1 //! A different sort of visitor for walking fn bodies. Unlike the
2 //! normal visitor, which just walks the entire body in one shot, the
3 //! `ExprUseVisitor` determines how expressions are being used.
4
5 use hir::def::DefKind;
6 // Export these here so that Clippy can use them.
7 pub use rustc_middle::hir::place::{Place, PlaceBase, PlaceWithHirId, Projection};
8
9 use rustc_data_structures::fx::FxIndexMap;
10 use rustc_hir as hir;
11 use rustc_hir::def::Res;
12 use rustc_hir::def_id::LocalDefId;
13 use rustc_hir::PatKind;
14 use rustc_index::vec::Idx;
15 use rustc_infer::infer::InferCtxt;
16 use rustc_middle::hir::place::ProjectionKind;
17 use rustc_middle::mir::FakeReadCause;
18 use rustc_middle::ty::{self, adjustment, AdtKind, Ty, TyCtxt};
19 use rustc_target::abi::VariantIdx;
20 use std::iter;
21
22 use crate::mem_categorization as mc;
23
24 /// This trait defines the callbacks you can expect to receive when
25 /// employing the ExprUseVisitor.
26 pub trait Delegate<'tcx> {
27 /// The value found at `place` is moved, depending
28 /// on `mode`. Where `diag_expr_id` is the id used for diagnostics for `place`.
29 ///
30 /// Use of a `Copy` type in a ByValue context is considered a use
31 /// by `ImmBorrow` and `borrow` is called instead. This is because
32 /// a shared borrow is the "minimum access" that would be needed
33 /// to perform a copy.
34 ///
35 ///
36 /// The parameter `diag_expr_id` indicates the HIR id that ought to be used for
37 /// diagnostics. Around pattern matching such as `let pat = expr`, the diagnostic
38 /// id will be the id of the expression `expr` but the place itself will have
39 /// the id of the binding in the pattern `pat`.
consume(&mut self, place_with_id: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId)40 fn consume(&mut self, place_with_id: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId);
41
42 /// The value found at `place` is being borrowed with kind `bk`.
43 /// `diag_expr_id` is the id used for diagnostics (see `consume` for more details).
borrow( &mut self, place_with_id: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId, bk: ty::BorrowKind, )44 fn borrow(
45 &mut self,
46 place_with_id: &PlaceWithHirId<'tcx>,
47 diag_expr_id: hir::HirId,
48 bk: ty::BorrowKind,
49 );
50
51 /// The path at `assignee_place` is being assigned to.
52 /// `diag_expr_id` is the id used for diagnostics (see `consume` for more details).
mutate(&mut self, assignee_place: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId)53 fn mutate(&mut self, assignee_place: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId);
54
55 /// The `place` should be a fake read because of specified `cause`.
fake_read(&mut self, place: Place<'tcx>, cause: FakeReadCause, diag_expr_id: hir::HirId)56 fn fake_read(&mut self, place: Place<'tcx>, cause: FakeReadCause, diag_expr_id: hir::HirId);
57 }
58
59 #[derive(Copy, Clone, PartialEq, Debug)]
60 enum ConsumeMode {
61 /// reference to x where x has a type that copies
62 Copy,
63 /// reference to x where x has a type that moves
64 Move,
65 }
66
67 #[derive(Copy, Clone, PartialEq, Debug)]
68 pub enum MutateMode {
69 Init,
70 /// Example: `x = y`
71 JustWrite,
72 /// Example: `x += y`
73 WriteAndRead,
74 }
75
76 /// The ExprUseVisitor type
77 ///
78 /// This is the code that actually walks the tree.
79 pub struct ExprUseVisitor<'a, 'tcx> {
80 mc: mc::MemCategorizationContext<'a, 'tcx>,
81 body_owner: LocalDefId,
82 delegate: &'a mut dyn Delegate<'tcx>,
83 }
84
85 /// If the MC results in an error, it's because the type check
86 /// failed (or will fail, when the error is uncovered and reported
87 /// during writeback). In this case, we just ignore this part of the
88 /// code.
89 ///
90 /// Note that this macro appears similar to try!(), but, unlike try!(),
91 /// it does not propagate the error.
