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, 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::*;
110 rustc_index::newtype_index! {
111 pub struct Variable {
112 DEBUG_FORMAT = "v({})",
116 rustc_index::newtype_index! {
117 pub struct LiveNode {
118 DEBUG_FORMAT = "ln({})",
122 #[derive(Copy, Clone, PartialEq, Debug)]
131 fn live_node_kind_to_string(lnk: LiveNodeKind, tcx: TyCtxt<'_>) -> String {
132 let sm = tcx.sess.source_map();
134 UpvarNode(s) => format!("Upvar node [{}]", sm.span_to_string(s)),
135 ExprNode(s) => format!("Expr node [{}]", sm.span_to_string(s)),
136 VarDefNode(s) => format!("Var def node [{}]", sm.span_to_string(s)),
137 ClosureNode => "Closure node".to_owned(),
138 ExitNode => "Exit node".to_owned(),
142 fn check_mod_liveness(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
143 tcx.hir().visit_item_likes_in_module(module_def_id, &mut IrMaps::new(tcx).as_deep_visitor());
146 pub fn provide(providers: &mut Providers) {
147 *providers = Providers { check_mod_liveness, ..*providers };
150 // ______________________________________________________________________
153 // This is the first pass and the one that drives the main
154 // computation. It walks up and down the IR once. On the way down,
155 // we count for each function the number of variables as well as
156 // liveness nodes. A liveness node is basically an expression or
157 // capture clause that does something of interest: either it has
158 // interesting control flow or it uses/defines a local variable.
160 // On the way back up, at each function node we create liveness sets
161 // (we now know precisely how big to make our various vectors and so
162 // forth) and then do the data-flow propagation to compute the set
163 // of live variables at each program point.
165 // Finally, we run back over the IR one last time and, using the
166 // computed liveness, check various safety conditions. For example,
167 // there must be no live nodes at the definition site for a variable
168 // unless it has an initializer. Similarly, each non-mutable local
169 // variable must not be assigned if there is some successor
170 // assignment. And so forth.
177 #[derive(Copy, Clone, Debug)]
184 #[derive(Copy, Clone, Debug)]
186 Param(HirId, Symbol),
188 Upvar(HirId, Symbol),
191 struct IrMaps<'tcx> {
193 live_node_map: HirIdMap<LiveNode>,
194 variable_map: HirIdMap<Variable>,
195 capture_info_map: HirIdMap<Rc<Vec<CaptureInfo>>>,
196 var_kinds: IndexVec<Variable, VarKind>,
197 lnks: IndexVec<LiveNode, LiveNodeKind>,
201 fn new(tcx: TyCtxt<'tcx>) -> IrMaps<'tcx> {
204 live_node_map: HirIdMap::default(),
205 variable_map: HirIdMap::default(),
206 capture_info_map: Default::default(),
207 var_kinds: IndexVec::new(),
208 lnks: IndexVec::new(),
212 fn add_live_node(&mut self, lnk: LiveNodeKind) -> LiveNode {
213 let ln = self.lnks.push(lnk);
215 debug!("{:?} is of kind {}", ln, live_node_kind_to_string(lnk, self.tcx));
220 fn add_live_node_for_node(&mut self, hir_id: HirId, lnk: LiveNodeKind) {
221 let ln = self.add_live_node(lnk);
222 self.live_node_map.insert(hir_id, ln);
224 debug!("{:?} is node {:?}", ln, hir_id);
227 fn add_variable(&mut self, vk: VarKind) -> Variable {
228 let v = self.var_kinds.push(vk);
231 Local(LocalInfo { id: node_id, .. }) | Param(node_id, _) | Upvar(node_id, _) => {
232 self.variable_map.insert(node_id, v);
236 debug!("{:?} is {:?}", v, vk);
241 fn variable(&self, hir_id: HirId, span: Span) -> Variable {
242 match self.variable_map.get(&hir_id) {
245 span_bug!(span, "no variable registered for id {:?}", hir_id);
250 fn variable_name(&self, var: Variable) -> Symbol {
251 match self.var_kinds[var] {
252 Local(LocalInfo { name, .. }) | Param(_, name) | Upvar(_, name) => name,
256 fn variable_is_shorthand(&self, var: Variable) -> bool {
257 match self.var_kinds[var] {
258 Local(LocalInfo { is_shorthand, .. }) => is_shorthand,
259 Param(..) | Upvar(..) => false,
263 fn set_captures(&mut self, hir_id: HirId, cs: Vec<CaptureInfo>) {
264 self.capture_info_map.insert(hir_id, Rc::new(cs));
267 fn add_from_pat(&mut self, pat: &hir::Pat<'tcx>) {
268 // For struct patterns, take note of which fields used shorthand
269 // (`x` rather than `x: x`).
