Document defaults to with xxx methods

[AshAnand34]

Pull Request Template

Checklist

• Confirmed that cargo run-checks command has been executed.
• Made sure the book is up to date with changes in this PR.

Tip

Want more detailed macro error diagnostics? This is especially useful for debugging tensor-related tests:

RUSTC_BOOTSTRAP=1 RUSTFLAGS="-Zmacro-backtrace" cargo run-checks

Related Issues/PRs

#2982

Changes

The Config derive macro was missing automatic documentation generation for config structs. This meant that:

1. Field documentation wasn't being propagated to the generated new function
2. Builder methods lacked proper documentation about their purpose and default values
3. Users had to manually document these generated methods, leading to potential inconsistencies.

I added automatic documentation generation to the Config derive macro that:

1. Propagates field documentation to the new function, creating a comprehensive list of all fields with their descriptions
2. Generates documentation for builder methods, including:
   • Purpose of the method
   • Default values for fields with defaults
   • Clear indication of optional fields
3. Handles both required fields, optional fields, and fields with default values appropriately

Testing

Unit tests in burn-core/tests/test_derive_config.rs:

• test_config_documentation() verifies that:
  • Documentation is properly generated for required fields
  • Documentation is properly generated for optional fields
  • Documentation is properly generated for fields with default values
  • Default values are correctly displayed in the documentation

[laggui]

Looks like there are some issues with the modified config derive (see CI).

[laggui]

The generated new method seems to be invalid.

 crates/burn-core/src/nn/conv/conv2d.rs:17:10:
  called `Result::unwrap()` on an `Err` value: Error("expected value", line: 1, column: 1)

Seems to originate from the serde_json::from_str(#value_str).unwrap(). The values are not captured properly it seems.

This also seems to be reflected in the docstrings, e.g.

Create a new instance of the config.

Fields:

#_name: #_doc
#_name: #_doc
#_name: #_doc Default: #_value_str
#_name: #_doc Default: #_value_str
#_name: #_doc Default: #_value_str
#_name: #_doc Default: #_value_str
#_name: #_doc Default: #value
#_name: #_doc Default: #_value_str