Add ui regression test for #134221

Author: GuillaumeGomez

tests/rustdoc-ui/doctest/comment-in-attr-134221.rs

@@ -0,0 +1,23 @@
+// Regression test for <https://github.com/rust-lang/rust/issues/134221>.
+// It checks that even if there are comments in the attributes, the attributes
+// will still be generated correctly (and therefore fail in this test).
+
+//@ compile-flags:--test --test-args --test-threads=1
+//@ failure-status: 101
+//@ normalize-stdout-test: "tests/rustdoc-ui" -> "$$DIR"
+//@ normalize-stdout-test: "finished in \d+\.\d+s" -> "finished in $$TIME"
+//@ normalize-stdout-test: ".rs:\d+:\d+" -> ".rs:$$LINE:$$COL"
+
+/*!
+```rust
+#![feature(
+  foo, //
+)]
+```
+
+```rust
+#![feature(
+  foo,
+)]
+```
+*/

tests/rustdoc-ui/doctest/comment-in-attr-134221.stdout

@@ -0,0 +1,36 @@
+
+running 2 tests
+test $DIR/doctest/comment-in-attr-134221.rs - (line 11) ... FAILED
+test $DIR/doctest/comment-in-attr-134221.rs - (line 17) ... FAILED
+
+failures:
+
+---- $DIR/doctest/comment-in-attr-134221.rs - (line 11) stdout ----
+error[E0635]: unknown feature `foo`
+  --> $DIR/doctest/comment-in-attr-134221.rs:$LINE:$COL
+   |
+LL |   foo, //
+   |   ^^^
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0635`.
+Couldn't compile the test.
+---- $DIR/doctest/comment-in-attr-134221.rs - (line 17) stdout ----
+error[E0635]: unknown feature `foo`
+  --> $DIR/doctest/comment-in-attr-134221.rs:$LINE:$COL
+   |
+LL |   foo,
+   |   ^^^
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0635`.
+Couldn't compile the test.
+
+failures:
+    $DIR/doctest/comment-in-attr-134221.rs - (line 11)
+    $DIR/doctest/comment-in-attr-134221.rs - (line 17)
+
+test result: FAILED. 0 passed; 2 failed; 0 ignored; 0 measured; 0 filtered out; finished in $TIME
+