270 let mut shorthand_field_ids = HirIdSet::default();
271 let mut pats = VecDeque::new();
273 while let Some(pat) = pats.pop_front() {
274 use rustc_hir::PatKind::*;
276 Binding(.., inner_pat) => {
277 pats.extend(inner_pat.iter());
279 Struct(_, fields, _) => {
280 let ids = fields.iter().filter(|f| f.is_shorthand).map(|f| f.pat.hir_id);
281 shorthand_field_ids.extend(ids);
283 Ref(inner_pat, _) | Box(inner_pat) => {
284 pats.push_back(inner_pat);
286 TupleStruct(_, inner_pats, _) | Tuple(inner_pats, _) | Or(inner_pats) => {
287 pats.extend(inner_pats.iter());
289 Slice(pre_pats, inner_pat, post_pats) => {
290 pats.extend(pre_pats.iter());
291 pats.extend(inner_pat.iter());
292 pats.extend(post_pats.iter());
298 pat.each_binding(|_, hir_id, _, ident| {
299 self.add_live_node_for_node(hir_id, VarDefNode(ident.span));
300 self.add_variable(Local(LocalInfo {
303 is_shorthand: shorthand_field_ids.contains(&hir_id),
309 impl<'tcx> Visitor<'tcx> for IrMaps<'tcx> {
310 type Map = Map<'tcx>;
312 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
313 NestedVisitorMap::OnlyBodies(self.tcx.hir())
316 fn visit_body(&mut self, body: &'tcx hir::Body<'tcx>) {
317 debug!("visit_body {:?}", body.id());
319 // swap in a new set of IR maps for this body
320 let mut maps = IrMaps::new(self.tcx);
321 let hir_id = maps.tcx.hir().body_owner(body.id());
322 let local_def_id = maps.tcx.hir().local_def_id(hir_id);
323 let def_id = local_def_id.to_def_id();
325 // Don't run unused pass for #[derive()]
326 if let Some(parent) = self.tcx.parent(def_id) {
327 if let DefKind::Impl = self.tcx.def_kind(parent.expect_local()) {
328 if self.tcx.has_attr(parent, sym::automatically_derived) {
334 if let Some(captures) = maps.tcx.typeck(local_def_id).closure_captures.get(&def_id) {
335 for &var_hir_id in captures.keys() {
336 let var_name = maps.tcx.hir().name(var_hir_id);
337 maps.add_variable(Upvar(var_hir_id, var_name));
341 // gather up the various local variables, significant expressions,
343 intravisit::walk_body(&mut maps, body);
346 let mut lsets = Liveness::new(&mut maps, local_def_id);
347 let entry_ln = lsets.compute(&body, hir_id);
348 lsets.log_liveness(entry_ln, body.id().hir_id);
350 // check for various error conditions
351 lsets.visit_body(body);
352 lsets.warn_about_unused_upvars(entry_ln);
353 lsets.warn_about_unused_args(body, entry_ln);
356 fn visit_local(&mut self, local: &'tcx hir::Local<'tcx>) {
357 self.add_from_pat(&local.pat);
358 intravisit::walk_local(self, local);
361 fn visit_arm(&mut self, arm: &'tcx hir::Arm<'tcx>) {
362 self.add_from_pat(&arm.pat);
363 if let Some(hir::Guard::IfLet(ref pat, _)) = arm.guard {
364 self.add_from_pat(pat);
366 intravisit::walk_arm(self, arm);
369 fn visit_param(&mut self, param: &'tcx hir::Param<'tcx>) {
370 param.pat.each_binding(|_bm, hir_id, _x, ident| {
371 let var = match param.pat.kind {
372 rustc_hir::PatKind::Struct(_, fields, _) => Local(LocalInfo {
377 .find(|f| f.ident == ident)
378 .map_or(false, |f| f.is_shorthand),
380 _ => Param(hir_id, ident.name),
382 self.add_variable(var);
384 intravisit::walk_param(self, param);
387 fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
389 // live nodes required for uses or definitions of variables:
390 hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => {
391 debug!("expr {}: path that leads to {:?}", expr.hir_id, path.res);
392 if let Res::Local(_var_hir_id) = path.res {
393 self.add_live_node_for_node(expr.hir_id, ExprNode(expr.span));
395 intravisit::walk_expr(self, expr);
397 hir::ExprKind::Closure(..) => {
398 // Interesting control flow (for loops can contain labeled
399 // breaks or continues)
400 self.add_live_node_for_node(expr.hir_id, ExprNode(expr.span));
402 // Make a live_node for each captured variable, with the span
403 // being the location that the variable is used. This results
404 // in better error messages than just pointing at the closure
405 // construction site.
406 let mut call_caps = Vec::new();
407 let closure_def_id = self.tcx.hir().local_def_id(expr.hir_id);
408 if let Some(captures) = self
410 .typeck(closure_def_id)
412 .get(&closure_def_id.to_def_id())
414 // If closure captures is Some, upvars_mentioned must also be Some
415 let upvars = self.tcx.upvars_mentioned(closure_def_id).unwrap();
416 call_caps.extend(captures.keys().map(|var_id| {
417 let upvar = upvars[var_id];
418 let upvar_ln = self.add_live_node(UpvarNode(upvar.span));
419 CaptureInfo { ln: upvar_ln, var_hid: *var_id }
422 self.set_captures(expr.hir_id, call_caps);
423 intravisit::walk_expr(self, expr);
426 // live nodes required for interesting control flow:
427 hir::ExprKind::If(..) | hir::ExprKind::Match(..) | hir::ExprKind::Loop(..) => {
428 self.add_live_node_for_node(expr.hir_id, ExprNode(expr.span));
429 intravisit::walk_expr(self, expr);
431 hir::ExprKind::Binary(op, ..) if op.node.is_lazy() => {
432 self.add_live_node_for_node(expr.hir_id, ExprNode(expr.span));
433 intravisit::walk_expr(self, expr);
436 // otherwise, live nodes are not required:
437 hir::ExprKind::Index(..)
438 | hir::ExprKind::Field(..)
439 | hir::ExprKind::Array(..)
440 | hir::ExprKind::Call(..)
