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//! A different sort of visitor for walking fn bodies. Unlike the
//! normal visitor, which just walks the entire body in one shot, the
//! `ExprUseVisitor` determines how expressions are being used.
use std::slice::from_ref;
use hir::def::DefKind;
use hir::Expr;
// Export these here so that Clippy can use them.
pub use rustc_middle::hir::place::{Place, PlaceBase, PlaceWithHirId, Projection};
use rustc_data_structures::fx::FxIndexMap;
use rustc_hir as hir;
use rustc_hir::def::Res;
use rustc_hir::def_id::LocalDefId;
use rustc_hir::PatKind;
use rustc_infer::infer::InferCtxt;
use rustc_middle::hir::place::ProjectionKind;
use rustc_middle::mir::FakeReadCause;
use rustc_middle::ty::{self, adjustment, AdtKind, Ty, TyCtxt};
use rustc_target::abi::FIRST_VARIANT;
use ty::BorrowKind::ImmBorrow;
use crate::mem_categorization as mc;
/// This trait defines the callbacks you can expect to receive when
/// employing the ExprUseVisitor.
pub trait Delegate<'tcx> {
/// The value found at `place` is moved, depending
/// on `mode`. Where `diag_expr_id` is the id used for diagnostics for `place`.
///
/// Use of a `Copy` type in a ByValue context is considered a use
/// by `ImmBorrow` and `borrow` is called instead. This is because
/// a shared borrow is the "minimum access" that would be needed
/// to perform a copy.
///
///
/// The parameter `diag_expr_id` indicates the HIR id that ought to be used for
/// diagnostics. Around pattern matching such as `let pat = expr`, the diagnostic
/// id will be the id of the expression `expr` but the place itself will have
/// the id of the binding in the pattern `pat`.
fn consume(&mut self, place_with_id: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId);
/// The value found at `place` is being borrowed with kind `bk`.
/// `diag_expr_id` is the id used for diagnostics (see `consume` for more details).
fn borrow(
&mut self,
place_with_id: &PlaceWithHirId<'tcx>,
diag_expr_id: hir::HirId,
bk: ty::BorrowKind,
);
/// The value found at `place` is being copied.
/// `diag_expr_id` is the id used for diagnostics (see `consume` for more details).
fn copy(&mut self, place_with_id: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) {
// In most cases, copying data from `x` is equivalent to doing `*&x`, so by default
// we treat a copy of `x` as a borrow of `x`.
self.borrow(place_with_id, diag_expr_id, ty::BorrowKind::ImmBorrow)
}
/// The path at `assignee_place` is being assigned to.
/// `diag_expr_id` is the id used for diagnostics (see `consume` for more details).
fn mutate(&mut self, assignee_place: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId);
/// The path at `binding_place` is a binding that is being initialized.
///
/// This covers cases such as `let x = 42;`
fn bind(&mut self, binding_place: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) {
// Bindings can normally be treated as a regular assignment, so by default we
// forward this to the mutate callback.
self.mutate(binding_place, diag_expr_id)
}
/// The `place` should be a fake read because of specified `cause`.
fn fake_read(
&mut self,
place_with_id: &PlaceWithHirId<'tcx>,
cause: FakeReadCause,
diag_expr_id: hir::HirId,
);
}
#[derive(Copy, Clone, PartialEq, Debug)]
enum ConsumeMode {
/// reference to x where x has a type that copies
Copy,
/// reference to x where x has a type that moves
Move,
}
/// The ExprUseVisitor type
///
/// This is the code that actually walks the tree.
pub struct ExprUseVisitor<'a, 'tcx> {
mc: mc::MemCategorizationContext<'a, 'tcx>,
body_owner: LocalDefId,
delegate: &'a mut dyn Delegate<'tcx>,
}
/// If the MC results in an error, it's because the type check
/// failed (or will fail, when the error is uncovered and reported
/// during writeback). In this case, we just ignore this part of the
/// code.
