>, S: AsRef<str>>(&self,
-                                                                         name: S)
-                                                                         -> Result<T> {
-        get_deserialized(name, &self.preprocess)
-    }
-
-    /// Try to get the configuration for a postprocessor, deserializing it as a
-    /// `T`.
-    pub fn try_get_postprocessor<'de, T: Deserialize<'de>, S: AsRef<str>>(&self,
-                                                                          name: S)
-                                                                          -> Result<T> {
-        get_deserialized(name, &self.postprocess)
+        if let Some(value) = self.get(name) {
+            value.clone()
+                 .try_into()
+                 .chain_err(|| "Couldn't deserialize the value")
+        } else {
+            bail!("Key not found, {:?}", name)
+        }
     }
 }
 
-/// Convenience function to load a value from some table then deserialize it.
-fn get_deserialized<'de, T: Deserialize<'de>, S: AsRef<str>>(name: S,
-                                                             table: &BTreeMap<String, Value>)
-                                                             -> Result<T> {
-    let name = name.as_ref();
+fn recursive_get<'a>(key: &[&str], table: &'a Table) -> Option<&'a Value> {
+    if key.is_empty() {
+        return None;
+    } else if key.len() == 1 {
+        return table.get(key[0]);
+    }
 
-    match table.get(name) {
-        Some(output) => {
-            output.clone()
-                  .try_into()
-                  .chain_err(|| "Couldn't deserialize the value")
+    let first = key[0];
+    let rest = &key[1..];
+
+    if let Some(&Value::Table(ref nested)) = table.get(first) {
+        recursive_get(rest, nested)
+    } else {
+        None
+    }
+}
+
+fn recursive_get_mut<'a>(key: &[&str], table: &'a mut Table) -> Option<&'a mut Value> {
+    // TODO: Figure out how to abstract over mutability to reduce copy-pasta
+    if key.is_empty() {
+        return None;
+    } else if key.len() == 1 {
+        return table.get_mut(key[0]);
+    }
+
+    let first = key[0];
+    let rest = &key[1..];
+
+    if let Some(&mut Value::Table(ref mut nested)) = table.get_mut(first) {
+        recursive_get_mut(rest, nested)
+    } else {
+        None
+    }
+}
+
+impl<'de> Deserialize<'de> for Config {
+    fn deserialize<D: Deserializer<'de>>(de: D) -> ::std::result::Result<Self, D::Error> {
+        let raw = Value::deserialize(de)?;
+        if let Value::Table(mut table) = raw {
+            let book: BookConfig = table.remove("book")
+                                        .and_then(|value| value.try_into().ok())
+                                        .unwrap_or_default();
+            Ok(Config {
+                   book: book,
+                   rest: table,
+               })
+        } else {
+            use serde::de::Error;
+            Err(D::Error::custom("A config file should always be a toml table"))
         }
-        None => bail!("Key Not Found, {}", name),
     }
 }
 
@@ -99,9 +138,9 @@ pub struct BookConfig {
     pub authors: Vec<String>,
     /// An optional description for the book.
     pub description: Option<String>,
-    /// Location of the book source, relative to the book's root directory.
+    /// Location of the book source relative to the book's root directory.
     pub src: PathBuf,
-    /// Where to put built artefacts, relative to the book's root directory.
+    /// Where to put built artefacts relative to the book's root directory.
     pub build_dir: PathBuf,
     /// Does this book support more than one language?
     pub multilingual: bool,
@@ -132,6 +171,7 @@ pub struct HtmlConfig {
     pub playpen: Playpen,
 }
 
+/// Configuration for tweaking how the the HTML renderer handles the playpen.
 #[derive(Debug, Clone, Default, PartialEq, Serialize, Deserialize)]
 pub struct Playpen {
     pub editor: PathBuf,
@@ -143,9 +183,7 @@ pub struct Playpen {
 mod tests {
     use super::*;
 
-    #[test]
-    fn load_a_complex_config_file() {
-        let src = r#"
+    const COMPLEX_CONFIG: &'static str = r#"
         [book]
         title = "Some Book"
         authors = ["Michael-F-Bryan <michaelfbryan@gmail.com>"]
@@ -165,6 +203,10 @@ mod tests {
         editor = "ace"
         "#;
 
+    #[test]
+    fn load_a_complex_config_file() {
+        let src = COMPLEX_CONFIG;
+
         let book_should_be = BookConfig {
             title: Some(String::from("Some Book")),
             authors: vec![String::from("Michael-F-Bryan <michaelfbryan@gmail.com>")],
@@ -216,8 +258,26 @@ mod tests {
         };
 
         let cfg = Config::from_str(src).unwrap();
-        let got: RandomOutput = cfg.try_get_output("random").unwrap();
+        let got: RandomOutput = cfg.get_deserialized("output.random").unwrap();
 
         assert_eq!(got, should_be);
+
+        let baz: Vec<bool> = cfg.get_deserialized("output.random.baz").unwrap();
+        let baz_should_be = vec![true, true, false];
+
+        assert_eq!(baz, baz_should_be);
     }
+
+#[test]
+fn mutate_some_stuff() {
+    // really this is just a sanity check to make sure the borrow checker
+    // is happy...
+    let src = COMPLEX_CONFIG;
+    let mut config = Config::from_str(src).unwrap();
+    let key = "output.html.playpen.editable";
+
+    assert_eq!(config.get(key).unwrap(), &Value::Boolean(true));
+    *config.get_mut(key).unwrap() = Value::Boolean(false);
+    assert_eq!(config.get(key).unwrap(), &Value::Boolean(false));
+}
 }