92 macro_rules! return_if_err {
93 ($inp: expr) => {
94 match $inp {
95 Ok(v) => v,
96 Err(()) => {
97 debug!("mc reported err");
98 return;
99 }
100 }
101 };
102 }
103
104 impl<'a, 'tcx> ExprUseVisitor<'a, 'tcx> {
105 /// Creates the ExprUseVisitor, configuring it with the various options provided:
106 ///
107 /// - `delegate` -- who receives the callbacks
108 /// - `param_env` --- parameter environment for trait lookups (esp. pertaining to `Copy`)
109 /// - `typeck_results` --- typeck results for the code being analyzed
new( delegate: &'a mut (dyn Delegate<'tcx> + 'a), infcx: &'a InferCtxt<'a, 'tcx>, body_owner: LocalDefId, param_env: ty::ParamEnv<'tcx>, typeck_results: &'a ty::TypeckResults<'tcx>, ) -> Self110 pub fn new(
111 delegate: &'a mut (dyn Delegate<'tcx> + 'a),
112 infcx: &'a InferCtxt<'a, 'tcx>,
113 body_owner: LocalDefId,
114 param_env: ty::ParamEnv<'tcx>,
115 typeck_results: &'a ty::TypeckResults<'tcx>,
116 ) -> Self {
117 ExprUseVisitor {
118 mc: mc::MemCategorizationContext::new(infcx, param_env, body_owner, typeck_results),
119 body_owner,
120 delegate,
121 }
122 }
123
124 #[instrument(skip(self), level = "debug")]
consume_body(&mut self, body: &hir::Body<'_>)125 pub fn consume_body(&mut self, body: &hir::Body<'_>) {
126 for param in body.params {
127 let param_ty = return_if_err!(self.mc.pat_ty_adjusted(param.pat));
128 debug!("consume_body: param_ty = {:?}", param_ty);
129
130 let param_place = self.mc.cat_rvalue(param.hir_id, param.pat.span, param_ty);
131
132 self.walk_irrefutable_pat(¶m_place, param.pat);
133 }
134
135 self.consume_expr(&body.value);
136 }
137
tcx(&self) -> TyCtxt<'tcx>138 fn tcx(&self) -> TyCtxt<'tcx> {
139 self.mc.tcx()
140 }
141
delegate_consume(&mut self, place_with_id: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId)142 fn delegate_consume(&mut self, place_with_id: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) {
143 delegate_consume(&self.mc, self.delegate, place_with_id, diag_expr_id)
144 }
145
consume_exprs(&mut self, exprs: &[hir::Expr<'_>])146 fn consume_exprs(&mut self, exprs: &[hir::Expr<'_>]) {
147 for expr in exprs {
148 self.consume_expr(expr);
149 }
150 }
151
consume_expr(&mut self, expr: &hir::Expr<'_>)152 pub fn consume_expr(&mut self, expr: &hir::Expr<'_>) {
153 debug!("consume_expr(expr={:?})", expr);
154
155 let place_with_id = return_if_err!(self.mc.cat_expr(expr));
156 self.delegate_consume(&place_with_id, place_with_id.hir_id);
157 self.walk_expr(expr);
158 }
159
mutate_expr(&mut self, expr: &hir::Expr<'_>)160 fn mutate_expr(&mut self, expr: &hir::Expr<'_>) {
161 let place_with_id = return_if_err!(self.mc.cat_expr(expr));
162 self.delegate.mutate(&place_with_id, place_with_id.hir_id);
163 self.walk_expr(expr);
164 }
165
borrow_expr(&mut self, expr: &hir::Expr<'_>, bk: ty::BorrowKind)166 fn borrow_expr(&mut self, expr: &hir::Expr<'_>, bk: ty::BorrowKind) {
167 debug!("borrow_expr(expr={:?}, bk={:?})", expr, bk);
168
169 let place_with_id = return_if_err!(self.mc.cat_expr(expr));
170 self.delegate.borrow(&place_with_id, place_with_id.hir_id, bk);
171
172 self.walk_expr(expr)
173 }
174
select_from_expr(&mut self, expr: &hir::Expr<'_>)175 fn select_from_expr(&mut self, expr: &hir::Expr<'_>) {
176 self.walk_expr(expr)
177 }
178
walk_expr(&mut self, expr: &hir::Expr<'_>)179 pub fn walk_expr(&mut self, expr: &hir::Expr<'_>) {
180 debug!("walk_expr(expr={:?})", expr);
181
182 self.walk_adjustment(expr);
183
184 match expr.kind {
185 hir::ExprKind::Path(_) => {}
186
187 hir::ExprKind::Type(subexpr, _) => self.walk_expr(subexpr),
188
189 hir::ExprKind::Unary(hir::UnOp::Deref, base) => {
190 // *base
191 self.select_from_expr(base);
192 }
193
194 hir::ExprKind::Field(base, _) => {
195 // base.f
196 self.select_from_expr(base);
197 }
198
199 hir::ExprKind::Index(lhs, rhs) => {
200 // lhs[rhs]
201 self.select_from_expr(lhs);
202 self.consume_expr(rhs);
203 }
204
