Auto merge of #127127 - notriddle:notriddle/pulldown-cmark-0.11, r=GuillaumeGomez

rustdoc: update to pulldown-cmark 0.11

r? rustdoc

This pull request updates rustdoc to the latest version of pulldown-cmark. Along with adding new markdown extensions (which this PR doesn't enable), the new pulldown-cmark version also fixes a large number of bugs. Because all text files successfully parse as markdown, these bugfixes change the output, which can break people's existing docs.

A crater run, https://github.com/rust-lang/rust/pull/121659, has already been run for this change.

The first commit upgrades and fixes rustdoc. The second commit adds a lint for the footnote and block quote parser changes, which break the largest numbers of docs in the Crater run. The strikethrough change was mitigated in pulldown-cmark itself.

Unblocks https://github.com/rust-lang/rust-clippy/pull/12876

Cargo.lock

@@ -3141,7 +3141,19 @@ dependencies = [
  "bitflags 2.5.0",
  "getopts",
  "memchr",
- "pulldown-cmark-escape",
+ "pulldown-cmark-escape 0.10.1",
+ "unicase",
+]
+
+[[package]]
+name = "pulldown-cmark"
+version = "0.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8746739f11d39ce5ad5c2520a9b75285310dbfe78c541ccf832d38615765aec0"
+dependencies = [
+ "bitflags 2.5.0",
+ "memchr",
+ "pulldown-cmark-escape 0.11.0",
  "unicase",
 ]
 
@@ -3151,6 +3163,12 @@ version = "0.10.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "bd348ff538bc9caeda7ee8cad2d1d48236a1f443c1fa3913c6a02fe0043b1dd3"
 
+[[package]]
+name = "pulldown-cmark-escape"
+version = "0.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "007d8adb5ddab6f8e3f491ac63566a7d5002cc7ed73901f72057943fa71ae1ae"
+
 [[package]]
 name = "pulldown-cmark-to-cmark"
 version = "13.0.0"
@@ -4604,7 +4622,7 @@ name = "rustc_resolve"
 version = "0.0.0"
 dependencies = [
  "bitflags 2.5.0",
- "pulldown-cmark 0.9.6",
+ "pulldown-cmark 0.11.0",
  "rustc_arena",
  "rustc_ast",
  "rustc_ast_pretty",
@@ -4883,6 +4901,7 @@ dependencies = [
  "indexmap",
  "itertools",
  "minifier",
+ "pulldown-cmark 0.9.6",
  "regex",
  "rustdoc-json-types",
  "serde",

compiler/rustc_data_structures/src/sync.rs

@@ -35,11 +35,11 @@
 //! |                         |                     |                                 |
 //! | `ParallelIterator`      | `Iterator`          | `rayon::iter::ParallelIterator` |
 //!
-//! [^1] `MTLock` is similar to `Lock`, but the serial version avoids the cost
+//! [^1]: `MTLock` is similar to `Lock`, but the serial version avoids the cost
 //! of a `RefCell`. This is appropriate when interior mutability is not
 //! required.
 //!
-//! [^2] `MTRef`, `MTLockRef` are type aliases.
+//! [^2]: `MTRef`, `MTLockRef` are type aliases.
 
 pub use crate::marker::*;
 use std::collections::HashMap;

compiler/rustc_resolve/Cargo.toml

@@ -6,7 +6,7 @@ edition = "2021"
 [dependencies]
 # tidy-alphabetical-start
 bitflags = "2.4.1"
-pulldown-cmark = { version = "0.9.6", default-features = false }
+pulldown-cmark = { version = "0.11", features = ["html"], default-features = false }
 rustc_arena = { path = "../rustc_arena" }
 rustc_ast = { path = "../rustc_ast" }
 rustc_ast_pretty = { path = "../rustc_ast_pretty" }

compiler/rustc_resolve/src/rustdoc.rs

@@ -1,4 +1,6 @@
-use pulldown_cmark::{BrokenLink, CowStr, Event, LinkType, Options, Parser, Tag};
+use pulldown_cmark::{
+    BrokenLink, BrokenLinkCallback, CowStr, Event, LinkType, Options, Parser, Tag,
+};
 use rustc_ast as ast;
 use rustc_ast::util::comments::beautify_doc_string;
 use rustc_data_structures::fx::FxHashMap;
@@ -427,7 +429,9 @@ fn parse_links<'md>(doc: &'md str) -> Vec<Box<str>> {
 
     while let Some(event) = event_iter.next() {
         match event {
-            Event::Start(Tag::Link(link_type, dest, _)) if may_be_doc_link(link_type) => {
+            Event::Start(Tag::Link { link_type, dest_url, title: _, id: _ })
+                if may_be_doc_link(link_type) =>
+            {
                 if matches!(
                     link_type,
                     LinkType::Inline
@@ -441,7 +445,7 @@ fn parse_links<'md>(doc: &'md str) -> Vec<Box<str>> {
                     }
                 }
 