441 | hir::ExprKind::MethodCall(..)
442 | hir::ExprKind::Tup(..)
443 | hir::ExprKind::Binary(..)
444 | hir::ExprKind::AddrOf(..)
445 | hir::ExprKind::Cast(..)
446 | hir::ExprKind::DropTemps(..)
447 | hir::ExprKind::Unary(..)
448 | hir::ExprKind::Break(..)
449 | hir::ExprKind::Continue(_)
450 | hir::ExprKind::Lit(_)
451 | hir::ExprKind::ConstBlock(..)
452 | hir::ExprKind::Ret(..)
453 | hir::ExprKind::Block(..)
454 | hir::ExprKind::Assign(..)
455 | hir::ExprKind::AssignOp(..)
456 | hir::ExprKind::Struct(..)
457 | hir::ExprKind::Repeat(..)
458 | hir::ExprKind::InlineAsm(..)
459 | hir::ExprKind::LlvmInlineAsm(..)
460 | hir::ExprKind::Box(..)
461 | hir::ExprKind::Yield(..)
462 | hir::ExprKind::Type(..)
464 | hir::ExprKind::Path(hir::QPath::TypeRelative(..))
465 | hir::ExprKind::Path(hir::QPath::LangItem(..)) => {
466 intravisit::walk_expr(self, expr);
472 // ______________________________________________________________________
473 // Computing liveness sets
475 // Actually we compute just a bit more than just liveness, but we use
476 // the same basic propagation framework in all cases.
478 const ACC_READ: u32 = 1;
479 const ACC_WRITE: u32 = 2;
480 const ACC_USE: u32 = 4;
482 struct Liveness<'a, 'tcx> {
483 ir: &'a mut IrMaps<'tcx>,
484 body_owner: LocalDefId,
485 typeck_results: &'a ty::TypeckResults<'tcx>,
486 param_env: ty::ParamEnv<'tcx>,
487 upvars: Option<&'tcx FxIndexMap<hir::HirId, hir::Upvar>>,
488 closure_captures: Option<&'tcx FxIndexMap<hir::HirId, ty::UpvarId>>,
489 successors: IndexVec<LiveNode, Option<LiveNode>>,
490 rwu_table: rwu_table::RWUTable,
492 /// A live node representing a point of execution before closure entry &
493 /// after closure exit. Used to calculate liveness of captured variables
494 /// through calls to the same closure. Used for Fn & FnMut closures only.
495 closure_ln: LiveNode,
496 /// A live node representing every 'exit' from the function, whether it be
497 /// by explicit return, panic, or other means.
500 // mappings from loop node ID to LiveNode
501 // ("break" label should map to loop node ID,
502 // it probably doesn't now)
503 break_ln: HirIdMap<LiveNode>,
504 cont_ln: HirIdMap<LiveNode>,
507 impl<'a, 'tcx> Liveness<'a, 'tcx> {
508 fn new(ir: &'a mut IrMaps<'tcx>, body_owner: LocalDefId) -> Liveness<'a, 'tcx> {
509 let typeck_results = ir.tcx.typeck(body_owner);
510 let param_env = ir.tcx.param_env(body_owner);
511 let upvars = ir.tcx.upvars_mentioned(body_owner);
512 let closure_captures = typeck_results.closure_captures.get(&body_owner.to_def_id());
514 let closure_ln = ir.add_live_node(ClosureNode);
515 let exit_ln = ir.add_live_node(ExitNode);
517 let num_live_nodes = ir.lnks.len();
518 let num_vars = ir.var_kinds.len();
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_captures) = self.closure_captures {
711 // Mark upvars captured by reference as used after closure exits.
712 // Since closure_captures is Some, upvars must exists too.
713 let upvars = self.upvars.unwrap();
714 for (&var_hir_id, upvar_id) in closure_captures {
715 let upvar = upvars[&var_hir_id];
716 match self.typeck_results.upvar_capture(*upvar_id) {
717 ty::UpvarCapture::ByRef(_) => {
718 let var = self.variable(var_hir_id, upvar.span);
719 self.acc(self.exit_ln, var, ACC_READ | ACC_USE);
721 ty::UpvarCapture::ByValue(_) => {}
726 let succ = self.propagate_through_expr(&body.value, self.exit_ln);
728 if self.closure_captures.is_none() {
729 // Either not a closure, or closure without any captured variables.
730 // No need to determine liveness of captured variables, since there
735 let ty = self.typeck_results.node_type(hir_id);
737 ty::Closure(_def_id, substs) => match substs.as_closure().kind() {
738 ty::ClosureKind::Fn => {}
739 ty::ClosureKind::FnMut => {}
740 ty::ClosureKind::FnOnce => return succ,
742 ty::Generator(..) => return succ,
746 "{} has upvars so it should have a closure type: {:?}",
753 // Propagate through calls to the closure.