205 hir::ExprKind::Call(callee, args) => {
206 // callee(args)
207 self.consume_expr(callee);
208 self.consume_exprs(args);
209 }
210
211 hir::ExprKind::MethodCall(.., args, _) => {
212 // callee.m(args)
213 self.consume_exprs(args);
214 }
215
216 hir::ExprKind::Struct(_, fields, ref opt_with) => {
217 self.walk_struct_expr(fields, opt_with);
218 }
219
220 hir::ExprKind::Tup(exprs) => {
221 self.consume_exprs(exprs);
222 }
223
224 hir::ExprKind::If(ref cond_expr, ref then_expr, ref opt_else_expr) => {
225 self.consume_expr(cond_expr);
226 self.consume_expr(then_expr);
227 if let Some(ref else_expr) = *opt_else_expr {
228 self.consume_expr(else_expr);
229 }
230 }
231
232 hir::ExprKind::Let(pat, ref expr, _) => {
233 self.walk_local(expr, pat, |t| t.borrow_expr(expr, ty::ImmBorrow));
234 }
235
236 hir::ExprKind::Match(ref discr, arms, _) => {
237 let discr_place = return_if_err!(self.mc.cat_expr(discr));
238
239 // Matching should not always be considered a use of the place, hence
240 // discr does not necessarily need to be borrowed.
241 // We only want to borrow discr if the pattern contain something other
242 // than wildcards.
243 let ExprUseVisitor { ref mc, body_owner: _, delegate: _ } = *self;
244 let mut needs_to_be_read = false;
245 for arm in arms.iter() {
246 return_if_err!(mc.cat_pattern(discr_place.clone(), arm.pat, |place, pat| {
247 match &pat.kind {
248 PatKind::Binding(.., opt_sub_pat) => {
249 // If the opt_sub_pat is None, than the binding does not count as
250 // a wildcard for the purpose of borrowing discr.
251 if opt_sub_pat.is_none() {
252 needs_to_be_read = true;
253 }
254 }
255 PatKind::Path(qpath) => {
256 // A `Path` pattern is just a name like `Foo`. This is either a
257 // named constant or else it refers to an ADT variant
258
259 let res = self.mc.typeck_results.qpath_res(qpath, pat.hir_id);
260 match res {
261 Res::Def(DefKind::Const, _)
262 | Res::Def(DefKind::AssocConst, _) => {
263 // Named constants have to be equated with the value
264 // being matched, so that's a read of the value being matched.
265 //
266 // FIXME: We don't actually reads for ZSTs.
267 needs_to_be_read = true;
268 }
269 _ => {
270 // Otherwise, this is a struct/enum variant, and so it's
271 // only a read if we need to read the discriminant.
272 needs_to_be_read |= is_multivariant_adt(place.place.ty());
273 }
274 }
275 }
276 PatKind::TupleStruct(..) | PatKind::Struct(..) | PatKind::Tuple(..) => {
277 // For `Foo(..)`, `Foo { ... }` and `(...)` patterns, check if we are matching
278 // against a multivariant enum or struct. In that case, we have to read
279 // the discriminant. Otherwise this kind of pattern doesn't actually
280 // read anything (we'll get invoked for the `...`, which may indeed
281 // perform some reads).
282
283 let place_ty = place.place.ty();
284 needs_to_be_read |= is_multivariant_adt(place_ty);
285 }
286 PatKind::Lit(_) | PatKind::Range(..) => {
287 // If the PatKind is a Lit or a Range then we want
288 // to borrow discr.
289 needs_to_be_read = true;
290 }
291 PatKind::Or(_)
292 | PatKind::Box(_)
293 | PatKind::Slice(..)
294 | PatKind::Ref(..)
295 | PatKind::Wild => {
296 // If the PatKind is Or, Box, Slice or Ref, the decision is made later
297 // as these patterns contains subpatterns
298 // If the PatKind is Wild, the decision is made based on the other patterns being
299 // examined
300 }
301 }
302 }));
303 }
304
305 if needs_to_be_read {
306 self.borrow_expr(discr, ty::ImmBorrow);
307 } else {
308 let closure_def_id = match discr_place.place.base {
309 PlaceBase::Upvar(upvar_id) => Some(upvar_id.closure_expr_id.to_def_id()),
310 _ => None,
311 };
312
313 self.delegate.fake_read(
314 discr_place.place.clone(),
315 FakeReadCause::ForMatchedPlace(closure_def_id),
316 discr_place.hir_id,
317 );
318
319 // We always want to walk the discriminant. We want to make sure, for instance,
320 // that the discriminant has been initialized.
