Implement custom classes for rustdoc code blocks with custom_code_classes_in_docs feature

src/librustdoc/passes/check_custom_code_classes.rs

@@ -0,0 +1,77 @@
+//! NIGHTLY & UNSTABLE CHECK: custom_code_classes_in_docs
+//!
+//! This pass will produce errors when finding custom classes outside of
+//! nightly + relevant feature active.
+
+use super::Pass;
+use crate::clean::{Crate, Item};
+use crate::core::DocContext;
+use crate::fold::DocFolder;
+use crate::html::markdown::{find_codes, ErrorCodes, LangString};
+
+use rustc_session::parse::feature_err;
+use rustc_span::symbol::sym;
+
+pub(crate) const CHECK_CUSTOM_CODE_CLASSES: Pass = Pass {
+    name: "check-custom-code-classes",
+    run: check_custom_code_classes,
+    description: "check for custom code classes without the feature-gate enabled",
+};
+
+pub(crate) fn check_custom_code_classes(krate: Crate, cx: &mut DocContext<'_>) -> Crate {
+    let mut coll = CustomCodeClassLinter { cx };
+
+    coll.fold_crate(krate)
+}
+
+struct CustomCodeClassLinter<'a, 'tcx> {
+    cx: &'a DocContext<'tcx>,
+}
+
+impl<'a, 'tcx> DocFolder for CustomCodeClassLinter<'a, 'tcx> {
+    fn fold_item(&mut self, item: Item) -> Option<Item> {
+        look_for_custom_classes(&self.cx, &item);
+        Some(self.fold_item_recur(item))
+    }
+}
+
+#[derive(Debug)]
+struct TestsWithCustomClasses {
+    custom_classes_found: Vec<String>,
+}
+
+impl crate::doctest::Tester for TestsWithCustomClasses {
+    fn add_test(&mut self, _: String, config: LangString, _: usize) {
+        self.custom_classes_found.extend(config.added_classes.into_iter());
+    }
+}
+
+pub(crate) fn look_for_custom_classes<'tcx>(cx: &DocContext<'tcx>, item: &Item) {
+    if !item.item_id.is_local() {
+        // If non-local, no need to check anything.
+        return;
+    }
+
+    let mut tests = TestsWithCustomClasses { custom_classes_found: vec![] };
+
+    let dox = item.attrs.collapsed_doc_value().unwrap_or_default();
+    find_codes(&dox, &mut tests, ErrorCodes::No, false, None, true);
+
+    if !tests.custom_classes_found.is_empty() && !cx.tcx.features().custom_code_classes_in_docs {
+        feature_err(
+            &cx.tcx.sess.parse_sess,
+            sym::custom_code_classes_in_docs,
+            item.attr_span(cx.tcx),
+            "custom classes in code blocks are unstable",
+        )
+        .note(
+            // This will list the wrong items to make them more easily searchable.
+            // To ensure the most correct hits, it adds back the 'class:' that was stripped.
+            &format!(
+                "found these custom classes: class={}",
+                tests.custom_classes_found.join(",class=")
+            ),
+        )
+        .emit();
+    }
+}