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
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
use crate::errors;
use rustc_ast::ptr::P;
use rustc_ast::visit::{self, Visitor};
use rustc_ast::{self as ast, attr, NodeId};
use rustc_ast_pretty::pprust;
use rustc_expand::base::{parse_macro_name_and_helper_attrs, ExtCtxt, ResolverExpand};
use rustc_expand::expand::{AstFragment, ExpansionConfig};
use rustc_feature::Features;
use rustc_session::Session;
use rustc_span::hygiene::AstPass;
use rustc_span::source_map::SourceMap;
use rustc_span::symbol::{kw, sym, Ident, Symbol};
use rustc_span::{Span, DUMMY_SP};
use smallvec::smallvec;
use std::mem;
use thin_vec::{thin_vec, ThinVec};

struct ProcMacroDerive {
    id: NodeId,
    trait_name: Symbol,
    function_name: Ident,
    span: Span,
    attrs: Vec<Symbol>,
}

struct ProcMacroDef {
    id: NodeId,
    function_name: Ident,
    span: Span,
}

enum ProcMacro {
    Derive(ProcMacroDerive),
    Attr(ProcMacroDef),
    Bang(ProcMacroDef),
}

struct CollectProcMacros<'a> {
    macros: Vec<ProcMacro>,
    in_root: bool,
    handler: &'a rustc_errors::Handler,
    source_map: &'a SourceMap,
    is_proc_macro_crate: bool,
    is_test_crate: bool,
}

pub fn inject(
    krate: &mut ast::Crate,
    sess: &Session,
    features: &Features,
    resolver: &mut dyn ResolverExpand,
    is_proc_macro_crate: bool,
    has_proc_macro_decls: bool,
    is_test_crate: bool,
    handler: &rustc_errors::Handler,
) {
    let ecfg = ExpansionConfig::default("proc_macro".to_string(), features);
    let mut cx = ExtCtxt::new(sess, ecfg, resolver, None);

    let mut collect = CollectProcMacros {
        macros: Vec::new(),
        in_root: true,
        handler,
        source_map: sess.source_map(),
        is_proc_macro_crate,
        is_test_crate,
    };

    if has_proc_macro_decls || is_proc_macro_crate {
        visit::walk_crate(&mut collect, krate);
    }
    let macros = collect.macros;

    if !is_proc_macro_crate {
        return;
    }

    if is_test_crate {
        return;
    }

    let decls = mk_decls(&mut cx, &macros);
    krate.items.push(decls);
}

impl<'a> CollectProcMacros<'a> {
    fn check_not_pub_in_root(&self, vis: &ast::Visibility, sp: Span) {
        if self.is_proc_macro_crate && self.in_root && vis.kind.is_pub() {
            self.handler.emit_err(errors::ProcMacro { span: sp });
        }
    }

    fn collect_custom_derive(&mut self, item: &'a ast::Item, attr: &'a ast::Attribute) {
        let Some((trait_name, proc_attrs)) =
            parse_macro_name_and_helper_attrs(self.handler, attr, "derive")
        else {
            return;
        };

        if self.in_root && item.vis.kind.is_pub() {
            self.macros.push(ProcMacro::Derive(ProcMacroDerive {
                id: item.id,
                span: item.span,
                trait_name,
                function_name: item.ident,
                attrs: proc_attrs,
            }));
        } else {
            let msg = if !self.in_root {
                "functions tagged with `#[proc_macro_derive]` must \
                 currently reside in the root of the crate"
            } else {
                "functions tagged with `#[proc_macro_derive]` must be `pub`"
            };
            self.handler.span_err(self.source_map.guess_head_span(item.span), msg);
        }
    }

    fn collect_attr_proc_macro(&mut self, item: &'a ast::Item) {
        if self.in_root && item.vis.kind.is_pub() {
            self.macros.push(ProcMacro::Attr(ProcMacroDef {
                id: item.id,
                span: item.span,
                function_name: item.ident,
            }));
        } else {
            let msg = if !self.in_root {
                "functions tagged with `#[proc_macro_attribute]` must \
                 currently reside in the root of the crate"
            } else {
                "functions tagged with `#[proc_macro_attribute]` must be `pub`"
            };
            self.handler.span_err(self.source_map.guess_head_span(item.span), msg);
        }
    }