///
/// Note that this macro appears similar to try!(), but, unlike try!(),
/// it does not propagate the error.
macro_rules! return_if_err {
($inp: expr) => {
match $inp {
Ok(v) => v,
Err(()) => {
debug!("mc reported err");
return;
}
}
};
}
impl<'a, 'tcx> ExprUseVisitor<'a, 'tcx> {
/// Creates the ExprUseVisitor, configuring it with the various options provided:
///
/// - `delegate` -- who receives the callbacks
/// - `param_env` --- parameter environment for trait lookups (esp. pertaining to `Copy`)
/// - `typeck_results` --- typeck results for the code being analyzed
pub fn new(
delegate: &'a mut (dyn Delegate<'tcx> + 'a),
infcx: &'a InferCtxt<'tcx>,
body_owner: LocalDefId,
param_env: ty::ParamEnv<'tcx>,
typeck_results: &'a ty::TypeckResults<'tcx>,
) -> Self {
ExprUseVisitor {
mc: mc::MemCategorizationContext::new(infcx, param_env, body_owner, typeck_results),
body_owner,
delegate,
}
}
#[instrument(skip(self), level = "debug")]
pub fn consume_body(&mut self, body: &hir::Body<'_>) {
for param in body.params {
let param_ty = return_if_err!(self.mc.pat_ty_adjusted(param.pat));
debug!("consume_body: param_ty = {:?}", param_ty);
let param_place = self.mc.cat_rvalue(param.hir_id, param.pat.span, param_ty);
self.walk_irrefutable_pat(¶m_place, param.pat);
}
self.consume_expr(&body.value);
}
fn tcx(&self) -> TyCtxt<'tcx> {
self.mc.tcx()
}
fn delegate_consume(&mut self, place_with_id: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) {
delegate_consume(&self.mc, self.delegate, place_with_id, diag_expr_id)
}
fn consume_exprs(&mut self, exprs: &[hir::Expr<'_>]) {
for expr in exprs {
self.consume_expr(expr);
}
}
pub fn consume_expr(&mut self, expr: &hir::Expr<'_>) {
debug!("consume_expr(expr={:?})", expr);
let place_with_id = return_if_err!(self.mc.cat_expr(expr));
self.delegate_consume(&place_with_id, place_with_id.hir_id);
self.walk_expr(expr);
}
fn mutate_expr(&mut self, expr: &hir::Expr<'_>) {
let place_with_id = return_if_err!(self.mc.cat_expr(expr));
self.delegate.mutate(&place_with_id, place_with_id.hir_id);
self.walk_expr(expr);
}
fn borrow_expr(&mut self, expr: &hir::Expr<'_>, bk: ty::BorrowKind) {
debug!("borrow_expr(expr={:?}, bk={:?})", expr, bk);
let place_with_id = return_if_err!(self.mc.cat_expr(expr));
self.delegate.borrow(&place_with_id, place_with_id.hir_id, bk);
self.walk_expr(expr)
}
fn select_from_expr(&mut self, expr: &hir::Expr<'_>) {
self.walk_expr(expr)
}
pub fn walk_expr(&mut self, expr: &hir::Expr<'_>) {
debug!("walk_expr(expr={:?})", expr);
self.walk_adjustment(expr);
match expr.kind {
hir::ExprKind::Path(_) => {}
hir::ExprKind::Type(subexpr, _) => self.walk_expr(subexpr),
hir::ExprKind::Unary(hir::UnOp::Deref, base) => {
// *base
self.select_from_expr(base);
}
hir::ExprKind::Field(base, _) => {
// base.f
self.select_from_expr(base);
}
hir::ExprKind::Index(lhs, rhs, _) => {
// lhs[rhs]
self.select_from_expr(lhs);
self.consume_expr(rhs);
}
hir::ExprKind::Call(callee, args) => {
// callee(args)
self.consume_expr(callee);
self.consume_exprs(args);
}
hir::ExprKind::MethodCall(.., receiver, args, _) => {
// callee.m(args)
self.consume_expr(receiver);
self.consume_exprs(args);
}
hir::ExprKind::Struct(_, fields, ref opt_with) => {
self.walk_struct_expr(fields, opt_with);
}
hir::ExprKind::Tup(exprs) => {
self.consume_exprs(exprs);
}
hir::ExprKind::If(ref cond_expr, ref then_expr, ref opt_else_expr) => {
self.consume_expr(cond_expr);
self.consume_expr(then_expr);
if let Some(ref else_expr) = *opt_else_expr {
self.consume_expr(else_expr);
}
}
hir::ExprKind::Let(hir::Let { pat, init, .. }) => {
self.walk_local(init, pat, None, |t| t.borrow_expr(init, ty::ImmBorrow))
}
hir::ExprKind::Match(ref discr, arms, _) => {
let discr_place = return_if_err!(self.mc.cat_expr(discr));
return_if_err!(self.maybe_read_scrutinee(
discr,
discr_place.clone(),
arms.iter().map(|arm| arm.pat),
));
// treatment of the discriminant is handled while walking the arms.
