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
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
use super::{AnonymousLifetimeMode, ImplTraitContext, LoweringContext, ParamMode};
use super::{GenericArgsCtor, ParenthesizedGenericArgs};

use rustc_ast::{self as ast, *};
use rustc_errors::{struct_span_err, Applicability};
use rustc_hir as hir;
use rustc_hir::def::{DefKind, PartialRes, Res};
use rustc_hir::def_id::DefId;
use rustc_hir::GenericArg;
use rustc_span::symbol::Ident;
use rustc_span::{BytePos, Span, DUMMY_SP};

use smallvec::smallvec;
use tracing::debug;

impl<'a, 'hir> LoweringContext<'a, 'hir> {
    crate fn lower_qpath(
        &mut self,
        id: NodeId,
        qself: &Option<QSelf>,
        p: &Path,
        param_mode: ParamMode,
        mut itctx: ImplTraitContext<'_, 'hir>,
    ) -> hir::QPath<'hir> {
        debug!("lower_qpath(id: {:?}, qself: {:?}, p: {:?})", id, qself, p);
        let qself_position = qself.as_ref().map(|q| q.position);
        let qself = qself.as_ref().map(|q| self.lower_ty(&q.ty, itctx.reborrow()));

        let partial_res =
            self.resolver.get_partial_res(id).unwrap_or_else(|| PartialRes::new(Res::Err));

        let path_span_lo = p.span.shrink_to_lo();
        let proj_start = p.segments.len() - partial_res.unresolved_segments();
        let path = self.arena.alloc(hir::Path {
            res: self.lower_res(partial_res.base_res()),
            segments: self.arena.alloc_from_iter(p.segments[..proj_start].iter().enumerate().map(
                |(i, segment)| {
                    let param_mode = match (qself_position, param_mode) {
                        (Some(j), ParamMode::Optional) if i < j => {
                            // This segment is part of the trait path in a
                            // qualified path - one of `a`, `b` or `Trait`
                            // in `<X as a::b::Trait>::T::U::method`.
                            ParamMode::Explicit
                        }
                        _ => param_mode,
                    };

                    // Figure out if this is a type/trait segment,
                    // which may need lifetime elision performed.
                    let parent_def_id = |this: &mut Self, def_id: DefId| DefId {
                        krate: def_id.krate,
                        index: this.resolver.def_key(def_id).parent.expect("missing parent"),
                    };
                    let type_def_id = match partial_res.base_res() {
                        Res::Def(DefKind::AssocTy, def_id) if i + 2 == proj_start => {
                            Some(parent_def_id(self, def_id))
                        }
                        Res::Def(DefKind::Variant, def_id) if i + 1 == proj_start => {
                            Some(parent_def_id(self, def_id))
                        }
                        Res::Def(DefKind::Struct, def_id)
                        | Res::Def(DefKind::Union, def_id)
                        | Res::Def(DefKind::Enum, def_id)
                        | Res::Def(DefKind::TyAlias, def_id)
                        | Res::Def(DefKind::Trait, def_id)
                            if i + 1 == proj_start =>
                        {
                            Some(def_id)
                        }
                        _ => None,
                    };
                    let parenthesized_generic_args = match partial_res.base_res() {
                        // `a::b::Trait(Args)`
                        Res::Def(DefKind::Trait, _) if i + 1 == proj_start => {
                            ParenthesizedGenericArgs::Ok
                        }
                        // `a::b::Trait(Args)::TraitItem`
                        Res::Def(DefKind::AssocFn, _)
                        | Res::Def(DefKind::AssocConst, _)
                        | Res::Def(DefKind::AssocTy, _)
                            if i + 2 == proj_start =>
                        {
                            ParenthesizedGenericArgs::Ok
                        }
                        // Avoid duplicated errors.
                        Res::Err => ParenthesizedGenericArgs::Ok,
                        // An error
                        _ => ParenthesizedGenericArgs::Err,
                    };

                    let num_lifetimes = type_def_id
                        .map_or(0, |def_id| self.resolver.item_generics_num_lifetimes(def_id));
                    self.lower_path_segment(
                        p.span,
                        segment,
                        param_mode,
                        num_lifetimes,
                        parenthesized_generic_args,
                        itctx.reborrow(),
                    )
                },
            )),
            span: self.lower_span(
                p.segments[..proj_start]
                    .last()
                    .map_or(path_span_lo, |segment| path_span_lo.to(segment.span())),
            ),
        });