321 self.walk_expr(discr);
322 }
323
324 // treatment of the discriminant is handled while walking the arms.
325 for arm in arms {
326 self.walk_arm(&discr_place, arm);
327 }
328 }
329
330 hir::ExprKind::Array(exprs) => {
331 self.consume_exprs(exprs);
332 }
333
334 hir::ExprKind::AddrOf(_, m, ref base) => {
335 // &base
336 // make sure that the thing we are pointing out stays valid
337 // for the lifetime `scope_r` of the resulting ptr:
338 let bk = ty::BorrowKind::from_mutbl(m);
339 self.borrow_expr(base, bk);
340 }
341
342 hir::ExprKind::InlineAsm(asm) => {
343 for (op, _op_sp) in asm.operands {
344 match op {
345 hir::InlineAsmOperand::In { expr, .. }
346 | hir::InlineAsmOperand::Sym { expr, .. } => self.consume_expr(expr),
347 hir::InlineAsmOperand::Out { expr: Some(expr), .. }
348 | hir::InlineAsmOperand::InOut { expr, .. } => {
349 self.mutate_expr(expr);
350 }
351 hir::InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
352 self.consume_expr(in_expr);
353 if let Some(out_expr) = out_expr {
354 self.mutate_expr(out_expr);
355 }
356 }
357 hir::InlineAsmOperand::Out { expr: None, .. }
358 | hir::InlineAsmOperand::Const { .. } => {}
359 }
360 }
361 }
362
363 hir::ExprKind::LlvmInlineAsm(ia) => {
364 for (o, output) in iter::zip(&ia.inner.outputs, ia.outputs_exprs) {
365 if o.is_indirect {
366 self.consume_expr(output);
367 } else {
368 self.mutate_expr(output);
369 }
370 }
371 self.consume_exprs(ia.inputs_exprs);
372 }
373
374 hir::ExprKind::Continue(..)
375 | hir::ExprKind::Lit(..)
376 | hir::ExprKind::ConstBlock(..)
377 | hir::ExprKind::Err => {}
378
379 hir::ExprKind::Loop(blk, ..) => {
380 self.walk_block(blk);
381 }
382
383 hir::ExprKind::Unary(_, lhs) => {
384 self.consume_expr(lhs);
385 }
386
387 hir::ExprKind::Binary(_, lhs, rhs) => {
388 self.consume_expr(lhs);
389 self.consume_expr(rhs);
390 }
391
392 hir::ExprKind::Block(blk, _) => {
393 self.walk_block(blk);
394 }
395
396 hir::ExprKind::Break(_, ref opt_expr) | hir::ExprKind::Ret(ref opt_expr) => {
397 if let Some(expr) = *opt_expr {
398 self.consume_expr(expr);
399 }
400 }
401
402 hir::ExprKind::Assign(lhs, rhs, _) => {
403 self.mutate_expr(lhs);
404 self.consume_expr(rhs);
405 }
406
407 hir::ExprKind::Cast(base, _) => {
408 self.consume_expr(base);
409 }
410
411 hir::ExprKind::DropTemps(expr) => {
412 self.consume_expr(expr);
413 }
414
415 hir::ExprKind::AssignOp(_, lhs, rhs) => {
416 if self.mc.typeck_results.is_method_call(expr) {
417 self.consume_expr(lhs);
418 } else {
419 self.mutate_expr(lhs);
420 }
421 self.consume_expr(rhs);
422 }
423
424 hir::ExprKind::Repeat(base, _) => {
425 self.consume_expr(base);
426 }
427
428 hir::ExprKind::Closure(..) => {
429 self.walk_captures(expr);
430 }
431
432 hir::ExprKind::Box(ref base) => {
433 self.consume_expr(base);
434 }
435
436 hir::ExprKind::Yield(value, _) => {
437 self.consume_expr(value);
438 }
439 }
440 }
441
walk_stmt(&mut self, stmt: &hir::Stmt<'_>)442 fn walk_stmt(&mut self, stmt: &hir::Stmt<'_>) {
443 match stmt.kind {
444 hir::StmtKind::Local(hir::Local { pat, init: Some(expr), .. }) => {
445 self.walk_local(expr, pat, |_| {});
446 }
447
448 hir::StmtKind::Local(_) => {}
449
450 hir::StmtKind::Item(_) => {
451 // We don't visit nested items in this visitor,
452 // only the fn body we were given.
