Allow treating a missing highlight language as error (#2642)

components/config/src/config/markup.rs

@@ -27,6 +27,8 @@ pub struct ThemeCss {
 pub struct Markdown {
     /// Whether to highlight all code blocks found in markdown files. Defaults to false
     pub highlight_code: bool,
+    /// Emit an error for missing highlight languages. Defaults to false
+    pub error_on_missing_highlight: bool,
     /// Which themes to use for code highlighting. See Readme for supported themes
     /// Defaults to "base16-ocean-dark"
     pub highlight_theme: String,
@@ -198,6 +200,7 @@ impl Default for Markdown {
     fn default() -> Markdown {
         Markdown {
             highlight_code: false,
+            error_on_missing_highlight: false,
             highlight_theme: DEFAULT_HIGHLIGHT_THEME.to_owned(),
             highlight_themes_css: Vec::new(),
             render_emoji: false,

components/markdown/src/codeblock/mod.rs

@@ -3,6 +3,7 @@ mod highlight;
 
 use std::ops::RangeInclusive;
 
+use errors::{bail, Result};
 use libs::syntect::util::LinesWithEndings;
 
 use crate::codeblock::highlight::SyntaxHighlighter;
@@ -75,14 +76,19 @@ impl<'config> CodeBlock<'config> {
         config: &'config Config,
         // path to the current file if there is one, to point where the error is
         path: Option<&'config str>,
-    ) -> (Self, String) {
+    ) -> Result<(Self, String)> {
         let syntax_and_theme = resolve_syntax_and_theme(fence.language, config);
         if syntax_and_theme.source == HighlightSource::NotFound && config.markdown.highlight_code {
             let lang = fence.language.unwrap();
-            if let Some(p) = path {
-                eprintln!("Warning: Highlight language {} not found in {}", lang, p);
+            let msg = if let Some(p) = path {
+                format!("Highlight language {} not found in {}", lang, p)
             } else {
-                eprintln!("Warning: Highlight language {} not found", lang);
+                format!("Highlight language {} not found", lang)
+            };
+            if config.markdown.error_on_missing_highlight {
+                bail!(msg);
+            } else {
+                eprintln!("Warning: {}", msg);
             }
         }
         let highlighter = SyntaxHighlighter::new(config.markdown.highlight_code, syntax_and_theme);
@@ -93,7 +99,7 @@ impl<'config> CodeBlock<'config> {
             highlighter.pre_class(),
             fence.line_numbers,
         );
-        (
+        Ok((
             Self {
                 highlighter,
                 line_numbers: fence.line_numbers,
@@ -102,7 +108,7 @@ impl<'config> CodeBlock<'config> {
                 hide_lines: fence.hide_lines,
             },
             html_start,
-        )
+        ))
     }
 
     pub fn highlight(&mut self, content: &str) -> String {

components/markdown/src/markdown.rs

@@ -559,7 +559,13 @@ pub fn markdown_to_html(
                         cmark::CodeBlockKind::Fenced(fence_info) => FenceSettings::new(fence_info),
                         _ => FenceSettings::new(""),
                     };
-                    let (block, begin) = CodeBlock::new(fence, context.config, path);
+                    let (block, begin) = match CodeBlock::new(fence, context.config, path) {
+                        Ok(cb) => cb,
+                        Err(e) => {
+                            error = Some(e);
+                            break;
+                        }
+                    };
                     code_block = Some(block);
                     events.push(Event::Html(begin.into()));
                 }

docs/content/documentation/getting-started/configuration.md

@@ -114,6 +114,9 @@ generate_robots_txt = true
 # When set to "true", all code blocks are highlighted.
 highlight_code = false
 
+# When set to "true", missing highlight languages are treated as errors. Defaults to false.
+error_on_missing_highlight = false
+
 # A list of directories used to search for additional `.sublime-syntax` and `.tmTheme` files.
 extra_syntaxes_and_themes = []