1 //! A classic liveness analysis based on dataflow over the AST. Computes,
2 //! for each local variable in a function, whether that variable is live
3 //! at a given point. Program execution points are identified by their
8 //! The basic model is that each local variable is assigned an index. We
9 //! represent sets of local variables using a vector indexed by this
10 //! index. The value in the vector is either 0, indicating the variable
11 //! is dead, or the ID of an expression that uses the variable.
13 //! We conceptually walk over the AST in reverse execution order. If we
14 //! find a use of a variable, we add it to the set of live variables. If
15 //! we find an assignment to a variable, we remove it from the set of live
16 //! variables. When we have to merge two flows, we take the union of
17 //! those two flows -- if the variable is live on both paths, we simply
18 //! pick one ID. In the event of loops, we continue doing this until a
19 //! fixed point is reached.
21 //! ## Checking initialization
23 //! At the function entry point, all variables must be dead. If this is
24 //! not the case, we can report an error using the ID found in the set of
25 //! live variables, which identifies a use of the variable which is not
26 //! dominated by an assignment.
30 //! After each explicit move, the variable must be dead.
32 //! ## Computing last uses
34 //! Any use of the variable where the variable is dead afterwards is a
37 //! # Implementation details
39 //! The actual implementation contains two (nested) walks over the AST.
40 //! The outer walk has the job of building up the ir_maps instance for the
41 //! enclosing function. On the way down the tree, it identifies those AST
42 //! nodes and variable IDs that will be needed for the liveness analysis
43 //! and assigns them contiguous IDs. The liveness ID for an AST node is
44 //! called a `live_node` (it's a newtype'd `u32`) and the ID for a variable
45 //! is called a `variable` (another newtype'd `u32`).
47 //! On the way back up the tree, as we are about to exit from a function
48 //! declaration we allocate a `liveness` instance. Now that we know
49 //! precisely how many nodes and variables we need, we can allocate all
50 //! the various arrays that we will need to precisely the right size. We then
51 //! perform the actual propagation on the `liveness` instance.
53 //! This propagation is encoded in the various `propagate_through_*()`
54 //! methods. It effectively does a reverse walk of the AST; whenever we
55 //! reach a loop node, we iterate until a fixed point is reached.
57 //! ## The `RWU` struct
59 //! At each live node `N`, we track three pieces of information for each
60 //! variable `V` (these are encapsulated in the `RWU` struct):
62 //! - `reader`: the `LiveNode` ID of some node which will read the value
63 //! that `V` holds on entry to `N`. Formally: a node `M` such
64 //! that there exists a path `P` from `N` to `M` where `P` does not
65 //! write `V`. If the `reader` is `None`, then the current
66 //! value will never be read (the variable is dead, essentially).
68 //! - `writer`: the `LiveNode` ID of some node which will write the
69 //! variable `V` and which is reachable from `N`. Formally: a node `M`
70 //! such that there exists a path `P` from `N` to `M` and `M` writes
71 //! `V`. If the `writer` is `None`, then there is no writer
72 //! of `V` that follows `N`.
74 //! - `used`: a boolean value indicating whether `V` is *used*. We
75 //! distinguish a *read* from a *use* in that a *use* is some read that
76 //! is not just used to generate a new value. For example, `x += 1` is
77 //! a read but not a use. This is used to generate better warnings.
79 //! ## Special nodes and variables
81 //! We generate various special nodes for various, well, special purposes.
82 //! These are described in the `Liveness` struct.
84 use self::LiveNodeKind::*;
87 use rustc_ast::InlineAsmOptions;
88 use rustc_data_structures::fx::FxIndexMap;
89 use rustc_errors::Applicability;
91 use rustc_hir::def::*;
92 use rustc_hir::def_id::LocalDefId;
93 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
94 use rustc_hir::{Expr, HirId, HirIdMap, HirIdSet};
95 use rustc_index::vec::IndexVec;
96 use rustc_middle::hir::map::Map;
97 use rustc_middle::ty::query::Providers;
98 use rustc_middle::ty::{self, DefIdTree, RootVariableMinCaptureList, Ty, TyCtxt};
99 use rustc_session::lint;
100 use rustc_span::symbol::{kw, sym, Symbol};
101 use rustc_span::Span;
103 use std::collections::VecDeque;
105 use std::io::prelude::*;
111 rustc_index::newtype_index! {
112 pub struct Variable {
113 DEBUG_FORMAT = "v({})",
117 rustc_index::newtype_index! {
118 pub struct LiveNode {
119 DEBUG_FORMAT = "ln({})",
123 #[derive(Copy, Clone, PartialEq, Debug)]
126 ExprNode(Span, HirId),
127 VarDefNode(Span, HirId),
132 fn live_node_kind_to_string(lnk: LiveNodeKind, tcx: TyCtxt<'_>) -> String {
133 let sm = tcx.sess.source_map();
135 UpvarNode(s) => format!("Upvar node [{}]", sm.span_to_diagnostic_string(s)),
136 ExprNode(s, _) => format!("Expr node [{}]", sm.span_to_diagnostic_string(s)),
137 VarDefNode(s, _) => format!("Var def node [{}]", sm.span_to_diagnostic_string(s)),
138 ClosureNode => "Closure node".to_owned(),
139 ExitNode => "Exit node".to_owned(),
143 fn check_mod_liveness(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
144 tcx.hir().visit_item_likes_in_module(module_def_id, &mut IrMaps::new(tcx).as_deep_visitor());
147 pub fn provide(providers: &mut Providers) {
148 *providers = Providers { check_mod_liveness, ..*providers };
151 // ______________________________________________________________________
154 // This is the first pass and the one that drives the main
155 // computation. It walks up and down the IR once. On the way down,
156 // we count for each function the number of variables as well as
157 // liveness nodes. A liveness node is basically an expression or
158 // capture clause that does something of interest: either it has
159 // interesting control flow or it uses/defines a local variable.
161 // On the way back up, at each function node we create liveness sets
162 // (we now know precisely how big to make our various vectors and so
163 // forth) and then do the data-flow propagation to compute the set
164 // of live variables at each program point.
166 // Finally, we run back over the IR one last time and, using the
167 // computed liveness, check various safety conditions. For example,
168 // there must be no live nodes at the definition site for a variable
169 // unless it has an initializer. Similarly, each non-mutable local
170 // variable must not be assigned if there is some successor
171 // assignment. And so forth.
