diff options
Diffstat (limited to '')
-rw-r--r-- | compiler/rustc_passes/src/liveness.rs | 1687 |
1 files changed, 1687 insertions, 0 deletions
diff --git a/compiler/rustc_passes/src/liveness.rs b/compiler/rustc_passes/src/liveness.rs new file mode 100644 index 000000000..461dd52b9 --- /dev/null +++ b/compiler/rustc_passes/src/liveness.rs @@ -0,0 +1,1687 @@ +//! A classic liveness analysis based on dataflow over the AST. Computes, +//! for each local variable in a function, whether that variable is live +//! at a given point. Program execution points are identified by their +//! IDs. +//! +//! # Basic idea +//! +//! The basic model is that each local variable is assigned an index. We +//! represent sets of local variables using a vector indexed by this +//! index. The value in the vector is either 0, indicating the variable +//! is dead, or the ID of an expression that uses the variable. +//! +//! We conceptually walk over the AST in reverse execution order. If we +//! find a use of a variable, we add it to the set of live variables. If +//! we find an assignment to a variable, we remove it from the set of live +//! variables. When we have to merge two flows, we take the union of +//! those two flows -- if the variable is live on both paths, we simply +//! pick one ID. In the event of loops, we continue doing this until a +//! fixed point is reached. +//! +//! ## Checking initialization +//! +//! At the function entry point, all variables must be dead. If this is +//! not the case, we can report an error using the ID found in the set of +//! live variables, which identifies a use of the variable which is not +//! dominated by an assignment. +//! +//! ## Checking moves +//! +//! After each explicit move, the variable must be dead. +//! +//! ## Computing last uses +//! +//! Any use of the variable where the variable is dead afterwards is a +//! last use. +//! +//! # Implementation details +//! +//! The actual implementation contains two (nested) walks over the AST. +//! The outer walk has the job of building up the ir_maps instance for the +//! enclosing function. On the way down the tree, it identifies those AST +//! nodes and variable IDs that will be needed for the liveness analysis +//! and assigns them contiguous IDs. The liveness ID for an AST node is +//! called a `live_node` (it's a newtype'd `u32`) and the ID for a variable +//! is called a `variable` (another newtype'd `u32`). +//! +//! On the way back up the tree, as we are about to exit from a function +//! declaration we allocate a `liveness` instance. Now that we know +//! precisely how many nodes and variables we need, we can allocate all +//! the various arrays that we will need to precisely the right size. We then +//! perform the actual propagation on the `liveness` instance. +//! +//! This propagation is encoded in the various `propagate_through_*()` +//! methods. It effectively does a reverse walk of the AST; whenever we +//! reach a loop node, we iterate until a fixed point is reached. +//! +//! ## The `RWU` struct +//! +//! At each live node `N`, we track three pieces of information for each +//! variable `V` (these are encapsulated in the `RWU` struct): +//! +//! - `reader`: the `LiveNode` ID of some node which will read the value +//! that `V` holds on entry to `N`. Formally: a node `M` such +//! that there exists a path `P` from `N` to `M` where `P` does not +//! write `V`. If the `reader` is `None`, then the current +//! value will never be read (the variable is dead, essentially). +//! +//! - `writer`: the `LiveNode` ID of some node which will write the +//! variable `V` and which is reachable from `N`. Formally: a node `M` +//! such that there exists a path `P` from `N` to `M` and `M` writes +//! `V`. If the `writer` is `None`, then there is no writer +//! of `V` that follows `N`. +//! +//! - `used`: a boolean value indicating whether `V` is *used*. We +//! distinguish a *read* from a *use* in that a *use* is some read that +//! is not just used to generate a new value. For example, `x += 1` is +//! a read but not a use. This is used to generate better warnings. +//! +//! ## Special nodes and variables +//! +//! We generate various special nodes for various, well, special purposes. +//! These are described in the `Liveness` struct. + +use self::LiveNodeKind::*; +use self::VarKind::*; + +use rustc_ast::InlineAsmOptions; +use rustc_data_structures::fx::FxIndexMap; +use rustc_errors::Applicability; +use rustc_hir as hir; +use rustc_hir::def::*; +use rustc_hir::def_id::LocalDefId; +use rustc_hir::intravisit::{self, Visitor}; +use rustc_hir::{Expr, HirId, HirIdMap, HirIdSet}; +use rustc_index::vec::IndexVec; +use rustc_middle::hir::nested_filter; +use rustc_middle::ty::query::Providers; +use rustc_middle::ty::{self, DefIdTree, RootVariableMinCaptureList, Ty, TyCtxt}; +use rustc_session::lint; +use rustc_span::symbol::{kw, sym, Symbol}; +use rustc_span::Span; + +use std::collections::VecDeque; +use std::io; +use std::io::prelude::*; +use std::rc::Rc; + +mod rwu_table; + +rustc_index::newtype_index! { + pub struct Variable { + DEBUG_FORMAT = "v({})", + } +} + +rustc_index::newtype_index! { + pub struct LiveNode { + DEBUG_FORMAT = "ln({})", + } +} + +#[derive(Copy, Clone, PartialEq, Debug)] +enum LiveNodeKind { + UpvarNode(Span), + ExprNode(Span, HirId), + VarDefNode(Span, HirId), + ClosureNode, + ExitNode, +} + +fn live_node_kind_to_string(lnk: LiveNodeKind, tcx: TyCtxt<'_>) -> String { + let sm = tcx.sess.source_map(); + match lnk { + UpvarNode(s) => format!("Upvar node [{}]", sm.span_to_diagnostic_string(s)), + ExprNode(s, _) => format!("Expr node [{}]", sm.span_to_diagnostic_string(s)), + VarDefNode(s, _) => format!("Var def node [{}]", sm.span_to_diagnostic_string(s)), + ClosureNode => "Closure node".to_owned(), + ExitNode => "Exit node".to_owned(), + } +} + +fn check_mod_liveness(tcx: TyCtxt<'_>, module_def_id: LocalDefId) { + tcx.hir().visit_item_likes_in_module(module_def_id, &mut IrMaps::new(tcx)); +} + +pub fn provide(providers: &mut Providers) { + *providers = Providers { check_mod_liveness, ..*providers }; +} + +// ______________________________________________________________________ +// Creating ir_maps +// +// This is the first pass and the one that drives the main +// computation. It walks up and down the IR once. On the way down, +// we count for each function the number of variables as well as +// liveness nodes. A liveness node is basically an expression or +// capture clause that does something of interest: either it has +// interesting control flow or it uses/defines a local variable. +// +// On the way back up, at each function node we create liveness sets +// (we now know precisely how big to make our various vectors and so +// forth) and then do the data-flow propagation to compute the set +// of live variables at each program point. +// +// Finally, we run back over the IR one last time and, using the +// computed liveness, check various safety conditions. For example, +// there must be no live nodes at the definition site for a variable +// unless it has an initializer. Similarly, each non-mutable local +// variable must not be assigned if there is some successor +// assignment. And so forth. + +struct CaptureInfo { + ln: LiveNode, + var_hid: HirId, +} + +#[derive(Copy, Clone, Debug)] +struct LocalInfo { + id: HirId, + name: Symbol, + is_shorthand: bool, +} + +#[derive(Copy, Clone, Debug)] +enum VarKind { + Param(HirId, Symbol), + Local(LocalInfo), + Upvar(HirId, Symbol), +} + +struct IrMaps<'tcx> { + tcx: TyCtxt<'tcx>, + live_node_map: HirIdMap<LiveNode>, + variable_map: HirIdMap<Variable>, + capture_info_map: HirIdMap<Rc<Vec<CaptureInfo>>>, + var_kinds: IndexVec<Variable, VarKind>, + lnks: IndexVec<LiveNode, LiveNodeKind>, +} + +impl<'tcx> IrMaps<'tcx> { + fn new(tcx: TyCtxt<'tcx>) -> IrMaps<'tcx> { + IrMaps { + tcx, + live_node_map: HirIdMap::default(), + variable_map: HirIdMap::default(), + capture_info_map: Default::default(), + var_kinds: IndexVec::new(), + lnks: IndexVec::new(), + } + } + + fn add_live_node(&mut self, lnk: LiveNodeKind) -> LiveNode { + let ln = self.lnks.push(lnk); + + debug!("{:?} is of kind {}", ln, live_node_kind_to_string(lnk, self.tcx)); + + ln + } + + fn add_live_node_for_node(&mut self, hir_id: HirId, lnk: LiveNodeKind) { + let ln = self.add_live_node(lnk); + self.live_node_map.insert(hir_id, ln); + + debug!("{:?} is node {:?}", ln, hir_id); + } + + fn add_variable(&mut self, vk: VarKind) -> Variable { + let v = self.var_kinds.push(vk); + + match vk { + Local(LocalInfo { id: node_id, .. }) | Param(node_id, _) | Upvar(node_id, _) => { + self.variable_map.insert(node_id, v); + } + } + + debug!("{:?} is {:?}", v, vk); + + v + } + + fn variable(&self, hir_id: HirId, span: Span) -> Variable { + match self.variable_map.get(&hir_id) { + Some(&var) => var, + None => { + span_bug!(span, "no variable registered for id {:?}", hir_id); + } + } + } + + fn variable_name(&self, var: Variable) -> Symbol { + match self.var_kinds[var] { + Local(LocalInfo { name, .. }) | Param(_, name) | Upvar(_, name) => name, + } + } + + fn variable_is_shorthand(&self, var: Variable) -> bool { + match self.var_kinds[var] { + Local(LocalInfo { is_shorthand, .. }) => is_shorthand, + Param(..) | Upvar(..) => false, + } + } + + fn set_captures(&mut self, hir_id: HirId, cs: Vec<CaptureInfo>) { + self.capture_info_map.insert(hir_id, Rc::new(cs)); + } + + fn collect_shorthand_field_ids(&self, pat: &hir::Pat<'tcx>) -> HirIdSet { + // For struct patterns, take note of which fields used shorthand + // (`x` rather than `x: x`). + let mut shorthand_field_ids = HirIdSet::default(); + let mut pats = VecDeque::new(); + pats.push_back(pat); + + while let Some(pat) = pats.pop_front() { + use rustc_hir::PatKind::*; + match &pat.kind { + Binding(.., inner_pat) => { + pats.extend(inner_pat.iter()); + } + Struct(_, fields, _) => { + let (short, not_short): (Vec<_>, _) = + fields.iter().partition(|f| f.is_shorthand); + shorthand_field_ids.extend(short.iter().map(|f| f.pat.hir_id)); + pats.extend(not_short.iter().map(|f| f.pat)); + } + Ref(inner_pat, _) | Box(inner_pat) => { + pats.push_back(inner_pat); + } + TupleStruct(_, inner_pats, _) | Tuple(inner_pats, _) | Or(inner_pats) => { + pats.extend(inner_pats.iter()); + } + Slice(pre_pats, inner_pat, post_pats) => { + pats.extend(pre_pats.iter()); + pats.extend(inner_pat.iter()); + pats.extend(post_pats.iter()); + } + _ => {} + } + } + + shorthand_field_ids + } + + fn add_from_pat(&mut self, pat: &hir::Pat<'tcx>) { + let shorthand_field_ids = self.collect_shorthand_field_ids(pat); + + pat.each_binding(|_, hir_id, _, ident| { + self.add_live_node_for_node(hir_id, VarDefNode(ident.span, hir_id)); + self.add_variable(Local(LocalInfo { + id: hir_id, + name: ident.name, + is_shorthand: shorthand_field_ids.contains(&hir_id), + })); + }); + } +} + +impl<'tcx> Visitor<'tcx> for IrMaps<'tcx> { + type NestedFilter = nested_filter::OnlyBodies; + + fn nested_visit_map(&mut self) -> Self::Map { + self.tcx.hir() + } + + fn visit_body(&mut self, body: &'tcx hir::Body<'tcx>) { + debug!("visit_body {:?}", body.id()); + + // swap in a new set of IR maps for this body + let mut maps = IrMaps::new(self.tcx); + let hir_id = maps.tcx.hir().body_owner(body.id()); + let local_def_id = maps.tcx.hir().local_def_id(hir_id); + let def_id = local_def_id.to_def_id(); + + // Don't run unused pass for #[derive()] + let parent = self.tcx.local_parent(local_def_id); + if let DefKind::Impl = self.tcx.def_kind(parent) + && self.tcx.has_attr(parent.to_def_id(), sym::automatically_derived) + { + return; + } + + // Don't run unused pass for #[naked] + if self.tcx.has_attr(def_id, sym::naked) { + return; + } + + if let Some(upvars) = maps.tcx.upvars_mentioned(def_id) { + for &var_hir_id in upvars.keys() { + let var_name = maps.tcx.hir().name(var_hir_id); + maps.add_variable(Upvar(var_hir_id, var_name)); + } + } + + // gather up the various local variables, significant expressions, + // and so forth: + intravisit::walk_body(&mut maps, body); + + // compute liveness + let mut lsets = Liveness::new(&mut maps, local_def_id); + let entry_ln = lsets.compute(&body, hir_id); + lsets.log_liveness(entry_ln, body.id().hir_id); + + // check for various error conditions + lsets.visit_body(body); + lsets.warn_about_unused_upvars(entry_ln); + lsets.warn_about_unused_args(body, entry_ln); + } + + fn visit_local(&mut self, local: &'tcx hir::Local<'tcx>) { + self.add_from_pat(&local.pat); + if local.els.is_some() { + self.add_live_node_for_node(local.hir_id, ExprNode(local.span, local.hir_id)); + } + intravisit::walk_local(self, local); + } + + fn visit_arm(&mut self, arm: &'tcx hir::Arm<'tcx>) { + self.add_from_pat(&arm.pat); + if let Some(hir::Guard::IfLet(ref let_expr)) = arm.guard { + self.add_from_pat(let_expr.pat); + } + intravisit::walk_arm(self, arm); + } + + fn visit_param(&mut self, param: &'tcx hir::Param<'tcx>) { + let shorthand_field_ids = self.collect_shorthand_field_ids(param.pat); + param.pat.each_binding(|_bm, hir_id, _x, ident| { + let var = match param.pat.kind { + rustc_hir::PatKind::Struct(..) => Local(LocalInfo { + id: hir_id, + name: ident.name, + is_shorthand: shorthand_field_ids.contains(&hir_id), + }), + _ => Param(hir_id, ident.name), + }; + self.add_variable(var); + }); + intravisit::walk_param(self, param); + } + + fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) { + match expr.kind { + // live nodes required for uses or definitions of variables: + hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => { + debug!("expr {}: path that leads to {:?}", expr.hir_id, path.res); + if let Res::Local(_var_hir_id) = path.res { + self.add_live_node_for_node(expr.hir_id, ExprNode(expr.span, expr.hir_id)); + } + intravisit::walk_expr(self, expr); + } + hir::ExprKind::Closure { .. } => { + // Interesting control flow (for loops can contain labeled + // breaks or continues) + self.add_live_node_for_node(expr.hir_id, ExprNode(expr.span, expr.hir_id)); + + // Make a live_node for each mentioned variable, with the span + // being the location that the variable is used. This results + // in better error messages than just pointing at the closure + // construction site. + let mut call_caps = Vec::new(); + let closure_def_id = self.tcx.hir().local_def_id(expr.hir_id); + if let Some(upvars) = self.tcx.upvars_mentioned(closure_def_id) { + call_caps.extend(upvars.keys().map(|var_id| { + let upvar = upvars[var_id]; + let upvar_ln = self.add_live_node(UpvarNode(upvar.span)); + CaptureInfo { ln: upvar_ln, var_hid: *var_id } + })); + } + self.set_captures(expr.hir_id, call_caps); + intravisit::walk_expr(self, expr); + } + + hir::ExprKind::Let(let_expr) => { + self.add_from_pat(let_expr.pat); + intravisit::walk_expr(self, expr); + } + + // live nodes required for interesting control flow: + hir::ExprKind::If(..) + | hir::ExprKind::Match(..) + | hir::ExprKind::Loop(..) + | hir::ExprKind::Yield(..) => { + self.add_live_node_for_node(expr.hir_id, ExprNode(expr.span, expr.hir_id)); + intravisit::walk_expr(self, expr); + } + hir::ExprKind::Binary(op, ..) if op.node.is_lazy() => { + self.add_live_node_for_node(expr.hir_id, ExprNode(expr.span, expr.hir_id)); + intravisit::walk_expr(self, expr); + } + + // otherwise, live nodes are not required: + hir::ExprKind::Index(..) + | hir::ExprKind::Field(..) + | hir::ExprKind::Array(..) + | hir::ExprKind::Call(..) + | hir::ExprKind::MethodCall(..) + | hir::ExprKind::Tup(..) + | hir::ExprKind::Binary(..) + | hir::ExprKind::AddrOf(..) + | hir::ExprKind::Cast(..) + | hir::ExprKind::DropTemps(..) + | hir::ExprKind::Unary(..) + | hir::ExprKind::Break(..) + | hir::ExprKind::Continue(_) + | hir::ExprKind::Lit(_) + | hir::ExprKind::ConstBlock(..) + | hir::ExprKind::Ret(..) + | hir::ExprKind::Block(..) + | hir::ExprKind::Assign(..) + | hir::ExprKind::AssignOp(..) + | hir::ExprKind::Struct(..) + | hir::ExprKind::Repeat(..) + | hir::ExprKind::InlineAsm(..) + | hir::ExprKind::Box(..) + | hir::ExprKind::Type(..) + | hir::ExprKind::Err + | hir::ExprKind::Path(hir::QPath::TypeRelative(..)) + | hir::ExprKind::Path(hir::QPath::LangItem(..)) => { + intravisit::walk_expr(self, expr); + } + } + } +} + +// ______________________________________________________________________ +// Computing liveness sets +// +// Actually we compute just a bit more than just liveness, but we use +// the same basic propagation framework in all cases. + +const ACC_READ: u32 = 1; +const ACC_WRITE: u32 = 2; +const ACC_USE: u32 = 4; + +struct Liveness<'a, 'tcx> { + ir: &'a mut IrMaps<'tcx>, + typeck_results: &'a ty::TypeckResults<'tcx>, + param_env: ty::ParamEnv<'tcx>, + closure_min_captures: Option<&'tcx RootVariableMinCaptureList<'tcx>>, + successors: IndexVec<LiveNode, Option<LiveNode>>, + rwu_table: rwu_table::RWUTable, + + /// A live node representing a point of execution before closure entry & + /// after closure exit. Used to calculate liveness of captured variables + /// through calls to the same closure. Used for Fn & FnMut closures only. + closure_ln: LiveNode, + /// A live node representing every 'exit' from the function, whether it be + /// by explicit return, panic, or other means. + exit_ln: LiveNode, + + // mappings from loop node ID to LiveNode + // ("break" label should map to loop node ID, + // it probably doesn't now) + break_ln: HirIdMap<LiveNode>, + cont_ln: HirIdMap<LiveNode>, +} + +impl<'a, 'tcx> Liveness<'a, 'tcx> { + fn new(ir: &'a mut IrMaps<'tcx>, body_owner: LocalDefId) -> Liveness<'a, 'tcx> { + let typeck_results = ir.tcx.typeck(body_owner); + let param_env = ir.tcx.param_env(body_owner); + let closure_min_captures = typeck_results.closure_min_captures.get(&body_owner); + let closure_ln = ir.add_live_node(ClosureNode); + let exit_ln = ir.add_live_node(ExitNode); + + let num_live_nodes = ir.lnks.len(); + let num_vars = ir.var_kinds.len(); + + Liveness { + ir, + typeck_results, + param_env, + closure_min_captures, + successors: IndexVec::from_elem_n(None, num_live_nodes), + rwu_table: rwu_table::RWUTable::new(num_live_nodes, num_vars), + closure_ln, + exit_ln, + break_ln: Default::default(), + cont_ln: Default::default(), + } + } + + fn live_node(&self, hir_id: HirId, span: Span) -> LiveNode { + match self.ir.live_node_map.get(&hir_id) { + Some(&ln) => ln, + None => { + // This must be a mismatch between the ir_map construction + // above and the propagation code below; the two sets of + // code have to agree about which AST nodes are worth + // creating liveness nodes for. + span_bug!(span, "no live node registered for node {:?}", hir_id); + } + } + } + + fn variable(&self, hir_id: HirId, span: Span) -> Variable { + self.ir.variable(hir_id, span) + } + + fn define_bindings_in_pat(&mut self, pat: &hir::Pat<'_>, mut succ: LiveNode) -> LiveNode { + // In an or-pattern, only consider the first pattern; any later patterns + // must have the same bindings, and we also consider the first pattern + // to be the "authoritative" set of ids. + pat.each_binding_or_first(&mut |_, hir_id, pat_sp, ident| { + let ln = self.live_node(hir_id, pat_sp); + let var = self.variable(hir_id, ident.span); + self.init_from_succ(ln, succ); + self.define(ln, var); + succ = ln; + }); + succ + } + + fn live_on_entry(&self, ln: LiveNode, var: Variable) -> bool { + self.rwu_table.get_reader(ln, var) + } + + // Is this variable live on entry to any of its successor nodes? + fn live_on_exit(&self, ln: LiveNode, var: Variable) -> bool { + let successor = self.successors[ln].unwrap(); + self.live_on_entry(successor, var) + } + + fn used_on_entry(&self, ln: LiveNode, var: Variable) -> bool { + self.rwu_table.get_used(ln, var) + } + + fn assigned_on_entry(&self, ln: LiveNode, var: Variable) -> bool { + self.rwu_table.get_writer(ln, var) + } + + fn assigned_on_exit(&self, ln: LiveNode, var: Variable) -> bool { + let successor = self.successors[ln].unwrap(); + self.assigned_on_entry(successor, var) + } + + fn write_vars<F>(&self, wr: &mut dyn Write, mut test: F) -> io::Result<()> + where + F: FnMut(Variable) -> bool, + { + for var_idx in 0..self.ir.var_kinds.len() { + let var = Variable::from(var_idx); + if test(var) { + write!(wr, " {:?}", var)?; + } + } + Ok(()) + } + + #[allow(unused_must_use)] + fn ln_str(&self, ln: LiveNode) -> String { + let mut wr = Vec::new(); + { + let wr = &mut wr as &mut dyn Write; + write!(wr, "[{:?} of kind {:?} reads", ln, self.ir.lnks[ln]); + self.write_vars(wr, |var| self.rwu_table.get_reader(ln, var)); + write!(wr, " writes"); + self.write_vars(wr, |var| self.rwu_table.get_writer(ln, var)); + write!(wr, " uses"); + self.write_vars(wr, |var| self.rwu_table.get_used(ln, var)); + + write!(wr, " precedes {:?}]", self.successors[ln]); + } + String::from_utf8(wr).unwrap() + } + + fn log_liveness(&self, entry_ln: LiveNode, hir_id: hir::HirId) { + // hack to skip the loop unless debug! is enabled: + debug!( + "^^ liveness computation results for body {} (entry={:?})", + { + for ln_idx in 0..self.ir.lnks.len() { + debug!("{:?}", self.ln_str(LiveNode::from(ln_idx))); + } + hir_id + }, + entry_ln + ); + } + + fn init_empty(&mut self, ln: LiveNode, succ_ln: LiveNode) { + self.successors[ln] = Some(succ_ln); + + // It is not necessary to initialize the RWUs here because they are all + // empty when created, and the sets only grow during iterations. + } + + fn init_from_succ(&mut self, ln: LiveNode, succ_ln: LiveNode) { + // more efficient version of init_empty() / merge_from_succ() + self.successors[ln] = Some(succ_ln); + self.rwu_table.copy(ln, succ_ln); + debug!("init_from_succ(ln={}, succ={})", self.ln_str(ln), self.ln_str(succ_ln)); + } + + fn merge_from_succ(&mut self, ln: LiveNode, succ_ln: LiveNode) -> bool { + if ln == succ_ln { + return false; + } + + let changed = self.rwu_table.union(ln, succ_ln); + debug!("merge_from_succ(ln={:?}, succ={}, changed={})", ln, self.ln_str(succ_ln), changed); + changed + } + + // Indicates that a local variable was *defined*; we know that no + // uses of the variable can precede the definition (resolve checks + // this) so we just clear out all the data. + fn define(&mut self, writer: LiveNode, var: Variable) { + let used = self.rwu_table.get_used(writer, var); + self.rwu_table.set(writer, var, rwu_table::RWU { reader: false, writer: false, used }); + debug!("{:?} defines {:?}: {}", writer, var, self.ln_str(writer)); + } + + // Either read, write, or both depending on the acc bitset + fn acc(&mut self, ln: LiveNode, var: Variable, acc: u32) { + debug!("{:?} accesses[{:x}] {:?}: {}", ln, acc, var, self.ln_str(ln)); + + let mut rwu = self.rwu_table.get(ln, var); + + if (acc & ACC_WRITE) != 0 { + rwu.reader = false; + rwu.writer = true; + } + + // Important: if we both read/write, must do read second + // or else the write will override. + if (acc & ACC_READ) != 0 { + rwu.reader = true; + } + + if (acc & ACC_USE) != 0 { + rwu.used = true; + } + + self.rwu_table.set(ln, var, rwu); + } + + fn compute(&mut self, body: &hir::Body<'_>, hir_id: HirId) -> LiveNode { + debug!("compute: for body {:?}", body.id().hir_id); + + // # Liveness of captured variables + // + // When computing the liveness for captured variables we take into + // account how variable is captured (ByRef vs ByValue) and what is the + // closure kind (Generator / FnOnce vs Fn / FnMut). + // + // Variables captured by reference are assumed to be used on the exit + // from the closure. + // + // In FnOnce closures, variables captured by value are known to be dead + // on exit since it is impossible to call the closure again. + // + // In Fn / FnMut closures, variables captured by value are live on exit + // if they are live on the entry to the closure, since only the closure + // itself can access them on subsequent calls. + + if let Some(closure_min_captures) = self.closure_min_captures { + // Mark upvars captured by reference as used after closure exits. + for (&var_hir_id, min_capture_list) in closure_min_captures { + for captured_place in min_capture_list { + match captured_place.info.capture_kind { + ty::UpvarCapture::ByRef(_) => { + let var = self.variable( + var_hir_id, + captured_place.get_capture_kind_span(self.ir.tcx), + ); + self.acc(self.exit_ln, var, ACC_READ | ACC_USE); + } + ty::UpvarCapture::ByValue => {} + } + } + } + } + + let succ = self.propagate_through_expr(&body.value, self.exit_ln); + + if self.closure_min_captures.is_none() { + // Either not a closure, or closure without any captured variables. + // No need to determine liveness of captured variables, since there + // are none. + return succ; + } + + let ty = self.typeck_results.node_type(hir_id); + match ty.kind() { + ty::Closure(_def_id, substs) => match substs.as_closure().kind() { + ty::ClosureKind::Fn => {} + ty::ClosureKind::FnMut => {} + ty::ClosureKind::FnOnce => return succ, + }, + ty::Generator(..) => return succ, + _ => { + span_bug!( + body.value.span, + "{} has upvars so it should have a closure type: {:?}", + hir_id, + ty + ); + } + }; + + // Propagate through calls to the closure. + loop { + self.init_from_succ(self.closure_ln, succ); + for param in body.params { + param.pat.each_binding(|_bm, hir_id, _x, ident| { + let var = self.variable(hir_id, ident.span); + self.define(self.closure_ln, var); + }) + } + + if !self.merge_from_succ(self.exit_ln, self.closure_ln) { + break; + } + assert_eq!