fix enumeration of nested code blocks

src/book/mod.rs

@@ -251,6 +251,18 @@ impl MDBook {
         self
     }
 
+    fn prefix_matches(line: &str, prefix: &String) -> bool {
+        let lang = line.trim_matches('`');
+        let prefix_length = line.len() - lang.len();
+        prefix_length == prefix.len()
+    }
+
+    fn parse_prefix(line: &str) -> (&str, &str) {
+        let lang = line.trim_matches('`');
+        let prefix_length = line.len() - lang.len();
+        (&line[0..prefix_length], lang)
+    }
+
     fn enumerate_blocks(content: &String, target_language: &str) -> Vec<CodeSnippet> {
         // Read the file line by line looking for ```{target_language} blocks.
         let mut result: Vec<CodeSnippet> = Vec::new();
@@ -259,9 +271,12 @@ impl MDBook {
         let mut sample: String = String::new();
         let mut index: i32 = 1;
         let mut start: i32 = 1;
+        let mut prefix: String = String::new();
         for line in content.lines() {
-            if line.starts_with("```") {
-                if in_block {
+            if line.starts_with("```")
+                && (!in_block || (in_block && MDBook::prefix_matches(line, &prefix)))
+            {
+                if in_block && MDBook::prefix_matches(line, &prefix) {
                     in_block = false;
                     if is_target {
                         // this block is our target language!
@@ -274,8 +289,9 @@ impl MDBook {
                         is_target = false;
                     }
                 } else {
+                    let (p, lang) = MDBook::parse_prefix(line);
+                    prefix = p.to_string();
                     in_block = true;
-                    let lang = line.trim_matches('`');
                     if lang == target_language {
                         is_target = true;
                         start = index;

src/renderer/html_handlebars/helpers/navigation.rs

@@ -149,8 +149,8 @@ fn render(
     _h.template()
         .ok_or_else(|| RenderError::new("Error with the handlebars template"))
         .and_then(|t| {
-            let mut local_rc = rc.clone();
             let local_ctx = Context::wraps(&context)?;
+            let mut local_rc = rc.clone();
             t.render(r, &local_ctx, &mut local_rc, out)
         })?;