Add doc for #[pyclass_repr] (#8110)

lib/edge/python/codegen/src/lib.rs

@@ -1,5 +1,45 @@
 mod pyclass_repr;
 
+/// `#[pyclass_repr]` - implements `trait Repr`.
+///
+/// Only methods with `#[getter]` are included into the output.
+///
+/// # Usage example
+///
+/// Input:
+/// ```ignore
+/// #[pyclass_repr]
+/// #[pymethods]
+/// impl PyMyStruct {
+///     #[getter]
+///     pub fn foo(&self) -> &str {
+///         &self.0.foo
+///     }
+///
+///     #[getter]
+///     pub fn bar(&self) -> f32  {
+///         self.0.bar
+///     }
+///
+///     pub fn __repr__(&self) -> String {
+///         self.repr()
+///     }
+/// }
+/// ```
+///
+/// Generated output is roughly equivalent to:
+/// ```ignore
+/// impl crate::repr::Repr for PyMyStruct {
+///     fn fmt(&self, f: &mut crate::repr::Formatter<'_>) -> std::fmt::Result {
+///         use crate::repr::WriteExt as _;
+///
+///         f.class::<Self>(&[
+///             ("foo", &self.foo()),
+///             ("bar", &self.bar()),
+///         ])
+///     }
+/// }
+/// ```
 #[proc_macro_attribute]
 pub fn pyclass_repr(
     _attributes: proc_macro::TokenStream,