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android / toolchain / rustc / 5139364148b53d79de1b5e778004d41a6a33a4a2 / . / compiler / rustc_hir_typeck / src / upvar.rs
blob: 17b81acd506af541907532a789670a547fa94ec1 [file] [log] [blame]
//! ### Inferring borrow kinds for upvars
//!
//! Whenever there is a closure expression, we need to determine how each
//! upvar is used. We do this by initially assigning each upvar an
//! immutable "borrow kind" (see `ty::BorrowKind` for details) and then
//! "escalating" the kind as needed. The borrow kind proceeds according to
//! the following lattice:
//! ```ignore (not-rust)
//! ty::ImmBorrow -> ty::UniqueImmBorrow -> ty::MutBorrow
//! ```
//! So, for example, if we see an assignment `x = 5` to an upvar `x`, we
//! will promote its borrow kind to mutable borrow. If we see an `&mut x`
//! we'll do the same. Naturally, this applies not just to the upvar, but
//! to everything owned by `x`, so the result is the same for something
//! like `x.f = 5` and so on (presuming `x` is not a borrowed pointer to a
//! struct). These adjustments are performed in
//! `adjust_upvar_borrow_kind()` (you can trace backwards through the code
//! from there).
//!
//! The fact that we are inferring borrow kinds as we go results in a
//! semi-hacky interaction with mem-categorization. In particular,
//! mem-categorization will query the current borrow kind as it
//! categorizes, and we'll return the *current* value, but this may get
//! adjusted later. Therefore, in this module, we generally ignore the
//! borrow kind (and derived mutabilities) that are returned from
//! mem-categorization, since they may be inaccurate. (Another option
//! would be to use a unification scheme, where instead of returning a
//! concrete borrow kind like `ty::ImmBorrow`, we return a
//! `ty::InferBorrow(upvar_id)` or something like that, but this would
//! then mean that all later passes would have to check for these figments
//! and report an error, and it just seems like more mess in the end.)
use super::FnCtxt;
use crate::expr_use_visitor as euv;
use rustc_data_structures::unord::{ExtendUnord, UnordSet};
use rustc_errors::{Applicability, MultiSpan};
use rustc_hir as hir;
use rustc_hir::def_id::LocalDefId;
use rustc_hir::intravisit::{self, Visitor};
use rustc_infer::infer::UpvarRegion;
use rustc_middle::hir::place::{Place, PlaceBase, PlaceWithHirId, Projection, ProjectionKind};
use rustc_middle::mir::FakeReadCause;
use rustc_middle::traits::ObligationCauseCode;
use rustc_middle::ty::{
self, ClosureSizeProfileData, Ty, TyCtxt, TypeckResults, UpvarArgs, UpvarCapture,
};
use rustc_session::lint;
use rustc_span::sym;
use rustc_span::{BytePos, Pos, Span, Symbol};
use rustc_trait_selection::infer::InferCtxtExt;
use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
use rustc_target::abi::FIRST_VARIANT;
use std::iter;
/// Describe the relationship between the paths of two places
/// eg:
/// - `foo` is ancestor of `foo.bar.baz`
/// - `foo.bar.baz` is an descendant of `foo.bar`
/// - `foo.bar` and `foo.baz` are divergent
enum PlaceAncestryRelation {
Ancestor,
Descendant,
SamePlace,
Divergent,
}
/// Intermediate format to store a captured `Place` and associated `ty::CaptureInfo`
/// during capture analysis. Information in this map feeds into the minimum capture
/// analysis pass.
type InferredCaptureInformation<'tcx> = Vec<(Place<'tcx>, ty::CaptureInfo)>;
impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
pub fn closure_analyze(&self, body: &'tcx hir::Body<'tcx>) {
InferBorrowKindVisitor { fcx: self }.visit_body(body);
// it's our job to process these.
assert!(self.deferred_call_resolutions.borrow().is_empty());
}
}
/// Intermediate format to store the hir_id pointing to the use that resulted in the
/// corresponding place being captured and a String which contains the captured value's
/// name (i.e: a.b.c)
#[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
enum UpvarMigrationInfo {
/// We previously captured all of `x`, but now we capture some sub-path.
CapturingPrecise { source_expr: Option<hir::HirId>, var_name: String },
CapturingNothing {
// where the variable appears in the closure (but is not captured)
use_span: Span,
},
}
/// Reasons that we might issue a migration warning.
#[derive(Clone, Debug, Default, PartialEq, Eq, PartialOrd, Ord, Hash)]
struct MigrationWarningReason {
/// When we used to capture `x` in its entirety, we implemented the auto-trait(s)
/// in this vec, but now we don't.
auto_traits: Vec<&'static str>,
/// When we used to capture `x` in its entirety, we would execute some destructors
/// at a different time.
drop_order: bool,
}
impl MigrationWarningReason {
fn migration_message(&self) -> String {
let base = "changes to closure capture in Rust 2021 will affect";
if !self.auto_traits.is_empty() && self.drop_order {
format!("{base} drop order and which traits the closure implements")
} else if self.drop_order {
format!("{base} drop order")
} else {
format!("{base} which traits the closure implements")
}
}
}
/// Intermediate format to store information needed to generate a note in the migration lint.
struct MigrationLintNote {
captures_info: UpvarMigrationInfo,
/// reasons why migration is needed for this capture
reason: MigrationWarningReason,
}
/// Intermediate format to store the hir id of the root variable and a HashSet containing
/// information on why the root variable should be fully captured
struct NeededMigration {
var_hir_id: hir::HirId,
diagnostics_info: Vec<MigrationLintNote>,
}
struct InferBorrowKindVisitor<'a, 'tcx> {
fcx: &'a FnCtxt<'a, 'tcx>,
}
impl<'a, 'tcx> Visitor<'tcx> for InferBorrowKindVisitor<'a, 'tcx> {
fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) {
match expr.kind {
hir::ExprKind::Closure(&hir::Closure { capture_clause, body: body_id, .. }) => {
let body = self.fcx.tcx.hir().body(body_id);
self.visit_body(body);
self.fcx.analyze_closure(expr.hir_id, expr.span, body_id, body, capture_clause);
}
hir::ExprKind::ConstBlock(anon_const) => {
let body = self.fcx.tcx.hir().body(anon_const.body);
self.visit_body(body);
}
_ => {}
}
intravisit::walk_expr(self, expr);
}
}
impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
/// Analysis starting point.
#[instrument(skip(self, body), level = "debug")]
fn analyze_closure(
&self,
closure_hir_id: hir::HirId,
span: Span,
body_id: hir::BodyId,
body: &'tcx hir::Body<'tcx>,
capture_clause: hir::CaptureBy,
) {
// Extract the type of the closure.
let ty = self.node_ty(closure_hir_id);
let (closure_def_id, args) = match *ty.kind() {
ty::Closure(def_id, args) => (def_id, UpvarArgs::Closure(args)),
ty::Coroutine(def_id, args, _) => (def_id, UpvarArgs::Coroutine(args)),
ty::Error(_) => {
// #51714: skip analysis when we have already encountered type errors
return;
}
_ => {
span_bug!(
span,
"type of closure expr {:?} is not a closure {:?}",
closure_hir_id,
ty
);
}
};
let closure_def_id = closure_def_id.expect_local();
let infer_kind = if let UpvarArgs::Closure(closure_args) = args {
self.closure_kind(closure_args).is_none().then_some(closure_args)
} else {
None
};
assert_eq!(self.tcx.hir().body_owner_def_id(body.id()), closure_def_id);
let mut delegate = InferBorrowKind {
closure_def_id,
capture_information: Default::default(),
fake_reads: Default::default(),
};
euv::ExprUseVisitor::new(
&mut delegate,
&self.infcx,
closure_def_id,
self.param_env,
&self.typeck_results.borrow(),
)
.consume_body(body);
debug!(
"For closure={:?}, capture_information={:#?}",
closure_def_id, delegate.capture_information
);
self.log_capture_analysis_first_pass(closure_def_id, &delegate.capture_information, span);
let (capture_information, closure_kind, origin) = self
.process_collected_capture_information(capture_clause, delegate.capture_information);
self.compute_min_captures(closure_def_id, capture_information, span);
let closure_hir_id = self.tcx.hir().local_def_id_to_hir_id(closure_def_id);
if should_do_rust_2021_incompatible_closure_captures_analysis(self.tcx, closure_hir_id) {
self.perform_2229_migration_analysis(closure_def_id, body_id, capture_clause, span);
}
let after_feature_tys = self.final_upvar_tys(closure_def_id);
// We now fake capture information for all variables that are mentioned within the closure
// We do this after handling migrations so that min_captures computes before
if !enable_precise_capture(span) {
let mut capture_information: InferredCaptureInformation<'tcx> = Default::default();
if let Some(upvars) = self.tcx.upvars_mentioned(closure_def_id) {
for var_hir_id in upvars.keys() {
let place = self.place_for_root_variable(closure_def_id, *var_hir_id);
debug!("seed place {:?}", place);
let capture_kind = self.init_capture_kind_for_place(&place, capture_clause);
let fake_info = ty::CaptureInfo {
capture_kind_expr_id: None,
path_expr_id: None,
capture_kind,
};
capture_information.push((place, fake_info));
}
}
// This will update the min captures based on this new fake information.