-                links.push(preprocess_link(&dest));
+                links.push(preprocess_link(&dest_url));
             }
             _ => {}
         }
@@ -451,8 +455,8 @@ fn parse_links<'md>(doc: &'md str) -> Vec<Box<str>> {
 }
 
 /// Collects additional data of link.
-fn collect_link_data<'input, 'callback>(
+fn collect_link_data<'input, F: BrokenLinkCallback<'input>>(
-    event_iter: &mut Parser<'input, 'callback>,
+    event_iter: &mut Parser<'input, F>,
 ) -> Option<Box<str>> {
     let mut display_text: Option<String> = None;
     let mut append_text = |text: CowStr<'_>| {

src/librustdoc/Cargo.toml

@@ -13,6 +13,7 @@ base64 = "0.21.7"
 itertools = "0.12"
 indexmap = "2"
 minifier = "0.3.0"
+pulldown-cmark-old = { version = "0.9.6", package = "pulldown-cmark", default-features = false }
 regex = "1"
 rustdoc-json-types = { path = "../rustdoc-json-types" }
 serde_json = "1.0"

src/librustdoc/html/markdown.rs

@@ -54,7 +54,8 @@
 use crate::html::toc::TocBuilder;
 
 use pulldown_cmark::{
-    html, BrokenLink, CodeBlockKind, CowStr, Event, LinkType, OffsetIter, Options, Parser, Tag,
+    html, BrokenLink, BrokenLinkCallback, CodeBlockKind, CowStr, Event, LinkType, OffsetIter,
+    Options, Parser, Tag, TagEnd,
 };
 
 #[cfg(test)]
@@ -230,7 +231,7 @@ fn next(&mut self) -> Option<Self::Item> {
         let mut original_text = String::new();
         for event in &mut self.inner {
             match event {
-                Event::End(Tag::CodeBlock(..)) => break,
+                Event::End(TagEnd::CodeBlock) => break,
                 Event::Text(ref s) => {
                     original_text.push_str(s);
                 }
@@ -359,16 +360,17 @@ fn next(&mut self) -> Option<Self::Item> {
         match &mut event {
             // This is a shortcut link that was resolved by the broken_link_callback: `[fn@f]`
             // Remove any disambiguator.
-            Some(Event::Start(Tag::Link(
+            Some(Event::Start(Tag::Link {
                 // [fn@f] or [fn@f][]
-                LinkType::ShortcutUnknown | LinkType::CollapsedUnknown,
+                link_type: LinkType::ShortcutUnknown | LinkType::CollapsedUnknown,
-                dest,
+                dest_url,
                 title,
-            ))) => {
+                ..
-                debug!("saw start of shortcut link to {dest} with title {title}");
+            })) => {
+                debug!("saw start of shortcut link to {dest_url} with title {title}");
                 // If this is a shortcut link, it was resolved by the broken_link_callback.
                 // So the URL will already be updated properly.
-                let link = self.links.iter().find(|&link| *link.href == **dest);
+                let link = self.links.iter().find(|&link| *link.href == **dest_url);
                 // Since this is an external iterator, we can't replace the inner text just yet.
                 // Store that we saw a link so we know to replace it later.
                 if let Some(link) = link {
@@ -381,17 +383,10 @@ fn next(&mut self) -> Option<Self::Item> {
                 }
             }
             // Now that we're done with the shortcut link, don't replace any more text.
-            Some(Event::End(Tag::Link(
+            Some(Event::End(TagEnd::Link)) if self.shortcut_link.is_some() => {
-                LinkType::ShortcutUnknown | LinkType::CollapsedUnknown,
+                debug!("saw end of shortcut link");
-                dest,
-                _,
-            ))) => {
-                debug!("saw end of shortcut link to {dest}");
-                if self.links.iter().any(|link| *link.href == **dest) {
-                    assert!(self.shortcut_link.is_some(), "saw closing link without opening tag");
                 self.shortcut_link = None;
             }
-            }
             // Handle backticks in inline code blocks, but only if we're in the middle of a shortcut link.
             // [`fn@f`]
             Some(Event::Code(text)) => {
@@ -433,9 +428,11 @@ fn next(&mut self) -> Option<Self::Item> {
             }
             // If this is a link, but not a shortcut link,
             // replace the URL, since the broken_link_callback was not called.
-            Some(Event::Start(Tag::Link(_, dest, title))) => {
+            Some(Event::Start(Tag::Link { dest_url, title, .. })) => {
-                if let Some(link) = self.links.iter().find(|&link| *link.original_text == **dest) {
+                if let Some(link) =
-                    *dest = CowStr::Borrowed(link.href.as_ref());
+                    self.links.iter().find(|&link| *link.original_text == **dest_url)
+                {
+                    *dest_url = CowStr::Borrowed(link.href.as_ref());
                     if title.is_empty() && !link.tooltip.is_empty() {
                         *title = CowStr::Borrowed(link.tooltip.as_ref());
                     }
@@ -477,9 +474,9 @@ fn next(&mut self) -> Option<Self::Item> {
                 self.stored_events.push_back(Event::Start(Tag::Table(t)));
                 Event::Html(CowStr::Borrowed("<div>"))
             }
-            Event::End(Tag::Table(t)) => {
+            Event::End(TagEnd::Table) => {
                 self.stored_events.push_back(Event::Html(CowStr::Borrowed("</div>")));
-                Event::End(Tag::Table(t))
+                Event::End(TagEnd::Table)
             }
             e => e,
         })
@@ -519,11 +516,11 @@ fn next(&mut self) -> Option<Self::Item> {
         }
 