178 #[derive(Copy, Clone, Debug)]
185 #[derive(Copy, Clone, Debug)]
187 Param(HirId, Symbol),
189 Upvar(HirId, Symbol),
192 struct IrMaps<'tcx> {
194 live_node_map: HirIdMap<LiveNode>,
195 variable_map: HirIdMap<Variable>,
196 capture_info_map: HirIdMap<Rc<Vec<CaptureInfo>>>,
197 var_kinds: IndexVec<Variable, VarKind>,
198 lnks: IndexVec<LiveNode, LiveNodeKind>,
202 fn new(tcx: TyCtxt<'tcx>) -> IrMaps<'tcx> {
205 live_node_map: HirIdMap::default(),
206 variable_map: HirIdMap::default(),
207 capture_info_map: Default::default(),
208 var_kinds: IndexVec::new(),
209 lnks: IndexVec::new(),
213 fn add_live_node(&mut self, lnk: LiveNodeKind) -> LiveNode {
214 let ln = self.lnks.push(lnk);
216 debug!("{:?} is of kind {}", ln, live_node_kind_to_string(lnk, self.tcx));
221 fn add_live_node_for_node(&mut self, hir_id: HirId, lnk: LiveNodeKind) {
222 let ln = self.add_live_node(lnk);
223 self.live_node_map.insert(hir_id, ln);
225 debug!("{:?} is node {:?}", ln, hir_id);
228 fn add_variable(&mut self, vk: VarKind) -> Variable {
229 let v = self.var_kinds.push(vk);
232 Local(LocalInfo { id: node_id, .. }) | Param(node_id, _) | Upvar(node_id, _) => {
233 self.variable_map.insert(node_id, v);
237 debug!("{:?} is {:?}", v, vk);
242 fn variable(&self, hir_id: HirId, span: Span) -> Variable {
243 match self.variable_map.get(&hir_id) {
246 span_bug!(span, "no variable registered for id {:?}", hir_id);
251 fn variable_name(&self, var: Variable) -> Symbol {
252 match self.var_kinds[var] {
253 Local(LocalInfo { name, .. }) | Param(_, name) | Upvar(_, name) => name,
257 fn variable_is_shorthand(&self, var: Variable) -> bool {
258 match self.var_kinds[var] {
259 Local(LocalInfo { is_shorthand, .. }) => is_shorthand,
260 Param(..) | Upvar(..) => false,
264 fn set_captures(&mut self, hir_id: HirId, cs: Vec<CaptureInfo>) {
265 self.capture_info_map.insert(hir_id, Rc::new(cs));
268 fn add_from_pat(&mut self, pat: &hir::Pat<'tcx>) {
269 // For struct patterns, take note of which fields used shorthand
270 // (`x` rather than `x: x`).
271 let mut shorthand_field_ids = HirIdSet::default();
272 let mut pats = VecDeque::new();
274 while let Some(pat) = pats.pop_front() {
275 use rustc_hir::PatKind::*;
277 Binding(.., inner_pat) => {
278 pats.extend(inner_pat.iter());
280 Struct(_, fields, _) => {
281 let ids = fields.iter().filter(|f| f.is_shorthand).map(|f| f.pat.hir_id);
282 shorthand_field_ids.extend(ids);
284 Ref(inner_pat, _) | Box(inner_pat) => {
285 pats.push_back(inner_pat);
287 TupleStruct(_, inner_pats, _) | Tuple(inner_pats, _) | Or(inner_pats) => {
288 pats.extend(inner_pats.iter());
290 Slice(pre_pats, inner_pat, post_pats) => {
291 pats.extend(pre_pats.iter());
292 pats.extend(inner_pat.iter());
293 pats.extend(post_pats.iter());
299 pat.each_binding(|_, hir_id, _, ident| {
300 self.add_live_node_for_node(hir_id, VarDefNode(ident.span, hir_id));
301 self.add_variable(Local(LocalInfo {
304 is_shorthand: shorthand_field_ids.contains(&hir_id),
310 impl<'tcx> Visitor<'tcx> for IrMaps<'tcx> {
311 type Map = Map<'tcx>;
313 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
314 NestedVisitorMap::OnlyBodies(self.tcx.hir())
317 fn visit_body(&mut self, body: &'tcx hir::Body<'tcx>) {
318 debug!("visit_body {:?}", body.id());
320 // swap in a new set of IR maps for this body
321 let mut maps = IrMaps::new(self.tcx);
322 let hir_id = maps.tcx.hir().body_owner(body.id());
323 let local_def_id = maps.tcx.hir().local_def_id(hir_id);
324 let def_id = local_def_id.to_def_id();
326 // Don't run unused pass for #[derive()]
327 if let Some(parent) = self.tcx.parent(def_id) {
328 if let DefKind::Impl = self.tcx.def_kind(parent.expect_local()) {
329 if self.tcx.has_attr(parent, sym::automatically_derived) {
335 // Don't run unused pass for #[naked]
336 if self.tcx.has_attr(def_id, sym::naked) {
340 if let Some(upvars) = maps.tcx.upvars_mentioned(def_id) {
341 for &var_hir_id in upvars.keys() {
342 let var_name = maps.tcx.hir().name(var_hir_id);
343 maps.add_variable(Upvar(var_hir_id, var_name));
347 // gather up the various local variables, significant expressions,
349 intravisit::walk_body(&mut maps, body);
352 let mut lsets = Liveness::new(&mut maps, local_def_id);
353 let entry_ln = lsets.compute(&body, hir_id);
354 lsets.log_liveness(entry_ln, body.id().hir_id);
356 // check for various error conditions
357 lsets.visit_body(body);
358 lsets.warn_about_unused_upvars(entry_ln);
359 lsets.warn_about_unused_args(body, entry_ln);
362 fn visit_local(&mut self, local: &'tcx hir::Local<'tcx>) {
363 self.add_from_pat(&local.pat);
364 intravisit::walk_local(self, local);
367 fn visit_arm(&mut self, arm: &'tcx hir::Arm<'tcx>) {
368 self.add_from_pat(&arm.pat);
369 if let Some(hir::Guard::IfLet(ref pat, _)) = arm.guard {
370 self.add_from_pat(pat);
372 intravisit::walk_arm(self, arm);
375 fn visit_param(&mut self, param: &'tcx hir::Param<'tcx>) {
376 param.pat.each_binding(|_bm, hir_id, _x, ident| {
377 let var = match param.pat.kind {
378 rustc_hir::PatKind::Struct(_, fields, _) => Local(LocalInfo {
383 .find(|f| f.ident == ident)
384 .map_or(false, |f| f.is_shorthand),
386 _ => Param(hir_id, ident.name),
388 self.add_variable(var);
390 intravisit::walk_param(self, param);
393 fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
395 // live nodes required for uses or definitions of variables:
396 hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => {
397 debug!("expr {}: path that leads to {:?}", expr.hir_id, path.res);
398 if let Res::Local(_var_hir_id) = path.res {
399 self.add_live_node_for_node(expr.hir_id, ExprNode(expr.span, expr.hir_id));
401 intravisit::walk_expr(self, expr);
403 hir::ExprKind::Closure(..) => {
404 // Interesting control flow (for loops can contain labeled
405 // breaks or continues)
406 self.add_live_node_for_node(expr.hir_id, ExprNode(expr.span, expr.hir_id));
408 // Make a live_node for each mentioned variable, with the span
409 // being the location that the variable is used. This results
410 // in better error messages than just pointing at the closure
411 // construction site.
