disincentivize usage of functions that expose toml::Table in Config

examples/nop-preprocessor.rs

@@ -71,6 +71,7 @@ fn handle_supports(pre: &dyn Preprocessor, sub_args: &ArgMatches) -> ! {
 /// in your main `lib.rs` file.
 mod nop_lib {
     use super::*;
+    use serde::Deserialize;
 
     /// A no-op preprocessor.
     pub struct Nop;
@@ -87,10 +88,18 @@ mod nop_lib {
         }
 
         fn run(&self, ctx: &PreprocessorContext, book: Book) -> Result<Book, Error> {
+            // The config options our preprocessor uses, deserialized from the book.toml that
+            // mdbook uses
+            #[derive(Deserialize)]
+            struct Config {
+                blow_up: bool,
+            }
+
             // In testing we want to tell the preprocessor to blow up by setting a
             // particular config value
-            if let Some(nop_cfg) = ctx.config.get_preprocessor(self.name()) {
-                if nop_cfg.contains_key("blow-up") {
+            let nop_cfg: Option<Config> = ctx.config.get_preprocessor_deserialized(self.name())?;
+            if let Some(nop_cfg) = nop_cfg {
+                if nop_cfg.blow_up {
                     anyhow::bail!("Boom!!1!");
                 }
             }

src/config.rs

@@ -240,17 +240,39 @@ impl Config {
     }
 
     /// Get the table associated with a particular renderer.
+    #[deprecated = "prefer get_renderer_deserialized over get_renderer"]
     pub fn get_renderer<I: AsRef<str>>(&self, index: I) -> Option<&Table> {
         let key = format!("output.{}", index.as_ref());
         self.get(&key).and_then(Value::as_table)
     }
 
+    /// Convenience function to fetch the renderer section from the config and deserialize it
+    /// into some arbitrary type.
+    pub fn get_renderer_deserialized<'de, T: Deserialize<'de>, I: AsRef<str>>(
+        &self,
+        index: I,
+    ) -> Result<Option<T>> {
+        let key = format!("output.{}", index.as_ref());
+        self.get_deserialized_opt(key)
+    }
+
     /// Get the table associated with a particular preprocessor.
+    #[deprecated = "prefer get_preprocessor_deserialized over get_preprocessor"]
     pub fn get_preprocessor<I: AsRef<str>>(&self, index: I) -> Option<&Table> {
         let key = format!("preprocessor.{}", index.as_ref());
         self.get(&key).and_then(Value::as_table)
     }
 
+    /// Convenience function to fetch the preprocessor section from the config and deserialize it
+    /// into some arbitrary type.
+    pub fn get_preprocessor_deserialized<'de, T: Deserialize<'de>, I: AsRef<str>>(
+        &self,
+        index: I,
+    ) -> Result<Option<T>> {
+        let key = format!("preprocessor.{}", index.as_ref());
+        self.get_deserialized_opt(key)
+    }
+
     fn from_legacy(mut table: Value) -> Config {
         let mut cfg = Config::default();
 

tests/custom_preprocessors.rs

@@ -37,7 +37,7 @@ fn ask_the_preprocessor_to_blow_up() {
     md.with_preprocessor(example());
 
     md.config
-        .set("preprocessor.nop-preprocessor.blow-up", true)
+        .set("preprocessor.nop-preprocessor.blow_up", true)
         .unwrap();
 
     let got = md.build();