for arm in arms {
self.walk_arm(&discr_place, arm);
}
}
hir::ExprKind::Array(exprs) => {
self.consume_exprs(exprs);
}
hir::ExprKind::AddrOf(_, m, ref base) => {
// &base
// make sure that the thing we are pointing out stays valid
// for the lifetime `scope_r` of the resulting ptr:
let bk = ty::BorrowKind::from_mutbl(m);
self.borrow_expr(base, bk);
}
hir::ExprKind::InlineAsm(asm) => {
for (op, _op_sp) in asm.operands {
match op {
hir::InlineAsmOperand::In { expr, .. } => self.consume_expr(expr),
hir::InlineAsmOperand::Out { expr: Some(expr), .. }
| hir::InlineAsmOperand::InOut { expr, .. } => {
self.mutate_expr(expr);
}
hir::InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
self.consume_expr(in_expr);
if let Some(out_expr) = out_expr {
self.mutate_expr(out_expr);
}
}
hir::InlineAsmOperand::Out { expr: None, .. }
| hir::InlineAsmOperand::Const { .. }
| hir::InlineAsmOperand::SymFn { .. }
| hir::InlineAsmOperand::SymStatic { .. } => {}
}
}
}
hir::ExprKind::Continue(..)
| hir::ExprKind::Lit(..)
| hir::ExprKind::ConstBlock(..)
| hir::ExprKind::OffsetOf(..)
| hir::ExprKind::Err(_) => {}
hir::ExprKind::Loop(blk, ..) => {
self.walk_block(blk);
}
hir::ExprKind::Unary(_, lhs) => {
self.consume_expr(lhs);
}
hir::ExprKind::Binary(_, lhs, rhs) => {
self.consume_expr(lhs);
self.consume_expr(rhs);
}
hir::ExprKind::Block(blk, _) => {
self.walk_block(blk);
}
hir::ExprKind::Break(_, ref opt_expr) | hir::ExprKind::Ret(ref opt_expr) => {
if let Some(expr) = *opt_expr {
self.consume_expr(expr);
}
}
hir::ExprKind::Become(call) => {
self.consume_expr(call);
}
hir::ExprKind::Assign(lhs, rhs, _) => {
self.mutate_expr(lhs);
self.consume_expr(rhs);
}
hir::ExprKind::Cast(base, _) => {
self.consume_expr(base);
}
hir::ExprKind::DropTemps(expr) => {
self.consume_expr(expr);
}
hir::ExprKind::AssignOp(_, lhs, rhs) => {
if self.mc.typeck_results.is_method_call(expr) {
self.consume_expr(lhs);
} else {
self.mutate_expr(lhs);
}
self.consume_expr(rhs);
}
hir::ExprKind::Repeat(base, _) => {
self.consume_expr(base);
}
hir::ExprKind::Closure(closure) => {
self.walk_captures(closure);
}
hir::ExprKind::Yield(value, _) => {
self.consume_expr(value);
}
}
}
fn walk_stmt(&mut self, stmt: &hir::Stmt<'_>) {
match stmt.kind {
hir::StmtKind::Local(hir::Local { pat, init: Some(expr), els, .. }) => {
self.walk_local(expr, pat, *els, |_| {})
}
hir::StmtKind::Local(_) => {}
hir::StmtKind::Item(_) => {
// We don't visit nested items in this visitor,
// only the fn body we were given.
