Inspect markdown code fences to determine whether to apply syntax highlighting

crates/ra_ide/src/snapshots/highlight_doctest.html

@@ -73,9 +73,13 @@ pre                 { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padd
     <span class="comment">///</span>
     <span class="comment">/// ```</span>
     <span class="comment">///</span>
-    <span class="comment">/// ```</span>
+    <span class="comment">/// ```rust,no_run</span>
     <span class="comment">/// </span><span class="keyword">let</span> <span class="variable declaration">foobar</span> = <span class="struct">Foo</span>::<span class="function">new</span>().<span class="function">bar</span>();
     <span class="comment">/// ```</span>
+    <span class="comment">///</span>
+    <span class="comment">/// ```sh</span>
+    <span class="comment">/// echo 1</span>
+    <span class="comment">/// ```</span>
     <span class="keyword">pub</span> <span class="keyword">fn</span> <span class="function declaration">foo</span>(&<span class="self_keyword">self</span>) -&gt; <span class="builtin_type">bool</span> {
         <span class="bool_literal">true</span>
     }

crates/ra_ide/src/syntax_highlighting/injection.rs

@@ -53,6 +53,10 @@ pub(super) fn highlight_injection(
 /// Mapping from extracted documentation code to original code
 type RangesMap = BTreeMap<TextSize, TextSize>;
 
+const RUSTDOC_FENCE: &'static str = "```";
+const RUSTDOC_FENCE_TOKENS: &[&'static str] =
+    &["", "rust", "should_panic", "ignore", "no_run", "compile_fail", "edition2015", "edition2018"];
+
 /// Extracts Rust code from documentation comments as well as a mapping from
 /// the extracted source code back to the original source ranges.
 /// Lastly, a vector of new comment highlight ranges (spanning only the
@@ -67,6 +71,7 @@ pub(super) fn extract_doc_comments(
     // Mapping from extracted documentation code to original code
     let mut range_mapping: RangesMap = BTreeMap::new();
     let mut line_start = TextSize::try_from(prefix.len()).unwrap();
+    let mut is_codeblock = false;
     let mut is_doctest = false;
     // Replace the original, line-spanning comment ranges by new, only comment-prefix
     // spanning comment ranges.
@@ -76,8 +81,13 @@ pub(super) fn extract_doc_comments(
         .filter_map(|el| el.into_token().and_then(ast::Comment::cast))
         .filter(|comment| comment.kind().doc.is_some())
         .filter(|comment| {
-            if comment.text().contains("```") {
+            if let Some(idx) = comment.text().find(RUSTDOC_FENCE) {
-                is_doctest = !is_doctest;
+                is_codeblock = !is_codeblock;
+                // Check whether code is rust by inspecting fence guards
+                let guards = &comment.text()[idx + RUSTDOC_FENCE.len()..];
+                let is_rust =
+                    guards.split(',').all(|sub| RUSTDOC_FENCE_TOKENS.contains(&sub.trim()));
+                is_doctest = is_codeblock && is_rust;
                 false
             } else {
                 is_doctest

crates/ra_ide/src/syntax_highlighting/tests.rs

@@ -329,9 +329,13 @@ impl Foo {
     ///
     /// ```
     ///
-    /// ```
+    /// ```rust,no_run
     /// let foobar = Foo::new().bar();
     /// ```
+    ///
+    /// ```sh
+    /// echo 1
+    /// ```
     pub fn foo(&self) -> bool {
         true
     }