453 }
454
455 hir::StmtKind::Expr(ref expr) | hir::StmtKind::Semi(ref expr) => {
456 self.consume_expr(expr);
457 }
458 }
459 }
460
walk_local<F>(&mut self, expr: &hir::Expr<'_>, pat: &hir::Pat<'_>, mut f: F) where F: FnMut(&mut Self),461 fn walk_local<F>(&mut self, expr: &hir::Expr<'_>, pat: &hir::Pat<'_>, mut f: F)
462 where
463 F: FnMut(&mut Self),
464 {
465 self.walk_expr(expr);
466 let expr_place = return_if_err!(self.mc.cat_expr(expr));
467 f(self);
468 self.walk_irrefutable_pat(&expr_place, &pat);
469 }
470
471 /// Indicates that the value of `blk` will be consumed, meaning either copied or moved
472 /// depending on its type.
walk_block(&mut self, blk: &hir::Block<'_>)473 fn walk_block(&mut self, blk: &hir::Block<'_>) {
474 debug!("walk_block(blk.hir_id={})", blk.hir_id);
475
476 for stmt in blk.stmts {
477 self.walk_stmt(stmt);
478 }
479
480 if let Some(ref tail_expr) = blk.expr {
481 self.consume_expr(tail_expr);
482 }
483 }
484
walk_struct_expr( &mut self, fields: &[hir::ExprField<'_>], opt_with: &Option<&'hir hir::Expr<'_>>, )485 fn walk_struct_expr(
486 &mut self,
487 fields: &[hir::ExprField<'_>],
488 opt_with: &Option<&'hir hir::Expr<'_>>,
489 ) {
490 // Consume the expressions supplying values for each field.
491 for field in fields {
492 self.consume_expr(field.expr);
493 }
494
495 let with_expr = match *opt_with {
496 Some(w) => &*w,
497 None => {
498 return;
499 }
500 };
501
502 let with_place = return_if_err!(self.mc.cat_expr(with_expr));
503
504 // Select just those fields of the `with`
505 // expression that will actually be used
506 match with_place.place.ty().kind() {
507 ty::Adt(adt, substs) if adt.is_struct() => {
508 // Consume those fields of the with expression that are needed.
509 for (f_index, with_field) in adt.non_enum_variant().fields.iter().enumerate() {
510 let is_mentioned = fields.iter().any(|f| {
511 self.tcx().field_index(f.hir_id, self.mc.typeck_results) == f_index
512 });
513 if !is_mentioned {
514 let field_place = self.mc.cat_projection(
515 &*with_expr,
516 with_place.clone(),
517 with_field.ty(self.tcx(), substs),
518 ProjectionKind::Field(f_index as u32, VariantIdx::new(0)),
519 );
520 self.delegate_consume(&field_place, field_place.hir_id);
521 }
522 }
523 }
524 _ => {
525 // the base expression should always evaluate to a
526 // struct; however, when EUV is run during typeck, it
527 // may not. This will generate an error earlier in typeck,
528 // so we can just ignore it.
529 if !self.tcx().sess.has_errors() {
530 span_bug!(with_expr.span, "with expression doesn't evaluate to a struct");
531 }
532 }
533 }
534
535 // walk the with expression so that complex expressions
536 // are properly handled.
537 self.walk_expr(with_expr);
538 }
539
540 /// Invoke the appropriate delegate calls for anything that gets
541 /// consumed or borrowed as part of the automatic adjustment
542 /// process.
walk_adjustment(&mut self, expr: &hir::Expr<'_>)543 fn walk_adjustment(&mut self, expr: &hir::Expr<'_>) {
544 let adjustments = self.mc.typeck_results.expr_adjustments(expr);
545 let mut place_with_id = return_if_err!(self.mc.cat_expr_unadjusted(expr));
546 for adjustment in adjustments {
547 debug!("walk_adjustment expr={:?} adj={:?}", expr, adjustment);
548 match adjustment.kind {
549 adjustment::Adjust::NeverToAny | adjustment::Adjust::Pointer(_) => {
550 // Creating a closure/fn-pointer or unsizing consumes
551 // the input and stores it into the resulting rvalue.
552 self.delegate_consume(&place_with_id, place_with_id.hir_id);
553 }
554
555 adjustment::Adjust::Deref(None) => {}
556
557 // Autoderefs for overloaded Deref calls in fact reference
558 // their receiver. That is, if we have `(*x)` where `x`
559 // is of type `Rc<T>`, then this in fact is equivalent to
560 // `x.deref()`. Since `deref()` is declared with `&self`,
561 // this is an autoref of `x`.
