Tracking issue for builtin declarative macros

[edwin0cheng]

Here is the full list of builtin declarative macros current rustc supported:

• asm: asm::expand_asm
• assert: assert::expand_assert
• cfg: cfg::expand_cfg (Implement builtin cfg! macro #7964)
• column: source_util::expand_column (Expand column!() #2355 by @kjeremy)
• compile_error: compile_error::expand_compile_error (Expand compile_error! #2362 by @kjeremy)
• concat_idents: concat_idents::expand_concat_idents
• concat: concat::expand_concat(Implement concat eager macro  #3392 by @edwin0cheng)
• env: env::expand_env(Implement env! macro #3549 by @edwin0cheng)
• file: source_util::expand_file (Expand file! to dummy "" #2357 by @kjeremy)
• format_args_nl: format::expand_format_args_nl (Implement format_args #2489 by @flodiebold)
• format_args: format::expand_format_args (Implement format_args #2489 by @flodiebold)
• global_asm: global_asm::expand_global_asm
• include_bytes: source_util::expand_include_bytes(Add support for include_bytes! #5102 by @lnicola)
• include_str: source_util::expand_include_str (Add support for include_str #5100 by @lnicola)
• include: source_util::expand_include (Implement include macro #3494 by @edwin0cheng)
• line: source_util::expand_line (Implement bulitin line! macro #2205 @edwin0cheng)
• log_syntax: log_syntax::expand_log_syntax
• module_path: source_util::expand_mod (Implement module_path!() #6874)
• option_env: env::expand_option_env(Implement env! macro #3549 by @edwin0cheng)
• stringify: source_util::expand_stringify (Add support for stringify! builtin macro #2348 by @piotr-szpetkowski)
• trace_macros: trace_macros::expand_trace_macros

[edwin0cheng]

After #2205 is landed, some of the builtin declarative macros are:

Trivial to implement:

• stringify, column, compile_error, etc

Trivial to implement for IDE purpose: (A dummy implementation will work here)

• asm, global_asm, etc

Need OUTDIR metadata support:

• env, etc

Need eager macro expansion support:
concat, include, etc

[matklad]

Priority wise, handling include!(concat!(env!("OUT_DIR"), "/foo.rs")) would be sweet!

[edwin0cheng]

I will take concat! to see how to support eager expansion in current infrastructure.

But I still can't figure it out how name resolution works inside inner expansion phase 🤣

[kjeremy]

@edwin0cheng what does compile_error! expand to? Just a string with the error contents?

[edwin0cheng]

Um... something as ! result type? e.g loop { "Compiler Error" } for now ? @matklad

[matklad]

Yeah, I think loop {} is good

[Tehnix]

NOTE: This might be out of scope for this issue, so feel free to let me know and I'll create a separate issue.

---

With Rust 1.54 recently introducing support for #[doc = include_str!("compile_fail.rs")] I was curious if the "support" that is aim for here also includes expanded these macros in the generated docs on hover?

Take for example the following code:

/// The GraphQL schema for our mock service.
///
/// ```graphql
#[doc = include_str!("schema.graphql")]
/// ```
pub struct Query;

It pulls in an external file, schema.graphql, which includes the full schema of the Query. At the moment, the tooltip in VS Code will ignore the #[doc = include_str!("schema.graphql")] part in the documentation it shows:

If you run cargo doc --open it does show up in the final documentation though: