Auto merge of #11140 - Centri3:four_forward_slashes, r=blyxyas

New lint [`four_forward_slashes`]

Closes #9212

changelog: New lint [`four_forward_slashes`]

tests/ui/four_forward_slashes.fixed

@@ -0,0 +1,48 @@
+//@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() {}
+
+fn i() {
+    //// don't lint me bozo
+    todo!()
+}
+
+external! {
+    //// don't lint me bozo
+    fn e() {}
+}
+
+with_span! {
+    span
+    //// don't lint me bozo
+    fn f() {}
+}

tests/ui/four_forward_slashes.rs

@@ -0,0 +1,48 @@
+//@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() {}
+
+fn i() {
+    //// don't lint me bozo
+    todo!()
+}
+
+external! {
+    //// don't lint me bozo
+    fn e() {}
+}
+
+with_span! {
+    span
+    //// don't lint me bozo
+    fn f() {}
+}

tests/ui/four_forward_slashes.stderr

@@ -0,0 +1,68 @@
+error: this item has comments with 4 forward slashes (`////`). These look like doc comments, but they aren't
+  --> $DIR/four_forward_slashes.rs:12:1
+   |
+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: this item has comments with 4 forward slashes (`////`). These look like doc comments, but they aren't
+  --> $DIR/four_forward_slashes.rs:15:1
+   |
+LL | / //// whoops
+LL | | #[allow(dead_code)]
+LL | | fn b() {}
+   | |_
+   |
+help: make this a doc comment by removing one `/`
+   |
+LL + /// whoops
+   |
+
+error: this item has comments with 4 forward slashes (`////`). These look like doc comments, but they aren't
+  --> $DIR/four_forward_slashes.rs:19:1
+   |
+LL | / //// whoops
+LL | | //// two borked comments!
+LL | | #[track_caller]
+LL | | fn c() {}
+   | |_
+   |
+help: turn these into doc comments by removing one `/`
+   |
+LL + /// whoops
+LL ~ /// two borked comments!
+   |
+
+error: this item has comments with 4 forward slashes (`////`). These look like doc comments, but they aren't
+  --> $DIR/four_forward_slashes.rs:27:1
+   |
+LL | / //// between attributes
+LL | | #[allow(dead_code)]
+LL | | fn g() {}
+   | |_
+   |
+help: make this a doc comment by removing one `/`
+   |
+LL + /// between attributes
+   |
+
+error: this item has comments with 4 forward slashes (`////`). These look like doc comments, but they aren't
+  --> $DIR/four_forward_slashes.rs:31:1
+   |
+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 5 previous errors
+

tests/ui/four_forward_slashes_first_line.fixed

@@ -0,0 +1,7 @@
+/// borked doc comment on the first line. doesn't combust!
+fn a() {}
+
+//@run-rustfix
+// This test's entire purpose is to make sure we don't panic if the comment with four slashes
+// extends to the first line of the file. This is likely pretty rare in production, but an ICE is an
+// ICE.

tests/ui/four_forward_slashes_first_line.rs

@@ -0,0 +1,7 @@
+//// borked doc comment on the first line. doesn't combust!
+fn a() {}
+
+//@run-rustfix
+// This test's entire purpose is to make sure we don't panic if the comment with four slashes
+// extends to the first line of the file. This is likely pretty rare in production, but an ICE is an
+// ICE.

tests/ui/four_forward_slashes_first_line.stderr

@@ -0,0 +1,15 @@
+error: this item has comments with 4 forward slashes (`////`). These look like doc comments, but they aren't
+  --> $DIR/four_forward_slashes_first_line.rs:1:1
+   |
+LL | / //// borked doc comment on the first line. doesn't combust!
+LL | | fn a() {}
+   | |_
+   |
+   = note: `-D clippy::four-forward-slashes` implied by `-D warnings`
+help: make this a doc comment by removing one `/`
+   |
+LL + /// borked doc comment on the first line. doesn't combust!
+   |
+
+error: aborting due to previous error
+