562 adjustment::Adjust::Deref(Some(ref deref)) => {
563 let bk = ty::BorrowKind::from_mutbl(deref.mutbl);
564 self.delegate.borrow(&place_with_id, place_with_id.hir_id, bk);
565 }
566
567 adjustment::Adjust::Borrow(ref autoref) => {
568 self.walk_autoref(expr, &place_with_id, autoref);
569 }
570 }
571 place_with_id =
572 return_if_err!(self.mc.cat_expr_adjusted(expr, place_with_id, adjustment));
573 }
574 }
575
576 /// Walks the autoref `autoref` applied to the autoderef'd
577 /// `expr`. `base_place` is the mem-categorized form of `expr`
578 /// after all relevant autoderefs have occurred.
walk_autoref( &mut self, expr: &hir::Expr<'_>, base_place: &PlaceWithHirId<'tcx>, autoref: &adjustment::AutoBorrow<'tcx>, )579 fn walk_autoref(
580 &mut self,
581 expr: &hir::Expr<'_>,
582 base_place: &PlaceWithHirId<'tcx>,
583 autoref: &adjustment::AutoBorrow<'tcx>,
584 ) {
585 debug!(
586 "walk_autoref(expr.hir_id={} base_place={:?} autoref={:?})",
587 expr.hir_id, base_place, autoref
588 );
589
590 match *autoref {
591 adjustment::AutoBorrow::Ref(_, m) => {
592 self.delegate.borrow(
593 base_place,
594 base_place.hir_id,
595 ty::BorrowKind::from_mutbl(m.into()),
596 );
597 }
598
599 adjustment::AutoBorrow::RawPtr(m) => {
600 debug!("walk_autoref: expr.hir_id={} base_place={:?}", expr.hir_id, base_place);
601
602 self.delegate.borrow(base_place, base_place.hir_id, ty::BorrowKind::from_mutbl(m));
603 }
604 }
605 }
606
walk_arm(&mut self, discr_place: &PlaceWithHirId<'tcx>, arm: &hir::Arm<'_>)607 fn walk_arm(&mut self, discr_place: &PlaceWithHirId<'tcx>, arm: &hir::Arm<'_>) {
608 let closure_def_id = match discr_place.place.base {
609 PlaceBase::Upvar(upvar_id) => Some(upvar_id.closure_expr_id.to_def_id()),
610 _ => None,
611 };
612
613 self.delegate.fake_read(
614 discr_place.place.clone(),
615 FakeReadCause::ForMatchedPlace(closure_def_id),
616 discr_place.hir_id,
617 );
618 self.walk_pat(discr_place, arm.pat);
619
620 if let Some(hir::Guard::If(e)) = arm.guard {
621 self.consume_expr(e)
622 } else if let Some(hir::Guard::IfLet(_, ref e)) = arm.guard {
623 self.consume_expr(e)
624 }
625
626 self.consume_expr(arm.body);
627 }
628
629 /// Walks a pat that occurs in isolation (i.e., top-level of fn argument or
630 /// let binding, and *not* a match arm or nested pat.)
walk_irrefutable_pat(&mut self, discr_place: &PlaceWithHirId<'tcx>, pat: &hir::Pat<'_>)631 fn walk_irrefutable_pat(&mut self, discr_place: &PlaceWithHirId<'tcx>, pat: &hir::Pat<'_>) {
632 let closure_def_id = match discr_place.place.base {
633 PlaceBase::Upvar(upvar_id) => Some(upvar_id.closure_expr_id.to_def_id()),
634 _ => None,
635 };
636
637 self.delegate.fake_read(
638 discr_place.place.clone(),
639 FakeReadCause::ForLet(closure_def_id),
640 discr_place.hir_id,
641 );
642 self.walk_pat(discr_place, pat);
643 }
644
645 /// The core driver for walking a pattern
walk_pat(&mut self, discr_place: &PlaceWithHirId<'tcx>, pat: &hir::Pat<'_>)646 fn walk_pat(&mut self, discr_place: &PlaceWithHirId<'tcx>, pat: &hir::Pat<'_>) {
647 debug!("walk_pat(discr_place={:?}, pat={:?})", discr_place, pat);
648
649 let tcx = self.tcx();
650 let ExprUseVisitor { ref mc, body_owner: _, ref mut delegate } = *self;
651 return_if_err!(mc.cat_pattern(discr_place.clone(), pat, |place, pat| {
652 if let PatKind::Binding(_, canonical_id, ..) = pat.kind {
653 debug!("walk_pat: binding place={:?} pat={:?}", place, pat,);
654 if let Some(bm) =
655 mc.typeck_results.extract_binding_mode(tcx.sess, pat.hir_id, pat.span)
656 {
657 debug!("walk_pat: pat.hir_id={:?} bm={:?}", pat.hir_id, bm);
658
659 // pat_ty: the type of the binding being produced.
