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

use super::{kw, Override, Visibility};
use proc_macro2::Span;
use std::{
    collections::HashSet,
    fmt,
    hash::{Hash, Hasher},
    mem,
};
use syn::{
    parse::{Parse, ParseStream},
    Error, Result,
};

/// A list of unique variable attributes.
#[derive(Clone, Debug)]
pub struct VariableAttributes(pub HashSet<VariableAttribute>);

impl Parse for VariableAttributes {
    fn parse(input: ParseStream<'_>) -> Result<Self> {
        let mut attributes = HashSet::new();
        while let Ok(attribute) = input.parse::<VariableAttribute>() {
            let error = |prev: &VariableAttribute| {
                let mut e = Error::new(attribute.span(), "duplicate attribute");
                e.combine(Error::new(prev.span(), "previous declaration is here"));
                e
            };

            // Only one of: `constant`, `immutable`
            match attribute {
                VariableAttribute::Constant(_) => {
                    if let Some(prev) =
                        attributes.get(&VariableAttribute::Immutable(Default::default()))
                    {
                        return Err(error(prev))
                    }
                }
                VariableAttribute::Immutable(_) => {
                    if let Some(prev) =
                        attributes.get(&VariableAttribute::Constant(Default::default()))
                    {
                        return Err(error(prev))
                    }
                }
                _ => {}
            }

            if let Some(prev) = attributes.get(&attribute) {
                return Err(error(prev))
            }
            attributes.insert(attribute);
        }
        Ok(Self(attributes))
    }
}

/// A variable attribute.
#[derive(Clone)]
pub enum VariableAttribute {
    /// A [Visibility] attribute.
    Visibility(Visibility),
    /// `constant`.
    Constant(kw::constant),
    /// `immutable`.
    Immutable(kw::immutable),
    /// An [Override] attribute.
    Override(Override),
}

impl fmt::Debug for VariableAttribute {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::Visibility(v) => v.fmt(f),
            Self::Constant(_) => f.write_str("Constant"),
            Self::Immutable(_) => f.write_str("Immutable"),
            Self::Override(o) => o.fmt(f),
        }
    }
}

impl PartialEq for VariableAttribute {
    fn eq(&self, other: &Self) -> bool {
        mem::discriminant(self) == mem::discriminant(other)
    }
}

impl Eq for VariableAttribute {}

impl Hash for VariableAttribute {
    fn hash<H: Hasher>(&self, state: &mut H) {
        mem::discriminant(self).hash(state)
    }
}

impl Parse for VariableAttribute {
    fn parse(input: ParseStream<'_>) -> Result<Self> {
        let lookahead = input.lookahead1();
        if Visibility::peek(&lookahead) {
            input.parse().map(Self::Visibility)
        } else if lookahead.peek(kw::constant) {
            input.parse().map(Self::Constant)
        } else if lookahead.peek(kw::Override) {
            input.parse().map(Self::Override)
        } else if lookahead.peek(kw::immutable) {
            input.parse().map(Self::Immutable)
        } else {
            Err(lookahead.error())
        }
    }
}

impl VariableAttribute {
    pub fn span(&self) -> Span {
        match self {
            Self::Visibility(v) => v.span(),
            Self::Constant(c) => c.span,
            Self::Override(o) => o.span(),
            Self::Immutable(i) => i.span,
        }
    }

    pub fn set_span(&mut self, span: Span) {
        match self {
            Self::Visibility(v) => v.set_span(span),
            Self::Constant(c) => c.span = span,
            Self::Override(o) => o.set_span(span),
            Self::Immutable(i) => i.span = span,
        }
    }
}