         let event = self.inner.next();
-        if let Some((Event::Start(Tag::Heading(level, _, _)), _)) = event {
+        if let Some((Event::Start(Tag::Heading { level, .. }), _)) = event {
             let mut id = String::new();
             for event in &mut self.inner {
                 match &event.0 {
-                    Event::End(Tag::Heading(..)) => break,
+                    Event::End(TagEnd::Heading(_)) => break,
                     Event::Text(text) | Event::Code(text) => {
                         id.extend(text.chars().filter_map(slugify));
                         self.buf.push_back(event);
@@ -566,27 +563,27 @@ fn new(iter: I) -> Self {
     }
 }
 
-fn check_if_allowed_tag(t: &Tag<'_>) -> bool {
+fn check_if_allowed_tag(t: &TagEnd) -> bool {
     matches!(
         t,
-        Tag::Paragraph
+        TagEnd::Paragraph
-            | Tag::Emphasis
+            | TagEnd::Emphasis
-            | Tag::Strong
+            | TagEnd::Strong
-            | Tag::Strikethrough
+            | TagEnd::Strikethrough
-            | Tag::Link(..)
+            | TagEnd::Link
-            | Tag::BlockQuote
+            | TagEnd::BlockQuote
     )
 }
 
-fn is_forbidden_tag(t: &Tag<'_>) -> bool {
+fn is_forbidden_tag(t: &TagEnd) -> bool {
     matches!(
         t,
-        Tag::CodeBlock(_)
+        TagEnd::CodeBlock
-            | Tag::Table(_)
+            | TagEnd::Table
-            | Tag::TableHead
+            | TagEnd::TableHead
-            | Tag::TableRow
+            | TagEnd::TableRow
-            | Tag::TableCell
+            | TagEnd::TableCell
-            | Tag::FootnoteDefinition(_)
+            | TagEnd::FootnoteDefinition
     )
 }
 
@@ -604,12 +601,12 @@ fn next(&mut self) -> Option<Self::Item> {
             let mut is_start = true;
             let is_allowed_tag = match event {
                 Event::Start(ref c) => {
-                    if is_forbidden_tag(c) {
+                    if is_forbidden_tag(&c.to_end()) {
                         self.skipped_tags += 1;
                         return None;
                     }
                     self.depth += 1;
-                    check_if_allowed_tag(c)
+                    check_if_allowed_tag(&c.to_end())
                 }
                 Event::End(ref c) => {
                     if is_forbidden_tag(c) {
@@ -633,7 +630,7 @@ fn next(&mut self) -> Option<Self::Item> {
                 if is_start {
                     Some(Event::Start(Tag::Paragraph))
                 } else {
-                    Some(Event::End(Tag::Paragraph))
+                    Some(Event::End(TagEnd::Paragraph))
                 }
             } else {
                 Some(event)
@@ -679,7 +676,7 @@ fn next(&mut self) -> Option<Self::Item> {
                 Some((Event::Start(Tag::FootnoteDefinition(def)), _)) => {
                     let mut content = Vec::new();
                     for (event, _) in &mut self.inner {
-                        if let Event::End(Tag::FootnoteDefinition(..)) = event {
+                        if let Event::End(TagEnd::FootnoteDefinition) = event {
                             break;
                         }
                         content.push(event);
@@ -696,7 +693,7 @@ fn next(&mut self) -> Option<Self::Item> {
                         for (mut content, id) in v {
                             write!(ret, "<li id=\"fn{id}\">").unwrap();
                             let mut is_paragraph = false;
-                            if let Some(&Event::End(Tag::Paragraph)) = content.last() {
+                            if let Some(&Event::End(TagEnd::Paragraph)) = content.last() {
                                 content.pop();
                                 is_paragraph = true;
                             }
@@ -806,7 +803,7 @@ pub(crate) fn find_codes<T: doctest::DoctestVisitor>(
                 tests.visit_test(text, block_info, line);
                 prev_offset = offset.start;
             }
-            Event::Start(Tag::Heading(level, _, _)) => {
+            Event::Start(Tag::Heading { level, .. }) => {
                 register_header = Some(level as u32);
             }
             Event::Text(ref s) if register_header.is_some() => {
@@ -1432,7 +1429,7 @@ pub(crate) fn into_string(self) -> String {
 
         // Treat inline HTML as plain text.
         let p = p.map(|event| match event.0 {
-            Event::Html(text) => (Event::Text(text), event.1),
+            Event::Html(text) | Event::InlineHtml(text) => (Event::Text(text), event.1),
             _ => event,
         });
 