self.compute_min_captures(closure_def_id, capture_information, span);
}
let before_feature_tys = self.final_upvar_tys(closure_def_id);
if let Some(closure_args) = infer_kind {
// Unify the (as yet unbound) type variable in the closure
// args with the kind we inferred.
let closure_kind_ty = closure_args.as_closure().kind_ty();
self.demand_eqtype(span, closure_kind.to_ty(self.tcx), closure_kind_ty);
// If we have an origin, store it.
if let Some(mut origin) = origin {
if !enable_precise_capture(span) {
// Without precise captures, we just capture the base and ignore
// the projections.
origin.1.projections.clear()
}
self.typeck_results
.borrow_mut()
.closure_kind_origins_mut()
.insert(closure_hir_id, origin);
}
}
self.log_closure_min_capture_info(closure_def_id, span);
// Now that we've analyzed the closure, we know how each
// variable is borrowed, and we know what traits the closure
// implements (Fn vs FnMut etc). We now have some updates to do
// with that information.
//
// Note that no closure type C may have an upvar of type C
// (though it may reference itself via a trait object). This
// results from the desugaring of closures to a struct like
// `Foo<..., UV0...UVn>`. If one of those upvars referenced
// C, then the type would have infinite size (and the
// inference algorithm will reject it).
// Equate the type variables for the upvars with the actual types.
let final_upvar_tys = self.final_upvar_tys(closure_def_id);
debug!(?closure_hir_id, ?args, ?final_upvar_tys);
if self.tcx.features().unsized_locals || self.tcx.features().unsized_fn_params {
for capture in
self.typeck_results.borrow().closure_min_captures_flattened(closure_def_id)
{
if let UpvarCapture::ByValue = capture.info.capture_kind {
self.require_type_is_sized(
capture.place.ty(),
capture.get_path_span(self.tcx),
ObligationCauseCode::SizedClosureCapture(closure_def_id),
);
}
}
}
// Build a tuple (U0..Un) of the final upvar types U0..Un
// and unify the upvar tuple type in the closure with it:
let final_tupled_upvars_type = Ty::new_tup(self.tcx, &final_upvar_tys);
self.demand_suptype(span, args.tupled_upvars_ty(), final_tupled_upvars_type);
let fake_reads = delegate
.fake_reads
.into_iter()
.map(|(place, cause, hir_id)| (place, cause, hir_id))
.collect();
self.typeck_results.borrow_mut().closure_fake_reads.insert(closure_def_id, fake_reads);
if self.tcx.sess.opts.unstable_opts.profile_closures {
self.typeck_results.borrow_mut().closure_size_eval.insert(
closure_def_id,
ClosureSizeProfileData {
before_feature_tys: Ty::new_tup(self.tcx, &before_feature_tys),
after_feature_tys: Ty::new_tup(self.tcx, &after_feature_tys),
},
);
}
// If we are also inferred the closure kind here,
// process any deferred resolutions.
let deferred_call_resolutions = self.remove_deferred_call_resolutions(closure_def_id);
for deferred_call_resolution in deferred_call_resolutions {
deferred_call_resolution.resolve(self);
}
}
// Returns a list of `Ty`s for each upvar.
fn final_upvar_tys(&self, closure_id: LocalDefId) -> Vec<Ty<'tcx>> {
self.typeck_results
.borrow()
.closure_min_captures_flattened(closure_id)
.map(|captured_place| {
let upvar_ty = captured_place.place.ty();
let capture = captured_place.info.capture_kind;
debug!(?captured_place.place, ?upvar_ty, ?capture, ?captured_place.mutability);
apply_capture_kind_on_capture_ty(self.tcx, upvar_ty, capture, captured_place.region)
})
.collect()
}
/// Adjusts the closure capture information to ensure that the operations aren't unsafe,
/// and that the path can be captured with required capture kind (depending on use in closure,
/// move closure etc.)
///
/// Returns the set of adjusted information along with the inferred closure kind and span
/// associated with the closure kind inference.
///
/// Note that we *always* infer a minimal kind, even if
/// we don't always *use* that in the final result (i.e., sometimes
/// we've taken the closure kind from the expectations instead, and
/// for coroutines we don't even implement the closure traits
/// really).