}
hir::StmtKind::Expr(ref expr) | hir::StmtKind::Semi(ref expr) => {
self.consume_expr(expr);
}
}
}
fn maybe_read_scrutinee<'t>(
&mut self,
discr: &Expr<'_>,
discr_place: PlaceWithHirId<'tcx>,
pats: impl Iterator<Item = &'t hir::Pat<'t>>,
) -> Result<(), ()> {
// Matching should not always be considered a use of the place, hence
// discr does not necessarily need to be borrowed.
// We only want to borrow discr if the pattern contain something other
// than wildcards.
let ExprUseVisitor { ref mc, body_owner: _, delegate: _ } = *self;
let mut needs_to_be_read = false;
for pat in pats {
mc.cat_pattern(discr_place.clone(), pat, |place, pat| {
match &pat.kind {
PatKind::Binding(.., opt_sub_pat) => {
// If the opt_sub_pat is None, than the binding does not count as
// a wildcard for the purpose of borrowing discr.
if opt_sub_pat.is_none() {
needs_to_be_read = true;
}
}
PatKind::Path(qpath) => {
// A `Path` pattern is just a name like `Foo`. This is either a
// named constant or else it refers to an ADT variant
let res = self.mc.typeck_results.qpath_res(qpath, pat.hir_id);
match res {
Res::Def(DefKind::Const, _) | Res::Def(DefKind::AssocConst, _) => {
// Named constants have to be equated with the value
// being matched, so that's a read of the value being matched.
//
// FIXME: We don't actually reads for ZSTs.
needs_to_be_read = true;
}
_ => {
// Otherwise, this is a struct/enum variant, and so it's
// only a read if we need to read the discriminant.
needs_to_be_read |= is_multivariant_adt(place.place.ty());
}
}
}
PatKind::TupleStruct(..) | PatKind::Struct(..) | PatKind::Tuple(..) => {
// For `Foo(..)`, `Foo { ... }` and `(...)` patterns, check if we are matching
// against a multivariant enum or struct. In that case, we have to read
// the discriminant. Otherwise this kind of pattern doesn't actually
// read anything (we'll get invoked for the `...`, which may indeed
// perform some reads).
let place_ty = place.place.ty();
needs_to_be_read |= is_multivariant_adt(place_ty);
}
PatKind::Lit(_) | PatKind::Range(..) => {
// If the PatKind is a Lit or a Range then we want
// to borrow discr.
needs_to_be_read = true;
}
PatKind::Slice(lhs, wild, rhs) => {
// We don't need to test the length if the pattern is `[..]`
if matches!((lhs, wild, rhs), (&[], Some(_), &[]))
// Arrays have a statically known size, so
// there is no need to read their length
|| place.place.ty().peel_refs().is_array()
{
} else {
needs_to_be_read = true;
}
}
PatKind::Or(_) | PatKind::Box(_) | PatKind::Ref(..) | PatKind::Wild => {
// If the PatKind is Or, Box, or Ref, the decision is made later
// as these patterns contains subpatterns
// If the PatKind is Wild, the decision is made based on the other patterns being
// examined
}
}
})?