412 let mut call_caps = Vec::new();
413 let closure_def_id = self.tcx.hir().local_def_id(expr.hir_id);
414 if let Some(upvars) = self.tcx.upvars_mentioned(closure_def_id) {
415 call_caps.extend(upvars.keys().map(|var_id| {
416 let upvar = upvars[var_id];
417 let upvar_ln = self.add_live_node(UpvarNode(upvar.span));
418 CaptureInfo { ln: upvar_ln, var_hid: *var_id }
421 self.set_captures(expr.hir_id, call_caps);
422 intravisit::walk_expr(self, expr);
425 hir::ExprKind::Let(ref pat, ..) => {
426 self.add_from_pat(pat);
427 intravisit::walk_expr(self, expr);
430 // live nodes required for interesting control flow:
431 hir::ExprKind::If(..)
432 | hir::ExprKind::Match(..)
433 | hir::ExprKind::Loop(..)
434 | hir::ExprKind::Yield(..) => {
435 self.add_live_node_for_node(expr.hir_id, ExprNode(expr.span, expr.hir_id));
436 intravisit::walk_expr(self, expr);
438 hir::ExprKind::Binary(op, ..) if op.node.is_lazy() => {
439 self.add_live_node_for_node(expr.hir_id, ExprNode(expr.span, expr.hir_id));
440 intravisit::walk_expr(self, expr);
443 // otherwise, live nodes are not required:
444 hir::ExprKind::Index(..)
445 | hir::ExprKind::Field(..)
446 | hir::ExprKind::Array(..)
447 | hir::ExprKind::Call(..)
448 | hir::ExprKind::MethodCall(..)
449 | hir::ExprKind::Tup(..)
450 | hir::ExprKind::Binary(..)
451 | hir::ExprKind::AddrOf(..)
452 | hir::ExprKind::Cast(..)
453 | hir::ExprKind::DropTemps(..)
454 | hir::ExprKind::Unary(..)
455 | hir::ExprKind::Break(..)
456 | hir::ExprKind::Continue(_)
457 | hir::ExprKind::Lit(_)
458 | hir::ExprKind::ConstBlock(..)
459 | hir::ExprKind::Ret(..)
460 | hir::ExprKind::Block(..)
461 | hir::ExprKind::Assign(..)
462 | hir::ExprKind::AssignOp(..)
463 | hir::ExprKind::Struct(..)
464 | hir::ExprKind::Repeat(..)
465 | hir::ExprKind::InlineAsm(..)
466 | hir::ExprKind::LlvmInlineAsm(..)
467 | hir::ExprKind::Box(..)
468 | hir::ExprKind::Type(..)
470 | hir::ExprKind::Path(hir::QPath::TypeRelative(..))
471 | hir::ExprKind::Path(hir::QPath::LangItem(..)) => {
472 intravisit::walk_expr(self, expr);
478 // ______________________________________________________________________
479 // Computing liveness sets
481 // Actually we compute just a bit more than just liveness, but we use
482 // the same basic propagation framework in all cases.
484 const ACC_READ: u32 = 1;
485 const ACC_WRITE: u32 = 2;
486 const ACC_USE: u32 = 4;
488 struct Liveness<'a, 'tcx> {
489 ir: &'a mut IrMaps<'tcx>,
490 typeck_results: &'a ty::TypeckResults<'tcx>,
491 param_env: ty::ParamEnv<'tcx>,
492 closure_min_captures: Option<&'tcx RootVariableMinCaptureList<'tcx>>,
493 successors: IndexVec<LiveNode, Option<LiveNode>>,
494 rwu_table: rwu_table::RWUTable,
496 /// A live node representing a point of execution before closure entry &
497 /// after closure exit. Used to calculate liveness of captured variables
498 /// through calls to the same closure. Used for Fn & FnMut closures only.
499 closure_ln: LiveNode,
500 /// A live node representing every 'exit' from the function, whether it be
501 /// by explicit return, panic, or other means.
504 // mappings from loop node ID to LiveNode
505 // ("break" label should map to loop node ID,
506 // it probably doesn't now)
507 break_ln: HirIdMap<LiveNode>,
508 cont_ln: HirIdMap<LiveNode>,
511 impl<'a, 'tcx> Liveness<'a, 'tcx> {
512 fn new(ir: &'a mut IrMaps<'tcx>, body_owner: LocalDefId) -> Liveness<'a, 'tcx> {
513 let typeck_results = ir.tcx.typeck(body_owner);
514 let param_env = ir.tcx.param_env(body_owner);
515 let closure_min_captures = typeck_results.closure_min_captures.get(&body_owner.to_def_id());
516 let closure_ln = ir.add_live_node(ClosureNode);
517 let exit_ln = ir.add_live_node(ExitNode);
519 let num_live_nodes = ir.lnks.len();
520 let num_vars = ir.var_kinds.len();
526 closure_min_captures,
527 successors: IndexVec::from_elem_n(None, num_live_nodes),
528 rwu_table: rwu_table::RWUTable::new(num_live_nodes, num_vars),
531 break_ln: Default::default(),
532 cont_ln: Default::default(),
536 fn live_node(&self, hir_id: HirId, span: Span) -> LiveNode {
537 match self.ir.live_node_map.get(&hir_id) {
540 // This must be a mismatch between the ir_map construction
541 // above and the propagation code below; the two sets of
542 // code have to agree about which AST nodes are worth
543 // creating liveness nodes for.
544 span_bug!(span, "no live node registered for node {:?}", hir_id);
549 fn variable(&self, hir_id: HirId, span: Span) -> Variable {
550 self.ir.variable(hir_id, span)
553 fn define_bindings_in_pat(&mut self, pat: &hir::Pat<'_>, mut succ: LiveNode) -> LiveNode {
554 // In an or-pattern, only consider the first pattern; any later patterns
555 // must have the same bindings, and we also consider the first pattern
556 // to be the "authoritative" set of ids.
557 pat.each_binding_or_first(&mut |_, hir_id, pat_sp, ident| {
558 let ln = self.live_node(hir_id, pat_sp);
559 let var = self.variable(hir_id, ident.span);
560 self.init_from_succ(ln, succ);
561 self.define(ln, var);
567 fn live_on_entry(&self, ln: LiveNode, var: Variable) -> bool {
568 self.rwu_table.get_reader(ln, var)
571 // Is this variable live on entry to any of its successor nodes?
