include! should allow inner doc comments and directives

[joshtriplett]

Currently, include! cannot include a file that contains inner doc comments (//! ...) or directives (#![...]). That creates a challenge when trying to generate a crate's top-level contents with a build script.

See https://internals.rust-lang.org/t/include-raw-directive-for-raw-textual-inclusion-of-generated-code/11405 for discussion. @dtolnay pointed out that we can fix this backwards-compatibly, as it would just turn an error into a non-error.

[Centril]

cc @petrochenkov @matklad

[Xaeroxe]

This has been a constant source of pain for me during my time with Rust, both professionally and personally. I'd like to put an end to it. Is there any ongoing work for this that I should be aware of before I start working on it?

[fmease]

I don't remember anybody working on it.l, so go for it! :)

You want to look at expand_include in rustc_builtin_macros and nominate the future PR for T-lang discussion with the label I-lang-nominated Nominated for discussion during a lang team meeting. .

This might be obvious, but please make sure that we continue to reject inner attributes originating from the expansion of includes that are preceded by items.

Furthermore, it might be worthwhile to add the following question to the future nomination for T-lang to think about:

Should we (eventually) expand this behavior / feature to all macros (which "expand to items")? If so, should we relax the grammar and classify inner attributes as items? Again, if so, should inner attributes following (then) non-inner-attribute items become a semantic error or stay a syntactic one?