Correctly escape hashtags when running invalid_rust_codeblocks lint

src/librustdoc/doctest.rs

@@ -786,6 +786,7 @@ impl IndividualTestOptions {
 /// [`clean`]: crate::clean
 /// [`run_merged_tests`]: crate::doctest::runner::DocTestRunner::run_merged_tests
 /// [`generate_unique_doctest`]: crate::doctest::make::DocTestBuilder::generate_unique_doctest
+#[derive(Debug)]
 pub(crate) struct ScrapedDocTest {
     filename: FileName,
     line: usize,

src/librustdoc/html/markdown.rs

@@ -140,7 +140,7 @@ impl ErrorCodes {
 /// Controls whether a line will be hidden or shown in HTML output.
 ///
 /// All lines are used in documentation tests.
-enum Line<'a> {
+pub(crate) enum Line<'a> {
     Hidden(&'a str),
     Shown(Cow<'a, str>),
 }
@@ -153,20 +153,22 @@ impl<'a> Line<'a> {
         }
     }
 
-    fn for_code(self) -> Cow<'a, str> {
+    pub(crate) fn for_code(self) -> Cow<'a, str> {
         match self {
             Line::Shown(l) => l,
             Line::Hidden(l) => Cow::Borrowed(l),
         }
     }
 }
 
+/// This function is used to handle the "hidden lines" (ie starting with `#`) in
+/// doctests. It also transforms `##` back into `#`.
 // FIXME: There is a minor inconsistency here. For lines that start with ##, we
 // have no easy way of removing a potential single space after the hashes, which
 // is done in the single # case. This inconsistency seems okay, if non-ideal. In
 // order to fix it we'd have to iterate to find the first non-# character, and
 // then reallocate to remove it; which would make us return a String.
-fn map_line(s: &str) -> Line<'_> {
+pub(crate) fn map_line(s: &str) -> Line<'_> {
     let trimmed = s.trim();
     if trimmed.starts_with("##") {
         Line::Shown(Cow::Owned(s.replacen("##", "#", 1)))

src/librustdoc/passes/lint/check_code_block_syntax.rs

@@ -1,5 +1,6 @@
 //! Validates syntax inside Rust code blocks (\`\`\`rust).
 
+use std::borrow::Cow;
 use std::sync::Arc;
 
 use rustc_data_structures::sync::Lock;
@@ -43,7 +44,11 @@ fn check_rust_syntax(
 
     let sm = Arc::new(SourceMap::new(FilePathMapping::empty()));
     let dcx = DiagCtxt::new(Box::new(emitter)).disable_warnings();
-    let source = dox[code_block.code].to_owned();
+    let source = dox[code_block.code]
+        .lines()
+        .map(|line| crate::html::markdown::map_line(line).for_code())
+        .intersperse(Cow::Borrowed("\n"))
+        .collect::<String>();
     let psess = ParseSess::with_dcx(dcx, sm);
 
     let edition = code_block.lang_string.edition.unwrap_or_else(|| cx.tcx.sess.edition());

tests/rustdoc-ui/hashtag-doctest.rs

@@ -0,0 +1,17 @@
+// This test ensures that `##` are not emitting a warning when generating
+// docs with the 2024 edition (or any edition).
+// Regression test for <https://github.com/rust-lang/rust/issues/136899>.
+
+//@ check-pass
+//@revisions: edition2021 edition2024
+//@[edition2021] edition:2021
+//@[edition2024] edition:2024
+
+#![deny(warnings)]
+
+//! Test
+//!
+//! ```
+//! ##[allow(dead_code)]
+//! println!("hello world");
+//! ```