660 let pat_ty = return_if_err!(mc.node_ty(pat.hir_id));
661 debug!("walk_pat: pat_ty={:?}", pat_ty);
662
663 // Each match binding is effectively an assignment to the
664 // binding being produced.
665 let def = Res::Local(canonical_id);
666 if let Ok(ref binding_place) = mc.cat_res(pat.hir_id, pat.span, pat_ty, def) {
667 delegate.mutate(binding_place, binding_place.hir_id);
668 }
669
670 // It is also a borrow or copy/move of the value being matched.
671 // In a cases of pattern like `let pat = upvar`, don't use the span
672 // of the pattern, as this just looks confusing, instead use the span
673 // of the discriminant.
674 match bm {
675 ty::BindByReference(m) => {
676 let bk = ty::BorrowKind::from_mutbl(m);
677 delegate.borrow(place, discr_place.hir_id, bk);
678 }
679 ty::BindByValue(..) => {
680 debug!("walk_pat binding consuming pat");
681 delegate_consume(mc, *delegate, place, discr_place.hir_id);
682 }
683 }
684 }
685 }
686 }));
687 }
688
689 /// Handle the case where the current body contains a closure.
690 ///
691 /// When the current body being handled is a closure, then we must make sure that
692 /// - The parent closure only captures Places from the nested closure that are not local to it.
693 ///
694 /// In the following example the closures `c` only captures `p.x` even though `incr`
695 /// is a capture of the nested closure
696 ///
697 /// ```rust,ignore(cannot-test-this-because-pseudo-code)
698 /// let p = ..;
699 /// let c = || {
700 /// let incr = 10;
701 /// let nested = || p.x += incr;
702 /// }
703 /// ```
704 ///
705 /// - When reporting the Place back to the Delegate, ensure that the UpvarId uses the enclosing
706 /// closure as the DefId.
walk_captures(&mut self, closure_expr: &hir::Expr<'_>)707 fn walk_captures(&mut self, closure_expr: &hir::Expr<'_>) {
708 fn upvar_is_local_variable(
709 upvars: Option<&'tcx FxIndexMap<hir::HirId, hir::Upvar>>,
710 upvar_id: &hir::HirId,
711 body_owner_is_closure: bool,
712 ) -> bool {
713 upvars.map(|upvars| !upvars.contains_key(upvar_id)).unwrap_or(body_owner_is_closure)
714 }
715
716 debug!("walk_captures({:?})", closure_expr);
717
718 let closure_def_id = self.tcx().hir().local_def_id(closure_expr.hir_id).to_def_id();
719 let upvars = self.tcx().upvars_mentioned(self.body_owner);
720
721 // For purposes of this function, generator and closures are equivalent.
722 let body_owner_is_closure = matches!(
723 self.tcx().type_of(self.body_owner.to_def_id()).kind(),
724 ty::Closure(..) | ty::Generator(..)
725 );
726
727 // If we have a nested closure, we want to include the fake reads present in the nested closure.
728 if let Some(fake_reads) = self.mc.typeck_results.closure_fake_reads.get(&closure_def_id) {
729 for (fake_read, cause, hir_id) in fake_reads.iter() {
730 match fake_read.base {
731 PlaceBase::Upvar(upvar_id) => {
732 if upvar_is_local_variable(
733 upvars,
734 &upvar_id.var_path.hir_id,
735 body_owner_is_closure,
736 ) {
737 // The nested closure might be fake reading the current (enclosing) closure's local variables.
738 // The only places we want to fake read before creating the parent closure are the ones that
739 // are not local to it/ defined by it.
740 //
741 // ```rust,ignore(cannot-test-this-because-pseudo-code)
742 // let v1 = (0, 1);
743 // let c = || { // fake reads: v1
744 // let v2 = (0, 1);
745 // let e = || { // fake reads: v1, v2
746 // let (_, t1) = v1;
747 // let (_, t2) = v2;
748 // }
749 // }
750 // ```
751 // This check is performed when visiting the body of the outermost closure (`c`) and ensures
752 // that we don't add a fake read of v2 in c.
