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

//! Deserialization for untagged enums:
//!
//! ```ignore
//! #[serde(untagged)]
//! enum Enum {}
//! ```

use crate::de::struct_;
use crate::de::tuple;
use crate::de::{
    effective_style, expr_is_missing, unwrap_to_variant_closure, Parameters, StructForm, TupleForm,
};
use crate::fragment::{Expr, Fragment};
use crate::internals::ast::{Field, Style, Variant};
use crate::internals::attr;
use crate::private;
use proc_macro2::TokenStream;
use quote::{quote, quote_spanned};
use syn::spanned::Spanned;

/// Generates `Deserialize::deserialize` body for an `enum Enum {...}` with `#[serde(untagged)]` attribute
pub(super) fn deserialize(
    params: &Parameters,
    variants: &[Variant],
    cattrs: &attr::Container,
    first_attempt: Option<TokenStream>,
) -> Fragment {
    let attempts = variants
        .iter()
        .filter(|variant| !variant.attrs.skip_deserializing())
        .map(|variant| Expr(deserialize_variant(params, variant, cattrs)));
    // TODO this message could be better by saving the errors from the failed
    // attempts. The heuristic used by TOML was to count the number of fields
    // processed before an error, and use the error that happened after the
    // largest number of fields. I'm not sure I like that. Maybe it would be
    // better to save all the errors and combine them into one message that
    // explains why none of the variants matched.
    let fallthrough_msg = format!(
        "data did not match any variant of untagged enum {}",
        params.type_name()
    );
    let fallthrough_msg = cattrs.expecting().unwrap_or(&fallthrough_msg);

    let private2 = private;
    quote_block! {
        let __content = _serde::de::DeserializeSeed::deserialize(_serde::#private::de::ContentVisitor::new(), __deserializer)?;
        let __deserializer = _serde::#private::de::ContentRefDeserializer::<__D::Error>::new(&__content);

        #first_attempt

        #(
            if let _serde::#private2::Ok(__ok) = #attempts {
                return _serde::#private2::Ok(__ok);
            }
        )*

        _serde::#private::Err(_serde::de::Error::custom(#fallthrough_msg))
    }
}

// Also used by adjacently tagged enums
pub(super) fn deserialize_variant(
    params: &Parameters,
    variant: &Variant,
    cattrs: &attr::Container,
) -> Fragment {
    if let Some(path) = variant.attrs.deserialize_with() {
        let unwrap_fn = unwrap_to_variant_closure(params, variant, false);
        return quote_block! {
            _serde::#private::Result::map(#path(__deserializer), #unwrap_fn)
        };
    }

    let variant_ident = &variant.ident;

    match effective_style(variant) {
        Style::Unit => {
            let this_value = &params.this_value;
            let type_name = params.type_name();
            let variant_name = variant.ident.to_string();
            let default = variant.fields.first().map(|field| {
                let default = Expr(expr_is_missing(field, cattrs));
                quote!((#default))
            });
            quote_expr! {
                match _serde::Deserializer::deserialize_any(
                    __deserializer,
                    _serde::#private::de::UntaggedUnitVisitor::new(#type_name, #variant_name)
                ) {
                    _serde::#private::Ok(()) => _serde::#private::Ok(#this_value::#variant_ident #default),
                    _serde::#private::Err(__err) => _serde::#private::Err(__err),
                }
            }
        }
        Style::Newtype => deserialize_newtype_variant(variant_ident, params, &variant.fields[0]),
        Style::Tuple => tuple::deserialize(
            params,
            &variant.fields,
            cattrs,
            TupleForm::Untagged(variant_ident),
        ),
        Style::Struct => struct_::deserialize(
            params,
            &variant.fields,
            cattrs,
            StructForm::Untagged(variant_ident),
        ),
    }
}

// Also used by internally tagged enums
// Implicitly (via `generate_variant`) used by adjacently tagged enums
pub(super) fn deserialize_newtype_variant(
    variant_ident: &syn::Ident,
    params: &Parameters,
    field: &Field,
) -> Fragment {
    let this_value = &params.this_value;
    let field_ty = field.ty;
    match field.attrs.deserialize_with() {
        None => {
            let span = field.original.span();
            let func = quote_spanned!(span=> <#field_ty as _serde::Deserialize>::deserialize);
            quote_expr! {
                _serde::#private::Result::map(#func(__deserializer), #this_value::#variant_ident)
            }
        }
        Some(path) => {
            quote_block! {
                let __value: _serde::#private::Result<#field_ty, _> = #path(__deserializer);
                _serde::#private::Result::map(__value, #this_value::#variant_ident)
            }
        }
    }
}