Log HtmlConfig deserialization errors

src/config.rs

@@ -62,6 +62,7 @@ use toml_query::insert::TomlValueInsertExt;
 use toml_query::read::TomlValueReadExt;
 
 use crate::errors::*;
+use crate::utils;
 
 /// The overall configuration object for MDBook, essentially an in-memory
 /// representation of `book.toml`.
@@ -168,7 +169,13 @@ impl Config {
     /// HTML renderer is refactored to be less coupled to `mdbook` internals.
     #[doc(hidden)]
     pub fn html_config(&self) -> Option<HtmlConfig> {
-        self.get_deserialized("output.html").ok()
+        match self.get_deserialized("output.html") {
+            Ok(config) => Some(config),
+            Err(e) => {
+                utils::log_backtrace(&e.chain_err(|| "Parsing configuration [output.html]"));
+                None
+            }
+        }
     }
 
     /// Convenience function to fetch a value from the config and deserialize it