        // Simple case, either no projections, or only fully-qualified.
        // E.g., `std::mem::size_of` or `<I as Iterator>::Item`.
        if partial_res.unresolved_segments() == 0 {
            return hir::QPath::Resolved(qself, path);
        }

        // Create the innermost type that we're projecting from.
        let mut ty = if path.segments.is_empty() {
            // If the base path is empty that means there exists a
            // syntactical `Self`, e.g., `&i32` in `<&i32>::clone`.
            qself.expect("missing QSelf for <T>::...")
        } else {
            // Otherwise, the base path is an implicit `Self` type path,
            // e.g., `Vec` in `Vec::new` or `<I as Iterator>::Item` in
            // `<I as Iterator>::Item::default`.
            let new_id = self.next_id();
            self.arena.alloc(self.ty_path(new_id, path.span, hir::QPath::Resolved(qself, path)))
        };

        // Anything after the base path are associated "extensions",
        // out of which all but the last one are associated types,
        // e.g., for `std::vec::Vec::<T>::IntoIter::Item::clone`:
        // * base path is `std::vec::Vec<T>`
        // * "extensions" are `IntoIter`, `Item` and `clone`
        // * type nodes are:
        //   1. `std::vec::Vec<T>` (created above)
        //   2. `<std::vec::Vec<T>>::IntoIter`
        //   3. `<<std::vec::Vec<T>>::IntoIter>::Item`
        // * final path is `<<<std::vec::Vec<T>>::IntoIter>::Item>::clone`
        for (i, segment) in p.segments.iter().enumerate().skip(proj_start) {
            let hir_segment = self.arena.alloc(self.lower_path_segment(
                p.span,
                segment,
                param_mode,
                0,
                ParenthesizedGenericArgs::Err,
                itctx.reborrow(),
            ));
            let qpath = hir::QPath::TypeRelative(ty, hir_segment);

            // It's finished, return the extension of the right node type.
            if i == p.segments.len() - 1 {
                return qpath;
            }

            // Wrap the associated extension in another type node.
            let new_id = self.next_id();
            ty = self.arena.alloc(self.ty_path(new_id, path_span_lo.to(segment.span()), qpath));
        }

        // We should've returned in the for loop above.

        self.sess.diagnostic().span_bug(
            p.span,
            &format!(
                "lower_qpath: no final extension segment in {}..{}",
                proj_start,
                p.segments.len()
            ),
        );
    }

    crate fn lower_path_extra(
        &mut self,
        res: Res,
        p: &Path,
        param_mode: ParamMode,
    ) -> &'hir hir::Path<'hir> {
        self.arena.alloc(hir::Path {
            res,
            segments: self.arena.alloc_from_iter(p.segments.iter().map(|segment| {
                self.lower_path_segment(
                    p.span,
                    segment,
                    param_mode,
                    0,
                    ParenthesizedGenericArgs::Err,
                    ImplTraitContext::disallowed(),
                )
            })),
            span: self.lower_span(p.span),
        })
    }

    crate fn lower_path(
        &mut self,
        id: NodeId,
        p: &Path,
        param_mode: ParamMode,
    ) -> &'hir hir::Path<'hir> {
        let res = self.expect_full_res(id);
        let res = self.lower_res(res);
        self.lower_path_extra(res, p, param_mode)
    }