}
if needs_to_be_read {
self.borrow_expr(discr, ty::ImmBorrow);
} else {
let closure_def_id = match discr_place.place.base {
PlaceBase::Upvar(upvar_id) => Some(upvar_id.closure_expr_id),
_ => None,
};
self.delegate.fake_read(
&discr_place,
FakeReadCause::ForMatchedPlace(closure_def_id),
discr_place.hir_id,
);
// We always want to walk the discriminant. We want to make sure, for instance,
// that the discriminant has been initialized.
self.walk_expr(discr);
}
Ok(())
}
fn walk_local<F>(
&mut self,
expr: &hir::Expr<'_>,
pat: &hir::Pat<'_>,
els: Option<&hir::Block<'_>>,
mut f: F,
) where
F: FnMut(&mut Self),
{
self.walk_expr(expr);
let expr_place = return_if_err!(self.mc.cat_expr(expr));
f(self);
if let Some(els) = els {
// borrowing because we need to test the discriminant
return_if_err!(self.maybe_read_scrutinee(
expr,
expr_place.clone(),
from_ref(pat).iter()
));
self.walk_block(els)
}
self.walk_irrefutable_pat(&expr_place, &pat);
}
/// Indicates that the value of `blk` will be consumed, meaning either copied or moved
/// depending on its type.
fn walk_block(&mut self, blk: &hir::Block<'_>) {
debug!("walk_block(blk.hir_id={})", blk.hir_id);
for stmt in blk.stmts {
self.walk_stmt(stmt);
}
if let Some(ref tail_expr) = blk.expr {
self.consume_expr(tail_expr);
}
}
fn walk_struct_expr<'hir>(
&mut self,
fields: &[hir::ExprField<'_>],
opt_with: &Option<&'hir hir::Expr<'_>>,
) {
// Consume the expressions supplying values for each field.
for field in fields {
self.consume_expr(field.expr);
// The struct path probably didn't resolve
if self.mc.typeck_results.opt_field_index(field.hir_id).is_none() {
self.tcx().sess.delay_span_bug(field.span, "couldn't resolve index for field");
}
}
let with_expr = match *opt_with {
Some(w) => &*w,
None => {
return;
}
};
let with_place = return_if_err!(self.mc.cat_expr(with_expr));
// Select just those fields of the `with`
// expression that will actually be used
match with_place.place.ty().kind() {
ty::Adt(adt, args) if adt.is_struct() => {
// Consume those fields of the with expression that are needed.
for (f_index, with_field) in adt.non_enum_variant().fields.iter_enumerated() {
let is_mentioned = fields
.iter()
.any(|f| self.mc.typeck_results.opt_field_index(f.hir_id) == Some(f_index));
if !is_mentioned {
let field_place = self.mc.cat_projection(
&*with_expr,
with_place.clone(),
with_field.ty(self.tcx(), args),
ProjectionKind::Field(f_index, FIRST_VARIANT),
);
self.delegate_consume(&field_place, field_place.hir_id);
}
}
}
_ => {
// the base expression should always evaluate to a
// struct; however, when EUV is run during typeck, it
// may not. This will generate an error earlier in typeck,
// so we can just ignore it.
if self.tcx().sess.has_errors().is_none() {
span_bug!(with_expr.span, "with expression doesn't evaluate to a struct");
}
}
}
// walk the with expression so that complex expressions
// are properly handled.
self.walk_expr(with_expr);
}
/// Invoke the appropriate delegate calls for anything that gets
/// consumed or borrowed as part of the automatic adjustment
/// process.
fn walk_adjustment(&mut self, expr: &hir::Expr<'_>) {
let adjustments = self.mc.typeck_results.expr_adjustments(expr);
let mut place_with_id = return_if_err!(self.mc.cat_expr_unadjusted(expr));
for adjustment in adjustments {
debug!("walk_adjustment expr={:?} adj={:?}", expr, adjustment);
match adjustment.kind {
adjustment::Adjust::NeverToAny
| adjustment::Adjust::Pointer(_)
| adjustment::Adjust::DynStar => {
// Creating a closure/fn-pointer or unsizing consumes
// the input and stores it into the resulting rvalue.
