derive_builder_core/
default_expression.rs

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1use crate::BlockContents;
2use proc_macro2::Span;
3use quote::ToTokens;
4
5/// A `DefaultExpression` can be either explicit or refer to the canonical trait.
6#[derive(Debug, Clone)]
7pub enum DefaultExpression {
8    Explicit(BlockContents),
9    Trait,
10}
11
12impl DefaultExpression {
13    /// Add the crate root path so the default expression can be emitted
14    /// to a `TokenStream`.
15    ///
16    /// This function is needed because the crate root is inherited from the container, so it cannot
17    /// be provided at parse time to [`darling::FromMeta::from_word`] when reading, and [`ToTokens`] does not
18    /// accept any additional parameters, so it annot be provided at emit time.
19    pub fn with_crate_root<'a>(&'a self, crate_root: &'a syn::Path) -> impl 'a + ToTokens {
20        DefaultExpressionWithCrateRoot {
21            crate_root,
22            expr: self,
23        }
24    }
25
26    pub fn span(&self) -> Span {
27        match self {
28            DefaultExpression::Explicit(block) => block.span(),
29            DefaultExpression::Trait => Span::call_site(),
30        }
31    }
32
33    #[cfg(test)]
34    pub fn explicit<I: Into<BlockContents>>(content: I) -> Self {
35        DefaultExpression::Explicit(content.into())
36    }
37}
38
39impl darling::FromMeta for DefaultExpression {
40    fn from_word() -> darling::Result<Self> {
41        Ok(DefaultExpression::Trait)
42    }
43
44    fn from_expr(expr: &syn::Expr) -> darling::Result<Self> {
45        if let syn::Expr::Lit(el) = expr {
46            if let syn::Lit::Str(_) = el.lit {
47                return Self::from_value(&el.lit);
48            }
49        }
50
51        Ok(Self::Explicit(expr.clone().into()))
52    }
53
54    fn from_value(value: &syn::Lit) -> darling::Result<Self> {
55        Ok(Self::Explicit(BlockContents::from_value(value)?))
56    }
57}
58
59/// Wrapper for `DefaultExpression`
60struct DefaultExpressionWithCrateRoot<'a> {
61    crate_root: &'a syn::Path,
62    expr: &'a DefaultExpression,
63}
64
65impl<'a> ToTokens for DefaultExpressionWithCrateRoot<'a> {
66    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
67        let crate_root = self.crate_root;
68        match self.expr {
69            DefaultExpression::Explicit(ref block) => block.to_tokens(tokens),
70            DefaultExpression::Trait => quote!(
71                #crate_root::export::core::default::Default::default()
72            )
73            .to_tokens(tokens),
74        }
75    }
76}
derive_builder_core/default_expression.rs

derive_builder_core/
default_expression.rs