@@ -1442,7 +1439,7 @@ pub(crate) fn into_string(self) -> String {
         let p = Footnotes::new(p);
         let p = TableWrapper::new(p.map(|(ev, _)| ev));
         let p = p.filter(|event| {
-            !matches!(event, Event::Start(Tag::Paragraph) | Event::End(Tag::Paragraph))
+            !matches!(event, Event::Start(Tag::Paragraph) | Event::End(TagEnd::Paragraph))
         });
         html::push_html(&mut s, p);
 
@@ -1472,7 +1469,7 @@ pub(crate) fn into_string_with_has_more_content(self) -> (String, bool) {
         let mut s = String::new();
 
         let without_paragraphs = LinkReplacer::new(&mut summary, links).filter(|event| {
-            !matches!(event, Event::Start(Tag::Paragraph) | Event::End(Tag::Paragraph))
+            !matches!(event, Event::Start(Tag::Paragraph) | Event::End(TagEnd::Paragraph))
         });
 
         html::push_html(&mut s, without_paragraphs);
@@ -1544,8 +1541,8 @@ fn markdown_summary_with_limit(
                 _ => {}
             },
             Event::End(tag) => match tag {
-                Tag::Emphasis | Tag::Strong => buf.close_tag(),
+                TagEnd::Emphasis | TagEnd::Strong => buf.close_tag(),
-                Tag::Paragraph | Tag::Heading(..) => return ControlFlow::Break(()),
+                TagEnd::Paragraph | TagEnd::Heading(_) => return ControlFlow::Break(()),
                 _ => {}
             },
             Event::HardBreak | Event::SoftBreak => buf.push(" ")?,
@@ -1605,8 +1602,8 @@ pub(crate) fn plain_text_summary(md: &str, link_names: &[RenderedLink]) -> Strin
             }
             Event::HardBreak | Event::SoftBreak => s.push(' '),
             Event::Start(Tag::CodeBlock(..)) => break,
-            Event::End(Tag::Paragraph) => break,
+            Event::End(TagEnd::Paragraph) => break,
-            Event::End(Tag::Heading(..)) => break,
+            Event::End(TagEnd::Heading(..)) => break,
             _ => (),
         }
     }
@@ -1765,7 +1762,7 @@ pub(crate) fn markdown_links<'md, R>(
 
     while let Some((event, span)) = event_iter.next() {
         match event {
-            Event::Start(Tag::Link(link_type, dest, _)) if may_be_doc_link(link_type) => {
+            Event::Start(Tag::Link { link_type, dest_url, .. }) if may_be_doc_link(link_type) => {
                 let range = match link_type {
                     // Link is pulled from the link itself.
                     LinkType::ReferenceUnknown | LinkType::ShortcutUnknown => {
@@ -1775,7 +1772,7 @@ pub(crate) fn markdown_links<'md, R>(
                     LinkType::Inline => span_for_offset_backward(span, b'(', b')'),
                     // Link is pulled from elsewhere in the document.
                     LinkType::Reference | LinkType::Collapsed | LinkType::Shortcut => {
-                        span_for_link(&dest, span)
+                        span_for_link(&dest_url, span)
                     }
                     LinkType::Autolink | LinkType::Email => unreachable!(),
                 };
@@ -1795,7 +1792,7 @@ pub(crate) fn markdown_links<'md, R>(
 
                 if let Some(link) = preprocess_link(MarkdownLink {
                     kind: link_type,
-                    link: dest.into_string(),
+                    link: dest_url.into_string(),
                     display_text,
                     range,
                 }) {
@@ -1810,8 +1807,8 @@ pub(crate) fn markdown_links<'md, R>(
 }
 
 /// Collects additional data of link.
-fn collect_link_data<'input, 'callback>(
+fn collect_link_data<'input, F: BrokenLinkCallback<'input>>(
-    event_iter: &mut OffsetIter<'input, 'callback>,
+    event_iter: &mut OffsetIter<'input, F>,
 ) -> Option<String> {
     let mut display_text: Option<String> = None;
     let mut append_text = |text: CowStr<'_>| {

src/librustdoc/lint.rs

@@ -196,6 +196,14 @@ macro_rules! declare_rustdoc_lint {
     "detects redundant explicit links in doc comments"
 }
 