572 fn live_on_exit(&self, ln: LiveNode, var: Variable) -> bool {
573 let successor = self.successors[ln].unwrap();
574 self.live_on_entry(successor, var)
577 fn used_on_entry(&self, ln: LiveNode, var: Variable) -> bool {
578 self.rwu_table.get_used(ln, var)
581 fn assigned_on_entry(&self, ln: LiveNode, var: Variable) -> bool {
582 self.rwu_table.get_writer(ln, var)
585 fn assigned_on_exit(&self, ln: LiveNode, var: Variable) -> bool {
586 let successor = self.successors[ln].unwrap();
587 self.assigned_on_entry(successor, var)
590 fn write_vars<F>(&self, wr: &mut dyn Write, mut test: F) -> io::Result<()>
592 F: FnMut(Variable) -> bool,
594 for var_idx in 0..self.ir.var_kinds.len() {
595 let var = Variable::from(var_idx);
597 write!(wr, " {:?}", var)?;
603 #[allow(unused_must_use)]
604 fn ln_str(&self, ln: LiveNode) -> String {
605 let mut wr = Vec::new();
607 let wr = &mut wr as &mut dyn Write;
608 write!(wr, "[{:?} of kind {:?} reads", ln, self.ir.lnks[ln]);
609 self.write_vars(wr, |var| self.rwu_table.get_reader(ln, var));
610 write!(wr, " writes");
611 self.write_vars(wr, |var| self.rwu_table.get_writer(ln, var));
613 self.write_vars(wr, |var| self.rwu_table.get_used(ln, var));
615 write!(wr, " precedes {:?}]", self.successors[ln]);
617 String::from_utf8(wr).unwrap()
620 fn log_liveness(&self, entry_ln: LiveNode, hir_id: hir::HirId) {
621 // hack to skip the loop unless debug! is enabled:
623 "^^ liveness computation results for body {} (entry={:?})",
625 for ln_idx in 0..self.ir.lnks.len() {
626 debug!("{:?}", self.ln_str(LiveNode::from(ln_idx)));
634 fn init_empty(&mut self, ln: LiveNode, succ_ln: LiveNode) {
635 self.successors[ln] = Some(succ_ln);
637 // It is not necessary to initialize the RWUs here because they are all
638 // empty when created, and the sets only grow during iterations.
641 fn init_from_succ(&mut self, ln: LiveNode, succ_ln: LiveNode) {
642 // more efficient version of init_empty() / merge_from_succ()
643 self.successors[ln] = Some(succ_ln);
644 self.rwu_table.copy(ln, succ_ln);
645 debug!("init_from_succ(ln={}, succ={})", self.ln_str(ln), self.ln_str(succ_ln));
648 fn merge_from_succ(&mut self, ln: LiveNode, succ_ln: LiveNode) -> bool {
653 let changed = self.rwu_table.union(ln, succ_ln);
654 debug!("merge_from_succ(ln={:?}, succ={}, changed={})", ln, self.ln_str(succ_ln), changed);
658 // Indicates that a local variable was *defined*; we know that no
659 // uses of the variable can precede the definition (resolve checks
660 // this) so we just clear out all the data.
661 fn define(&mut self, writer: LiveNode, var: Variable) {
662 let used = self.rwu_table.get_used(writer, var);
663 self.rwu_table.set(writer, var, rwu_table::RWU { reader: false, writer: false, used });
664 debug!("{:?} defines {:?}: {}", writer, var, self.ln_str(writer));
667 // Either read, write, or both depending on the acc bitset
668 fn acc(&mut self, ln: LiveNode, var: Variable, acc: u32) {
669 debug!("{:?} accesses[{:x}] {:?}: {}", ln, acc, var, self.ln_str(ln));
671 let mut rwu = self.rwu_table.get(ln, var);
673 if (acc & ACC_WRITE) != 0 {
678 // Important: if we both read/write, must do read second
679 // or else the write will override.
680 if (acc & ACC_READ) != 0 {
684 if (acc & ACC_USE) != 0 {
688 self.rwu_table.set(ln, var, rwu);
691 fn compute(&mut self, body: &hir::Body<'_>, hir_id: HirId) -> LiveNode {
692 debug!("compute: for body {:?}", body.id().hir_id);
694 // # Liveness of captured variables
696 // When computing the liveness for captured variables we take into
697 // account how variable is captured (ByRef vs ByValue) and what is the
698 // closure kind (Generator / FnOnce vs Fn / FnMut).
700 // Variables captured by reference are assumed to be used on the exit
703 // In FnOnce closures, variables captured by value are known to be dead
704 // on exit since it is impossible to call the closure again.
706 // In Fn / FnMut closures, variables captured by value are live on exit
707 // if they are live on the entry to the closure, since only the closure
708 // itself can access them on subsequent calls.
710 if let Some(closure_min_captures) = self.closure_min_captures {
711 // Mark upvars captured by reference as used after closure exits.
712 for (&var_hir_id, min_capture_list) in closure_min_captures {
713 for captured_place in min_capture_list {
714 match captured_place.info.capture_kind {
715 ty::UpvarCapture::ByRef(_) => {
716 let var = self.variable(
718 captured_place.get_capture_kind_span(self.ir.tcx),
720 self.acc(self.exit_ln, var, ACC_READ | ACC_USE);
722 ty::UpvarCapture::ByValue(_) => {}
728 let succ = self.propagate_through_expr(&body.value, self.exit_ln);
730 if self.closure_min_captures.is_none() {
731 // Either not a closure, or closure without any captured variables.
732 // No need to determine liveness of captured variables, since there
737 let ty = self.typeck_results.node_type(hir_id);
739 ty::Closure(_def_id, substs) => match substs.as_closure().kind() {
740 ty::ClosureKind::Fn => {}
741 ty::ClosureKind::FnMut => {}
742 ty::ClosureKind::FnOnce => return succ,
744 ty::Generator(..) => return succ,
748 "{} has upvars so it should have a closure type: {:?}",
755 // Propagate through calls to the closure.
757 self.init_from_succ(self.closure_ln, succ);
758 for param in body.params {
759 param.pat.each_binding(|_bm, hir_id, _x, ident| {
760 let var = self.variable(hir_id, ident.span);
761 self.define(self.closure_ln, var);
765 if !self.merge_from_succ(self.exit_ln, self.closure_ln) {
768 assert_eq!(succ, self.propagate_through_expr(&body.value, self.exit_ln));
774 fn propagate_through_block(&mut self, blk: &hir::Block<'_>, succ: LiveNode) -> LiveNode {
775 if blk.targeted_by_break {
776 self.break_ln.insert(blk.hir_id, succ);
778 let succ = self.propagate_through_opt_expr(blk.expr.as_deref(), succ);
779 blk.stmts.iter().rev().fold(succ, |succ, stmt| self.propagate_through_stmt(stmt, succ))
782 fn propagate_through_stmt(&mut self, stmt: &hir::Stmt<'_>, succ: LiveNode) -> LiveNode {
784 hir::StmtKind::Local(ref local) => {
785 // Note: we mark the variable as defined regardless of whether
786 // there is an initializer. Initially I had thought to only mark
787 // the live variable as defined if it was initialized, and then we
788 // could check for uninit variables just by scanning what is live
789 // at the start of the function. But that doesn't work so well for
790 // immutable variables defined in a loop:
791 // loop { let x; x = 5; }
792 // because the "assignment" loops back around and generates an error.