    crate fn lower_path_segment(
        &mut self,
        path_span: Span,
        segment: &PathSegment,
        param_mode: ParamMode,
        expected_lifetimes: usize,
        parenthesized_generic_args: ParenthesizedGenericArgs,
        itctx: ImplTraitContext<'_, 'hir>,
    ) -> hir::PathSegment<'hir> {
        debug!(
            "path_span: {:?}, lower_path_segment(segment: {:?}, expected_lifetimes: {:?})",
            path_span, segment, expected_lifetimes
        );
        let (mut generic_args, infer_args) = if let Some(ref generic_args) = segment.args {
            let msg = "parenthesized type parameters may only be used with a `Fn` trait";
            match **generic_args {
                GenericArgs::AngleBracketed(ref data) => {
                    self.lower_angle_bracketed_parameter_data(data, param_mode, itctx)
                }
                GenericArgs::Parenthesized(ref data) => match parenthesized_generic_args {
                    ParenthesizedGenericArgs::Ok => self.lower_parenthesized_parameter_data(data),
                    ParenthesizedGenericArgs::Err => {
                        let mut err = struct_span_err!(self.sess, data.span, E0214, "{}", msg);
                        err.span_label(data.span, "only `Fn` traits may use parentheses");
                        if let Ok(snippet) = self.sess.source_map().span_to_snippet(data.span) {
                            // Do not suggest going from `Trait()` to `Trait<>`
                            if !data.inputs.is_empty() {
                                // Suggest replacing `(` and `)` with `<` and `>`
                                // The snippet may be missing the closing `)`, skip that case
                                if snippet.ends_with(')') {
                                    if let Some(split) = snippet.find('(') {
                                        let trait_name = &snippet[0..split];
                                        let args = &snippet[split + 1..snippet.len() - 1];
                                        err.span_suggestion(
                                            data.span,
                                            "use angle brackets instead",
                                            format!("{}<{}>", trait_name, args),
                                            Applicability::MaybeIncorrect,
                                        );
                                    }
                                }
                            }
                        };
                        err.emit();
                        (
                            self.lower_angle_bracketed_parameter_data(
                                &data.as_angle_bracketed_args(),
                                param_mode,
                                itctx,
                            )
                            .0,
                            false,
                        )
                    }
                },
            }
        } else {
            (
                GenericArgsCtor {
                    args: Default::default(),
                    bindings: &[],
                    parenthesized: false,
                    span: path_span.shrink_to_hi(),
                },
                param_mode == ParamMode::Optional,
            )
        };

        let has_lifetimes =
            generic_args.args.iter().any(|arg| matches!(arg, GenericArg::Lifetime(_)));
        if !generic_args.parenthesized && !has_lifetimes && expected_lifetimes > 0 {
            // Note: these spans are used for diagnostics when they can't be inferred.
            // See rustc_resolve::late::lifetimes::LifetimeContext::add_missing_lifetime_specifiers_label
            let elided_lifetime_span = if generic_args.span.is_empty() {
                // If there are no brackets, use the identifier span.
                // HACK: we use find_ancestor_inside to properly suggest elided spans in paths
                // originating from macros, since the segment's span might be from a macro arg.
                segment.ident.span.find_ancestor_inside(path_span).unwrap_or(path_span)
            } else if generic_args.is_empty() {
                // If there are brackets, but not generic arguments, then use the opening bracket
                generic_args.span.with_hi(generic_args.span.lo() + BytePos(1))
            } else {
                // Else use an empty span right after the opening bracket.
                generic_args.span.with_lo(generic_args.span.lo() + BytePos(1)).shrink_to_lo()
            };
            generic_args.args = self
                .elided_path_lifetimes(elided_lifetime_span, expected_lifetimes, param_mode)
                .map(GenericArg::Lifetime)
                .chain(generic_args.args.into_iter())
                .collect();
            // In create-parameter mode we error here because we don't want to support
            // deprecated impl elision in new features like impl elision and `async fn`,
            // both of which work using the `CreateParameter` mode:
            //
            //     impl Foo for std::cell::Ref<u32> // note lack of '_
            //     async fn foo(_: std::cell::Ref<u32>) { ... }
            if let (ParamMode::Explicit, AnonymousLifetimeMode::CreateParameter) =
                (param_mode, self.anonymous_lifetime_mode)
            {
                let anon_lt_suggestion = vec!["'_"; expected_lifetimes].join(", ");
                let no_non_lt_args = generic_args.args.len() == expected_lifetimes;
                let no_bindings = generic_args.bindings.is_empty();
                let (incl_angl_brckt, suggestion) = if no_non_lt_args && no_bindings {
                    // If there are no generic args, our suggestion can include the angle brackets.
                    (true, format!("<{}>", anon_lt_suggestion))
                } else {
                    // Otherwise we'll insert a `'_, ` right after the opening bracket.
                    (false, format!("{}, ", anon_lt_suggestion))
                };
                let insertion_sp = elided_lifetime_span.shrink_to_hi();
                let mut err = struct_span_err!(
                    self.sess,
                    path_span,
                    E0726,
                    "implicit elided lifetime not allowed here"
                );
                rustc_errors::add_elided_lifetime_in_path_suggestion(
                    &self.sess.source_map(),
                    &mut err,
                    expected_lifetimes,
                    path_span,
                    incl_angl_brckt,
                    insertion_sp,
                    suggestion,
                );
                err.note("assuming a `'static` lifetime...");
                err.emit();
            }
        }