+declare_rustdoc_lint! {
+    /// This compatibility lint checks for Markdown syntax that works in the old engine but not
+    /// the new one.
+    UNPORTABLE_MARKDOWN,
+    Warn,
+    "detects markdown that is interpreted differently in different parser"
+}
+
 pub(crate) static RUSTDOC_LINTS: Lazy<Vec<&'static Lint>> = Lazy::new(|| {
     vec![
         BROKEN_INTRA_DOC_LINKS,
@@ -209,6 +217,7 @@ macro_rules! declare_rustdoc_lint {
         MISSING_CRATE_LEVEL_DOCS,
         UNESCAPED_BACKTICKS,
         REDUNDANT_EXPLICIT_LINKS,
+        UNPORTABLE_MARKDOWN,
     ]
 });
 

src/librustdoc/passes/lint.rs

@@ -6,6 +6,7 @@
 mod html_tags;
 mod redundant_explicit_links;
 mod unescaped_backticks;
+mod unportable_markdown;
 
 use super::Pass;
 use crate::clean::*;
@@ -31,6 +32,7 @@ fn visit_item(&mut self, item: &Item) {
         html_tags::visit_item(self.cx, item);
         unescaped_backticks::visit_item(self.cx, item);
         redundant_explicit_links::visit_item(self.cx, item);
+        unportable_markdown::visit_item(self.cx, item);
 
         self.visit_item_recur(item)
     }

src/librustdoc/passes/lint/bare_urls.rs

@@ -42,11 +42,11 @@ pub(super) fn visit_item(cx: &DocContext<'_>, item: &Item) {
             match event {
                 Event::Text(s) => find_raw_urls(cx, &s, range, &report_diag),
                 // We don't want to check the text inside code blocks or links.
-                Event::Start(tag @ (Tag::CodeBlock(_) | Tag::Link(..))) => {
+                Event::Start(tag @ (Tag::CodeBlock(_) | Tag::Link { .. })) => {
                     while let Some((event, _)) = p.next() {
                         match event {
                             Event::End(end)
-                                if mem::discriminant(&end) == mem::discriminant(&tag) =>
+                                if mem::discriminant(&end) == mem::discriminant(&tag.to_end()) =>
                             {
                                 break;
                             }

src/librustdoc/passes/lint/html_tags.rs

@@ -4,7 +4,7 @@
 use crate::core::DocContext;
 use crate::html::markdown::main_body_opts;
 
-use pulldown_cmark::{BrokenLink, Event, LinkType, Parser, Tag};
+use pulldown_cmark::{BrokenLink, Event, LinkType, Parser, Tag, TagEnd};
 use rustc_resolve::rustdoc::source_span_for_markdown_range;
 
 use std::iter::Peekable;
@@ -140,10 +140,10 @@ pub(crate) fn visit_item(cx: &DocContext<'_>, item: &Item) {
         for (event, range) in p {
             match event {
                 Event::Start(Tag::CodeBlock(_)) => in_code_block = true,
-                Event::Html(text) if !in_code_block => {
+                Event::Html(text) | Event::InlineHtml(text) if !in_code_block => {
                     extract_tags(&mut tags, &text, range, &mut is_in_comment, &report_diag)
                 }
-                Event::End(Tag::CodeBlock(_)) => in_code_block = false,
+                Event::End(TagEnd::CodeBlock) => in_code_block = false,
                 _ => {}
             }
         }

src/librustdoc/passes/lint/redundant_explicit_links.rs

@@ -1,6 +1,8 @@
 use std::ops::Range;
 
-use pulldown_cmark::{BrokenLink, CowStr, Event, LinkType, OffsetIter, Parser, Tag};
+use pulldown_cmark::{
+    BrokenLink, BrokenLinkCallback, CowStr, Event, LinkType, OffsetIter, Parser, Tag,
+};
 use rustc_ast::NodeId;
 use rustc_errors::SuggestionStyle;
 use rustc_hir::def::{DefKind, DocLinkResMap, Namespace, Res};
@@ -95,7 +97,7 @@ fn check_redundant_explicit_link<'md>(
 
     while let Some((event, link_range)) = offset_iter.next() {
         match event {
-            Event::Start(Tag::Link(link_type, dest, _)) => {
+            Event::Start(Tag::Link { link_type, dest_url, .. }) => {
                 let link_data = collect_link_data(&mut offset_iter);
 
                 if let Some(resolvable_link) = link_data.resolvable_link.as_ref() {
@@ -108,7 +110,7 @@ fn check_redundant_explicit_link<'md>(
                     }
                 }
 
-                let explicit_link = dest.to_string();
+                let explicit_link = dest_url.to_string();
                 let display_link = link_data.resolvable_link.clone()?;
 
                 if explicit_link.ends_with(&display_link) || display_link.ends_with(&explicit_link)
@@ -122,7 +124,7 @@ fn check_redundant_explicit_link<'md>(
                                 doc,
                                 resolutions,
                                 link_range,
-                                dest.to_string(),
+                                dest_url.to_string(),
                                 link_data,
                                 if link_type == LinkType::Inline {
                                     (b'(', b')')
@@ -139,7 +141,7 @@ fn check_redundant_explicit_link<'md>(
                                 doc,
                                 resolutions,
                                 link_range,
-                                &dest,
+                                &dest_url,
                                 link_data,
                             );
                         }
@@ -259,7 +261,9 @@ fn find_resolution(resolutions: &DocLinkResMap, path: &str) -> Option<Res<NodeId
 }
 