794 // So now we just check that variables defined w/o an
795 // initializer are not live at the point of their
796 // initialization, which is mildly more complex than checking
797 // once at the func header but otherwise equivalent.
799 let succ = self.propagate_through_opt_expr(local.init.as_deref(), succ);
800 self.define_bindings_in_pat(&local.pat, succ)
802 hir::StmtKind::Item(..) => succ,
803 hir::StmtKind::Expr(ref expr) | hir::StmtKind::Semi(ref expr) => {
804 self.propagate_through_expr(&expr, succ)
809 fn propagate_through_exprs(&mut self, exprs: &[Expr<'_>], succ: LiveNode) -> LiveNode {
810 exprs.iter().rev().fold(succ, |succ, expr| self.propagate_through_expr(&expr, succ))
813 fn propagate_through_opt_expr(
815 opt_expr: Option<&Expr<'_>>,
818 opt_expr.map_or(succ, |expr| self.propagate_through_expr(expr, succ))
821 fn propagate_through_expr(&mut self, expr: &Expr<'_>, succ: LiveNode) -> LiveNode {
822 debug!("propagate_through_expr: {:?}", expr);
825 // Interesting cases with control flow or which gen/kill
826 hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => {
827 self.access_path(expr.hir_id, path, succ, ACC_READ | ACC_USE)
830 hir::ExprKind::Field(ref e, _) => self.propagate_through_expr(&e, succ),
832 hir::ExprKind::Closure(..) => {
833 debug!("{:?} is an ExprKind::Closure", expr);
835 // the construction of a closure itself is not important,
836 // but we have to consider the closed over variables.
842 .unwrap_or_else(|| span_bug!(expr.span, "no registered caps"));
844 caps.iter().rev().fold(succ, |succ, cap| {
845 self.init_from_succ(cap.ln, succ);
846 let var = self.variable(cap.var_hid, expr.span);
847 self.acc(cap.ln, var, ACC_READ | ACC_USE);
852 hir::ExprKind::Let(ref pat, ref scrutinee, _) => {
853 let succ = self.propagate_through_expr(scrutinee, succ);
854 self.define_bindings_in_pat(pat, succ)
857 // Note that labels have been resolved, so we don't need to look
858 // at the label ident
859 hir::ExprKind::Loop(ref blk, ..) => self.propagate_through_loop(expr, &blk, succ),
861 hir::ExprKind::Yield(ref e, ..) => {
862 let yield_ln = self.live_node(expr.hir_id, expr.span);
863 self.init_from_succ(yield_ln, succ);
864 self.merge_from_succ(yield_ln, self.exit_ln);
865 self.propagate_through_expr(e, yield_ln)
868 hir::ExprKind::If(ref cond, ref then, ref else_opt) => {
883 self.propagate_through_opt_expr(else_opt.as_ref().map(|e| &**e), succ);
884 let then_ln = self.propagate_through_expr(&then, succ);
885 let ln = self.live_node(expr.hir_id, expr.span);
886 self.init_from_succ(ln, else_ln);
887 self.merge_from_succ(ln, then_ln);
888 self.propagate_through_expr(&cond, ln)
891 hir::ExprKind::Match(ref e, arms, _) => {
906 let ln = self.live_node(expr.hir_id, expr.span);
907 self.init_empty(ln, succ);
909 let body_succ = self.propagate_through_expr(&arm.body, succ);
911 let guard_succ = arm.guard.as_ref().map_or(body_succ, |g| match g {
912 hir::Guard::If(e) => self.propagate_through_expr(e, body_succ),
913 hir::Guard::IfLet(pat, e) => {
914 let let_bind = self.define_bindings_in_pat(pat, body_succ);
915 self.propagate_through_expr(e, let_bind)
918 let arm_succ = self.define_bindings_in_pat(&arm.pat, guard_succ);
919 self.merge_from_succ(ln, arm_succ);
921 self.propagate_through_expr(&e, ln)
924 hir::ExprKind::Ret(ref o_e) => {
925 // Ignore succ and subst exit_ln.
926 self.propagate_through_opt_expr(o_e.as_ref().map(|e| &**e), self.exit_ln)
929 hir::ExprKind::Break(label, ref opt_expr) => {
930 // Find which label this break jumps to
931 let target = match label.target_id {
932 Ok(hir_id) => self.break_ln.get(&hir_id),
933 Err(err) => span_bug!(expr.span, "loop scope error: {}", err),
937 // Now that we know the label we're going to,
938 // look it up in the break loop nodes table
941 Some(b) => self.propagate_through_opt_expr(opt_expr.as_ref().map(|e| &**e), b),
942 None => span_bug!(expr.span, "`break` to unknown label"),
946 hir::ExprKind::Continue(label) => {
947 // Find which label this expr continues to
950 .unwrap_or_else(|err| span_bug!(expr.span, "loop scope error: {}", err));
952 // Now that we know the label we're going to,
953 // look it up in the continue loop nodes table
957 .unwrap_or_else(|| span_bug!(expr.span, "continue to unknown label"))
960 hir::ExprKind::Assign(ref l, ref r, _) => {
961 // see comment on places in
962 // propagate_through_place_components()
963 let succ = self.write_place(&l, succ, ACC_WRITE);
964 let succ = self.propagate_through_place_components(&l, succ);
965 self.propagate_through_expr(&r, succ)
968 hir::ExprKind::AssignOp(_, ref l, ref r) => {
969 // an overloaded assign op is like a method call
970 if self.typeck_results.is_method_call(expr) {
971 let succ = self.propagate_through_expr(&l, succ);
972 self.propagate_through_expr(&r, succ)
974 // see comment on places in
975 // propagate_through_place_components()
976 let succ = self.write_place(&l, succ, ACC_WRITE | ACC_READ);
977 let succ = self.propagate_through_expr(&r, succ);
978 self.propagate_through_place_components(&l, succ)
982 // Uninteresting cases: just propagate in rev exec order
983 hir::ExprKind::Array(ref exprs) => self.propagate_through_exprs(exprs, succ),
985 hir::ExprKind::Struct(_, ref fields, ref with_expr) => {
986 let succ = self.propagate_through_opt_expr(with_expr.as_ref().map(|e| &**e), succ);
990 .fold(succ, |succ, field| self.propagate_through_expr(&field.expr, succ))
993 hir::ExprKind::Call(ref f, ref args) => {
994 let succ = self.check_is_ty_uninhabited(expr, succ);
995 let succ = self.propagate_through_exprs(args, succ);
996 self.propagate_through_expr(&f, succ)
999 hir::ExprKind::MethodCall(.., ref args, _) => {