///
/// If we inferred that the closure needs to be FnMut/FnOnce, last element of the returned tuple
/// contains a `Some()` with the `Place` that caused us to do so.
fn process_collected_capture_information(
&self,
capture_clause: hir::CaptureBy,
capture_information: InferredCaptureInformation<'tcx>,
) -> (InferredCaptureInformation<'tcx>, ty::ClosureKind, Option<(Span, Place<'tcx>)>) {
let mut closure_kind = ty::ClosureKind::LATTICE_BOTTOM;
let mut origin: Option<(Span, Place<'tcx>)> = None;
let processed = capture_information
.into_iter()
.map(|(place, mut capture_info)| {
// Apply rules for safety before inferring closure kind
let (place, capture_kind) =
restrict_capture_precision(place, capture_info.capture_kind);
let (place, capture_kind) = truncate_capture_for_optimization(place, capture_kind);
let usage_span = if let Some(usage_expr) = capture_info.path_expr_id {
self.tcx.hir().span(usage_expr)
} else {
unreachable!()
};
let updated = match capture_kind {
ty::UpvarCapture::ByValue => match closure_kind {
ty::ClosureKind::Fn | ty::ClosureKind::FnMut => {
(ty::ClosureKind::FnOnce, Some((usage_span, place.clone())))
}
// If closure is already FnOnce, don't update
ty::ClosureKind::FnOnce => (closure_kind, origin.take()),
},
ty::UpvarCapture::ByRef(
ty::BorrowKind::MutBorrow | ty::BorrowKind::UniqueImmBorrow,
) => {
match closure_kind {
ty::ClosureKind::Fn => {
(ty::ClosureKind::FnMut, Some((usage_span, place.clone())))
}
// Don't update the origin
ty::ClosureKind::FnMut | ty::ClosureKind::FnOnce => {
(closure_kind, origin.take())
}
}
}
_ => (closure_kind, origin.take()),
};
closure_kind = updated.0;
origin = updated.1;
let (place, capture_kind) = match capture_clause {
hir::CaptureBy::Value { .. } => adjust_for_move_closure(place, capture_kind),
hir::CaptureBy::Ref => adjust_for_non_move_closure(place, capture_kind),
};
// This restriction needs to be applied after we have handled adjustments for `move`
// closures. We want to make sure any adjustment that might make us move the place into
// the closure gets handled.
let (place, capture_kind) =
restrict_precision_for_drop_types(self, place, capture_kind);
capture_info.capture_kind = capture_kind;
(place, capture_info)
})
.collect();
(processed, closure_kind, origin)
}
/// Analyzes the information collected by `InferBorrowKind` to compute the min number of
/// Places (and corresponding capture kind) that we need to keep track of to support all
/// the required captured paths.
///
///
/// Note: If this function is called multiple times for the same closure, it will update
/// the existing min_capture map that is stored in TypeckResults.
///
/// Eg:
/// ```
/// #[derive(Debug)]
/// struct Point { x: i32, y: i32 }
///
/// let s = String::from("s"); // hir_id_s
/// let mut p = Point { x: 2, y: -2 }; // his_id_p
/// let c = || {
/// println!("{s:?}"); // L1
/// p.x += 10; // L2
/// println!("{}" , p.y); // L3
/// println!("{p:?}"); // L4
/// drop(s); // L5
/// };
/// ```
/// and let hir_id_L1..5 be the expressions pointing to use of a captured variable on
/// the lines L1..5 respectively.
