Impl ToTokens for syn::Error and syn::Result<T: ToTokens>?

[marcianx]

I had a foo: syn::Result<Expr> and wrote:

foo
    .map(ToTokens::into_token_stream)
    .unwrap_or_else(syn::Error::into_compile_error)
    .into()

and it made me wonder:

1. Why can't we just do quote! { #foo } given that syn::Error has an idiomatic conversion to a TokenStream -- IOW, implement ToTokens for syn::Result<T: ToTokens>.
2. Does it make sense to also implement ToTokens for syn::Error?

Thoughts?

[dtolnay]

I think this would be a similar design mistake as Serde implementing Serialize and Deserialize for Result<T, E>. The way it would play out in practice is the intentional uses would be rare and the mistaken uses (someone wrote too few ?) would be rampant and hard to identify. I think .unwrap_or_else(syn::Error::into_compile_error) is the right level of easy and clear for the cases where this is the behavior someone wants.