fromit 0.1.2

A super powerful macro for generating new structs with getters, setters, and `From` or `TryFrom` implementation based on the given struct.
Documentation 
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
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137

use super::*;

pub(super) fn generate_from(
  src_name: &syn::Ident,
  opts: &StructOpts,
  final_generics: &FinalGenerics,
) -> syn::Result<proc_macro2::TokenStream> {
  if opts.converter.try_from.is_none() && opts.converter.from.is_none() {
    return Ok(quote!());
  }
  let (try_, style, error) = match (&opts.converter.try_from, &opts.converter.from) {
    (None, None) => return Ok(quote!()),
    (None, Some(from)) => (false, *from, None),
    (Some(try_from), None) => (true, try_from.style, try_from.error.clone()),
    (Some(_), Some(_)) => {
      return Err(syn::Error::new_spanned(
        &opts.name,
        "Cannot have both `try_from` and `from`",
      ))
    }
  };

  let mut try_from_fields = Vec::new();
  let mut ctr = 0;
  if let Some(extra) = &opts.extra {
    for field in extra.fields.values() {
      let name = field
        .name
        .clone()
        .unwrap_or_else(|| format_ident!("{}", ctr));
      ctr += usize::from(field.named);
      let default = field
        .default
        .as_ref()
        .map(|d| quote!(#d()))
        .unwrap_or(quote! { ::core::default::Default::default() });

      try_from_fields.push(quote! {
          #name: #default,
      });
    }
  }

  for (src_name, field) in &opts.fields {
    if field.skip.is_some() {
      continue;
    }
    let name = field.rename.clone().unwrap_or_else(|| {
      if field.named {
        format_ident!("{}", src_name)
      } else {
        format_ident!("{}", ctr)
      }
    });
    let src_name = format_ident!("{}", src_name);
    ctr += usize::from(field.named);

    match &field.from {
      Some(from) => {
        let final_style = from.style.unwrap_or(style);

        let converter = if try_ {
          from
            .func
            .as_ref()
            .map(|f| quote!(#f(#final_style s.#src_name)?))
            .unwrap_or_else(|| {
              quote! {
                  ::core::convert::TryInto::try_into(#final_style s.#src_name)?
              }
            })
        } else {
          from
            .func
            .as_ref()
            .map(|f| quote!(#f(#final_style s.#src_name)))
            .unwrap_or_else(|| {
              quote! {
                  ::core::convert::Into::into(#final_style s.#src_name)
              }
            })
        };
        try_from_fields.push(quote! {
            #name: #converter,
        });
      }
      None => {
        if try_ {
          try_from_fields.push(quote! {
              #name: ::core::convert::TryInto::try_into(#style s.#src_name)?,
          });
        } else {
          try_from_fields.push(quote! {
              #name: ::core::convert::Into::into(#style s.#src_name),
          });
        }
      }
    }
  }

  let final_impl_generics = &final_generics.final_impl_generics;
  let self_ty_generics = &final_generics.ty_generics;
  let final_where_clause = &final_generics.final_where_clause;
  let src_ty_generics = &final_generics.src_ty_generics;

  let name = &opts.name;
  if try_ {
    let error = error.map(|t| quote!(#t)).unwrap_or_else(|| {
      quote!(
        ::std::boxed::Box<
          dyn ::std::error::Error + ::core::marker::Send + ::core::marker::Sync + 'static,
        >
      )
    });
    Ok(quote! {
        impl #final_impl_generics ::core::convert::TryFrom<#style #src_name #src_ty_generics> for #name #self_ty_generics #final_where_clause {
            type Error = #error;

            fn try_from(s: #style #src_name #src_ty_generics) -> ::core::result::Result<Self, Self::Error> {
                ::core::result::Result::Ok(Self {
                    #(#try_from_fields)*
                })
            }
        }
    })
  } else {
    Ok(quote! {
        impl #final_impl_generics ::core::convert::From<#style #src_name #src_ty_generics> for #name #self_ty_generics #final_where_clause {
            fn from(s: #style #src_name #src_ty_generics) -> Self {
                Self {
                    #(#try_from_fields)*
                }
            }
        }
    })
  }
}