1000 let succ = self.check_is_ty_uninhabited(expr, succ);
1001 self.propagate_through_exprs(args, succ)
1004 hir::ExprKind::Tup(ref exprs) => self.propagate_through_exprs(exprs, succ),
1006 hir::ExprKind::Binary(op, ref l, ref r) if op.node.is_lazy() => {
1007 let r_succ = self.propagate_through_expr(&r, succ);
1009 let ln = self.live_node(expr.hir_id, expr.span);
1010 self.init_from_succ(ln, succ);
1011 self.merge_from_succ(ln, r_succ);
1013 self.propagate_through_expr(&l, ln)
1016 hir::ExprKind::Index(ref l, ref r) | hir::ExprKind::Binary(_, ref l, ref r) => {
1017 let r_succ = self.propagate_through_expr(&r, succ);
1018 self.propagate_through_expr(&l, r_succ)
1021 hir::ExprKind::Box(ref e)
1022 | hir::ExprKind::AddrOf(_, _, ref e)
1023 | hir::ExprKind::Cast(ref e, _)
1024 | hir::ExprKind::Type(ref e, _)
1025 | hir::ExprKind::DropTemps(ref e)
1026 | hir::ExprKind::Unary(_, ref e)
1027 | hir::ExprKind::Repeat(ref e, _) => self.propagate_through_expr(&e, succ),
1029 hir::ExprKind::InlineAsm(ref asm) => {
1030 // Handle non-returning asm
1031 let mut succ = if asm.options.contains(InlineAsmOptions::NORETURN) {
1037 // Do a first pass for writing outputs only
1038 for (op, _op_sp) in asm.operands.iter().rev() {
1040 hir::InlineAsmOperand::In { .. }
1041 | hir::InlineAsmOperand::Const { .. }
1042 | hir::InlineAsmOperand::Sym { .. } => {}
1043 hir::InlineAsmOperand::Out { expr, .. } => {
1044 if let Some(expr) = expr {
1045 succ = self.write_place(expr, succ, ACC_WRITE);
1048 hir::InlineAsmOperand::InOut { expr, .. } => {
1049 succ = self.write_place(expr, succ, ACC_READ | ACC_WRITE | ACC_USE);
1051 hir::InlineAsmOperand::SplitInOut { out_expr, .. } => {
1052 if let Some(expr) = out_expr {
1053 succ = self.write_place(expr, succ, ACC_WRITE);
1059 // Then do a second pass for inputs
1060 let mut succ = succ;
1061 for (op, _op_sp) in asm.operands.iter().rev() {
1063 hir::InlineAsmOperand::In { expr, .. }
1064 | hir::InlineAsmOperand::Sym { expr, .. } => {
1065 succ = self.propagate_through_expr(expr, succ)
1067 hir::InlineAsmOperand::Out { expr, .. } => {
1068 if let Some(expr) = expr {
1069 succ = self.propagate_through_place_components(expr, succ);
1072 hir::InlineAsmOperand::InOut { expr, .. } => {
1073 succ = self.propagate_through_place_components(expr, succ);
1075 hir::InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
1076 if let Some(expr) = out_expr {
1077 succ = self.propagate_through_place_components(expr, succ);
1079 succ = self.propagate_through_expr(in_expr, succ);
1081 hir::InlineAsmOperand::Const { .. } => {}
1087 hir::ExprKind::LlvmInlineAsm(ref asm) => {
1088 let ia = &asm.inner;
1089 let outputs = asm.outputs_exprs;
1090 let inputs = asm.inputs_exprs;
1091 let succ = iter::zip(&ia.outputs, outputs).rev().fold(succ, |succ, (o, output)| {
1092 // see comment on places
1093 // in propagate_through_place_components()
1095 self.propagate_through_expr(output, succ)
1097 let acc = if o.is_rw { ACC_WRITE | ACC_READ } else { ACC_WRITE };
1098 let succ = self.write_place(output, succ, acc);
1099 self.propagate_through_place_components(output, succ)
1103 // Inputs are executed first. Propagate last because of rev order
1104 self.propagate_through_exprs(inputs, succ)
1107 hir::ExprKind::Lit(..)
1108 | hir::ExprKind::ConstBlock(..)
1109 | hir::ExprKind::Err
1110 | hir::ExprKind::Path(hir::QPath::TypeRelative(..))
1111 | hir::ExprKind::Path(hir::QPath::LangItem(..)) => succ,
1113 // Note that labels have been resolved, so we don't need to look
1114 // at the label ident
1115 hir::ExprKind::Block(ref blk, _) => self.propagate_through_block(&blk, succ),
1119 fn propagate_through_place_components(&mut self, expr: &Expr<'_>, succ: LiveNode) -> LiveNode {
1122 // In general, the full flow graph structure for an
1123 // assignment/move/etc can be handled in one of two ways,
1124 // depending on whether what is being assigned is a "tracked
1125 // value" or not. A tracked value is basically a local
1126 // variable or argument.
1128 // The two kinds of graphs are:
1130 // Tracked place Untracked place
1131 // ----------------------++-----------------------
1135 // (rvalue) || (rvalue)
1138 // (write of place) || (place components)
1143 // ----------------------++-----------------------
1145 // I will cover the two cases in turn:
1149 // A tracked place is a local variable/argument `x`. In
1150 // these cases, the link_node where the write occurs is linked
1151 // to node id of `x`. The `write_place()` routine generates
1152 // the contents of this node. There are no subcomponents to
1155 // # Non-tracked places
1157 // These are places like `x[5]` or `x.f`. In that case, we
1158 // basically ignore the value which is written to but generate
1159 // reads for the components---`x` in these two examples. The
1160 // components reads are generated by
1161 // `propagate_through_place_components()` (this fn).
1165 // It is still possible to observe assignments to non-places;
1166 // these errors are detected in the later pass borrowck. We
1167 // just ignore such cases and treat them as reads.
1170 hir::ExprKind::Path(_) => succ,
1171 hir::ExprKind::Field(ref e, _) => self.propagate_through_expr(&e, succ),
1172 _ => self.propagate_through_expr(expr, succ),
1176 // see comment on propagate_through_place()
1177 fn write_place(&mut self, expr: &Expr<'_>, succ: LiveNode, acc: u32) -> LiveNode {
1179 hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => {
1180 self.access_path(expr.hir_id, path, succ, acc)
1183 // We do not track other places, so just propagate through
1184 // to their subcomponents. Also, it may happen that
1185 // non-places occur here, because those are detected in the
1186 // later pass borrowck.
