rustc_passes/liveness.rs
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//! 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 std::io;
use std::io::prelude::*;
use std::rc::Rc;
use rustc_data_structures::fx::FxIndexMap;
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::IndexVec;
use rustc_middle::query::Providers;
use rustc_middle::span_bug;
use rustc_middle::ty::{self, RootVariableMinCaptureList, Ty, TyCtxt};
use rustc_session::lint;
use rustc_span::symbol::{Symbol, kw, sym};
use rustc_span::{BytePos, Span};
use tracing::{debug, instrument};
use self::LiveNodeKind::*;
use self::VarKind::*;
use crate::errors;
mod rwu_table;
rustc_index::newtype_index! {
#[debug_format = "v({})"]
pub struct Variable {}
}
rustc_index::newtype_index! {
#[debug_format = "ln({})"]
pub struct LiveNode {}
}
#[derive(Copy, Clone, PartialEq, Debug)]
enum LiveNodeKind {
UpvarNode(Span),
ExprNode(Span, HirId),
VarDefNode(Span, HirId),
ClosureNode,
ExitNode,
ErrNode,
}
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(),
ErrNode => "Error node".to_owned(),
}
}
fn check_liveness(tcx: TyCtxt<'_>, def_id: LocalDefId) {
// Don't run unused pass for #[derive()]
let parent = tcx.local_parent(def_id);
if let DefKind::Impl { .. } = tcx.def_kind(parent)
&& tcx.has_attr(parent, sym::automatically_derived)
{
return;
}
// Don't run unused pass for #[naked]
if tcx.has_attr(def_id.to_def_id(), sym::naked) {
return;
}
let mut maps = IrMaps::new(tcx);
let body = tcx.hir().body_owned_by(def_id);
let hir_id = tcx.hir().body_owner(body.id());
if let Some(upvars) = tcx.upvars_mentioned(def_id) {
for &var_hir_id in upvars.keys() {
let var_name = 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:
maps.visit_body(&body);
// compute liveness
let mut lsets = Liveness::new(&mut maps, 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);
}
pub(crate) fn provide(providers: &mut Providers) {
*providers = Providers { check_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 CollectLitsVisitor<'tcx> {
lit_exprs: Vec<&'tcx hir::Expr<'tcx>>,
}
impl<'tcx> Visitor<'tcx> for CollectLitsVisitor<'tcx> {
fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
if let hir::ExprKind::Lit(_) = expr.kind {
self.lit_exprs.push(expr);
}
intravisit::walk_expr(self, expr);
}
}
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();
pat.walk_always(|pat| {
if let hir::PatKind::Struct(_, fields, _) = pat.kind {
let short = fields.iter().filter(|f| f.is_shorthand);
shorthand_field_ids.extend(short.map(|f| f.pat.hir_id));
}
});
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> {
fn visit_local(&mut self, local: &'tcx hir::LetStmt<'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);
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(_, 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));
}
}
hir::ExprKind::Closure(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();
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);
}
hir::ExprKind::Let(let_expr) => {
self.add_from_pat(let_expr.pat);
}
// 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));
}
hir::ExprKind::Binary(op, ..) if op.node.is_lazy() => {
self.add_live_node_for_node(expr.hir_id, ExprNode(expr.span, expr.hir_id));
}
// Inline assembly may contain labels.
hir::ExprKind::InlineAsm(asm) if asm.contains_label() => {
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::Become(..)
| hir::ExprKind::Block(..)
| hir::ExprKind::Assign(..)
| hir::ExprKind::AssignOp(..)
| hir::ExprKind::Struct(..)
| hir::ExprKind::Repeat(..)
| hir::ExprKind::InlineAsm(..)
| hir::ExprKind::OffsetOf(..)
| 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>,
typing_env: ty::TypingEnv<'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);
// FIXME(#132279): we're in a body here.
let typing_env = ty::TypingEnv::non_body_analysis(ir.tcx, 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,
typing_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 non-never pattern; any later patterns
// must have the same bindings, and we also consider that 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 {
match self.successors[ln] {
Some(successor) => self.assigned_on_entry(successor, var),
None => {
self.ir.tcx.dcx().delayed_bug("no successor");
true
}
}
}
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: 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 (Coroutine / 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, args) => match args.as_closure().kind() {
ty::ClosureKind::Fn => {}
ty::ClosureKind::FnMut => {}
ty::ClosureKind::FnOnce => return succ,
},
ty::CoroutineClosure(_def_id, args) => match args.as_coroutine_closure().kind() {
ty::ClosureKind::Fn => {}
ty::ClosureKind::FnMut => {}
ty::ClosureKind::FnOnce => return succ,
},
ty::Coroutine(..) => 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::Let(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(_, 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(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_deref(), 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| self.propagate_through_expr(g, body_succ));
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_deref(), self.exit_ln)
}
hir::ExprKind::Become(e) => {
// Ignore succ and subst exit_ln.