(succ, self.propagate_through_expr(&body.value, self.exit_ln)); + } + + succ + } + + fn propagate_through_block(&mut self, blk: &hir::Block<'_>, succ: LiveNode) -> LiveNode { + if blk.targeted_by_break { + self.break_ln.insert(blk.hir_id, succ); + } + let succ = self.propagate_through_opt_expr(blk.expr, succ); + blk.stmts.iter().rev().fold(succ, |succ, stmt| self.propagate_through_stmt(stmt, succ)) + } + + fn propagate_through_stmt(&mut self, stmt: &hir::Stmt<'_>, succ: LiveNode) -> LiveNode { + match stmt.kind { + hir::StmtKind::Local(ref local) => { + // Note: we mark the variable as defined regardless of whether + // there is an initializer. Initially I had thought to only mark + // the live variable as defined if it was initialized, and then we + // could check for uninit variables just by scanning what is live + // at the start of the function. But that doesn't work so well for + // immutable variables defined in a loop: + // loop { let x; x = 5; } + // because the "assignment" loops back around and generates an error. + // + // So now we just check that variables defined w/o an + // initializer are not live at the point of their + // initialization, which is mildly more complex than checking + // once at the func header but otherwise equivalent. + + if let Some(els) = local.els { + // Eventually, `let pat: ty = init else { els };` is mostly equivalent to + // `let (bindings, ...) = match init { pat => (bindings, ...), _ => els };` + // except that extended lifetime applies at the `init` location. + // + // (e) + // | + // v + // (expr) + // / \ + // | | + // v v + // bindings els + // | + // v + // ( succ ) + // + if let Some(init) = local.init { + let else_ln = self.propagate_through_block(els, succ); + let ln = self.live_node(local.hir_id, local.span); + self.init_from_succ(ln, succ); + self.merge_from_succ(ln, else_ln); + let succ = self.propagate_through_expr(init, ln); + self.define_bindings_in_pat(&local.pat, succ) + } else { + span_bug!( + stmt.span, + "variable is uninitialized but an unexpected else branch is found" + ) + } + } else { + let succ = self.propagate_through_opt_expr(local.init, succ); + self.define_bindings_in_pat(&local.pat, succ) + } + } + hir::StmtKind::Item(..) => succ, + hir::StmtKind::Expr(ref expr) | hir::StmtKind::Semi(ref expr) => { + self.propagate_through_expr(&expr, succ) + } + } + } + + fn propagate_through_exprs(&mut self, exprs: &[Expr<'_>], succ: LiveNode) -> LiveNode { + exprs.iter().rev().fold(succ, |succ, expr| self.propagate_through_expr(&expr, succ)) + } + + fn propagate_through_opt_expr( + &mut self, + opt_expr: Option<&Expr<'_>>, + succ: LiveNode, + ) -> LiveNode { + opt_expr.map_or(succ, |expr| self.propagate_through_expr(expr, succ)) + } + + fn propagate_through_expr(&mut self, expr: &Expr<'_>, succ: LiveNode) -> LiveNode { + debug!("propagate_through_expr: {:?}", expr); + + match expr.kind { + // Interesting cases with control flow or which gen/kill + hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => { + self.access_path(expr.hir_id, path, succ, ACC_READ | ACC_USE) + } + + hir::ExprKind::Field(ref e, _) => self.propagate_through_expr(&e, succ), + + hir::ExprKind::Closure { .. } => { + debug!("{:?} is an ExprKind::Closure", expr); + + // the construction of a closure itself is not important, + // but we have to consider the closed over variables. + let caps = self + .ir + .capture_info_map + .get(&expr.hir_id) + .cloned() + .unwrap_or_else(|| span_bug!(expr.span, "no registered caps")); + + caps.iter().rev().fold(succ, |succ, cap| { + self.init_from_succ(cap.ln, succ); + let var = self.variable(cap.var_hid, expr.span); + self.acc(cap.ln, var, ACC_READ | ACC_USE); + cap.ln + }) + } + + hir::ExprKind::Let(let_expr) => { + let succ = self.propagate_through_expr(let_expr.init, succ); + self.define_bindings_in_pat(let_expr.pat, succ) + } + + // Note that labels have been resolved, so we don't need to look + // at the label ident + hir::ExprKind::Loop(ref blk, ..) => self.propagate_through_loop(expr, &blk, succ), + + hir::ExprKind::Yield(ref e, ..) => { + let yield_ln = self.live_node(expr.hir_id, expr.span); + self.init_from_succ(yield_ln, succ); + self.merge_from_succ(yield_ln, self.exit_ln); + self.propagate_through_expr(e, yield_ln) + } + + hir::ExprKind::If(ref cond, ref then, ref else_opt) => { + // + // (cond) + // | + // v + // (expr) + // / \ + // | | + // v v + // (then)(els) + // | | + // v v + // ( succ ) + // + let else_ln = + self.propagate_through_opt_expr(else_opt.as_ref().map(|e| &**e), succ); + let then_ln = self.propagate_through_expr(&then, succ); + let ln = self.live_node(expr.hir_id, expr.span); + self.init_from_succ(ln, else_ln); + self.merge_from_succ(ln, then_ln); + self.propagate_through_expr(&cond, ln) + } + + hir::ExprKind::Match(ref e, arms, _) => { + // + // (e) + // | + // v + // (expr) + // / | \ + // | | | + // v v v + // (..arms..) + // | | | + // v v v + // ( succ ) + // + // + let ln = self.live_node(expr.hir_id, expr.span); + self.init_empty(ln, succ); + for arm in arms { + let body_succ = self.propagate_through_expr(&arm.body, succ); + + let guard_succ = arm.guard.as_ref().map_or(body_succ, |g| match g { + hir::Guard::If(e) => self.propagate_through_expr(e, body_succ), + hir::Guard::IfLet(let_expr) => { + let let_bind = self.define_bindings_in_pat(let_expr.pat, body_succ); + self.propagate_through_expr(let_expr.init, let_bind) + } + }); + let arm_succ = self.define_bindings_in_pat(&arm.pat, guard_succ); + self.merge_from_succ(ln, arm_succ); + } + self.propagate_through_expr(&e, ln) + } + + hir::ExprKind::Ret(ref o_e) => { + // Ignore succ and subst exit_ln. + self.propagate_through_opt_expr(o_e.as_ref().map(|e| &**e), self.exit_ln) + } + + hir::ExprKind::Break(label, ref opt_expr) => { + // Find which label this break jumps to + let target = match label.target_id { + Ok(hir_id) => self.break_ln.get(&hir_id), + Err(err) => span_bug!(expr.span, "loop scope error: {}", err), + } + .cloned(); + + // Now that we know the label we're going to, + // look it up in the break loop nodes table + + match target { + Some(b) => self.propagate_through_opt_expr(opt_expr.as_ref().map(|e| &**e), b), + None => span_bug!(expr.span, "`break` to unknown label"), + } + } + + hir::ExprKind::Continue(label) => { + // Find which label this expr continues to + let sc = label + .target_id + .unwrap_or_else(|err| span_bug!(expr.span, "loop scope error: {}", err)); + + // Now that we know the label we're going to, + // look it up in the continue loop nodes table + self.cont_ln + .get(&sc) + .cloned() + .unwrap_or_else(|| span_bug!