1199 let ln = self.live_node(hir_id, span);
1201 self.init_from_succ(ln, succ);
1202 let var = self.variable(var_hid, span);
1203 self.acc(ln, var, acc);
1211 path: &hir::Path<'_>,
1216 Res::Local(hid) => self.access_var(hir_id, hid, succ, acc, path.span),
1221 fn propagate_through_loop(
1224 body: &hir::Block<'_>,
1228 We model control flow like this:
1235 Note that a `continue` expression targeting the `loop` will have a successor of `expr`.
1236 Meanwhile, a `break` expression will have a successor of `succ`.
1240 let ln = self.live_node(expr.hir_id, expr.span);
1241 self.init_empty(ln, succ);
1242 debug!("propagate_through_loop: using id for loop body {} {:?}", expr.hir_id, body);
1244 self.break_ln.insert(expr.hir_id, succ);
1246 self.cont_ln.insert(expr.hir_id, ln);
1248 let body_ln = self.propagate_through_block(body, ln);
1250 // repeat until fixed point is reached:
1251 while self.merge_from_succ(ln, body_ln) {
1252 assert_eq!(body_ln, self.propagate_through_block(body, ln));
1258 fn check_is_ty_uninhabited(&mut self, expr: &Expr<'_>, succ: LiveNode) -> LiveNode {
1259 let ty = self.typeck_results.expr_ty(expr);
1260 let m = self.ir.tcx.parent_module(expr.hir_id).to_def_id();
1261 if self.ir.tcx.is_ty_uninhabited_from(m, ty, self.param_env) {
1262 match self.ir.lnks[succ] {
1263 LiveNodeKind::ExprNode(succ_span, succ_id) => {
1264 self.warn_about_unreachable(expr.span, ty, succ_span, succ_id, "expression");
1266 LiveNodeKind::VarDefNode(succ_span, succ_id) => {
1267 self.warn_about_unreachable(expr.span, ty, succ_span, succ_id, "definition");
1277 fn warn_about_unreachable(
1285 if !orig_ty.is_never() {
1286 // Unreachable code warnings are already emitted during type checking.
1287 // However, during type checking, full type information is being
1288 // calculated but not yet available, so the check for diverging
1289 // expressions due to uninhabited result types is pretty crude and
1290 // only checks whether ty.is_never(). Here, we have full type
1291 // information available and can issue warnings for less obviously
1292 // uninhabited types (e.g. empty enums). The check above is used so
1293 // that we do not emit the same warning twice if the uninhabited type
1296 self.ir.tcx.struct_span_lint_hir(
1297 lint::builtin::UNREACHABLE_CODE,
1301 let msg = format!("unreachable {}", descr);
1303 .span_label(expr_span, &msg)
1304 .span_label(orig_span, "any code following this expression is unreachable")
1308 "this expression has type `{}`, which is uninhabited",
1319 // _______________________________________________________________________
1320 // Checking for error conditions
1322 impl<'a, 'tcx> Visitor<'tcx> for Liveness<'a, 'tcx> {
1323 type Map = intravisit::ErasedMap<'tcx>;
1325 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1326 NestedVisitorMap::None
1329 fn visit_local(&mut self, local: &'tcx hir::Local<'tcx>) {
1330 self.check_unused_vars_in_pat(&local.pat, None, |spans, hir_id, ln, var| {
1331 if local.init.is_some() {
1332 self.warn_about_dead_assign(spans, hir_id, ln, var);
1336 intravisit::walk_local(self, local);
1339 fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) {
1340 check_expr(self, ex);
1341 intravisit::walk_expr(self, ex);
1344 fn visit_arm(&mut self, arm: &'tcx hir::Arm<'tcx>) {
1345 self.check_unused_vars_in_pat(&arm.pat, None, |_, _, _, _| {});
1346 intravisit::walk_arm(self, arm);
1350 fn check_expr<'tcx>(this: &mut Liveness<'_, 'tcx>, expr: &'tcx Expr<'tcx>) {
1352 hir::ExprKind::Assign(ref l, ..) => {
1353 this.check_place(&l);
1356 hir::ExprKind::AssignOp(_, ref l, _) => {
1357 if !this.typeck_results.is_method_call(expr) {
1358 this.check_place(&l);
1362 hir::ExprKind::InlineAsm(ref asm) => {
1363 for (op, _op_sp) in asm.operands {
1365 hir::InlineAsmOperand::Out { expr, .. } => {
1366 if let Some(expr) = expr {
1367 this.check_place(expr);
1370 hir::InlineAsmOperand::InOut { expr, .. } => {
1371 this.check_place(expr);
1373 hir::InlineAsmOperand::SplitInOut { out_expr, .. } => {
1374 if let Some(out_expr) = out_expr {
1375 this.check_place(out_expr);
1383 hir::ExprKind::LlvmInlineAsm(ref asm) => {
1384 for input in asm.inputs_exprs {
1385 this.visit_expr(input);
1388 // Output operands must be places
1389 for (o, output) in iter::zip(&asm.inner.outputs, asm.outputs_exprs) {
1391 this.check_place(output);
1393 this.visit_expr(output);
1397 hir::ExprKind::Let(ref pat, ..) => {
1398 this.check_unused_vars_in_pat(pat, None, |_, _, _, _| {});
1401 // no correctness conditions related to liveness
1402 hir::ExprKind::Call(..)
1403 | hir::ExprKind::MethodCall(..)
1404 | hir::ExprKind::Match(..)
1405 | hir::ExprKind::Loop(..)
1406 | hir::ExprKind::Index(..)
1407 | hir::ExprKind::Field(..)
1408 | hir::ExprKind::Array(..)
1409 | hir::ExprKind::Tup(..)
1410 | hir::ExprKind::Binary(..)
1411 | hir::ExprKind::Cast(..)
1412 | hir::ExprKind::If(..)
1413 | hir::ExprKind::DropTemps(..)
1414 | hir::ExprKind::Unary(..)
1415 | hir::ExprKind::Ret(..)
1416 | hir::ExprKind::Break(..)
1417 | hir::ExprKind::Continue(..)
1418 | hir::ExprKind::Lit(_)
1419 | hir::ExprKind::ConstBlock(..)
1420 | hir::ExprKind::Block(..)
1421 | hir::ExprKind::AddrOf(..)
1422 | hir::ExprKind::Struct(..)
1423 | hir::ExprKind::Repeat(..)
1424 | hir::ExprKind::Closure(..)
1425 | hir::ExprKind::Path(_)
1426 | hir::ExprKind::Yield(..)
1427 | hir::ExprKind::Box(..)
1428 | hir::ExprKind::Type(..)
1429 | hir::ExprKind::Err => {}
1433 impl<'tcx> Liveness<'_, 'tcx> {
1434 fn check_place(&mut self, expr: &'tcx Expr<'tcx>) {
1436 hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => {
1437 if let Res::Local(var_hid) = path.res {
1438 // Assignment to an immutable variable or argument: only legal
1439 // if there is no later assignment. If this local is actually
1440 // mutable, then check for a reassignment to flag the mutability
1442 let ln = self.live_node(expr.hir_id, expr.span);
1443 let var = self.variable(var_hid, expr.span);
1444 self.warn_about_dead_assign(vec![expr.span], expr.hir_id, ln, var);
1448 // For other kinds of places, no checks are required,
1449 // and any embedded expressions are actually rvalues
1450 intravisit::walk_expr(self, expr);
1455 fn should_warn(&self, var: Variable) -> Option<String> {
1456 let name = self.ir.variable_name(var);
1457 if name == kw::Empty {
1460 let name: &str = &name.as_str();
1461 if name.as_bytes()[0] == b'_' {
1464 Some(name.to_owned())
1467 fn warn_about_unused_upvars(&self, entry_ln: LiveNode) {
1468 let closure_min_captures = match self.closure_min_captures {
1470 Some(closure_min_captures) => closure_min_captures,
1473 // If closure_min_captures is Some(), upvars must be Some() too.