755 self.init_from_succ(self.closure_ln, succ);
756 for param in body.params {
757 param.pat.each_binding(|_bm, hir_id, _x, ident| {
758 let var = self.variable(hir_id, ident.span);
759 self.define(self.closure_ln, var);
763 if !self.merge_from_succ(self.exit_ln, self.closure_ln) {
766 assert_eq!(succ, self.propagate_through_expr(&body.value, self.exit_ln));
772 fn propagate_through_block(&mut self, blk: &hir::Block<'_>, succ: LiveNode) -> LiveNode {
773 if blk.targeted_by_break {
774 self.break_ln.insert(blk.hir_id, succ);
776 let succ = self.propagate_through_opt_expr(blk.expr.as_deref(), succ);
777 blk.stmts.iter().rev().fold(succ, |succ, stmt| self.propagate_through_stmt(stmt, succ))
780 fn propagate_through_stmt(&mut self, stmt: &hir::Stmt<'_>, succ: LiveNode) -> LiveNode {
782 hir::StmtKind::Local(ref local) => {
783 // Note: we mark the variable as defined regardless of whether
784 // there is an initializer. Initially I had thought to only mark
785 // the live variable as defined if it was initialized, and then we
786 // could check for uninit variables just by scanning what is live
787 // at the start of the function. But that doesn't work so well for
788 // immutable variables defined in a loop:
789 // loop { let x; x = 5; }
790 // because the "assignment" loops back around and generates an error.
792 // So now we just check that variables defined w/o an
793 // initializer are not live at the point of their
794 // initialization, which is mildly more complex than checking
795 // once at the func header but otherwise equivalent.
797 let succ = self.propagate_through_opt_expr(local.init.as_deref(), succ);
798 self.define_bindings_in_pat(&local.pat, succ)
800 hir::StmtKind::Item(..) => succ,
801 hir::StmtKind::Expr(ref expr) | hir::StmtKind::Semi(ref expr) => {
802 self.propagate_through_expr(&expr, succ)
807 fn propagate_through_exprs(&mut self, exprs: &[Expr<'_>], succ: LiveNode) -> LiveNode {
808 exprs.iter().rev().fold(succ, |succ, expr| self.propagate_through_expr(&expr, succ))
811 fn propagate_through_opt_expr(
813 opt_expr: Option<&Expr<'_>>,
816 opt_expr.map_or(succ, |expr| self.propagate_through_expr(expr, succ))
819 fn propagate_through_expr(&mut self, expr: &Expr<'_>, succ: LiveNode) -> LiveNode {
820 debug!("propagate_through_expr: {:?}", expr);
823 // Interesting cases with control flow or which gen/kill
824 hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => {
825 self.access_path(expr.hir_id, path, succ, ACC_READ | ACC_USE)
828 hir::ExprKind::Field(ref e, _) => self.propagate_through_expr(&e, succ),
830 hir::ExprKind::Closure(..) => {
831 debug!("{:?} is an ExprKind::Closure", expr);
833 // the construction of a closure itself is not important,
834 // but we have to consider the closed over variables.
840 .unwrap_or_else(|| span_bug!(expr.span, "no registered caps"));
842 caps.iter().rev().fold(succ, |succ, cap| {
843 self.init_from_succ(cap.ln, succ);
844 let var = self.variable(cap.var_hid, expr.span);
845 self.acc(cap.ln, var, ACC_READ | ACC_USE);
850 // Note that labels have been resolved, so we don't need to look
851 // at the label ident
852 hir::ExprKind::Loop(ref blk, ..) => self.propagate_through_loop(expr, &blk, succ),
854 hir::ExprKind::If(ref cond, ref then, ref else_opt) => {
869 self.propagate_through_opt_expr(else_opt.as_ref().map(|e| &**e), succ);
870 let then_ln = self.propagate_through_expr(&then, succ);
871 let ln = self.live_node(expr.hir_id, expr.span);
872 self.init_from_succ(ln, else_ln);
873 self.merge_from_succ(ln, then_ln);
874 self.propagate_through_expr(&cond, ln)
877 hir::ExprKind::Match(ref e, arms, _) => {
892 let ln = self.live_node(expr.hir_id, expr.span);
893 self.init_empty(ln, succ);
895 let body_succ = self.propagate_through_expr(&arm.body, succ);
897 let guard_succ = arm.guard.as_ref().map_or(body_succ, |g| match g {
898 hir::Guard::If(e) => self.propagate_through_expr(e, body_succ),
899 hir::Guard::IfLet(pat, e) => {
900 let let_bind = self.define_bindings_in_pat(pat, body_succ);
901 self.propagate_through_expr(e, let_bind)
904 let arm_succ = self.define_bindings_in_pat(&arm.pat, guard_succ);
905 self.merge_from_succ(ln, arm_succ);
907 self.propagate_through_expr(&e, ln)
910 hir::ExprKind::Ret(ref o_e) => {
911 // Ignore succ and subst exit_ln.
