Code change:
<ins> #![feature(external_doc)] #![crate_name = "foo"] // @has foo/struct.Example.html // @matches - '//pre[@class="rust rust-example-rendered"]'  //     '(?m)let example = Example::new()n    .first()n    .second()n    .build();Z' /// ```rust /// let example = Example::new() ///     .first() #[cfg_attr(not(feature = "one"), doc = "    .second()")] ///     .build(); /// ``` pub struct Example; // @has foo/struct.F.html // @matches - '//pre[@class="rust rust-example-rendered"]'  //     '(?m)let example = Example::new()n    .first()n    .another()n    .build();Z' ///```rust ///let example = Example::new() ///    .first() #[cfg_attr(not(feature = "one"), doc = "    .another()")] ///    .build(); /// ``` pub struct F; // @has foo/struct.G.html // @matches - '//pre[@class="rust rust-example-rendered"]'  //     '(?m)let example = Example::new()n.first()n    .another()n.build();Z' ///```rust ///let example = Example::new() ///.first() #[cfg_attr(not(feature = "one"), doc = "    .another()")] ///.build(); ///``` pub struct G; // @has foo/struct.H.html // @has - '//div[@class="docblock"]/p' 'no whitespace lol' ///no whitespace #[doc = " lol"] pub struct H; // @has foo/struct.I.html // @matches - '//pre[@class="rust rust-example-rendered"]' '(?m)4 whitespaces!Z' ///     4 whitespaces! #[doc = "something"] pub struct I; // @has foo/struct.J.html // @matches - '//div[@class="docblock"]/p' '(?m)anno whitespacenJust some text.Z' ///a ///no whitespace #[doc(include = "unindent.md")] pub struct J; // @has foo/struct.K.html // @matches - '//pre[@class="rust rust-example-rendered"]' '(?m)4 whitespaces!Z' ///a /// ///    4 whitespaces! /// #[doc(include = "unindent.md")] pub struct K; </ins>

Related discussion:
text: (x, "n bar();n"); //!
They are not supposed to be applied to a doc comment I do not think that. Your example would make sense for which I also consider to be wrong, but I am talking about which should insert the attribute conditionally but that is not the point. It might help to illustrate my thought process; We have some kind of documented item: rust /// let example = Example::new() /// .first() /// .build(); /// and each of those is turned into a doc attribute rust"] #[doc = "let example = Example::new()"] #[doc = " .first()"] #[doc = " .build();"] #[doc = " In a later step those attributes would then be concatenated and parsed as markdown or whatever. I want to use this behavior to document items conditionally, depending on which features the crate user has enabled. One way to do this would be to do rust let example = Example::new() .first() .build(); rust let example = Example::new() .first() .second() .build(); but that would blow up the source code with many duplicate lines, where only some minor things were changed. So I thought that it might make more sense to conditionally include a doc comment like this: rust /// let example = Example::new() /// .first() #[cfgattr(feature = "one", doc = " .second()")] /// .build(); /// which would turn into rust"] #[doc = "let example = Example::new()"] #[doc = " .first()"] #[doc = " .second()"] #[doc = " .build();"] #[doc = " or rust"] #[doc = "let example = Example::new()"] #[doc = " .first()"] #[doc = " .build();"] #[doc = " depending on whether the feature is enabled. So the attribute should not be inserted and not applied to the following doc comment. The weird thing is that the manually expanded version is working as expected. rust"] #[doc = "let example = Example::new()"] #[doc = " .first()"] #[cfg_attr(feature = "one", doc = " .second()")] #[doc = " .build();"] #[doc = " but this is very unhandy to work with :/
I was randomly looking at passes for another reason and noticed what is likely the source of this issue.