753 continue;
754 }
755 }
756 _ => {
757 bug!(
758 "Do not know how to get HirId out of Rvalue and StaticItem {:?}",
759 fake_read.base
760 );
761 }
762 };
763 self.delegate.fake_read(fake_read.clone(), *cause, *hir_id);
764 }
765 }
766
767 if let Some(min_captures) = self.mc.typeck_results.closure_min_captures.get(&closure_def_id)
768 {
769 for (var_hir_id, min_list) in min_captures.iter() {
770 if upvars.map_or(body_owner_is_closure, |upvars| !upvars.contains_key(var_hir_id)) {
771 // The nested closure might be capturing the current (enclosing) closure's local variables.
772 // We check if the root variable is ever mentioned within the enclosing closure, if not
773 // then for the current body (if it's a closure) these aren't captures, we will ignore them.
774 continue;
775 }
776 for captured_place in min_list {
777 let place = &captured_place.place;
778 let capture_info = captured_place.info;
779
780 let place_base = if body_owner_is_closure {
781 // Mark the place to be captured by the enclosing closure
782 PlaceBase::Upvar(ty::UpvarId::new(*var_hir_id, self.body_owner))
783 } else {
784 // If the body owner isn't a closure then the variable must
785 // be a local variable
786 PlaceBase::Local(*var_hir_id)
787 };
788 let place_with_id = PlaceWithHirId::new(
789 capture_info.path_expr_id.unwrap_or(
790 capture_info.capture_kind_expr_id.unwrap_or(closure_expr.hir_id),
791 ),
792 place.base_ty,
793 place_base,
794 place.projections.clone(),
795 );
796
797 match capture_info.capture_kind {
798 ty::UpvarCapture::ByValue(_) => {
799 self.delegate_consume(&place_with_id, place_with_id.hir_id);
800 }
801 ty::UpvarCapture::ByRef(upvar_borrow) => {
802 self.delegate.borrow(
803 &place_with_id,
804 place_with_id.hir_id,
805 upvar_borrow.kind,
806 );
807 }
808 }
809 }
810 }
811 }
812 }
813 }
814
copy_or_move<'a, 'tcx>( mc: &mc::MemCategorizationContext<'a, 'tcx>, place_with_id: &PlaceWithHirId<'tcx>, ) -> ConsumeMode815 fn copy_or_move<'a, 'tcx>(
816 mc: &mc::MemCategorizationContext<'a, 'tcx>,
817 place_with_id: &PlaceWithHirId<'tcx>,
818 ) -> ConsumeMode {
819 if !mc.type_is_copy_modulo_regions(
820 place_with_id.place.ty(),
821 mc.tcx().hir().span(place_with_id.hir_id),
822 ) {
823 ConsumeMode::Move
824 } else {
825 ConsumeMode::Copy
826 }
827 }
828
829 // - If a place is used in a `ByValue` context then move it if it's not a `Copy` type.
830 // - If the place that is a `Copy` type consider it an `ImmBorrow`.
delegate_consume<'a, 'tcx>( mc: &mc::MemCategorizationContext<'a, 'tcx>, delegate: &mut (dyn Delegate<'tcx> + 'a), place_with_id: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId, )831 fn delegate_consume<'a, 'tcx>(
832 mc: &mc::MemCategorizationContext<'a, 'tcx>,
833 delegate: &mut (dyn Delegate<'tcx> + 'a),
834 place_with_id: &PlaceWithHirId<'tcx>,
835 diag_expr_id: hir::HirId,
836 ) {
837 debug!("delegate_consume(place_with_id={:?})", place_with_id);
838
839 let mode = copy_or_move(mc, place_with_id);
840
841 match mode {
842 ConsumeMode::Move => delegate.consume(place_with_id, diag_expr_id),
843 ConsumeMode::Copy => {
844 delegate.borrow(place_with_id, diag_expr_id, ty::BorrowKind::ImmBorrow)
845 }
846 }
847 }
848
is_multivariant_adt(ty: Ty<'tcx>) -> bool849 fn is_multivariant_adt(ty: Ty<'tcx>) -> bool {
850 if let ty::Adt(def, _) = ty.kind() {
851 // Note that if a non-exhaustive SingleVariant is defined in another crate, we need
852 // to assume that more cases will be added to the variant in the future. This mean
853 // that we should handle non-exhaustive SingleVariant the same way we would handle
854 // a MultiVariant.
855 // If the variant is not local it must be defined in another crate.
856 let is_non_exhaustive = match def.adt_kind() {
857 AdtKind::Struct | AdtKind::Union => {
858 def.non_enum_variant().is_field_list_non_exhaustive()
859 }
860 AdtKind::Enum => def.is_variant_list_non_exhaustive(),
861 };
862 def.variants.len() > 1 || (!def.did.is_local() && is_non_exhaustive)
863 } else {
864 false
865 }
866 }
867