912 self.propagate_through_opt_expr(o_e.as_ref().map(|e| &**e), self.exit_ln)
915 hir::ExprKind::Break(label, ref opt_expr) => {
916 // Find which label this break jumps to
917 let target = match label.target_id {
918 Ok(hir_id) => self.break_ln.get(&hir_id),
919 Err(err) => span_bug!(expr.span, "loop scope error: {}", err),
923 // Now that we know the label we're going to,
924 // look it up in the break loop nodes table
927 Some(b) => self.propagate_through_opt_expr(opt_expr.as_ref().map(|e| &**e), b),
928 None => span_bug!(expr.span, "`break` to unknown label"),
932 hir::ExprKind::Continue(label) => {
933 // Find which label this expr continues to
936 .unwrap_or_else(|err| span_bug!(expr.span, "loop scope error: {}", err));
938 // Now that we know the label we're going to,
939 // look it up in the continue loop nodes table
943 .unwrap_or_else(|| span_bug!(expr.span, "continue to unknown label"))
946 hir::ExprKind::Assign(ref l, ref r, _) => {
947 // see comment on places in
948 // propagate_through_place_components()
949 let succ = self.write_place(&l, succ, ACC_WRITE);
950 let succ = self.propagate_through_place_components(&l, succ);
951 self.propagate_through_expr(&r, succ)
954 hir::ExprKind::AssignOp(_, ref l, ref r) => {
955 // an overloaded assign op is like a method call
956 if self.typeck_results.is_method_call(expr) {
957 let succ = self.propagate_through_expr(&l, succ);
958 self.propagate_through_expr(&r, succ)
960 // see comment on places in
961 // propagate_through_place_components()
962 let succ = self.write_place(&l, succ, ACC_WRITE | ACC_READ);
963 let succ = self.propagate_through_expr(&r, succ);
964 self.propagate_through_place_components(&l, succ)
968 // Uninteresting cases: just propagate in rev exec order
969 hir::ExprKind::Array(ref exprs) => self.propagate_through_exprs(exprs, succ),
971 hir::ExprKind::Struct(_, ref fields, ref with_expr) => {
972 let succ = self.propagate_through_opt_expr(with_expr.as_ref().map(|e| &**e), succ);
976 .fold(succ, |succ, field| self.propagate_through_expr(&field.expr, succ))
979 hir::ExprKind::Call(ref f, ref args) => {
980 let m = self.ir.tcx.parent_module(expr.hir_id).to_def_id();
981 let succ = if self.ir.tcx.is_ty_uninhabited_from(
983 self.typeck_results.expr_ty(expr),
990 let succ = self.propagate_through_exprs(args, succ);
991 self.propagate_through_expr(&f, succ)
994 hir::ExprKind::MethodCall(.., ref args, _) => {
995 let m = self.ir.tcx.parent_module(expr.hir_id).to_def_id();
996 let succ = if self.ir.tcx.is_ty_uninhabited_from(
998 self.typeck_results.expr_ty(expr),
1006 self.propagate_through_exprs(args, succ)
1009 hir::ExprKind::Tup(ref exprs) => self.propagate_through_exprs(exprs, succ),
1011 hir::ExprKind::Binary(op, ref l, ref r) if op.node.is_lazy() => {
1012 let r_succ = self.propagate_through_expr(&r, succ);
1014 let ln = self.live_node(expr.hir_id, expr.span);
1015 self.init_from_succ(ln, succ);
1016 self.merge_from_succ(ln, r_succ);
1018 self.propagate_through_expr(&l, ln)
1021 hir::ExprKind::Index(ref l, ref r) | hir::ExprKind::Binary(_, ref l, ref r) => {
1022 let r_succ = self.propagate_through_expr(&r, succ);
1023 self.propagate_through_expr(&l, r_succ)
1026 hir::ExprKind::Box(ref e)
1027 | hir::ExprKind::AddrOf(_, _, ref e)
1028 | hir::ExprKind::Cast(ref e, _)
1029 | hir::ExprKind::Type(ref e, _)
1030 | hir::ExprKind::DropTemps(ref e)
1031 | hir::ExprKind::Unary(_, ref e)
1032 | hir::ExprKind::Yield(ref e, _)
1033 | hir::ExprKind::Repeat(ref e, _) => self.propagate_through_expr(&e, succ),
1035 hir::ExprKind::InlineAsm(ref asm) => {
1036 // Handle non-returning asm
1037 let mut succ = if asm.options.contains(InlineAsmOptions::NORETURN) {
1043 // Do a first pass for writing outputs only
1044 for (op, _op_sp) in asm.operands.iter().rev() {
1046 hir::InlineAsmOperand::In { .. }
1047 | hir::InlineAsmOperand::Const { .. }
1048 | hir::InlineAsmOperand::Sym { .. } => {}
1049 hir::InlineAsmOperand::Out { expr, .. } => {
1050 if let Some(expr) = expr {
1051 succ = self.write_place(expr, succ, ACC_WRITE);
1054 hir::InlineAsmOperand::InOut { expr, .. } => {
1055 succ = self.write_place(expr, succ, ACC_READ | ACC_WRITE | ACC_USE);
1057 hir::InlineAsmOperand::SplitInOut { out_expr, .. } => {
1058 if let Some(expr) = out_expr {
1059 succ = self.write_place(expr, succ, ACC_WRITE);
1065 // Then do a second pass for inputs
1066 let mut succ = succ;
1067 for (op, _op_sp) in asm.operands.iter().rev() {
1069 hir::InlineAsmOperand::In { expr, .. }
1070 | hir::InlineAsmOperand::Const { expr, .. }
1071 | hir::InlineAsmOperand::Sym { expr, .. } => {
1072 succ = self.propagate_through_expr(expr, succ)
1074 hir::InlineAsmOperand::Out { expr, .. } => {
1075 if let Some(expr) = expr {
1076 succ = self.propagate_through_place_components(expr, succ);
1079 hir::InlineAsmOperand::InOut { expr, .. } => {
1080 succ = self.propagate_through_place_components(expr, succ);
1082 hir::InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
1083 if let Some(expr) = out_expr {
1084 succ = self.propagate_through_place_components(expr, succ);
1086 succ = self.propagate_through_expr(in_expr, succ);
1093 hir::ExprKind::LlvmInlineAsm(ref asm) => {
1094 let ia = &asm.inner;
1095 let outputs = asm.outputs_exprs;
1096 let inputs = asm.inputs_exprs;
1097 let succ = ia.outputs.iter().zip(outputs).rev().fold(succ, |succ, (o, output)| {
1098 // see comment on places
1099 // in propagate_through_place_components()
1101 self.propagate_through_expr(output, succ)
1103 let acc = if o.is_rw { ACC_WRITE | ACC_READ } else { ACC_WRITE };
1104 let succ = self.write_place(output, succ, acc);
1105 self.propagate_through_place_components(output, succ)
1109 // Inputs are executed first. Propagate last because of rev order
1110 self.propagate_through_exprs(inputs, succ)
1113 hir::ExprKind::Lit(..)