1474 for (&var_hir_id, min_capture_list) in closure_min_captures {
1475 for captured_place in min_capture_list {
1476 match captured_place.info.capture_kind {
1477 ty::UpvarCapture::ByValue(_) => {}
1478 ty::UpvarCapture::ByRef(..) => continue,
1480 let span = captured_place.get_capture_kind_span(self.ir.tcx);
1481 let var = self.variable(var_hir_id, span);
1482 if self.used_on_entry(entry_ln, var) {
1483 if !self.live_on_entry(entry_ln, var) {
1484 if let Some(name) = self.should_warn(var) {
1485 self.ir.tcx.struct_span_lint_hir(
1486 lint::builtin::UNUSED_ASSIGNMENTS,
1490 lint.build(&format!(
1491 "value captured by `{}` is never read",
1494 .help("did you mean to capture by reference instead?")
1501 if let Some(name) = self.should_warn(var) {
1502 self.ir.tcx.struct_span_lint_hir(
1503 lint::builtin::UNUSED_VARIABLES,
1507 lint.build(&format!("unused variable: `{}`", name))
1508 .help("did you mean to capture by reference instead?")
1518 fn warn_about_unused_args(&self, body: &hir::Body<'_>, entry_ln: LiveNode) {
1519 for p in body.params {
1520 self.check_unused_vars_in_pat(&p.pat, Some(entry_ln), |spans, hir_id, ln, var| {
1521 if !self.live_on_entry(ln, var) {
1522 self.report_unused_assign(hir_id, spans, var, |name| {
1523 format!("value passed to `{}` is never read", name)
1530 fn check_unused_vars_in_pat(
1533 entry_ln: Option<LiveNode>,
1534 on_used_on_entry: impl Fn(Vec<Span>, HirId, LiveNode, Variable),
1536 // In an or-pattern, only consider the variable; any later patterns must have the same
1537 // bindings, and we also consider the first pattern to be the "authoritative" set of ids.
1538 // However, we should take the ids and spans of variables with the same name from the later
1539 // patterns so the suggestions to prefix with underscores will apply to those too.
1540 let mut vars: FxIndexMap<Symbol, (LiveNode, Variable, Vec<(HirId, Span, Span)>)> =
1543 pat.each_binding(|_, hir_id, pat_sp, ident| {
1544 let ln = entry_ln.unwrap_or_else(|| self.live_node(hir_id, pat_sp));
1545 let var = self.variable(hir_id, ident.span);
1546 let id_and_sp = (hir_id, pat_sp, ident.span);
1547 vars.entry(self.ir.variable_name(var))
1548 .and_modify(|(.., hir_ids_and_spans)| hir_ids_and_spans.push(id_and_sp))
1549 .or_insert_with(|| (ln, var, vec![id_and_sp]));
1552 for (_, (ln, var, hir_ids_and_spans)) in vars {
1553 if self.used_on_entry(ln, var) {
1554 let id = hir_ids_and_spans[0].0;
1556 hir_ids_and_spans.into_iter().map(|(_, _, ident_span)| ident_span).collect();
1557 on_used_on_entry(spans, id, ln, var);
1559 self.report_unused(hir_ids_and_spans, ln, var);
1566 hir_ids_and_spans: Vec<(HirId, Span, Span)>,
1570 let first_hir_id = hir_ids_and_spans[0].0;
1572 if let Some(name) = self.should_warn(var).filter(|name| name != "self") {
1573 // annoying: for parameters in funcs like `fn(x: i32)
1574 // {ret}`, there is only one node, so asking about
1575 // assigned_on_exit() is not meaningful.
1577 if ln == self.exit_ln { false } else { self.assigned_on_exit(ln, var) };
1580 self.ir.tcx.struct_span_lint_hir(
1581 lint::builtin::UNUSED_VARIABLES,
1585 .map(|(_, _, ident_span)| ident_span)
1586 .collect::<Vec<_>>(),
1588 lint.build(&format!("variable `{}` is assigned to, but never used", name))
1589 .note(&format!("consider using `_{}` instead", name))
1594 let (shorthands, non_shorthands): (Vec<_>, Vec<_>) =
1595 hir_ids_and_spans.iter().copied().partition(|(hir_id, _, ident_span)| {
1596 let var = self.variable(*hir_id, *ident_span);
1597 self.ir.variable_is_shorthand(var)
1600 // If we have both shorthand and non-shorthand, prefer the "try ignoring
1601 // the field" message, and suggest `_` for the non-shorthands. If we only
1602 // have non-shorthand, then prefix with an underscore instead.
1603 if !shorthands.is_empty() {
1604 let shorthands = shorthands
1606 .map(|(_, pat_span, _)| (pat_span, format!("{}: _", name)))
1610 .map(|(_, pat_span, _)| (pat_span, "_".to_string())),
1612 .collect::<Vec<_>>();
1614 self.ir.tcx.struct_span_lint_hir(
1615 lint::builtin::UNUSED_VARIABLES,
1619 .map(|(_, pat_span, _)| *pat_span)
1620 .collect::<Vec<_>>(),
1622 let mut err = lint.build(&format!("unused variable: `{}`", name));
1623 err.multipart_suggestion(
1624 "try ignoring the field",
1626 Applicability::MachineApplicable,
1632 let non_shorthands = non_shorthands
1634 .map(|(_, _, ident_span)| (ident_span, format!("_{}", name)))
1635 .collect::<Vec<_>>();
1637 self.ir.tcx.struct_span_lint_hir(
1638 lint::builtin::UNUSED_VARIABLES,
1642 .map(|(_, _, ident_span)| *ident_span)
1643 .collect::<Vec<_>>(),
1645 let mut err = lint.build(&format!("unused variable: `{}`", name));
1646 err.multipart_suggestion(
1647 "if this is intentional, prefix it with an underscore",
1649 Applicability::MachineApplicable,
1659 fn warn_about_dead_assign(&self, spans: Vec<Span>, hir_id: HirId, ln: LiveNode, var: Variable) {
1660 if !self.live_on_exit(ln, var) {
1661 self.report_unused_assign(hir_id, spans, var, |name| {
1662 format!("value assigned to `{}` is never read", name)
1667 fn report_unused_assign(
1672 message: impl Fn(&str) -> String,
1674 if let Some(name) = self.should_warn(var) {
1675 self.ir.tcx.struct_span_lint_hir(
1676 lint::builtin::UNUSED_ASSIGNMENTS,
1680 lint.build(&message(&name))
1681 .help("maybe it is overwritten before being read?")