hir_expand/builtin/
attr_macro.rs

1//! Builtin attributes.
2use intern::sym;
3use span::Span;
4
5use crate::{ExpandResult, MacroCallId, MacroCallKind, db::ExpandDatabase, name, tt};
6
7use super::quote;
8
9macro_rules! register_builtin {
10    ($(($name:ident, $variant:ident) => $expand:ident),* ) => {
11        #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
12        pub enum BuiltinAttrExpander {
13            $($variant),*
14        }
15
16        impl BuiltinAttrExpander {
17            pub fn expander(&self) -> fn (&dyn ExpandDatabase, MacroCallId, &tt::TopSubtree, Span) -> ExpandResult<tt::TopSubtree>  {
18                match *self {
19                    $( BuiltinAttrExpander::$variant => $expand, )*
20                }
21            }
22
23            fn find_by_name(name: &name::Name) -> Option<Self> {
24                match name {
25                    $( id if id == &sym::$name => Some(BuiltinAttrExpander::$variant), )*
26                     _ => None,
27                }
28            }
29        }
30
31    };
32}
33
34impl BuiltinAttrExpander {
35    pub fn expand(
36        &self,
37        db: &dyn ExpandDatabase,
38        id: MacroCallId,
39        tt: &tt::TopSubtree,
40        span: Span,
41    ) -> ExpandResult<tt::TopSubtree> {
42        self.expander()(db, id, tt, span)
43    }
44
45    pub fn is_derive(self) -> bool {
46        matches!(self, BuiltinAttrExpander::Derive | BuiltinAttrExpander::DeriveConst)
47    }
48    pub fn is_test(self) -> bool {
49        matches!(self, BuiltinAttrExpander::Test)
50    }
51    pub fn is_bench(self) -> bool {
52        matches!(self, BuiltinAttrExpander::Bench)
53    }
54    pub fn is_test_case(self) -> bool {
55        matches!(self, BuiltinAttrExpander::TestCase)
56    }
57}
58
59register_builtin! {
60    (bench, Bench) => dummy_gate_test_expand,
61    (cfg_accessible, CfgAccessible) => dummy_attr_expand,
62    (cfg_eval, CfgEval) => dummy_attr_expand,
63    (derive, Derive) => derive_expand,
64    // derive const is equivalent to derive for our proposes.
65    (derive_const, DeriveConst) => derive_expand,
66    (global_allocator, GlobalAllocator) => dummy_attr_expand,
67    (test, Test) => dummy_gate_test_expand,
68    (test_case, TestCase) => dummy_gate_test_expand
69}
70
71pub fn find_builtin_attr(ident: &name::Name) -> Option<BuiltinAttrExpander> {
72    BuiltinAttrExpander::find_by_name(ident)
73}
74
75fn dummy_attr_expand(
76    _db: &dyn ExpandDatabase,
77    _id: MacroCallId,
78    tt: &tt::TopSubtree,
79    _span: Span,
80) -> ExpandResult<tt::TopSubtree> {
81    ExpandResult::ok(tt.clone())
82}
83
84fn dummy_gate_test_expand(
85    _db: &dyn ExpandDatabase,
86    _id: MacroCallId,
87    tt: &tt::TopSubtree,
88    span: Span,
89) -> ExpandResult<tt::TopSubtree> {
90    let result = quote::quote! { span=>
91        #[cfg(test)]
92        #tt
93    };
94    ExpandResult::ok(result)
95}
96
97/// We generate a very specific expansion here, as we do not actually expand the `#[derive]` attribute
98/// itself in name res, but we do want to expand it to something for the IDE layer, so that the input
99/// derive attributes can be downmapped, and resolved as proper paths.
100/// This is basically a hack, that simplifies the hacks we need in a lot of ide layer places to
101/// somewhat inconsistently resolve derive attributes.
102///
103/// As such, we expand `#[derive(Foo, bar::Bar)]` into
104/// ```ignore
105///  #![Foo]
106///  #![bar::Bar]
107/// ```
108/// which allows fallback path resolution in hir::Semantics to properly identify our derives.
109/// Since we do not expand the attribute in nameres though, we keep the original item.
110///
111/// The ideal expansion here would be for the `#[derive]` to re-emit the annotated item and somehow
112/// use the input paths in its output as well.
113/// But that would bring two problems with it, for one every derive would duplicate the item token tree
114/// wasting a lot of memory, and it would also require some way to use a path in a way that makes it
115/// always resolve as a derive without nameres recollecting them.
116/// So this hacky approach is a lot more friendly for us, though it does require a bit of support in
117/// [`hir::Semantics`] to make this work.
118fn derive_expand(
119    db: &dyn ExpandDatabase,
120    id: MacroCallId,
121    tt: &tt::TopSubtree,
122    span: Span,
123) -> ExpandResult<tt::TopSubtree> {
124    let loc = db.lookup_intern_macro_call(id);
125    let derives = match &loc.kind {
126        MacroCallKind::Attr { attr_args: Some(attr_args), .. } if loc.def.is_attribute_derive() => {
127            attr_args
128        }
129        _ => {
130            return ExpandResult::ok(tt::TopSubtree::empty(tt::DelimSpan {
131                open: span,
132                close: span,
133            }));
134        }
135    };
136    pseudo_derive_attr_expansion(tt, derives, span)
137}
138
139pub fn pseudo_derive_attr_expansion(
140    _: &tt::TopSubtree,
141    args: &tt::TopSubtree,
142    call_site: Span,
143) -> ExpandResult<tt::TopSubtree> {
144    let mk_leaf =
145        |char| tt::Leaf::Punct(tt::Punct { char, spacing: tt::Spacing::Alone, span: call_site });
146
147    let mut token_trees = tt::TopSubtreeBuilder::new(args.top_subtree().delimiter);
148    let iter = args.token_trees().split(|tt| {
149        matches!(tt, tt::TtElement::Leaf(tt::Leaf::Punct(tt::Punct { char: ',', .. })))
150    });
151    for tts in iter {
152        token_trees.extend([mk_leaf('#'), mk_leaf('!')]);
153        token_trees.open(tt::DelimiterKind::Bracket, call_site);
154        token_trees.extend_with_tt(tts);
155        token_trees.close(call_site);
156    }
157    ExpandResult::ok(token_trees.build())
158}
hir_expand/builtin/attr_macro.rs

hir_expand/builtin/
attr_macro.rs
