Macro parse_macro_input 

macro_rules! parse_macro_input {
    ($tokenstream:ident as $ty:ty) => { ... };
    ($tokenstream:ident with $parser:path) => { ... };
    ($tokenstream:ident) => { ... };
}

Available on crate feature _helpers only.

Helper utilities for building procedural macros Adjusted version of syn’s parse_macro_input! macro for #[anyhow_result] procedural macro attribute.

Unlike syn’s original parse_macro_input! macro, this version returns Ok(TokenStream) on parse errors instead of returning a TokenStream directly. This makes it more suitable for use in procedural macros which are returning anyhow::Result<TokenStream>. See anyhow_result macro.

Behavior

On successful parsing, the macro returns the parsed value directly. On parse errors, it returns Ok(TokenStream) containing the error as compile_error! tokens, allowing the error to be displayed at compile time while still providing a valid return value.

Syntax

// Parse as a specific type
let input = parse_macro_input!(tokens as DeriveInput);

// Parse with a custom parser
let input = parse_macro_input!(tokens with syn::punctuated::Punctuated::<syn::Expr, syn::Token![,]>::parse_terminated);

// Parse with type inference
let input = parse_macro_input!(tokens);

Examples

use easy_macros::{parse_macro_input, anyhow_result};
use proc_macro::TokenStream;
use syn::DeriveInput;

#[proc_macro_derive(MyDerive)]
#[anyhow_result]
pub fn my_derive(input: TokenStream) -> anyhow::Result<TokenStream> {
    // This will return compile errors automatically on parse failure
    let input = parse_macro_input!(input as DeriveInput);
     
    // Your macro logic here...
    Ok(quote::quote! {
        // Generated code
    }.into())
}

Advantages over syn’s version

• Returns Ok(TokenStream) on errors instead of raw TokenStream
• Better integration with macros that return for example anyhow::Result<TokenStream>

Parameters

• $tokenstream - The input TokenStream to parse
• $ty - The target type to parse into (with as syntax)
• $parser - A custom parser function (with with syntax)