    fn collect_bang_proc_macro(&mut self, item: &'a ast::Item) {
        if self.in_root && item.vis.kind.is_pub() {
            self.macros.push(ProcMacro::Bang(ProcMacroDef {
                id: item.id,
                span: item.span,
                function_name: item.ident,
            }));
        } else {
            let msg = if !self.in_root {
                "functions tagged with `#[proc_macro]` must \
                 currently reside in the root of the crate"
            } else {
                "functions tagged with `#[proc_macro]` must be `pub`"
            };
            self.handler.span_err(self.source_map.guess_head_span(item.span), msg);
        }
    }
}

impl<'a> Visitor<'a> for CollectProcMacros<'a> {
    fn visit_item(&mut self, item: &'a ast::Item) {
        if let ast::ItemKind::MacroDef(..) = item.kind {
            if self.is_proc_macro_crate && attr::contains_name(&item.attrs, sym::macro_export) {
                self.handler.emit_err(errors::ExportMacroRules {
                    span: self.source_map.guess_head_span(item.span),
                });
            }
        }

        // First up, make sure we're checking a bare function. If we're not then
        // we're just not interested in this item.
        //
        // If we find one, try to locate a `#[proc_macro_derive]` attribute on it.
        let is_fn = matches!(item.kind, ast::ItemKind::Fn(..));

        let mut found_attr: Option<&'a ast::Attribute> = None;

        for attr in &item.attrs {
            if attr.is_proc_macro_attr() {
                if let Some(prev_attr) = found_attr {
                    let prev_item = prev_attr.get_normal_item();
                    let item = attr.get_normal_item();
                    let path_str = pprust::path_to_string(&item.path);
                    let msg = if item.path.segments[0].ident.name
                        == prev_item.path.segments[0].ident.name
                    {
                        format!(
                            "only one `#[{path_str}]` attribute is allowed on any given function",
                        )
                    } else {
                        format!(
                            "`#[{}]` and `#[{}]` attributes cannot both be applied
                            to the same function",
                            path_str,
                            pprust::path_to_string(&prev_item.path),
                        )
                    };

                    self.handler
                        .struct_span_err(attr.span, msg)
                        .span_label(prev_attr.span, "previous attribute here")
                        .emit();

                    return;
                }

                found_attr = Some(attr);
            }
        }

        let Some(attr) = found_attr else {
            self.check_not_pub_in_root(&item.vis, self.source_map.guess_head_span(item.span));
            let prev_in_root = mem::replace(&mut self.in_root, false);
            visit::walk_item(self, item);
            self.in_root = prev_in_root;
            return;
        };

        if !is_fn {
            let msg = format!(
                "the `#[{}]` attribute may only be used on bare functions",
                pprust::path_to_string(&attr.get_normal_item().path),
            );

            self.handler.span_err(attr.span, msg);
            return;
        }

        if self.is_test_crate {
            return;
        }

        if !self.is_proc_macro_crate {
            let msg = format!(
                "the `#[{}]` attribute is only usable with crates of the `proc-macro` crate type",
                pprust::path_to_string(&attr.get_normal_item().path),
            );

            self.handler.span_err(attr.span, msg);
            return;
        }

        if attr.has_name(sym::proc_macro_derive) {
            self.collect_custom_derive(item, attr);
        } else if attr.has_name(sym::proc_macro_attribute) {
            self.collect_attr_proc_macro(item);
        } else if attr.has_name(sym::proc_macro) {
            self.collect_bang_proc_macro(item);
        };

        let prev_in_root = mem::replace(&mut self.in_root, false);
        visit::walk_item(self, item);
        self.in_root = prev_in_root;
    }
}