1114 | hir::ExprKind::ConstBlock(..)
1115 | hir::ExprKind::Err
1116 | hir::ExprKind::Path(hir::QPath::TypeRelative(..))
1117 | hir::ExprKind::Path(hir::QPath::LangItem(..)) => succ,
1119 // Note that labels have been resolved, so we don't need to look
1120 // at the label ident
1121 hir::ExprKind::Block(ref blk, _) => self.propagate_through_block(&blk, succ),
1125 fn propagate_through_place_components(&mut self, expr: &Expr<'_>, succ: LiveNode) -> LiveNode {
1128 // In general, the full flow graph structure for an
1129 // assignment/move/etc can be handled in one of two ways,
1130 // depending on whether what is being assigned is a "tracked
1131 // value" or not. A tracked value is basically a local
1132 // variable or argument.
1134 // The two kinds of graphs are:
1136 // Tracked place Untracked place
1137 // ----------------------++-----------------------
1141 // (rvalue) || (rvalue)
1144 // (write of place) || (place components)
1149 // ----------------------++-----------------------
1151 // I will cover the two cases in turn:
1155 // A tracked place is a local variable/argument `x`. In
1156 // these cases, the link_node where the write occurs is linked
1157 // to node id of `x`. The `write_place()` routine generates
1158 // the contents of this node. There are no subcomponents to
1161 // # Non-tracked places
1163 // These are places like `x[5]` or `x.f`. In that case, we
1164 // basically ignore the value which is written to but generate
1165 // reads for the components---`x` in these two examples. The
1166 // components reads are generated by
1167 // `propagate_through_place_components()` (this fn).
1171 // It is still possible to observe assignments to non-places;
1172 // these errors are detected in the later pass borrowck. We
1173 // just ignore such cases and treat them as reads.
1176 hir::ExprKind::Path(_) => succ,
1177 hir::ExprKind::Field(ref e, _) => self.propagate_through_expr(&e, succ),
1178 _ => self.propagate_through_expr(expr, succ),
1182 // see comment on propagate_through_place()
1183 fn write_place(&mut self, expr: &Expr<'_>, succ: LiveNode, acc: u32) -> LiveNode {
1185 hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => {
1186 self.access_path(expr.hir_id, path, succ, acc)
1189 // We do not track other places, so just propagate through
1190 // to their subcomponents. Also, it may happen that
1191 // non-places occur here, because those are detected in the
1192 // later pass borrowck.
1205 let ln = self.live_node(hir_id, span);
1207 self.init_from_succ(ln, succ);
1208 let var = self.variable(var_hid, span);
1209 self.acc(ln, var, acc);
1217 path: &hir::Path<'_>,
1222 Res::Local(hid) => {
1223 let in_upvars = self.upvars.map_or(false, |u| u.contains_key(&hid));
1224 let in_captures = self.closure_captures.map_or(false, |c| c.contains_key(&hid));
1226 match (in_upvars, in_captures) {
1227 (false, _) | (true, true) => self.access_var(hir_id, hid, succ, acc, path.span),
1229 // This case is possible when with RFC-2229, a wild pattern
1230 // is used within a closure.
1231 // eg: `let _ = x`. The closure doesn't capture x here,
1232 // even though it's mentioned in the closure.
