rust: module: improve parsing and errors

[ojeda]

• Simplified code.

• Repeated keys are not allowed anymore, e.g.

  module! {
      type: RustMinimal,
      type: RustMinimal,
  ...
  

• Better error messages:

  error: proc macro panicked
    --> ../samples/rust/rust_minimal.rs:10:1
     |
  10 | / module! {
  11 | |     type: RustMinimal,
  12 | |     name: b"rust_minimal",
  13 | |     description: b"Rust minimal sample",
  14 | |     author: b"Rust for Linux Contributors",
  15 | |     license: b"GPL v2",
  16 | | }
     | |_^
     |
     = help: message: Keys are not ordered as expected. Order them like: ["type", "name", "author", "description", "license"]
  
  error: proc macro panicked
    --> ../samples/rust/rust_minimal.rs:10:1
     |
  10 | / module! {
  11 | |     typo: RustMinimal,
  12 | |     name: b"rust_minimal",
  13 | |     author: b"Rust for Linux Contributors",
  14 | |     description: b"Rust minimal sample",
  15 | |     license: b"GPL v2",
  16 | | }
     | |_^
     |
     = help: message: Unknown key "typo". Valid keys are: ["type", "name", "author", "description", "license", "alias", "alias_rtnl_link", "params"].
  
  error: proc macro panicked
    --> ../samples/rust/rust_minimal.rs:10:1
     |
  10 | / module! {
  11 | |     type: RustMinimal,
  12 | |     name: b"rust_minimal",
  13 | |     author: b"Rust for Linux Contributors",
  14 | |     description: b"Rust minimal sample",
  15 | | }
     | |_^
     |
     = help: message: Missing required key "license".
  
  error: proc macro panicked
    --> ../samples/rust/rust_minimal.rs:10:1
     |
  10 | / module! {
  11 | |     type: RustMinimal,
  12 | |     name: b"rust_minimal",
  13 | |     license: b"GPL v2",
  14 | |     license: b"GPL v2",
  15 | | }
     | |_^
     |
     = help: message: Duplicated key "license". Keys can only be specified once.
  

Signed-off-by: Miguel Ojeda ojeda@kernel.org

[ojeda]

Related: #215 and #234.

[bjorn3]

error: proc macro panicked
  --> ../samples/rust/rust_minimal.rs:10:1
   |
10 | / module! {
11 | |     typo: RustMinimal,
12 | |     name: b"rust_minimal",
13 | |     author: b"Rust for Linux Contributors",
14 | |     description: b"Rust minimal sample",
15 | |     license: b"GPL v2",
16 | | }
   | |_^
   |
   = help: message: Unknown key "typo". Valid keys are: ["type", "name", "author", "description", "license", "alias", "alias_rtnl_link", "params"].

I think you can improve this error message by expanding to a compile_error!() macro invocation with the span set to that of typo.

[kloenk]

LGTM.

I'm not sure if compile_error! would make it better. Probably it would make the output more readable for the specific error message, but It also would mean that the focus of the error get's shifted away from the proc_macro. So I'm fine with either ways.

[ojeda]

I think you can improve this error message by expanding to a compile_error!() macro invocation with the span set to that of typo.

Tried that hack... it looks quite nice:

error: Duplicated key "type". Keys can only be specified once.
  --> ../samples/rust/rust_minimal.rs:12:5
   |
12 |     type: RustMinimal,
   |     ^^^^

Having said that, Rust should really stabilize something for proper error reporting in proc macros. Not sure if it is worth the pain at the moment...

[ojeda]

I'm not sure if compile_error! would make it better. Probably it would make the output more readable for the specific error message, but It also would mean that the focus of the error get's shifted away from the proc_macro. So I'm fine with either ways.

Yeah, good point, I would need to mention module! in the message.