diff --git a/CHANGELOG.md b/CHANGELOG.md
index b3b6e3b865f..ec62d399aa4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4867,6 +4867,7 @@ Released 2018-09-13
[`forget_ref`]: https://rust-lang.github.io/rust-clippy/master/index.html#forget_ref
[`format_in_format_args`]: https://rust-lang.github.io/rust-clippy/master/index.html#format_in_format_args
[`format_push_string`]: https://rust-lang.github.io/rust-clippy/master/index.html#format_push_string
+[`four_forward_slashes`]: https://rust-lang.github.io/rust-clippy/master/index.html#four_forward_slashes
[`from_iter_instead_of_collect`]: https://rust-lang.github.io/rust-clippy/master/index.html#from_iter_instead_of_collect
[`from_over_into`]: https://rust-lang.github.io/rust-clippy/master/index.html#from_over_into
[`from_raw_with_void_ptr`]: https://rust-lang.github.io/rust-clippy/master/index.html#from_raw_with_void_ptr
diff --git a/clippy_lints/src/declared_lints.rs b/clippy_lints/src/declared_lints.rs
index 3723de7299b..d8b14a9f967 100644
--- a/clippy_lints/src/declared_lints.rs
+++ b/clippy_lints/src/declared_lints.rs
@@ -184,6 +184,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
crate::formatting::SUSPICIOUS_ASSIGNMENT_FORMATTING_INFO,
crate::formatting::SUSPICIOUS_ELSE_FORMATTING_INFO,
crate::formatting::SUSPICIOUS_UNARY_OP_FORMATTING_INFO,
+ crate::four_forward_slashes::FOUR_FORWARD_SLASHES_INFO,
crate::from_over_into::FROM_OVER_INTO_INFO,
crate::from_raw_with_void_ptr::FROM_RAW_WITH_VOID_PTR_INFO,
crate::from_str_radix_10::FROM_STR_RADIX_10_INFO,
diff --git a/clippy_lints/src/four_forward_slashes.rs b/clippy_lints/src/four_forward_slashes.rs
new file mode 100644
index 00000000000..7efa8c1b31f
--- /dev/null
+++ b/clippy_lints/src/four_forward_slashes.rs
@@ -0,0 +1,82 @@
+use clippy_utils::{diagnostics::span_lint_and_sugg, source::snippet_opt};
+use rustc_errors::Applicability;
+use rustc_hir::Item;
+use rustc_lint::{LateContext, LateLintPass, LintContext};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_span::{Span, SyntaxContext};
+
+declare_clippy_lint! {
+ /// ### What it does
+ /// Checks for outer doc comments written with 4 forward slashes (`////`).
+ ///
+ /// ### Why is this bad?
+ /// This is (probably) a typo, and results in it not being a doc comment; just a regular
+ /// comment.
+ ///
+ /// ### Example
+ /// ```rust
+ /// //// My amazing data structure
+ /// pub struct Foo {
+ /// // ...
+ /// }
+ /// ```
+ ///
+ /// Use instead:
+ /// ```rust
+ /// /// My amazing data structure
+ /// pub struct Foo {
+ /// // ...
+ /// }
+ /// ```
+ #[clippy::version = "1.72.0"]
+ pub FOUR_FORWARD_SLASHES,
+ suspicious,
+ "comments with 4 forward slashes (`////`) likely intended to be doc comments (`///`)"
+}
+declare_lint_pass!(FourForwardSlashes => [FOUR_FORWARD_SLASHES]);
+
+impl<'tcx> LateLintPass<'tcx> for FourForwardSlashes {
+ fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
+ if item.span.from_expansion() {
+ return;
+ }
+ let src = cx.sess().source_map();
+ let item_and_attrs_span = cx
+ .tcx
+ .hir()
+ .attrs(item.hir_id())
+ .iter()
+ .fold(item.span.shrink_to_lo(), |span, attr| span.to(attr.span));
+ let (Some(file), _, _, end_line, _) = src.span_to_location_info(item_and_attrs_span) else {
+ return;
+ };
+ for line in (0..end_line.saturating_sub(1)).rev() {
+ let Some(contents) = file.get_line(line) else {
+ continue;
+ };
+ let contents = contents.trim();
+ if contents.is_empty() {
+ break;
+ }
+ if contents.starts_with("////") {
+ let bounds = file.line_bounds(line);
+ let span = Span::new(bounds.start, bounds.end, SyntaxContext::root(), None);
+
+ if snippet_opt(cx, span).is_some_and(|s| s.trim().starts_with("////")) {
+ span_lint_and_sugg(
+ cx,
+ FOUR_FORWARD_SLASHES,
+ span,
+ "comment with 4 forward slashes (`////`). This looks like a doc comment, but it isn't",
+ "make this a doc comment by removing one `/`",
+ // It's a little unfortunate but the span includes the `\n` yet the contents
+ // do not, so we must add it back. If some codebase uses `\r\n` instead they
+ // will need normalization but it should be fine
+ contents.replacen("////", "///", 1) + "\n",
+ Applicability::MachineApplicable,
+ );
+ }
+ }
+ }
+ }
+}
diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs
index cebe2e44c0f..607c718b562 100644
--- a/clippy_lints/src/lib.rs
+++ b/clippy_lints/src/lib.rs
@@ -137,6 +137,7 @@ mod format_args;
mod format_impl;
mod format_push_string;
mod formatting;
+mod four_forward_slashes;
mod from_over_into;
mod from_raw_with_void_ptr;
mod from_str_radix_10;
@@ -1081,6 +1082,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
store.register_early_pass(|| Box::new(visibility::Visibility));
store.register_late_pass(move |_| Box::new(tuple_array_conversions::TupleArrayConversions { msrv: msrv() }));
store.register_late_pass(|_| Box::new(manual_float_methods::ManualFloatMethods));
+ store.register_late_pass(|_| Box::new(four_forward_slashes::FourForwardSlashes));
// add lints here, do not remove this comment, it's used in `new_lint`
}
diff --git a/tests/ui/four_forward_slashes.fixed b/tests/ui/four_forward_slashes.fixed
new file mode 100644
index 00000000000..4f9b1f4b7c8
--- /dev/null
+++ b/tests/ui/four_forward_slashes.fixed
@@ -0,0 +1,44 @@
+//// first line borked doc comment. doesn't combust!
+//@run-rustfix
+//@aux-build:proc_macros.rs:proc-macro
+#![feature(custom_inner_attributes)]
+#![allow(unused)]
+#![warn(clippy::four_forward_slashes)]
+#![no_main]
+#![rustfmt::skip]
+
+#[macro_use]
+extern crate proc_macros;
+
+/// whoops
+fn a() {}
+
+/// whoops
+#[allow(dead_code)]
+fn b() {}
+
+/// whoops
+/// two borked comments!
+#[track_caller]
+fn c() {}
+
+fn d() {}
+
+#[test]
+/// between attributes
+#[allow(dead_code)]
+fn g() {}
+
+/// not very start of contents
+fn h() {}
+
+external! {
+ //// don't lint me bozo
+ fn e() {}
+}
+
+with_span! {
+ span
+ //// don't lint me bozo
+ fn f() {}
+}
diff --git a/tests/ui/four_forward_slashes.rs b/tests/ui/four_forward_slashes.rs
new file mode 100644
index 00000000000..02f2084c17c
--- /dev/null
+++ b/tests/ui/four_forward_slashes.rs
@@ -0,0 +1,44 @@
+//// first line borked doc comment. doesn't combust!
+//@run-rustfix
+//@aux-build:proc_macros.rs:proc-macro
+#![feature(custom_inner_attributes)]
+#![allow(unused)]
+#![warn(clippy::four_forward_slashes)]
+#![no_main]
+#![rustfmt::skip]
+
+#[macro_use]
+extern crate proc_macros;
+
+//// whoops
+fn a() {}
+
+//// whoops
+#[allow(dead_code)]
+fn b() {}
+
+//// whoops
+//// two borked comments!
+#[track_caller]
+fn c() {}
+
+fn d() {}
+
+#[test]
+//// between attributes
+#[allow(dead_code)]
+fn g() {}
+
+ //// not very start of contents
+fn h() {}
+
+external! {
+ //// don't lint me bozo
+ fn e() {}
+}
+
+with_span! {
+ span
+ //// don't lint me bozo
+ fn f() {}
+}
diff --git a/tests/ui/four_forward_slashes.stderr b/tests/ui/four_forward_slashes.stderr
new file mode 100644
index 00000000000..1640b241bf3
--- /dev/null
+++ b/tests/ui/four_forward_slashes.stderr
@@ -0,0 +1,75 @@
+error: comment with 4 forward slashes (`////`). This looks like a doc comment, but it isn't
+ --> $DIR/four_forward_slashes.rs:13:1
+ |
+LL | / //// whoops
+LL | | fn a() {}
+ | |_
+ |
+ = note: `-D clippy::four-forward-slashes` implied by `-D warnings`
+help: make this a doc comment by removing one `/`
+ |
+LL + /// whoops
+ |
+
+error: comment with 4 forward slashes (`////`). This looks like a doc comment, but it isn't
+ --> $DIR/four_forward_slashes.rs:16:1
+ |
+LL | / //// whoops
+LL | | #[allow(dead_code)]
+ | |_
+ |
+help: make this a doc comment by removing one `/`
+ |
+LL + /// whoops
+ |
+
+error: comment with 4 forward slashes (`////`). This looks like a doc comment, but it isn't
+ --> $DIR/four_forward_slashes.rs:21:1
+ |
+LL | / //// two borked comments!
+LL | | #[track_caller]
+ | |_
+ |
+help: make this a doc comment by removing one `/`
+ |
+LL + /// two borked comments!
+ |
+
+error: comment with 4 forward slashes (`////`). This looks like a doc comment, but it isn't
+ --> $DIR/four_forward_slashes.rs:20:1
+ |
+LL | / //// whoops
+LL | | //// two borked comments!
+ | |_
+ |
+help: make this a doc comment by removing one `/`
+ |
+LL + /// whoops
+ |
+
+error: comment with 4 forward slashes (`////`). This looks like a doc comment, but it isn't
+ --> $DIR/four_forward_slashes.rs:28:1
+ |
+LL | / //// between attributes
+LL | | #[allow(dead_code)]
+ | |_
+ |
+help: make this a doc comment by removing one `/`
+ |
+LL + /// between attributes
+ |
+
+error: comment with 4 forward slashes (`////`). This looks like a doc comment, but it isn't
+ --> $DIR/four_forward_slashes.rs:32:1
+ |
+LL | / //// not very start of contents
+LL | | fn h() {}
+ | |_
+ |
+help: make this a doc comment by removing one `/`
+ |
+LL + /// not very start of contents
+ |
+
+error: aborting due to 6 previous errors
+