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
148
149
150
151
152

use crate::cfg_eval::cfg_eval;
use crate::errors;

use rustc_ast as ast;
use rustc_ast::{GenericParamKind, ItemKind, MetaItemKind, NestedMetaItem, StmtKind};
use rustc_expand::base::{Annotatable, ExpandResult, ExtCtxt, Indeterminate, MultiItemModifier};
use rustc_feature::AttributeTemplate;
use rustc_parse::validate_attr;
use rustc_session::Session;
use rustc_span::symbol::{sym, Ident};
use rustc_span::{ErrorGuaranteed, Span};

pub(crate) struct Expander(pub bool);

impl MultiItemModifier for Expander {
    fn expand(
        &self,
        ecx: &mut ExtCtxt<'_>,
        span: Span,
        meta_item: &ast::MetaItem,
        item: Annotatable,
        _: bool,
    ) -> ExpandResult<Vec<Annotatable>, Annotatable> {
        let sess = ecx.sess;
        if report_bad_target(sess, &item, span).is_err() {
            // We don't want to pass inappropriate targets to derive macros to avoid
            // follow up errors, all other errors below are recoverable.
            return ExpandResult::Ready(vec![item]);
        }

        let (sess, features) = (ecx.sess, ecx.ecfg.features);
        let result =
            ecx.resolver.resolve_derives(ecx.current_expansion.id, ecx.force_mode, &|| {
                let template =
                    AttributeTemplate { list: Some("Trait1, Trait2, ..."), ..Default::default() };
                validate_attr::check_builtin_meta_item(
                    &sess.parse_sess,
                    &meta_item,
                    ast::AttrStyle::Outer,
                    sym::derive,
                    template,
                );

                let mut resolutions = match &meta_item.kind {
                    MetaItemKind::List(list) => {
                        list.iter()
                            .filter_map(|nested_meta| match nested_meta {
                                NestedMetaItem::MetaItem(meta) => Some(meta),
                                NestedMetaItem::Lit(lit) => {
                                    // Reject `#[derive("Debug")]`.
                                    report_unexpected_meta_item_lit(sess, &lit);
                                    None
                                }
                            })
                            .map(|meta| {
                                // Reject `#[derive(Debug = "value", Debug(abc))]`, but recover the
                                // paths.
                                report_path_args(sess, &meta);
                                meta.path.clone()
                            })
                            .map(|path| (path, dummy_annotatable(), None, self.0))
                            .collect()
                    }
                    _ => vec![],
                };

                // Do not configure or clone items unless necessary.
                match &mut resolutions[..] {
                    [] => {}
                    [(_, first_item, ..), others @ ..] => {
                        *first_item = cfg_eval(
                            sess,
                            features,
                            item.clone(),
                            ecx.current_expansion.lint_node_id,
                        );
                        for (_, item, _, _) in others {
                            *item = first_item.clone();
                        }
                    }
                }

                resolutions
            });

        match result {
            Ok(()) => ExpandResult::Ready(vec![item]),
            Err(Indeterminate) => ExpandResult::Retry(item),
        }
    }
}

// The cheapest `Annotatable` to construct.
fn dummy_annotatable() -> Annotatable {
    Annotatable::GenericParam(ast::GenericParam {
        id: ast::DUMMY_NODE_ID,
        ident: Ident::empty(),
        attrs: Default::default(),
        bounds: Default::default(),
        is_placeholder: false,
        kind: GenericParamKind::Lifetime,
        colon_span: None,
    })
}

fn report_bad_target(
    sess: &Session,
    item: &Annotatable,
    span: Span,
) -> Result<(), ErrorGuaranteed> {
    let item_kind = match item {
        Annotatable::Item(item) => Some(&item.kind),
        Annotatable::Stmt(stmt) => match &stmt.kind {
            StmtKind::Item(item) => Some(&item.kind),
            _ => None,
        },
        _ => None,
    };

    let bad_target =
        !matches!(item_kind, Some(ItemKind::Struct(..) | ItemKind::Enum(..) | ItemKind::Union(..)));
    if bad_target {
        return Err(sess.emit_err(errors::BadDeriveTarget { span, item: item.span() }));
    }
    Ok(())
}

fn report_unexpected_meta_item_lit(sess: &Session, lit: &ast::MetaItemLit) {
    let help = match lit.kind {
        ast::LitKind::Str(_, ast::StrStyle::Cooked)
            if rustc_lexer::is_ident(lit.symbol.as_str()) =>
        {
            errors::BadDeriveLitHelp::StrLit { sym: lit.symbol }
        }
        _ => errors::BadDeriveLitHelp::Other,
    };
    sess.emit_err(errors::BadDeriveLit { span: lit.span, help });
}

fn report_path_args(sess: &Session, meta: &ast::MetaItem) {
    let span = meta.span.with_lo(meta.path.span.hi());

    match meta.kind {
        MetaItemKind::Word => {}
        MetaItemKind::List(..) => {
            sess.emit_err(errors::DerivePathArgsList { span });
        }
        MetaItemKind::NameValue(..) => {
            sess.emit_err(errors::DerivePathArgsValue { span });
        }
    }
}