(expr.span, "continue to unknown label")) + } + + hir::ExprKind::Assign(ref l, ref r, _) => { + // see comment on places in + // propagate_through_place_components() + let succ = self.write_place(&l, succ, ACC_WRITE); + let succ = self.propagate_through_place_components(&l, succ); + self.propagate_through_expr(&r, succ) + } + + hir::ExprKind::AssignOp(_, ref l, ref r) => { + // an overloaded assign op is like a method call + if self.typeck_results.is_method_call(expr) { + let succ = self.propagate_through_expr(&l, succ); + self.propagate_through_expr(&r, succ) + } else { + // see comment on places in + // propagate_through_place_components() + let succ = self.write_place(&l, succ, ACC_WRITE | ACC_READ); + let succ = self.propagate_through_expr(&r, succ); + self.propagate_through_place_components(&l, succ) + } + } + + // Uninteresting cases: just propagate in rev exec order + hir::ExprKind::Array(ref exprs) => self.propagate_through_exprs(exprs, succ), + + hir::ExprKind::Struct(_, ref fields, ref with_expr) => { + let succ = self.propagate_through_opt_expr(with_expr.as_ref().map(|e| &**e), succ); + fields + .iter() + .rev() + .fold(succ, |succ, field| self.propagate_through_expr(&field.expr, succ)) + } + + hir::ExprKind::Call(ref f, ref args) => { + let succ = self.check_is_ty_uninhabited(expr, succ); + let succ = self.propagate_through_exprs(args, succ); + self.propagate_through_expr(&f, succ) + } + + hir::ExprKind::MethodCall(.., ref args, _) => { + let succ = self.check_is_ty_uninhabited(expr, succ); + self.propagate_through_exprs(args, succ) + } + + hir::ExprKind::Tup(ref exprs) => self.propagate_through_exprs(exprs, succ), + + hir::ExprKind::Binary(op, ref l, ref r) if op.node.is_lazy() => { + let r_succ = self.propagate_through_expr(&r, succ); + + let ln = self.live_node(expr.hir_id, expr.span); + self.init_from_succ(ln, succ); + self.merge_from_succ(ln, r_succ); + + self.propagate_through_expr(&l, ln) + } + + hir::ExprKind::Index(ref l, ref r) | hir::ExprKind::Binary(_, ref l, ref r) => { + let r_succ = self.propagate_through_expr(&r, succ); + self.propagate_through_expr(&l, r_succ) + } + + hir::ExprKind::Box(ref e) + | hir::ExprKind::AddrOf(_, _, ref e) + | hir::ExprKind::Cast(ref e, _) + | hir::ExprKind::Type(ref e, _) + | hir::ExprKind::DropTemps(ref e) + | hir::ExprKind::Unary(_, ref e) + | hir::ExprKind::Repeat(ref e, _) => self.propagate_through_expr(&e, succ), + + hir::ExprKind::InlineAsm(ref asm) => { + // Handle non-returning asm + let mut succ = if asm.options.contains(InlineAsmOptions::NORETURN) { + self.exit_ln + } else { + succ + }; + + // Do a first pass for writing outputs only + for (op, _op_sp) in asm.operands.iter().rev() { + match op { + hir::InlineAsmOperand::In { .. } + | hir::InlineAsmOperand::Const { .. } + | hir::InlineAsmOperand::SymFn { .. } + | hir::InlineAsmOperand::SymStatic { .. } => {} + hir::InlineAsmOperand::Out { expr, .. } => { + if let Some(expr) = expr { + succ = self.write_place(expr, succ, ACC_WRITE); + } + } + hir::InlineAsmOperand::InOut { expr, .. } => { + succ = self.write_place(expr, succ, ACC_READ | ACC_WRITE | ACC_USE); + } + hir::InlineAsmOperand::SplitInOut { out_expr, .. } => { + if let Some(expr) = out_expr { + succ = self.write_place(expr, succ, ACC_WRITE); + } + } + } + } + + // Then do a second pass for inputs + let mut succ = succ; + for (op, _op_sp) in asm.operands.iter().rev() { + match op { + hir::InlineAsmOperand::In { expr, .. } => { + succ = self.propagate_through_expr(expr, succ) + } + hir::InlineAsmOperand::Out { expr, .. } => { + if let Some(expr) = expr { + succ = self.propagate_through_place_components(expr, succ); + } + } + hir::InlineAsmOperand::InOut { expr, .. } => { + succ = self.propagate_through_place_components(expr, succ); + } + hir::InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => { + if let Some(expr) = out_expr { + succ = self.propagate_through_place_components(expr, succ); + } + succ = self.propagate_through_expr(in_expr, succ); + } + hir::InlineAsmOperand::Const { .. } + | hir::InlineAsmOperand::SymFn { .. } + | hir::InlineAsmOperand::SymStatic { .. } => {} + } + } + succ + } + + hir::ExprKind::Lit(..) + | hir::ExprKind::ConstBlock(..) + | hir::ExprKind::Err + | hir::ExprKind::Path(hir::QPath::TypeRelative(..)) + | hir::ExprKind::Path(hir::QPath::LangItem(..)) => succ, + + // Note that labels have been resolved, so we don't need to look + // at the label ident + hir::ExprKind::Block(ref blk, _) => self.propagate_through_block(&blk, succ), + } + } + + fn propagate_through_place_components(&mut self, expr: &Expr<'_>, succ: LiveNode) -> LiveNode { + // # Places + // + // In general, the full flow graph structure for an + // assignment/move/etc can be handled in one of two ways, + // depending on whether what is being assigned is a "tracked + // value" or not. A tracked value is basically a local + // variable or argument. + // + // The two kinds of graphs are: + // + // Tracked place Untracked place + // ----------------------++----------------------- + // || + // | || | + // v || v + // (rvalue) || (rvalue) + // | || | + // v || v + // (write of place) || (place components) + // | || | + // v || v + // (succ) || (succ) + // || + // ----------------------++----------------------- + // + // I will cover the two cases in turn: + // + // # Tracked places + // + // A tracked place is a local variable/argument `x`. In + // these cases, the link_node where the write occurs is linked + // to node id of `x`. The `write_place()` routine generates + // the contents of this node. There are no subcomponents to + // consider. + // + // # Non-tracked places + // + // These are places like `x[5]` or `x.f`. In that case, we + // basically ignore the value which is written to but generate + // reads for the components---`x` in these two examples. The + // components reads are generated by + // `propagate_through_place_components()` (this fn). + // + // # Illegal places + // + // It is still possible to observe assignments to non-places; + // these errors are detected in the later pass borrowck. We + // just ignore such cases and treat them as reads. + + match expr.kind { + hir::ExprKind::Path(_) => succ, + hir::ExprKind::Field(ref e, _) => self.propagate_through_expr(&e, succ), + _ => self.propagate_through_expr(expr, succ), + } + } + + // see comment on propagate_through_place() + fn write_place(&mut self, expr: &Expr<'_>, succ: LiveNode, acc: u32) -> LiveNode { + match expr.kind { + hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => { + self.access_path(expr.hir_id, path, succ, acc) + } + + // We do not track other places, so just propagate through + // to their subcomponents. Also, it may happen that + // non-places occur here, because those are detected in the + // later pass