// Creates a new module which looks like:
//
//      const _: () = {
//          extern crate proc_macro;
//
//          use proc_macro::bridge::client::ProcMacro;
//
//          #[rustc_proc_macro_decls]
//          #[used]
//          #[allow(deprecated)]
//          static DECLS: &[ProcMacro] = &[
//              ProcMacro::custom_derive($name_trait1, &[], ::$name1);
//              ProcMacro::custom_derive($name_trait2, &["attribute_name"], ::$name2);
//              // ...
//          ];
//      }
fn mk_decls(cx: &mut ExtCtxt<'_>, macros: &[ProcMacro]) -> P<ast::Item> {
    let expn_id = cx.resolver.expansion_for_ast_pass(
        DUMMY_SP,
        AstPass::ProcMacroHarness,
        &[sym::rustc_attrs, sym::proc_macro_internals],
        None,
    );
    let span = DUMMY_SP.with_def_site_ctxt(expn_id.to_expn_id());

    let proc_macro = Ident::new(sym::proc_macro, span);
    let krate = cx.item(span, proc_macro, ast::AttrVec::new(), ast::ItemKind::ExternCrate(None));

    let bridge = Ident::new(sym::bridge, span);
    let client = Ident::new(sym::client, span);
    let proc_macro_ty = Ident::new(sym::ProcMacro, span);
    let custom_derive = Ident::new(sym::custom_derive, span);
    let attr = Ident::new(sym::attr, span);
    let bang = Ident::new(sym::bang, span);

    // We add NodeIds to 'resolver.proc_macros' in the order
    // that we generate expressions. The position of each NodeId
    // in the 'proc_macros' Vec corresponds to its position
    // in the static array that will be generated
    let decls = macros
        .iter()
        .map(|m| {
            let harness_span = span;
            let span = match m {
                ProcMacro::Derive(m) => m.span,
                ProcMacro::Attr(m) | ProcMacro::Bang(m) => m.span,
            };
            let local_path = |cx: &ExtCtxt<'_>, name| cx.expr_path(cx.path(span, vec![name]));
            let proc_macro_ty_method_path = |cx: &ExtCtxt<'_>, method| {
                cx.expr_path(cx.path(
                    span.with_ctxt(harness_span.ctxt()),
                    vec![proc_macro, bridge, client, proc_macro_ty, method],
                ))
            };
            match m {
                ProcMacro::Derive(cd) => {
                    cx.resolver.declare_proc_macro(cd.id);
                    cx.expr_call(
                        span,
                        proc_macro_ty_method_path(cx, custom_derive),
                        thin_vec![
                            cx.expr_str(span, cd.trait_name),
                            cx.expr_array_ref(
                                span,
                                cd.attrs
                                    .iter()
                                    .map(|&s| cx.expr_str(span, s))
                                    .collect::<ThinVec<_>>(),
                            ),
                            local_path(cx, cd.function_name),
                        ],
                    )
                }
                ProcMacro::Attr(ca) | ProcMacro::Bang(ca) => {
                    cx.resolver.declare_proc_macro(ca.id);
                    let ident = match m {
                        ProcMacro::Attr(_) => attr,
                        ProcMacro::Bang(_) => bang,
                        ProcMacro::Derive(_) => unreachable!(),
                    };

                    cx.expr_call(
                        span,
                        proc_macro_ty_method_path(cx, ident),
                        thin_vec![
                            cx.expr_str(span, ca.function_name.name),
                            local_path(cx, ca.function_name),
                        ],
                    )
                }
            }
        })
        .collect();

    let decls_static = cx
        .item_static(
            span,
            Ident::new(sym::_DECLS, span),
            cx.ty_ref(
                span,
                cx.ty(
                    span,
                    ast::TyKind::Slice(
                        cx.ty_path(cx.path(span, vec![proc_macro, bridge, client, proc_macro_ty])),
                    ),
                ),
                None,
                ast::Mutability::Not,
            ),
            ast::Mutability::Not,
            cx.expr_array_ref(span, decls),
        )
        .map(|mut i| {
            i.attrs.push(cx.attr_word(sym::rustc_proc_macro_decls, span));
            i.attrs.push(cx.attr_word(sym::used, span));
            i.attrs.push(cx.attr_nested_word(sym::allow, sym::deprecated, span));
            i
        });

    let block = cx.expr_block(
        cx.block(span, thin_vec![cx.stmt_item(span, krate), cx.stmt_item(span, decls_static)]),
    );

    let anon_constant = cx.item_const(
        span,
        Ident::new(kw::Underscore, span),
        cx.ty(span, ast::TyKind::Tup(ThinVec::new())),
        block,
    );

    // Integrate the new item into existing module structures.
    let items = AstFragment::Items(smallvec![anon_constant]);
    cx.monotonic_expander().fully_expand_fragment(items).make_items().pop().unwrap()
}