self.propagate_through_expr(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_deref(), 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(|| {
self.ir.tcx.dcx().span_delayed_bug(expr.span, "continue to unknown label");
self.ir.add_live_node(ErrNode)
})
}
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(exprs) => self.propagate_through_exprs(exprs, succ),
hir::ExprKind::Struct(_, fields, ref with_expr) => {
let succ = self.propagate_through_opt_expr(with_expr.as_deref(), succ);
fields
.iter()
.rev()
.fold(succ, |succ, field| self.propagate_through_expr(field.expr, succ))
}
hir::ExprKind::Call(ref f, 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(.., receiver, args, _) => {
let succ = self.check_is_ty_uninhabited(expr, succ);
let succ = self.propagate_through_exprs(args, succ);
self.propagate_through_expr(receiver, succ)
}
hir::ExprKind::Tup(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::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(asm) => {
//
// (inputs)
// |
// v
// (outputs)
// / \
// | |
// v v
// (labels)(fallthrough)
// | |
// v v
// ( succ / exit_ln )
// Handle non-returning asm
let mut succ =
if self.typeck_results.expr_ty(expr).is_never() { self.exit_ln } else { succ };
// Do a first pass for labels only
if asm.contains_label() {
let ln = self.live_node(expr.hir_id, expr.span);
self.init_from_succ(ln, succ);
for (op, _op_sp) in asm.operands.iter().rev() {
match op {
hir::InlineAsmOperand::Label { block } => {
let label_ln = self.propagate_through_block(block, succ);
self.merge_from_succ(ln, label_ln);
}
hir::InlineAsmOperand::In { .. }
| hir::InlineAsmOperand::Out { .. }
| hir::InlineAsmOperand::InOut { .. }
| hir::InlineAsmOperand::SplitInOut { .. }
| hir::InlineAsmOperand::Const { .. }
| hir::InlineAsmOperand::SymFn { .. }
| hir::InlineAsmOperand::SymStatic { .. } => {}
}
}
succ = ln;
}
// Do a second 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::Label { .. } => {}
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 third pass for inputs
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 { .. }
| hir::InlineAsmOperand::Label { .. } => {}
}
}
succ
}
hir::ExprKind::Lit(..)
| hir::ExprKind::ConstBlock(..)
| hir::ExprKind::Err(_)
| hir::ExprKind::Path(hir::QPath::TypeRelative(..))
| hir::ExprKind::Path(hir::QPath::LangItem(..))
| hir::ExprKind::OffsetOf(..) => 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(_, 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 ty.is_inhabited_from(self.ir.tcx, m, self.typing_env) {
return succ;
}
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
}
fn warn_about_unreachable<'desc>(
&mut self,
orig_span: Span,
orig_ty: Ty<'tcx>,
expr_span: Span,
expr_id: HirId,
descr: &'desc 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.emit_node_span_lint(
lint::builtin::UNREACHABLE_CODE,
expr_id,
expr_span,
errors::UnreachableDueToUninhabited {
expr: expr_span,
orig: orig_span,
descr,
ty: orig_ty,
},
);
}
}
}
// _______________________________________________________________________
// Checking for error conditions
impl<'a, 'tcx> Visitor<'tcx> for Liveness<'a, 'tcx> {
fn visit_local(&mut self, local: &'tcx hir::LetStmt<'tcx>) {
self.check_unused_vars_in_pat(local.pat, None, 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, 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(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, 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::Become(..)
| hir::ExprKind::Break(..)
| hir::ExprKind::Continue(..)
| hir::ExprKind::Lit(_)
| hir::ExprKind::ConstBlock(..)
| hir::ExprKind::Block(..)
| hir::ExprKind::AddrOf(..)
| hir::ExprKind::OffsetOf(..)
| hir::ExprKind::Struct(..)
| hir::ExprKind::Repeat(..)
| hir::ExprKind::Closure { .. }
| hir::ExprKind::Path(_)
| hir::ExprKind::Yield(..)