1241 fn propagate_through_loop(
1244 body: &hir::Block<'_>,
1248 We model control flow like this:
1255 Note that a `continue` expression targeting the `loop` will have a successor of `expr`.
1256 Meanwhile, a `break` expression will have a successor of `succ`.
1260 let ln = self.live_node(expr.hir_id, expr.span);
1261 self.init_empty(ln, succ);
1262 debug!("propagate_through_loop: using id for loop body {} {:?}", expr.hir_id, body);
1264 self.break_ln.insert(expr.hir_id, succ);
1266 self.cont_ln.insert(expr.hir_id, ln);
1268 let body_ln = self.propagate_through_block(body, ln);
1270 // repeat until fixed point is reached:
1271 while self.merge_from_succ(ln, body_ln) {
1272 assert_eq!(body_ln, self.propagate_through_block(body, ln));
1279 // _______________________________________________________________________
1280 // Checking for error conditions
1282 impl<'a, 'tcx> Visitor<'tcx> for Liveness<'a, 'tcx> {
1283 type Map = intravisit::ErasedMap<'tcx>;
1285 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
1286 NestedVisitorMap::None
1289 fn visit_local(&mut self, local: &'tcx hir::Local<'tcx>) {
1290 self.check_unused_vars_in_pat(&local.pat, None, |spans, hir_id, ln, var| {
1291 if local.init.is_some() {
1292 self.warn_about_dead_assign(spans, hir_id, ln, var);
1296 intravisit::walk_local(self, local);
1299 fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) {
1300 check_expr(self, ex);
1303 fn visit_arm(&mut self, arm: &'tcx hir::Arm<'tcx>) {
1304 self.check_unused_vars_in_pat(&arm.pat, None, |_, _, _, _| {});
1305 intravisit::walk_arm(self, arm);
1309 fn check_expr<'tcx>(this: &mut Liveness<'_, 'tcx>, expr: &'tcx Expr<'tcx>) {
1311 hir::ExprKind::Assign(ref l, ..) => {
1312 this.check_place(&l);
1315 hir::ExprKind::AssignOp(_, ref l, _) => {
1316 if !this.typeck_results.is_method_call(expr) {
1317 this.check_place(&l);
1321 hir::ExprKind::InlineAsm(ref asm) => {
1322 for (op, _op_sp) in asm.operands {
1324 hir::InlineAsmOperand::Out { expr, .. } => {
1325 if let Some(expr) = expr {
1326 this.check_place(expr);
1329 hir::InlineAsmOperand::InOut { expr, .. } => {
1330 this.check_place(expr);
1332 hir::InlineAsmOperand::SplitInOut { out_expr, .. } => {
1333 if let Some(out_expr) = out_expr {
1334 this.check_place(out_expr);
1342 hir::ExprKind::LlvmInlineAsm(ref asm) => {
1343 for input in asm.inputs_exprs {
1344 this.visit_expr(input);
1347 // Output operands must be places
1348 for (o, output) in asm.inner.outputs.iter().zip(asm.outputs_exprs) {
1350 this.check_place(output);
1352 this.visit_expr(output);
1356 // no correctness conditions related to liveness
1357 hir::ExprKind::Call(..)
1358 | hir::ExprKind::MethodCall(..)
1359 | hir::ExprKind::Match(..)
1360 | hir::ExprKind::Loop(..)
1361 | hir::ExprKind::Index(..)
1362 | hir::ExprKind::Field(..)
1363 | hir::ExprKind::Array(..)
1364 | hir::ExprKind::Tup(..)
1365 | hir::ExprKind::Binary(..)
1366 | hir::ExprKind::Cast(..)
1367 | hir::ExprKind::If(..)
1368 | hir::ExprKind::DropTemps(..)
1369 | hir::ExprKind::Unary(..)
1370 | hir::ExprKind::Ret(..)
1371 | hir::ExprKind::Break(..)
1372 | hir::ExprKind::Continue(..)
1373 | hir::ExprKind::Lit(_)
1374 | hir::ExprKind::ConstBlock(..)
1375 | hir::ExprKind::Block(..)
1376 | hir::ExprKind::AddrOf(..)
1377 | hir::ExprKind::Struct(..)
1378 | hir::ExprKind::Repeat(..)
1379 | hir::ExprKind::Closure(..)
1380 | hir::ExprKind::Path(_)
1381 | hir::ExprKind::Yield(..)
1382 | hir::ExprKind::Box(..)
1383 | hir::ExprKind::Type(..)
1384 | hir::ExprKind::Err => {}
1387 intravisit::walk_expr(this, expr);
1390 impl<'tcx> Liveness<'_, 'tcx> {
1391 fn check_place(&mut self, expr: &'tcx Expr<'tcx>) {
1393 hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => {
1394 if let Res::Local(var_hid) = path.res {
1395 // Assignment to an immutable variable or argument: only legal
1396 // if there is no later assignment. If this local is actually
1397 // mutable, then check for a reassignment to flag the mutability
1399 let ln = self.live_node(expr.hir_id, expr.span);
1400 let var = self.variable(var_hid, expr.span);
1401 self.warn_about_dead_assign(vec![expr.span], expr.hir_id, ln, var);
1405 // For other kinds of places, no checks are required,
1406 // and any embedded expressions are actually rvalues
1407 intravisit::walk_expr(self, expr);
1412 fn should_warn(&self, var: Variable) -> Option<String> {
1413 let name = self.ir.variable_name(var);
1414 if name == kw::Empty {
1417 let name: &str = &name.as_str();
1418 if name.as_bytes()[0] == b'_' {
1421 Some(name.to_owned())
1424 fn warn_about_unused_upvars(&self, entry_ln: LiveNode) {
1425 let closure_captures = match self.closure_captures {
1427 Some(closure_captures) => closure_captures,
1430 // If closure_captures is Some(), upvars must be Some() too.
1431 let upvars = self.upvars.unwrap();
1432 for &var_hir_id in closure_captures.keys() {
1433 let upvar = upvars[&var_hir_id];
1434 let var = self.variable(var_hir_id, upvar.span);
1435 let upvar_id = ty::UpvarId {
1436 var_path: ty::UpvarPath { hir_id: var_hir_id },
1437 closure_expr_id: self.body_owner,
1439 match self.typeck_results.upvar_capture(upvar_id) {
1440 ty::UpvarCapture::ByValue(_) => {}
1441 ty::UpvarCapture::ByRef(..) => continue,
1443 if self.used_on_entry(entry_ln, var) {
1444 if !self.live_on_entry(entry_ln, var) {
1445 if let Some(name) = self.should_warn(var) {
1446 self.ir.tcx.struct_span_lint_hir(
1447 lint::builtin::UNUSED_ASSIGNMENTS,
1451 lint.build(&format!("value captured by `{}` is never read", name))
1452 .help("did you mean to capture by reference instead?")
1459 if let Some(name) = self.should_warn(var) {
1460 self.ir.tcx.struct_span_lint_hir(
1461 lint::builtin::UNUSED_VARIABLES,
1465 lint.build(&format!("unused variable: `{}`", name))
1466 .help("did you mean to capture by reference instead?")