        let res = self.expect_full_res(segment.id);
        let id = self.lower_node_id(segment.id);
        debug!(
            "lower_path_segment: ident={:?} original-id={:?} new-id={:?}",
            segment.ident, segment.id, id,
        );

        hir::PathSegment {
            ident: self.lower_ident(segment.ident),
            hir_id: Some(id),
            res: Some(self.lower_res(res)),
            infer_args,
            args: if generic_args.is_empty() && generic_args.span.is_empty() {
                None
            } else {
                Some(generic_args.into_generic_args(self))
            },
        }
    }

    pub(crate) fn lower_angle_bracketed_parameter_data(
        &mut self,
        data: &AngleBracketedArgs,
        param_mode: ParamMode,
        mut itctx: ImplTraitContext<'_, 'hir>,
    ) -> (GenericArgsCtor<'hir>, bool) {
        let has_non_lt_args = data.args.iter().any(|arg| match arg {
            AngleBracketedArg::Arg(ast::GenericArg::Lifetime(_))
            | AngleBracketedArg::Constraint(_) => false,
            AngleBracketedArg::Arg(ast::GenericArg::Type(_) | ast::GenericArg::Const(_)) => true,
        });
        let args = data
            .args
            .iter()
            .filter_map(|arg| match arg {
                AngleBracketedArg::Arg(arg) => Some(self.lower_generic_arg(arg, itctx.reborrow())),
                AngleBracketedArg::Constraint(_) => None,
            })
            .collect();
        let bindings = self.arena.alloc_from_iter(data.args.iter().filter_map(|arg| match arg {
            AngleBracketedArg::Constraint(c) => {
                Some(self.lower_assoc_ty_constraint(c, itctx.reborrow()))
            }
            AngleBracketedArg::Arg(_) => None,
        }));
        let ctor = GenericArgsCtor { args, bindings, parenthesized: false, span: data.span };
        (ctor, !has_non_lt_args && param_mode == ParamMode::Optional)
    }

    fn lower_parenthesized_parameter_data(
        &mut self,
        data: &ParenthesizedArgs,
    ) -> (GenericArgsCtor<'hir>, bool) {
        // Switch to `PassThrough` mode for anonymous lifetimes; this
        // means that we permit things like `&Ref<T>`, where `Ref` has
        // a hidden lifetime parameter. This is needed for backwards
        // compatibility, even in contexts like an impl header where
        // we generally don't permit such things (see #51008).
        self.with_anonymous_lifetime_mode(AnonymousLifetimeMode::PassThrough, |this| {
            let ParenthesizedArgs { span, inputs, inputs_span, output } = data;
            let inputs = this.arena.alloc_from_iter(
                inputs.iter().map(|ty| this.lower_ty_direct(ty, ImplTraitContext::disallowed())),
            );
            let output_ty = match output {
                FnRetTy::Ty(ty) => this.lower_ty(&ty, ImplTraitContext::disallowed()),
                FnRetTy::Default(_) => this.arena.alloc(this.ty_tup(*span, &[])),
            };
            let args = smallvec![GenericArg::Type(this.ty_tup(*inputs_span, inputs))];
            let binding = this.output_ty_binding(output_ty.span, output_ty);
            (
                GenericArgsCtor {
                    args,
                    bindings: arena_vec![this; binding],
                    parenthesized: true,
                    span: data.inputs_span,
                },
                false,
            )
        })
    }

    /// An associated type binding `Output = $ty`.
    crate fn output_ty_binding(
        &mut self,
        span: Span,
        ty: &'hir hir::Ty<'hir>,
    ) -> hir::TypeBinding<'hir> {
        let ident = Ident::with_dummy_span(hir::FN_OUTPUT_NAME);
        let kind = hir::TypeBindingKind::Equality { ty };
        let args = arena_vec![self;];
        let bindings = arena_vec![self;];
        let gen_args = self.arena.alloc(hir::GenericArgs {
            args,
            bindings,
            parenthesized: false,
            span_ext: DUMMY_SP,
        });
        hir::TypeBinding {
            hir_id: self.next_id(),
            gen_args,
            span: self.lower_span(span),
            ident,
            kind,
        }
    }
}