Proc Macro Warning

Emit warnings from inside proc macros.

Rust does not have native functions to produce warnings from inside proc macros. This crate provides "deprecated" warnings for your proc macro use-cases.

Example

Building a warning is easy with the builder pattern.

```rust use procmacrowarning::Warning; let warning = Warning::newdeprecated("mymacro") .old("mymacro()") .new("mymacro::new()") .helplink("https:://example.com") .span(procmacro2::Span::call_site()) .build();

// Use the warning in a proc macro let tokens = quote::quote!(#warning); ```

Used In

Substrate (not yet, but hopefully soon 😉) uses this to emit warnings for its FRAME eDSL on deprecated behaviour.

For example not putting a call_index on your functions produces: ``pre warning: use of deprecated constantpallet::warnings::ImplicitCallIndex0::w: It is deprecated to use implicit call indices. Please instead ensure that all calls have thepallet::call_indexattribute or that thedev-mode` of the pallet is enabled.

             For more info see:
                 <https://github.com/paritytech/substrate/pull/12891>
                 <https://github.com/paritytech/substrate/pull/11381>
--> frame/nomination-pools/src/lib.rs:2621:10
 |

2621 | pub fn claimcommission(origin: OriginFor, poolid: PoolId) -> DispatchResult { | ^^^^^^^^^^^^^^^^ | ```

Or using a hard-coded weight: ``pre warning: use of deprecated constantpallet::warnings::ConstantWeight0::w: It is deprecated to use hard-coded constant as call weight. Please instead benchmark all calls or put the pallet intodev` mode.

             For more info see:
                 <https://github.com/paritytech/substrate/pull/13798>
--> frame/nomination-pools/src/lib.rs:2620:20
 |

2620 | #[pallet::weight(0)] |
```