borrowck. + _ => succ, + } + } + + fn access_var( + &mut self, + hir_id: HirId, + var_hid: HirId, + succ: LiveNode, + acc: u32, + span: Span, + ) -> LiveNode { + let ln = self.live_node(hir_id, span); + if acc != 0 { + self.init_from_succ(ln, succ); + let var = self.variable(var_hid, span); + self.acc(ln, var, acc); + } + ln + } + + fn access_path( + &mut self, + hir_id: HirId, + path: &hir::Path<'_>, + succ: LiveNode, + acc: u32, + ) -> LiveNode { + match path.res { + Res::Local(hid) => self.access_var(hir_id, hid, succ, acc, path.span), + _ => succ, + } + } + + fn propagate_through_loop( + &mut self, + expr: &Expr<'_>, + body: &hir::Block<'_>, + succ: LiveNode, + ) -> LiveNode { + /* + We model control flow like this: + + (expr) <-+ + | | + v | + (body) --+ + + Note that a `continue` expression targeting the `loop` will have a successor of `expr`. + Meanwhile, a `break` expression will have a successor of `succ`. + */ + + // first iteration: + let ln = self.live_node(expr.hir_id, expr.span); + self.init_empty(ln, succ); + debug!("propagate_through_loop: using id for loop body {} {:?}", expr.hir_id, body); + + self.break_ln.insert(expr.hir_id, succ); + + self.cont_ln.insert(expr.hir_id, ln); + + let body_ln = self.propagate_through_block(body, ln); + + // repeat until fixed point is reached: + while self.merge_from_succ(ln, body_ln) { + assert_eq!(body_ln, self.propagate_through_block(body, ln)); + } + + ln + } + + fn check_is_ty_uninhabited(&mut self, expr: &Expr<'_>, succ: LiveNode) -> LiveNode { + let ty = self.typeck_results.expr_ty(expr); + let m = self.ir.tcx.parent_module(expr.hir_id).to_def_id(); + if self.ir.tcx.is_ty_uninhabited_from(m, ty, self.param_env) { + match self.ir.lnks[succ] { + LiveNodeKind::ExprNode(succ_span, succ_id) => { + self.warn_about_unreachable(expr.span, ty, succ_span, succ_id, "expression"); + } + LiveNodeKind::VarDefNode(succ_span, succ_id) => { + self.warn_about_unreachable(expr.span, ty, succ_span, succ_id, "definition"); + } + _ => {} + }; + self.exit_ln + } else { + succ + } + } + + fn warn_about_unreachable( + &mut self, + orig_span: Span, + orig_ty: Ty<'tcx>, + expr_span: Span, + expr_id: HirId, + descr: &str, + ) { + if !orig_ty.is_never() { + // Unreachable code warnings are already emitted during type checking. + // However, during type checking, full type information is being + // calculated but not yet available, so the check for diverging + // expressions due to uninhabited result types is pretty crude and + // only checks whether ty.is_never(). Here, we have full type + // information available and can issue warnings for less obviously + // uninhabited types (e.g. empty enums). The check above is used so + // that we do not emit the same warning twice if the uninhabited type + // is indeed `!`. + + self.ir.tcx.struct_span_lint_hir( + lint::builtin::UNREACHABLE_CODE, + expr_id, + expr_span, + |lint| { + let msg = format!("unreachable {}", descr); + lint.build(&msg) + .span_label(expr_span, &msg) + .span_label(orig_span, "any code following this expression is unreachable") + .span_note( + orig_span, + &format!( + "this expression has type `{}`, which is uninhabited", + orig_ty + ), + ) + .emit(); + }, + ); + } + } +} + +// _______________________________________________________________________ +// Checking for error conditions + +impl<'a, 'tcx> Visitor<'tcx> for Liveness<'a, 'tcx> { + fn visit_local(&mut self, local: &'tcx hir::Local<'tcx>) { + self.check_unused_vars_in_pat(&local.pat, None, |spans, hir_id, ln, var| { + if local.init.is_some() { + self.warn_about_dead_assign(spans, hir_id, ln, var); + } + }); + + intravisit::walk_local(self, local); + } + + fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) { + check_expr(self, ex); + intravisit::walk_expr(self, ex); + } + + fn visit_arm(&mut self, arm: &'tcx hir::Arm<'tcx>) { + self.check_unused_vars_in_pat(&arm.pat, None, |_, _, _, _| {}); + intravisit::walk_arm(self, arm); + } +} + +fn check_expr<'tcx>(this: &mut Liveness<'_, 'tcx>, expr: &'tcx Expr<'tcx>) { + match expr.kind { + hir::ExprKind::Assign(ref l, ..) => { + this.check_place(&l); + } + + hir::ExprKind::AssignOp(_, ref l, _) => { + if !this.typeck_results.is_method_call(expr) { + this.check_place(&l); + } + } + + hir::ExprKind::InlineAsm(ref asm) => { + for (op, _op_sp) in asm.operands { + match op { + hir::InlineAsmOperand::Out { expr, .. } => { + if let Some(expr) = expr { + this.check_place(expr); + } + } + hir::InlineAsmOperand::InOut { expr, .. } => { + this.check_place(expr); + } + hir::InlineAsmOperand::SplitInOut { out_expr, .. } => { + if let Some(out_expr) = out_expr { + this.check_place(out_expr); + } + } + _ => {} + } + } + } + + hir::ExprKind::Let(let_expr) => { + this.check_unused_vars_in_pat(let_expr.pat, None, |_, _, _, _| {}); + } + + // no correctness conditions related to liveness + hir::ExprKind::Call(..) + | hir::ExprKind::MethodCall(..) + | hir::ExprKind::Match(..) + | hir::ExprKind::Loop(..) + | hir::ExprKind::Index(..) + | hir::ExprKind::Field(..) + | hir::ExprKind::Array(..) + | hir::ExprKind::Tup(..) + | hir::ExprKind::Binary(..) + | hir::ExprKind::Cast(..) + | hir::ExprKind::If(..) + | hir::ExprKind::DropTemps(..) + | hir::ExprKind::Unary(..) + | hir::ExprKind::Ret(..) + | hir::ExprKind::Break(..) + | hir::ExprKind::Continue(..) + | hir::ExprKind::Lit(_) + | hir::ExprKind::ConstBlock(..) + | hir::ExprKind::Block(..) + | hir::ExprKind::AddrOf(..) + | hir::ExprKind::Struct(..) + | hir::ExprKind::Repeat(..) + | hir::ExprKind::Closure { .. } + | hir::ExprKind::Path(_) + | hir::ExprKind::Yield(..) + | hir::ExprKind::Box(..) + | hir::ExprKind::Type(..) + | hir::ExprKind::Err => {} + } +} + +impl<'tcx> Liveness<'_, 'tcx> { + fn check_place(&mut self, expr: &'tcx Expr<'tcx>) { + match expr.kind { + hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) => { + if let Res::Local(var_hid) = path.res { + // Assignment to an immutable variable or argument: only legal + // if there is no later assignment. If this local is actually + // mutable, then check for a reassignment to flag the mutability + // as being used. + let ln = self.live_node(expr.hir_id, expr.span); + let var = self.variable(var_hid, expr.span); + self.warn_about_dead_assign(vec![expr.span], expr.hir_id, ln, var); + } + } + _ => { + // For other kinds of places, no checks are required, + // and any embedded expressions are actually rvalues + intravisit::walk_expr(self, expr); + } + } + } + + fn