 /// Collects all necessary data of link.
-fn collect_link_data(offset_iter: &mut OffsetIter<'_, '_>) -> LinkData {
+fn collect_link_data<'input, F: BrokenLinkCallback<'input>>(
+    offset_iter: &mut OffsetIter<'input, F>,
+) -> LinkData {
     let mut resolvable_link = None;
     let mut resolvable_link_range = None;
     let mut display_link = String::new();

src/librustdoc/passes/lint/unportable_markdown.rs

@@ -0,0 +1,152 @@
+//! Detects specific markdown syntax that's different between pulldown-cmark
+//! 0.9 and 0.11.
+//!
+//! This is a mitigation for old parser bugs that affected some
+//! real crates' docs. The old parser claimed to comply with CommonMark,
+//! but it did not. These warnings will eventually be removed,
+//! though some of them may become Clippy lints.
+//!
+//! <https://github.com/rust-lang/rust/pull/121659#issuecomment-1992752820>
+//!
+//! <https://rustc-dev-guide.rust-lang.org/bug-fix-procedure.html#add-the-lint-to-the-list-of-removed-lists>
+
+use crate::clean::Item;
+use crate::core::DocContext;
+use pulldown_cmark as cmarkn;
+use pulldown_cmark_old as cmarko;
+use rustc_lint_defs::Applicability;
+use rustc_resolve::rustdoc::source_span_for_markdown_range;
+use std::collections::{BTreeMap, BTreeSet};
+
+pub(crate) fn visit_item(cx: &DocContext<'_>, item: &Item) {
+    let tcx = cx.tcx;
+    let Some(hir_id) = DocContext::as_local_hir_id(tcx, item.item_id) else {
+        // If non-local, no need to check anything.
+        return;
+    };
+
+    let dox = item.doc_value();
+    if dox.is_empty() {
+        return;
+    }
+
+    // P1: unintended strikethrough was fixed by requiring single-tildes to flank
+    // the same way underscores do, so nothing is done here
+
+    // P2: block quotes without following space parsed wrong
+    //
+    // This is the set of starting points for block quotes with no space after
+    // the `>`. It is populated by the new parser, and if the old parser fails to
+    // clear it out, it'll produce a warning.
+    let mut spaceless_block_quotes = BTreeSet::new();
+
+    // P3: missing footnote references
+    //
+    // This is populated by listening for FootnoteReference from
+    // the new parser and old parser.
+    let mut missing_footnote_references = BTreeMap::new();
+    let mut found_footnote_references = BTreeSet::new();
+
+    // populate problem cases from new parser
+    {
+        pub fn main_body_opts_new() -> cmarkn::Options {
+            cmarkn::Options::ENABLE_TABLES
+                | cmarkn::Options::ENABLE_FOOTNOTES
+                | cmarkn::Options::ENABLE_STRIKETHROUGH
+                | cmarkn::Options::ENABLE_TASKLISTS
+                | cmarkn::Options::ENABLE_SMART_PUNCTUATION
+        }
+        let mut parser_new = cmarkn::Parser::new_ext(&dox, main_body_opts_new()).into_offset_iter();
+        while let Some((event, span)) = parser_new.next() {
+            if let cmarkn::Event::Start(cmarkn::Tag::BlockQuote(_)) = event {
+                if !dox[span.clone()].starts_with("> ") {
+                    spaceless_block_quotes.insert(span.start);
+                }
+            }
+            if let cmarkn::Event::FootnoteReference(_) = event {
+                found_footnote_references.insert(span.start + 1);
+            }
+        }
+    }
+
+    // remove cases where they don't actually differ
+    {
+        pub fn main_body_opts_old() -> cmarko::Options {
+            cmarko::Options::ENABLE_TABLES
+                | cmarko::Options::ENABLE_FOOTNOTES
+                | cmarko::Options::ENABLE_STRIKETHROUGH
+                | cmarko::Options::ENABLE_TASKLISTS
+                | cmarko::Options::ENABLE_SMART_PUNCTUATION
+        }
+        let mut parser_old = cmarko::Parser::new_ext(&dox, main_body_opts_old()).into_offset_iter();
+        while let Some((event, span)) = parser_old.next() {
+            if let cmarko::Event::Start(cmarko::Tag::BlockQuote) = event {
+                if !dox[span.clone()].starts_with("> ") {
+                    spaceless_block_quotes.remove(&span.start);
+                }
+            }
+            if let cmarko::Event::FootnoteReference(_) = event {
+                if !found_footnote_references.contains(&(span.start + 1)) {
+                    missing_footnote_references.insert(span.start + 1, span);
+                }
+            }
+        }
+    }
+
+    for start in spaceless_block_quotes {
+        let (span, precise) =
+            source_span_for_markdown_range(tcx, &dox, &(start..start + 1), &item.attrs.doc_strings)
+                .map(|span| (span, true))
+                .unwrap_or_else(|| (item.attr_span(tcx), false));
+
+        tcx.node_span_lint(crate::lint::UNPORTABLE_MARKDOWN, hir_id, span, |lint| {
+            lint.primary_message("unportable markdown");
+            lint.help(format!("confusing block quote with no space after the `>` marker"));
+            if precise {
+                lint.span_suggestion(
+                    span.shrink_to_hi(),
+                    "if the quote is intended, add a space",
+                    " ",
+                    Applicability::MaybeIncorrect,
+                );
+                lint.span_suggestion(
+                    span.shrink_to_lo(),
+                    "if it should not be a quote, escape it",
+                    "\\",
+                    Applicability::MaybeIncorrect,
+                );
+            }
+        });
+    }
+    for (_caret, span) in missing_footnote_references {
+        let (ref_span, precise) =
+            source_span_for_markdown_range(tcx, &dox, &span, &item.attrs.doc_strings)
+                .map(|span| (span, true))
+                .unwrap_or_else(|| (item.attr_span(tcx), false));
+
+        tcx.node_span_lint(crate::lint::UNPORTABLE_MARKDOWN, hir_id, ref_span, |lint| {
+            lint.primary_message("unportable markdown");
+            if precise {
+                lint.span_suggestion(
+                    ref_span.shrink_to_lo(),
+                    "if it should not be a footnote, escape it",
+                    "\\",
+                    Applicability::MaybeIncorrect,
+                );
+            }
+            if dox.as_bytes().get(span.end) == Some(&b'[') {
+                lint.help("confusing footnote reference and link");
+                if precise {
+                    lint.span_suggestion(
+                        ref_span.shrink_to_hi(),
+                        "if the footnote is intended, add a space",
+                        " ",
+                        Applicability::MaybeIncorrect,
+                    );
+                } else {
+                    lint.help("there should be a space between the link and the footnote");
+                }
+            }
+        });
+    }
+}

