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

use crate::ast::{Enum, Field, Struct, Variant};
use syn::{Member, Type};

impl Struct<'_> {
    pub(crate) fn from_field(&self) -> Option<&Field> {
        from_field(&self.fields)
    }

    pub(crate) fn source_field(&self) -> Option<&Field> {
        source_field(&self.fields)
    }

    pub(crate) fn backtrace_field(&self) -> Option<&Field> {
        backtrace_field(&self.fields)
    }

    pub(crate) fn distinct_backtrace_field(&self) -> Option<&Field> {
        let backtrace_field = self.backtrace_field()?;
        distinct_backtrace_field(backtrace_field, self.from_field())
    }
}

impl Enum<'_> {
    pub(crate) fn has_source(&self) -> bool {
        self.variants
            .iter()
            .any(|variant| variant.source_field().is_some() || variant.attrs.transparent.is_some())
    }

    pub(crate) fn has_backtrace(&self) -> bool {
        self.variants
            .iter()
            .any(|variant| variant.backtrace_field().is_some())
    }

    pub(crate) fn has_display(&self) -> bool {
        self.attrs.display.is_some()
            || self.attrs.transparent.is_some()
            || self
                .variants
                .iter()
                .any(|variant| variant.attrs.display.is_some())
            || self
                .variants
                .iter()
                .all(|variant| variant.attrs.transparent.is_some())
    }
}

impl Variant<'_> {
    pub(crate) fn from_field(&self) -> Option<&Field> {
        from_field(&self.fields)
    }

    pub(crate) fn source_field(&self) -> Option<&Field> {
        source_field(&self.fields)
    }

    pub(crate) fn backtrace_field(&self) -> Option<&Field> {
        backtrace_field(&self.fields)
    }

    pub(crate) fn distinct_backtrace_field(&self) -> Option<&Field> {
        let backtrace_field = self.backtrace_field()?;
        distinct_backtrace_field(backtrace_field, self.from_field())
    }
}

impl Field<'_> {
    pub(crate) fn is_backtrace(&self) -> bool {
        type_is_backtrace(self.ty)
    }
}

fn from_field<'a, 'b>(fields: &'a [Field<'b>]) -> Option<&'a Field<'b>> {
    for field in fields {
        if field.attrs.from.is_some() {
            return Some(field);
        }
    }
    None
}

fn source_field<'a, 'b>(fields: &'a [Field<'b>]) -> Option<&'a Field<'b>> {
    for field in fields {
        if field.attrs.from.is_some() || field.attrs.source.is_some() {
            return Some(field);
        }
    }
    for field in fields {
        match &field.member {
            Member::Named(ident) if ident == "source" => return Some(field),
            _ => {}
        }
    }
    None
}

fn backtrace_field<'a, 'b>(fields: &'a [Field<'b>]) -> Option<&'a Field<'b>> {
    for field in fields {
        if field.attrs.backtrace.is_some() {
            return Some(field);
        }
    }
    for field in fields {
        if field.is_backtrace() {
            return Some(field);
        }
    }
    None
}

// The #[backtrace] field, if it is not the same as the #[from] field.
fn distinct_backtrace_field<'a, 'b>(
    backtrace_field: &'a Field<'b>,
    from_field: Option<&Field>,
) -> Option<&'a Field<'b>> {
    if from_field.map_or(false, |from_field| {
        from_field.member == backtrace_field.member
    }) {
        None
    } else {
        Some(backtrace_field)
    }
}

fn type_is_backtrace(ty: &Type) -> bool {
    let path = match ty {
        Type::Path(ty) => &ty.path,
        _ => return false,
    };

    let last = path.segments.last().unwrap();
    last.ident == "Backtrace" && last.arguments.is_empty()
}