Use old parser if custom_code_classes_in_docs feature is not enabled

src/librustdoc/html/markdown.rs

@@ -868,7 +868,7 @@ impl<'tcx> ExtraInfo<'tcx> {
 
 #[derive(Eq, PartialEq, Clone, Debug)]
 pub(crate) struct LangString {
-    original: String,
+    pub(crate) original: String,
     pub(crate) should_panic: bool,
     pub(crate) no_run: bool,
     pub(crate) ignore: Ignore,
@@ -1158,6 +1158,29 @@ impl<'a, 'tcx> Iterator for TagIterator<'a, 'tcx> {
     }
 }
 
+fn tokens(string: &str) -> impl Iterator<Item = LangStringToken<'_>> {
+    // Pandoc, which Rust once used for generating documentation,
+    // expects lang strings to be surrounded by `{}` and for each token
+    // to be proceeded by a `.`. Since some of these lang strings are still
+    // loose in the wild, we strip a pair of surrounding `{}` from the lang
+    // string and a leading `.` from each token.
+
+    let string = string.trim();
+
+    let first = string.chars().next();
+    let last = string.chars().last();
+
+    let string =
+        if first == Some('{') && last == Some('}') { &string[1..string.len() - 1] } else { string };
+
+    string
+        .split(|c| c == ',' || c == ' ' || c == '\t')
+        .map(str::trim)
+        .map(|token| token.strip_prefix('.').unwrap_or(token))
+        .filter(|token| !token.is_empty())
+        .map(|token| LangStringToken::LangToken(token))
+}
+
 impl Default for LangString {
     fn default() -> Self {
         Self {
@@ -1208,7 +1231,8 @@ impl LangString {
 
         data.original = string.to_owned();
 
-        for token in TagIterator::new(string, extra) {
+        let mut call = |tokens: &mut dyn Iterator<Item = LangStringToken<'_>>| {
+            for token in tokens {
                 match token {
                     LangStringToken::LangToken("should_panic") => {
                         data.should_panic = true;
@@ -1325,6 +1349,13 @@ impl LangString {
                     }
                 }
             }
+        };
+
+        if custom_code_classes_in_docs {
+            call(&mut TagIterator::new(string, extra).into_iter())
+        } else {
+            call(&mut tokens(string))
+        }
 
         // ignore-foo overrides ignore
         if !ignores.is_empty() {