src/tools/clippy/clippy_lints/src/doc/mod.rs

@@ -6,10 +6,10 @@
 use clippy_utils::visitors::Visitable;
 use clippy_utils::{in_constant, is_entrypoint_fn, is_trait_impl_item, method_chain_args};
 use pulldown_cmark::Event::{
-    Code, End, FootnoteReference, HardBreak, Html, Rule, SoftBreak, Start, TaskListMarker, Text,
+    Code, DisplayMath, End, FootnoteReference, HardBreak, Html, InlineHtml, InlineMath, Rule, SoftBreak, Start, TaskListMarker, Text,
 };
 use pulldown_cmark::Tag::{BlockQuote, CodeBlock, FootnoteDefinition, Heading, Item, Link, Paragraph};
-use pulldown_cmark::{BrokenLink, CodeBlockKind, CowStr, Options};
+use pulldown_cmark::{BrokenLink, CodeBlockKind, CowStr, Options, TagEnd};
 use rustc_ast::ast::Attribute;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_hir::intravisit::{self, Visitor};
@@ -659,7 +659,7 @@ fn check_doc<'a, Events: Iterator<Item = (pulldown_cmark::Event<'a>, Range<usize
 
     while let Some((event, range)) = events.next() {
         match event {
-            Html(tag) => {
+            Html(tag) | InlineHtml(tag) => {
                 if tag.starts_with("<code") {
                     code_level += 1;
                 } else if tag.starts_with("</code") {
@@ -670,11 +670,11 @@ fn check_doc<'a, Events: Iterator<Item = (pulldown_cmark::Event<'a>, Range<usize
                     blockquote_level -= 1;
                 }
             },
-            Start(BlockQuote) => {
+            Start(BlockQuote(_)) => {
                 blockquote_level += 1;
                 containers.push(Container::Blockquote);
             },
-            End(BlockQuote) => {
+            End(TagEnd::BlockQuote) => {
                 blockquote_level -= 1;
                 containers.pop();
             },
@@ -699,15 +699,15 @@ fn check_doc<'a, Events: Iterator<Item = (pulldown_cmark::Event<'a>, Range<usize
                     }
                 }
             },
-            End(CodeBlock(_)) => {
+            End(TagEnd::CodeBlock) => {
                 in_code = false;
                 is_rust = false;
                 ignore = false;
             },
-            Start(Link(_, url, _)) => in_link = Some(url),
+            Start(Link { dest_url, .. }) => in_link = Some(dest_url),
-            End(Link(..)) => in_link = None,
+            End(TagEnd::Link) => in_link = None,
-            Start(Heading(_, _, _) | Paragraph | Item) => {
+            Start(Heading { .. } | Paragraph | Item) => {
-                if let Start(Heading(_, _, _)) = event {
+                if let Start(Heading { .. }) = event {
                     in_heading = true;
                 }
                 if let Start(Item) = event {
@@ -720,11 +720,11 @@ fn check_doc<'a, Events: Iterator<Item = (pulldown_cmark::Event<'a>, Range<usize
                 ticks_unbalanced = false;
                 paragraph_range = range;
             },
-            End(Heading(_, _, _) | Paragraph | Item) => {
+            End(TagEnd::Heading(_) | TagEnd::Paragraph | TagEnd::Item) => {
-                if let End(Heading(_, _, _)) = event {
+                if let End(TagEnd::Heading(_)) = event {
                     in_heading = false;
                 }
-                if let End(Item) = event {
+                if let End(TagEnd::Item) = event {
                     containers.pop();
                 }
                 if ticks_unbalanced && let Some(span) = fragments.span(cx, paragraph_range.clone()) {
@@ -746,8 +746,8 @@ fn check_doc<'a, Events: Iterator<Item = (pulldown_cmark::Event<'a>, Range<usize
                 text_to_check = Vec::new();
             },
             Start(FootnoteDefinition(..)) => in_footnote_definition = true,
-            End(FootnoteDefinition(..)) => in_footnote_definition = false,
+            End(TagEnd::FootnoteDefinition) => in_footnote_definition = false,
-            Start(_tag) | End(_tag) => (), // We don't care about other tags
+            Start(_) | End(_) => (), // We don't care about other tags
             SoftBreak | HardBreak => {
                 if !containers.is_empty()
                     && let Some((next_event, next_range)) = events.peek()
@@ -765,7 +765,7 @@ fn check_doc<'a, Events: Iterator<Item = (pulldown_cmark::Event<'a>, Range<usize
                     );
                 }
             },
-            TaskListMarker(_) | Code(_) | Rule => (),
+            TaskListMarker(_) | Code(_) | Rule | InlineMath(..) | DisplayMath(..) => (),
             FootnoteReference(text) | Text(text) => {
                 paragraph_range.end = range.end;
                 ticks_unbalanced |= text.contains('`') && !in_code;

