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
138
139
140
141
142
143
144
145
146
147

//! Builtin attributes.
use span::{MacroCallId, Span};

use crate::{db::ExpandDatabase, name, tt, ExpandResult, MacroCallKind};

macro_rules! register_builtin {
    ($(($name:ident, $variant:ident) => $expand:ident),* ) => {
        #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
        pub enum BuiltinAttrExpander {
            $($variant),*
        }

        impl BuiltinAttrExpander {
            pub fn expander(&self) -> fn (&dyn ExpandDatabase, MacroCallId, &tt::Subtree, Span) -> ExpandResult<tt::Subtree>  {
                match *self {
                    $( BuiltinAttrExpander::$variant => $expand, )*
                }
            }

            fn find_by_name(name: &name::Name) -> Option<Self> {
                match name {
                    $( id if id == &name::name![$name] => Some(BuiltinAttrExpander::$variant), )*
                     _ => None,
                }
            }
        }

    };
}

impl BuiltinAttrExpander {
    pub fn expand(
        &self,
        db: &dyn ExpandDatabase,
        id: MacroCallId,
        tt: &tt::Subtree,
        span: Span,
    ) -> ExpandResult<tt::Subtree> {
        self.expander()(db, id, tt, span)
    }

    pub fn is_derive(self) -> bool {
        matches!(self, BuiltinAttrExpander::Derive | BuiltinAttrExpander::DeriveConst)
    }
    pub fn is_test(self) -> bool {
        matches!(self, BuiltinAttrExpander::Test)
    }
    pub fn is_bench(self) -> bool {
        matches!(self, BuiltinAttrExpander::Bench)
    }
}

register_builtin! {
    (bench, Bench) => dummy_attr_expand,
    (cfg, Cfg) => dummy_attr_expand,
    (cfg_attr, CfgAttr) => dummy_attr_expand,
    (cfg_accessible, CfgAccessible) => dummy_attr_expand,
    (cfg_eval, CfgEval) => dummy_attr_expand,
    (derive, Derive) => derive_expand,
    // derive const is equivalent to derive for our proposes.
    (derive_const, DeriveConst) => derive_expand,
    (global_allocator, GlobalAllocator) => dummy_attr_expand,
    (test, Test) => dummy_attr_expand,
    (test_case, TestCase) => dummy_attr_expand
}

pub fn find_builtin_attr(ident: &name::Name) -> Option<BuiltinAttrExpander> {
    BuiltinAttrExpander::find_by_name(ident)
}

fn dummy_attr_expand(
    _db: &dyn ExpandDatabase,
    _id: MacroCallId,
    tt: &tt::Subtree,
    _span: Span,
) -> ExpandResult<tt::Subtree> {
    ExpandResult::ok(tt.clone())
}

/// We generate a very specific expansion here, as we do not actually expand the `#[derive]` attribute
/// itself in name res, but we do want to expand it to something for the IDE layer, so that the input
/// derive attributes can be downmapped, and resolved as proper paths.
/// This is basically a hack, that simplifies the hacks we need in a lot of ide layer places to
/// somewhat inconsistently resolve derive attributes.
///
/// As such, we expand `#[derive(Foo, bar::Bar)]` into
/// ```
///  #![Foo]
///  #![bar::Bar]
/// ```
/// which allows fallback path resolution in hir::Semantics to properly identify our derives.
/// Since we do not expand the attribute in nameres though, we keep the original item.
///
/// The ideal expansion here would be for the `#[derive]` to re-emit the annotated item and somehow
/// use the input paths in its output as well.
/// But that would bring two problems with it, for one every derive would duplicate the item token tree
/// wasting a lot of memory, and it would also require some way to use a path in a way that makes it
/// always resolve as a derive without nameres recollecting them.
/// So this hacky approach is a lot more friendly for us, though it does require a bit of support in
/// [`hir::Semantics`] to make this work.
fn derive_expand(
    db: &dyn ExpandDatabase,
    id: MacroCallId,
    tt: &tt::Subtree,
    span: Span,
) -> ExpandResult<tt::Subtree> {
    let loc = db.lookup_intern_macro_call(id);
    let derives = match &loc.kind {
        MacroCallKind::Attr { attr_args: Some(attr_args), .. } if loc.def.is_attribute_derive() => {
            attr_args
        }
        _ => {
            return ExpandResult::ok(tt::Subtree::empty(tt::DelimSpan { open: span, close: span }))
        }
    };
    pseudo_derive_attr_expansion(tt, derives, span)
}

pub fn pseudo_derive_attr_expansion(
    _: &tt::Subtree,
    args: &tt::Subtree,
    call_site: Span,
) -> ExpandResult<tt::Subtree> {
    let mk_leaf = |char| {
        tt::TokenTree::Leaf(tt::Leaf::Punct(tt::Punct {
            char,
            spacing: tt::Spacing::Alone,
            span: call_site,
        }))
    };

    let mut token_trees = Vec::new();
    for tt in args
        .token_trees
        .split(|tt| matches!(tt, tt::TokenTree::Leaf(tt::Leaf::Punct(tt::Punct { char: ',', .. }))))
    {
        token_trees.push(mk_leaf('#'));
        token_trees.push(mk_leaf('!'));
        token_trees.push(mk_leaf('['));
        token_trees.extend(tt.iter().cloned());
        token_trees.push(mk_leaf(']'));
    }
    ExpandResult::ok(tt::Subtree {
        delimiter: args.delimiter,
        token_trees: token_trees.into_boxed_slice(),
    })
}