should_warn(&self, var: Variable) -> Option<String> { + let name = self.ir.variable_name(var); + if name == kw::Empty { + return None; + } + let name = name.as_str(); + if name.as_bytes()[0] == b'_' { + return None; + } + Some(name.to_owned()) + } + + fn warn_about_unused_upvars(&self, entry_ln: LiveNode) { + let Some(closure_min_captures) = self.closure_min_captures else { + return; + }; + + // If closure_min_captures is Some(), upvars must be Some() too. + for (&var_hir_id, min_capture_list) in closure_min_captures { + for captured_place in min_capture_list { + match captured_place.info.capture_kind { + ty::UpvarCapture::ByValue => {} + ty::UpvarCapture::ByRef(..) => continue, + }; + let span = captured_place.get_capture_kind_span(self.ir.tcx); + let var = self.variable(var_hir_id, span); + if self.used_on_entry(entry_ln, var) { + if !self.live_on_entry(entry_ln, var) { + if let Some(name) = self.should_warn(var) { + self.ir.tcx.struct_span_lint_hir( + lint::builtin::UNUSED_ASSIGNMENTS, + var_hir_id, + vec![span], + |lint| { + lint.build(&format!( + "value captured by `{}` is never read", + name + )) + .help("did you mean to capture by reference instead?") + .emit(); + }, + ); + } + } + } else { + if let Some(name) = self.should_warn(var) { + self.ir.tcx.struct_span_lint_hir( + lint::builtin::UNUSED_VARIABLES, + var_hir_id, + vec![span], + |lint| { + lint.build(&format!("unused variable: `{}`", name)) + .help("did you mean to capture by reference instead?") + .emit(); + }, + ); + } + } + } + } + } + + fn warn_about_unused_args(&self, body: &hir::Body<'_>, entry_ln: LiveNode) { + for p in body.params { + self.check_unused_vars_in_pat(&p.pat, Some(entry_ln), |spans, hir_id, ln, var| { + if !self.live_on_entry(ln, var) { + self.report_unused_assign(hir_id, spans, var, |name| { + format!("value passed to `{}` is never read", name) + }); + } + }); + } + } + + fn check_unused_vars_in_pat( + &self, + pat: &hir::Pat<'_>, + entry_ln: Option<LiveNode>, + on_used_on_entry: impl Fn(Vec<Span>, HirId, LiveNode, Variable), + ) { + // In an or-pattern, only consider the variable; any later patterns must have the same + // bindings, and we also consider the first pattern to be the "authoritative" set of ids. + // However, we should take the ids and spans of variables with the same name from the later + // patterns so the suggestions to prefix with underscores will apply to those too. + let mut vars: FxIndexMap<Symbol, (LiveNode, Variable, Vec<(HirId, Span, Span)>)> = + <_>::default(); + + pat.each_binding(|_, hir_id, pat_sp, ident| { + let ln = entry_ln.unwrap_or_else(|| self.live_node(hir_id, pat_sp)); + let var = self.variable(hir_id, ident.span); + let id_and_sp = (hir_id, pat_sp, ident.span); + vars.entry(self.ir.variable_name(var)) + .and_modify(|(.., hir_ids_and_spans)| hir_ids_and_spans.push(id_and_sp)) + .or_insert_with(|| (ln, var, vec![id_and_sp])); + }); + + for (_, (ln, var, hir_ids_and_spans)) in vars { + if self.used_on_entry(ln, var) { + let id = hir_ids_and_spans[0].0; + let spans = + hir_ids_and_spans.into_iter().map(|(_, _, ident_span)| ident_span).collect(); + on_used_on_entry(spans, id, ln, var); + } else { + self.report_unused(hir_ids_and_spans, ln, var); + } + } + } + + fn report_unused( + &self, + hir_ids_and_spans: Vec<(HirId, Span, Span)>, + ln: LiveNode, + var: Variable, + ) { + let first_hir_id = hir_ids_and_spans[0].0; + + if let Some(name) = self.should_warn(var).filter(|name| name != "self") { + // annoying: for parameters in funcs like `fn(x: i32) + // {ret}`, there is only one node, so asking about + // assigned_on_exit() is not meaningful. + let is_assigned = + if ln == self.exit_ln { false } else { self.assigned_on_exit(ln, var) }; + + if is_assigned { + self.ir.tcx.struct_span_lint_hir( + lint::builtin::UNUSED_VARIABLES, + first_hir_id, + hir_ids_and_spans + .into_iter() + .map(|(_, _, ident_span)| ident_span) + .collect::<Vec<_>>(), + |lint| { + lint.build(&format!("variable `{}` is assigned to, but never used", name)) + .note(&format!("consider using `_{}` instead", name)) + .emit(); + }, + ) + } else { + let (shorthands, non_shorthands): (Vec<_>, Vec<_>) = + hir_ids_and_spans.iter().copied().partition(|(hir_id, _, ident_span)| { + let var = self.variable(*hir_id, *ident_span); + self.ir.variable_is_shorthand(var) + }); + + // If we have both shorthand and non-shorthand, prefer the "try ignoring + // the field" message, and suggest `_` for the non-shorthands. If we only + // have non-shorthand, then prefix with an underscore instead. + if !shorthands.is_empty() { + let shorthands = shorthands + .into_iter() + .map(|(_, pat_span, _)| (pat_span, format!("{}: _", name))) + .chain( + non_shorthands + .into_iter() + .map(|(_, pat_span, _)| (pat_span, "_".to_string())), + ) + .collect::<Vec<_>>(); + + self.ir.tcx.struct_span_lint_hir( + lint::builtin::UNUSED_VARIABLES, + first_hir_id, + hir_ids_and_spans + .iter() + .map(|(_, pat_span, _)| *pat_span) + .collect::<Vec<_>>(), + |lint| { + let mut err = lint.build(&format!("unused variable: `{}`", name)); + err.multipart_suggestion( + "try ignoring the field", + shorthands, + Applicability::MachineApplicable, + ); + err.emit(); + }, + ); + } else { + let non_shorthands = non_shorthands + .into_iter() + .map(|(_, _, ident_span)| (ident_span, format!("_{}", name))) + .collect::<Vec<_>>(); + + self.ir.tcx.struct_span_lint_hir( + lint::builtin::UNUSED_VARIABLES, + first_hir_id, + hir_ids_and_spans + .iter() + .map(|(_, _, ident_span)| *ident_span) + .collect::<Vec<_>>(), + |lint| { + let mut err = lint.build(&format!("unused variable: `{}`", name)); + err.multipart_suggestion( + "if this is intentional, prefix it with an underscore", + non_shorthands, + Applicability::MachineApplicable, + ); + err.emit(); + }, + ); + } + } + } + } + + fn warn_about_dead_assign(&self, spans: Vec<Span>, hir_id: HirId, ln: LiveNode, var: Variable) { + if !self.live_on_exit(ln, var) { + self.report_unused_assign(hir_id, spans, var, |name| { + format!("value assigned to `{}` is never read", name) + }); + } + } + + fn report_unused_assign( + &self, + hir_id: HirId, + spans: Vec<Span>, + var: Variable, + message: impl Fn(&str) -> String, + ) { + if let Some(name) = self.should_warn(var) { + self.ir.tcx.struct_span_lint_hir( + lint::builtin::UNUSED_ASSIGNMENTS, + hir_id, + spans, + |lint| { + lint.build(&message(&name)) + .help("maybe it is overwritten before being read?") + .emit(); + }, + ) + } + } +} |