self.delegate_consume(&place_with_id, place_with_id.hir_id);
}
adjustment::Adjust::Deref(None) => {}
// Autoderefs for overloaded Deref calls in fact reference
// their receiver. That is, if we have `(*x)` where `x`
// is of type `Rc<T>`, then this in fact is equivalent to
// `x.deref()`. Since `deref()` is declared with `&self`,
// this is an autoref of `x`.
adjustment::Adjust::Deref(Some(ref deref)) => {
let bk = ty::BorrowKind::from_mutbl(deref.mutbl);
self.delegate.borrow(&place_with_id, place_with_id.hir_id, bk);
}
adjustment::Adjust::Borrow(ref autoref) => {
self.walk_autoref(expr, &place_with_id, autoref);
}
}
place_with_id =
return_if_err!(self.mc.cat_expr_adjusted(expr, place_with_id, adjustment));
}
}
/// Walks the autoref `autoref` applied to the autoderef'd
/// `expr`. `base_place` is the mem-categorized form of `expr`
/// after all relevant autoderefs have occurred.
fn walk_autoref(
&mut self,
expr: &hir::Expr<'_>,
base_place: &PlaceWithHirId<'tcx>,
autoref: &adjustment::AutoBorrow<'tcx>,
) {
debug!(
"walk_autoref(expr.hir_id={} base_place={:?} autoref={:?})",
expr.hir_id, base_place, autoref
);
match *autoref {
adjustment::AutoBorrow::Ref(_, m) => {
self.delegate.borrow(
base_place,
base_place.hir_id,
ty::BorrowKind::from_mutbl(m.into()),
);
}
adjustment::AutoBorrow::RawPtr(m) => {
debug!("walk_autoref: expr.hir_id={} base_place={:?}", expr.hir_id, base_place);
self.delegate.borrow(base_place, base_place.hir_id, ty::BorrowKind::from_mutbl(m));
}
}
}
fn walk_arm(&mut self, discr_place: &PlaceWithHirId<'tcx>, arm: &hir::Arm<'_>) {
let closure_def_id = match discr_place.place.base {
PlaceBase::Upvar(upvar_id) => Some(upvar_id.closure_expr_id),
_ => None,
};
self.delegate.fake_read(
discr_place,
FakeReadCause::ForMatchedPlace(closure_def_id),
discr_place.hir_id,
);
self.walk_pat(discr_place, arm.pat, arm.guard.is_some());
if let Some(hir::Guard::If(e)) = arm.guard {
self.consume_expr(e)
} else if let Some(hir::Guard::IfLet(ref l)) = arm.guard {
self.consume_expr(l.init)
}
self.consume_expr(arm.body);
}
/// Walks a pat that occurs in isolation (i.e., top-level of fn argument or
/// let binding, and *not* a match arm or nested pat.)
fn walk_irrefutable_pat(&mut self, discr_place: &PlaceWithHirId<'tcx>, pat: &hir::Pat<'_>) {
let closure_def_id = match discr_place.place.base {
PlaceBase::Upvar(upvar_id) => Some(upvar_id.closure_expr_id),
_ => None,
};
self.delegate.fake_read(
discr_place,
FakeReadCause::ForLet(closure_def_id),
discr_place.hir_id,
);
self.walk_pat(discr_place, pat, false);
}
/// The core driver for walking a pattern
fn walk_pat(
&mut self,
discr_place: &PlaceWithHirId<'tcx>,
pat: &hir::Pat<'_>,
has_guard: bool,
) {
debug!("walk_pat(discr_place={:?}, pat={:?}, has_guard={:?})", discr_place, pat, has_guard);
let tcx = self.tcx();
let ExprUseVisitor { ref mc, body_owner: _, ref mut delegate } = *self;
return_if_err!(mc.cat_pattern(discr_place.clone(), pat, |place, pat| {
if let PatKind::Binding(_, canonical_id, ..) = pat.kind {
debug!("walk_pat: binding place={:?} pat={:?}", place, pat);
if let Some(bm) =
mc.typeck_results.extract_binding_mode(tcx.sess, pat.hir_id, pat.span)
{
debug!("walk_pat: pat.hir_id={:?} bm={:?}", pat.hir_id, bm);
// pat_ty: the type of the binding being produced.