1475 fn warn_about_unused_args(&self, body: &hir::Body<'_>, entry_ln: LiveNode) {
1476 for p in body.params {
1477 self.check_unused_vars_in_pat(&p.pat, Some(entry_ln), |spans, hir_id, ln, var| {
1478 if !self.live_on_entry(ln, var) {
1479 self.report_unsed_assign(hir_id, spans, var, |name| {
1480 format!("value passed to `{}` is never read", name)
1487 fn check_unused_vars_in_pat(
1490 entry_ln: Option<LiveNode>,
1491 on_used_on_entry: impl Fn(Vec<Span>, HirId, LiveNode, Variable),
1493 // In an or-pattern, only consider the variable; any later patterns must have the same
1494 // bindings, and we also consider the first pattern to be the "authoritative" set of ids.
1495 // However, we should take the ids and spans of variables with the same name from the later
1496 // patterns so the suggestions to prefix with underscores will apply to those too.
1497 let mut vars: FxIndexMap<Symbol, (LiveNode, Variable, Vec<(HirId, Span, Span)>)> =
1500 pat.each_binding(|_, hir_id, pat_sp, ident| {
1501 let ln = entry_ln.unwrap_or_else(|| self.live_node(hir_id, pat_sp));
1502 let var = self.variable(hir_id, ident.span);
1503 let id_and_sp = (hir_id, pat_sp, ident.span);
1504 vars.entry(self.ir.variable_name(var))
1505 .and_modify(|(.., hir_ids_and_spans)| hir_ids_and_spans.push(id_and_sp))
1506 .or_insert_with(|| (ln, var, vec![id_and_sp]));
1509 for (_, (ln, var, hir_ids_and_spans)) in vars {
1510 if self.used_on_entry(ln, var) {
1511 let id = hir_ids_and_spans[0].0;
1513 hir_ids_and_spans.into_iter().map(|(_, _, ident_span)| ident_span).collect();
1514 on_used_on_entry(spans, id, ln, var);
1516 self.report_unused(hir_ids_and_spans, ln, var);
1523 hir_ids_and_spans: Vec<(HirId, Span, Span)>,
1527 let first_hir_id = hir_ids_and_spans[0].0;
1529 if let Some(name) = self.should_warn(var).filter(|name| name != "self") {
1530 // annoying: for parameters in funcs like `fn(x: i32)
1531 // {ret}`, there is only one node, so asking about
1532 // assigned_on_exit() is not meaningful.
1534 if ln == self.exit_ln { false } else { self.assigned_on_exit(ln, var) };
1537 self.ir.tcx.struct_span_lint_hir(
1538 lint::builtin::UNUSED_VARIABLES,
1542 .map(|(_, _, ident_span)| ident_span)
1543 .collect::<Vec<_>>(),
1545 lint.build(&format!("variable `{}` is assigned to, but never used", name))
1546 .note(&format!("consider using `_{}` instead", name))
1551 let (shorthands, non_shorthands): (Vec<_>, Vec<_>) =
1552 hir_ids_and_spans.iter().copied().partition(|(hir_id, _, ident_span)| {
1553 let var = self.variable(*hir_id, *ident_span);
1554 self.ir.variable_is_shorthand(var)
1557 // If we have both shorthand and non-shorthand, prefer the "try ignoring
1558 // the field" message, and suggest `_` for the non-shorthands. If we only
1559 // have non-shorthand, then prefix with an underscore instead.
1560 if !shorthands.is_empty() {
1561 let shorthands = shorthands
1563 .map(|(_, pat_span, _)| (pat_span, format!("{}: _", name)))
1567 .map(|(_, pat_span, _)| (pat_span, "_".to_string())),
1569 .collect::<Vec<_>>();
1571 self.ir.tcx.struct_span_lint_hir(
1572 lint::builtin::UNUSED_VARIABLES,
1576 .map(|(_, pat_span, _)| *pat_span)
1577 .collect::<Vec<_>>(),
1579 let mut err = lint.build(&format!("unused variable: `{}`", name));
1580 err.multipart_suggestion(
1581 "try ignoring the field",
1583 Applicability::MachineApplicable,
1589 let non_shorthands = non_shorthands
1591 .map(|(_, _, ident_span)| (ident_span, format!("_{}", name)))
1592 .collect::<Vec<_>>();
1594 self.ir.tcx.struct_span_lint_hir(
1595 lint::builtin::UNUSED_VARIABLES,
1599 .map(|(_, _, ident_span)| *ident_span)
1600 .collect::<Vec<_>>(),
1602 let mut err = lint.build(&format!("unused variable: `{}`", name));
1603 err.multipart_suggestion(
1604 "if this is intentional, prefix it with an underscore",
1606 Applicability::MachineApplicable,
1616 fn warn_about_dead_assign(&self, spans: Vec<Span>, hir_id: HirId, ln: LiveNode, var: Variable) {
1617 if !self.live_on_exit(ln, var) {
1618 self.report_unsed_assign(hir_id, spans, var, |name| {
1619 format!("value assigned to `{}` is never read", name)
1624 fn report_unsed_assign(
1629 message: impl Fn(&str) -> String,
1631 if let Some(name) = self.should_warn(var) {
1632 self.ir.tcx.struct_span_lint_hir(
1633 lint::builtin::UNUSED_ASSIGNMENTS,
1637 lint.build(&message(&name))
1638 .help("maybe it is overwritten before being read?")