src/tools/tidy/src/deps.rs

@@ -335,6 +335,7 @@
     "proc-macro2",
     "psm",
     "pulldown-cmark",
+    "pulldown-cmark-escape",
     "punycode",
     "quote",
     "r-efi",

tests/rustdoc-ui/unportable-markdown.rs

@@ -0,0 +1,63 @@
+// https://internals.rust-lang.org/t/proposal-migrate-the-syntax-of-rustdoc-markdown-footnotes-to-be-compatible-with-the-syntax-used-in-github/18929
+//
+// A series of test cases for CommonMark corner cases that pulldown-cmark 0.11 fixes.
+//
+// This version of the lint is targeted at two especially-common cases where docs got broken.
+// Other differences in parsing should not warn.
+#![allow(rustdoc::broken_intra_doc_links)]
+#![deny(rustdoc::unportable_markdown)]
+
+/// <https://github.com/pulldown-cmark/pulldown-cmark/pull/654>
+///
+/// Test footnote [^foot].
+///
+/// [^foot]: This is nested within the footnote now, but didn't used to be.
+///
+///     This is a multi-paragraph footnote.
+pub struct GfmFootnotes;
+
+/// <https://github.com/pulldown-cmark/pulldown-cmark/pull/773>
+///
+/// test [^foo][^bar]
+//~^ ERROR unportable markdown
+///
+/// [^foo]: test
+/// [^bar]: test2
+pub struct FootnoteSmashedName;
+
+/// <https://github.com/pulldown-cmark/pulldown-cmark/pull/829>
+///
+/// - _t
+///   # test
+///   t_
+pub struct NestingCornerCase;
+
+/// <https://github.com/pulldown-cmark/pulldown-cmark/pull/650>
+///
+/// *~~__emphasis strike strong__~~* ~~*__strike emphasis strong__*~~
+pub struct Emphasis1;
+
+/// <https://github.com/pulldown-cmark/pulldown-cmark/pull/732>
+///
+/// |
+/// |
+pub struct NotEnoughTable;
+
+/// <https://github.com/pulldown-cmark/pulldown-cmark/pull/675>
+///
+/// foo
+/// >bar
+//~^ ERROR unportable markdown
+pub struct BlockQuoteNoSpace;
+
+/// Negative test.
+///
+/// foo
+/// > bar
+pub struct BlockQuoteSpace;
+
+/// Negative test.
+///
+/// >bar
+/// baz
+pub struct BlockQuoteNoSpaceStart;

tests/rustdoc-ui/unportable-markdown.stderr

@@ -0,0 +1,39 @@
+error: unportable markdown
+  --> $DIR/unportable-markdown.rs:21:10
+   |
+LL | /// test [^foo][^bar]
+   |          ^^^^^^
+   |
+   = help: confusing footnote reference and link
+note: the lint level is defined here
+  --> $DIR/unportable-markdown.rs:8:9
+   |
+LL | #![deny(rustdoc::unportable_markdown)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: if it should not be a footnote, escape it
+   |
+LL | /// test \[^foo][^bar]
+   |          +
+help: if the footnote is intended, add a space
+   |
+LL | /// test [^foo] [^bar]
+   |                +
+
+error: unportable markdown
+  --> $DIR/unportable-markdown.rs:49:5
+   |
+LL | /// >bar
+   |     ^
+   |
+   = help: confusing block quote with no space after the `>` marker
+help: if the quote is intended, add a space
+   |
+LL | /// > bar
+   |      +
+help: if it should not be a quote, escape it
+   |
+LL | /// \>bar
+   |     +
+
+error: aborting due to 2 previous errors
+