| 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(_, 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.emit_node_span_lint(
lint::builtin::UNUSED_ASSIGNMENTS,
var_hir_id,
vec![span],
errors::UnusedCaptureMaybeCaptureRef { name },
);
}
}
} else if let Some(name) = self.should_warn(var) {
self.ir.tcx.emit_node_span_lint(
lint::builtin::UNUSED_VARIABLES,
var_hir_id,
vec![span],
errors::UnusedVarMaybeCaptureRef { name },
);
}
}
}
}
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),
Some(body),
|spans, hir_id, ln, var| {
if !self.live_on_entry(ln, var)
&& let Some(name) = self.should_warn(var)
{
self.ir.tcx.emit_node_span_lint(
lint::builtin::UNUSED_ASSIGNMENTS,
hir_id,
spans,
errors::UnusedAssignPassed { name },
);
}
},
);
}
}
fn check_unused_vars_in_pat(
&self,
pat: &hir::Pat<'_>,
entry_ln: Option<LiveNode>,
opt_body: Option<&hir::Body<'_>>,
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]));
});
let can_remove = match pat.kind {
hir::PatKind::Struct(_, fields, true) => {
// if all fields are shorthand, remove the struct field, otherwise, mark with _ as prefix
fields.iter().all(|f| f.is_shorthand)
}
_ => false,
};
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, can_remove, pat, opt_body);
}
}
}
#[instrument(skip(self), level = "INFO")]
fn report_unused(
&self,
hir_ids_and_spans: Vec<(HirId, Span, Span)>,
ln: LiveNode,
var: Variable,
can_remove: bool,
pat: &hir::Pat<'_>,
opt_body: Option<&hir::Body<'_>>,
) {
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.emit_node_span_lint(
lint::builtin::UNUSED_VARIABLES,
first_hir_id,
hir_ids_and_spans
.into_iter()
.map(|(_, _, ident_span)| ident_span)
.collect::<Vec<_>>(),
errors::UnusedVarAssignedOnly { name },
)
} else if can_remove {
let spans = hir_ids_and_spans
.iter()
.map(|(_, pat_span, _)| {
let span = self
.ir
.tcx
.sess
.source_map()
.span_extend_to_next_char(*pat_span, ',', true);
span.with_hi(BytePos(span.hi().0 + 1))
})
.collect();
self.ir.tcx.emit_node_span_lint(
lint::builtin::UNUSED_VARIABLES,
first_hir_id,
hir_ids_and_spans.iter().map(|(_, pat_span, _)| *pat_span).collect::<Vec<_>>(),
errors::UnusedVarRemoveField {
name,
sugg: errors::UnusedVarRemoveFieldSugg { spans },
},
);
} 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).collect();
let non_shorthands =
non_shorthands.into_iter().map(|(_, pat_span, _)| pat_span).collect();
self.ir.tcx.emit_node_span_lint(
lint::builtin::UNUSED_VARIABLES,
first_hir_id,
hir_ids_and_spans
.iter()
.map(|(_, pat_span, _)| *pat_span)
.collect::<Vec<_>>(),
errors::UnusedVarTryIgnore {
sugg: errors::UnusedVarTryIgnoreSugg {
shorthands,
non_shorthands,
name,
},
},
);
} else {
// #117284, when `pat_span` and `ident_span` have different contexts
// we can't provide a good suggestion, instead we pointed out the spans from macro
let from_macro = non_shorthands
.iter()
.find(|(_, pat_span, ident_span)| {
!pat_span.eq_ctxt(*ident_span) && pat_span.from_expansion()
})
.map(|(_, pat_span, _)| *pat_span);
let non_shorthands = non_shorthands
.into_iter()
.map(|(_, _, ident_span)| ident_span)
.collect::<Vec<_>>();
let suggestions = self.string_interp_suggestions(&name, opt_body);
let sugg = if let Some(span) = from_macro {
errors::UnusedVariableSugg::NoSugg { span, name: name.clone() }
} else {
errors::UnusedVariableSugg::TryPrefixSugg {
spans: non_shorthands,
name: name.clone(),
}
};
self.ir.tcx.emit_node_span_lint(
lint::builtin::UNUSED_VARIABLES,
first_hir_id,
hir_ids_and_spans
.iter()
.map(|(_, _, ident_span)| *ident_span)
.collect::<Vec<_>>(),
errors::UnusedVariableTryPrefix {
label: if !suggestions.is_empty() { Some(pat.span) } else { None },
name,
sugg,
string_interp: suggestions,
},
);
}
}
}
}
fn string_interp_suggestions(
&self,
name: &str,
opt_body: Option<&hir::Body<'_>>,
) -> Vec<errors::UnusedVariableStringInterp> {
let mut suggs = Vec::new();
let Some(opt_body) = opt_body else {
return suggs;
};
let mut visitor = CollectLitsVisitor { lit_exprs: vec![] };
intravisit::walk_body(&mut visitor, opt_body);
for lit_expr in visitor.lit_exprs {
let hir::ExprKind::Lit(litx) = &lit_expr.kind else { continue };
let rustc_ast::LitKind::Str(syb, _) = litx.node else {
continue;
};
let name_str: &str = syb.as_str();
let name_pa = format!("{{{name}}}");
if name_str.contains(&name_pa) {
suggs.push(errors::UnusedVariableStringInterp {
lit: lit_expr.span,
lo: lit_expr.span.shrink_to_lo(),
hi: lit_expr.span.shrink_to_hi(),
});
}
}
suggs
}
fn warn_about_dead_assign(&self, spans: Vec<Span>, hir_id: HirId, ln: LiveNode, var: Variable) {
if !self.live_on_exit(ln, var)
&& let Some(name) = self.should_warn(var)
{
self.ir.tcx.emit_node_span_lint(
lint::builtin::UNUSED_ASSIGNMENTS,
hir_id,
spans,
errors::UnusedAssign { name },
);
}
}
}