1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37

use crate::BlockContents;
use quote::{ToTokens, TokenStreamExt};

/// A `DefaultExpression` can be either explicit or refer to the canonical trait.
#[derive(Debug, Clone)]
pub enum DefaultExpression {
    Explicit(BlockContents),
    Trait,
}

impl DefaultExpression {
    #[cfg(test)]
    pub fn explicit<I: Into<BlockContents>>(content: I) -> Self {
        DefaultExpression::Explicit(content.into())
    }
}

impl darling::FromMeta for DefaultExpression {
    fn from_word() -> darling::Result<Self> {
        Ok(DefaultExpression::Trait)
    }

    fn from_value(value: &syn::Lit) -> darling::Result<Self> {
        Ok(Self::Explicit(BlockContents::from_value(value)?))
    }
}

impl ToTokens for DefaultExpression {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        match *self {
            Self::Explicit(ref block) => block.to_tokens(tokens),
            Self::Trait => tokens.append_all(quote!(
                ::derive_builder::export::core::default::Default::default()
            )),
        }
    }
}