let pat_ty = return_if_err!(mc.node_ty(pat.hir_id));
debug!("walk_pat: pat_ty={:?}", pat_ty);
let def = Res::Local(canonical_id);
if let Ok(ref binding_place) = mc.cat_res(pat.hir_id, pat.span, pat_ty, def) {
delegate.bind(binding_place, binding_place.hir_id);
}
// Subtle: MIR desugaring introduces immutable borrows for each pattern
// binding when lowering pattern guards to ensure that the guard does not
// modify the scrutinee.
if has_guard {
delegate.borrow(place, discr_place.hir_id, ImmBorrow);
}
// It is also a borrow or copy/move of the value being matched.
// In a cases of pattern like `let pat = upvar`, don't use the span
// of the pattern, as this just looks confusing, instead use the span
// of the discriminant.
match bm {
ty::BindByReference(m) => {
let bk = ty::BorrowKind::from_mutbl(m);
delegate.borrow(place, discr_place.hir_id, bk);
}
ty::BindByValue(..) => {
debug!("walk_pat binding consuming pat");
delegate_consume(mc, *delegate, place, discr_place.hir_id);
}
}
}
}
}));
}
/// Handle the case where the current body contains a closure.
///
/// When the current body being handled is a closure, then we must make sure that
/// - The parent closure only captures Places from the nested closure that are not local to it.
///
/// In the following example the closures `c` only captures `p.x` even though `incr`
/// is a capture of the nested closure
///
/// ```
/// struct P { x: i32 }
/// let mut p = P { x: 4 };
/// let c = || {
/// let incr = 10;
/// let nested = || p.x += incr;
/// };
/// ```
///
/// - When reporting the Place back to the Delegate, ensure that the UpvarId uses the enclosing
/// closure as the DefId.
fn walk_captures(&mut self, closure_expr: &hir::Closure<'_>) {
fn upvar_is_local_variable(
upvars: Option<&FxIndexMap<hir::HirId, hir::Upvar>>,
upvar_id: hir::HirId,
body_owner_is_closure: bool,
) -> bool {
upvars.map(|upvars| !upvars.contains_key(&upvar_id)).unwrap_or(body_owner_is_closure)
}
debug!("walk_captures({:?})", closure_expr);
let tcx = self.tcx();
let closure_def_id = closure_expr.def_id;
let upvars = tcx.upvars_mentioned(self.body_owner);
// For purposes of this function, generator and closures are equivalent.
let body_owner_is_closure =
matches!(tcx.hir().body_owner_kind(self.body_owner), hir::BodyOwnerKind::Closure,);
// If we have a nested closure, we want to include the fake reads present in the nested closure.
if let Some(fake_reads) = self.mc.typeck_results.closure_fake_reads.get(&closure_def_id) {
for (fake_read, cause, hir_id) in fake_reads.iter() {
match fake_read.base {
PlaceBase::Upvar(upvar_id) => {
if upvar_is_local_variable(
upvars,
upvar_id.var_path.hir_id,
body_owner_is_closure,
) {
// The nested closure might be fake reading the current (enclosing) closure's local variables.
// The only places we want to fake read before creating the parent closure are the ones that
// are not local to it/ defined by it.
