Add regression test for endless loop

This was fixed in pulldown_cmark 0.7.1, specifically
https://github.com/raphlinus/pulldown-cmark/pull/438

clippy_lints/Cargo.toml

@@ -21,7 +21,7 @@ cargo_metadata = "0.9.1"
 if_chain = "1.0.0"
 itertools = "0.9"
 lazy_static = "1.0.2"
-pulldown-cmark = { version = "0.7", default-features = false }
+pulldown-cmark = { version = "0.7.1", default-features = false }
 quine-mc_cluskey = "0.2.2"
 regex-syntax = "0.6"
 serde = { version = "1.0", features = ["derive"] }

tests/ui/crashes/regressions.rs

@@ -6,4 +6,8 @@ pub fn foo(bar: *const u8) {
     println!("{:#p}", bar);
 }
 
+// Regression test for https://github.com/rust-lang/rust-clippy/issues/4917
+/// <foo
+struct A {}
+
 fn main() {}