//
// ```rust,ignore(cannot-test-this-because-pseudo-code)
// let v1 = (0, 1);
// let c = || { // fake reads: v1
// let v2 = (0, 1);
// let e = || { // fake reads: v1, v2
// let (_, t1) = v1;
// let (_, t2) = v2;
// }
// }
// ```
// This check is performed when visiting the body of the outermost closure (`c`) and ensures
// that we don't add a fake read of v2 in c.
continue;
}
}
_ => {
bug!(
"Do not know how to get HirId out of Rvalue and StaticItem {:?}",
fake_read.base
);
}
};
self.delegate.fake_read(
&PlaceWithHirId { place: fake_read.clone(), hir_id: *hir_id },
*cause,
*hir_id,
);
}
}
if let Some(min_captures) = self.mc.typeck_results.closure_min_captures.get(&closure_def_id)
{
for (var_hir_id, min_list) in min_captures.iter() {
if upvars.map_or(body_owner_is_closure, |upvars| !upvars.contains_key(var_hir_id)) {
// The nested closure might be capturing the current (enclosing) closure's local variables.
// We check if the root variable is ever mentioned within the enclosing closure, if not
// then for the current body (if it's a closure) these aren't captures, we will ignore them.
continue;
}
for captured_place in min_list {
let place = &captured_place.place;
let capture_info = captured_place.info;
let place_base = if body_owner_is_closure {
// Mark the place to be captured by the enclosing closure
PlaceBase::Upvar(ty::UpvarId::new(*var_hir_id, self.body_owner))
} else {
// If the body owner isn't a closure then the variable must
// be a local variable
PlaceBase::Local(*var_hir_id)
};
let closure_hir_id = tcx.hir().local_def_id_to_hir_id(closure_def_id);
let place_with_id = PlaceWithHirId::new(
capture_info
.path_expr_id
.unwrap_or(capture_info.capture_kind_expr_id.unwrap_or(closure_hir_id)),
place.base_ty,
place_base,
place.projections.clone(),
);
match capture_info.capture_kind {
ty::UpvarCapture::ByValue => {
self.delegate_consume(&place_with_id, place_with_id.hir_id);
}
ty::UpvarCapture::ByRef(upvar_borrow) => {
self.delegate.borrow(
&place_with_id,
place_with_id.hir_id,
upvar_borrow,
);
}
}
}
}
}
}
}
fn copy_or_move<'a, 'tcx>(
mc: &mc::MemCategorizationContext<'a, 'tcx>,
place_with_id: &PlaceWithHirId<'tcx>,
) -> ConsumeMode {
if !mc.type_is_copy_modulo_regions(place_with_id.place.ty()) {
ConsumeMode::Move
} else {
ConsumeMode::Copy
}
}
// - If a place is used in a `ByValue` context then move it if it's not a `Copy` type.
// - If the place that is a `Copy` type consider it an `ImmBorrow`.
fn delegate_consume<'a, 'tcx>(
mc: &mc::MemCategorizationContext<'a, 'tcx>,
delegate: &mut (dyn Delegate<'tcx> + 'a),
place_with_id: &PlaceWithHirId<'tcx>,
diag_expr_id: hir::HirId,
) {
debug!("delegate_consume(place_with_id={:?})", place_with_id);
let mode = copy_or_move(mc, place_with_id);
match mode {
ConsumeMode::Move => delegate.consume(place_with_id, diag_expr_id),
ConsumeMode::Copy => delegate.copy(place_with_id, diag_expr_id),
}
}
fn is_multivariant_adt(ty: Ty<'_>) -> bool {
if let ty::Adt(def, _) = ty.kind() {
// Note that if a non-exhaustive SingleVariant is defined in another crate, we need
// to assume that more cases will be added to the variant in the future. This mean
// that we should handle non-exhaustive SingleVariant the same way we would handle
// a MultiVariant.
// If the variant is not local it must be defined in another crate.
let is_non_exhaustive = match def.adt_kind() {
AdtKind::Struct | AdtKind::Union => {
def.non_enum_variant().is_field_list_non_exhaustive()
}
AdtKind::Enum => def.is_variant_list_non_exhaustive(),
};
def.variants().len() > 1 || (!def.did().is_local() && is_non_exhaustive)
} else {
false
}
}