///
/// InferBorrowKind results in a structure like this:
///
/// ```ignore (illustrative)
/// {
/// Place(base: hir_id_s, projections: [], ....) -> {
/// capture_kind_expr: hir_id_L5,
/// path_expr_id: hir_id_L5,
/// capture_kind: ByValue
/// },
/// Place(base: hir_id_p, projections: [Field(0, 0)], ...) -> {
/// capture_kind_expr: hir_id_L2,
/// path_expr_id: hir_id_L2,
/// capture_kind: ByValue
/// },
/// Place(base: hir_id_p, projections: [Field(1, 0)], ...) -> {
/// capture_kind_expr: hir_id_L3,
/// path_expr_id: hir_id_L3,
/// capture_kind: ByValue
/// },
/// Place(base: hir_id_p, projections: [], ...) -> {
/// capture_kind_expr: hir_id_L4,
/// path_expr_id: hir_id_L4,
/// capture_kind: ByValue
/// },
/// }
/// ```
///
/// After the min capture analysis, we get:
/// ```ignore (illustrative)
/// {
/// hir_id_s -> [
/// Place(base: hir_id_s, projections: [], ....) -> {
/// capture_kind_expr: hir_id_L5,
/// path_expr_id: hir_id_L5,
/// capture_kind: ByValue
/// },
/// ],
/// hir_id_p -> [
/// Place(base: hir_id_p, projections: [], ...) -> {
/// capture_kind_expr: hir_id_L2,
/// path_expr_id: hir_id_L4,
/// capture_kind: ByValue
/// },
/// ],
/// }
/// ```
fn compute_min_captures(
&self,
closure_def_id: LocalDefId,
capture_information: InferredCaptureInformation<'tcx>,
closure_span: Span,
) {
if capture_information.is_empty() {
return;
}
let mut typeck_results = self.typeck_results.borrow_mut();
let mut root_var_min_capture_list =
typeck_results.closure_min_captures.remove(&closure_def_id).unwrap_or_default();
for (mut place, capture_info) in capture_information.into_iter() {
let var_hir_id = match place.base {
PlaceBase::Upvar(upvar_id) => upvar_id.var_path.hir_id,
base => bug!("Expected upvar, found={:?}", base),
};
let var_ident = self.tcx.hir().ident(var_hir_id);
let Some(min_cap_list) = root_var_min_capture_list.get_mut(&var_hir_id) else {
let mutability = self.determine_capture_mutability(&typeck_results, &place);
let min_cap_list = vec![ty::CapturedPlace {
var_ident,
place,
info: capture_info,
mutability,
region: None,
}];
root_var_min_capture_list.insert(var_hir_id, min_cap_list);
continue;
};
// Go through each entry in the current list of min_captures
// - if ancestor is found, update it's capture kind to account for current place's
// capture information.
//
// - if descendant is found, remove it from the list, and update the current place's
// capture information to account for the descendant's capture kind.
//
// We can never be in a case where the list contains both an ancestor and a descendant
// Also there can only be ancestor but in case of descendants there might be
// multiple.
let mut descendant_found = false;
let mut updated_capture_info = capture_info;
min_cap_list.retain(|possible_descendant| {
match determine_place_ancestry_relation(&place, &possible_descendant.place) {
// current place is ancestor of possible_descendant
PlaceAncestryRelation::Ancestor => {
descendant_found = true;
let mut possible_descendant = possible_descendant.clone();
let backup_path_expr_id = updated_capture_info.path_expr_id;
// Truncate the descendant (already in min_captures) to be same as the ancestor to handle any
// possible change in capture mode.
truncate_place_to_len_and_update_capture_kind(
&mut possible_descendant.place,
&mut possible_descendant.info.capture_kind,
place.projections.len(),
);
updated_capture_info =
determine_capture_info(updated_capture_info, possible_descendant.info);
// we need to keep the ancestor's `path_expr_id`
updated_capture_info.path_expr_id = backup_path_expr_id;
false
}
_ => true,
}
});
let mut ancestor_found = false;
if !descendant_found {
for possible_ancestor in min_cap_list.iter_mut() {
match determine_place_ancestry_relation(&place, &possible_ancestor.place) {
PlaceAncestryRelation::SamePlace => {
ancestor_found = true;
possible_ancestor.info = determine_capture_info(
possible_ancestor.info,
updated_capture_info,
);
// Only one related place will be in the list.
break;
}
// current place is descendant of possible_ancestor
PlaceAncestryRelation::Descendant => {
ancestor_found = true;
let backup_path_expr_id = possible_ancestor.info.path_expr_id;
// Truncate the descendant (current place) to be same as the ancestor to handle any
// possible change in capture mode.
truncate_place_to_len_and_update_capture_kind(
&mut place,
&mut updated_capture_info.capture_kind,
possible_ancestor.place.projections.len(),
);
possible_ancestor.info = determine_capture_info(
possible_ancestor.info,
updated_capture_info,
);
// we need to keep the ancestor's `path_expr_id`
possible_ancestor.info.path_expr_id = backup_path_expr_id;
// Only one related place will be in the list.
break;
}
_ => {}
}
}
}
// Only need to insert when we don't have an ancestor in the existing min capture list
if !ancestor_found {
let mutability = self.determine_capture_mutability(&typeck_results, &place);
let captured_place = ty::CapturedPlace {
var_ident,
place,
info: updated_capture_info,
mutability,
region: None,
};
min_cap_list.push(captured_place);
}
}
// For each capture that is determined to be captured by ref, add region info.
for (_, captures) in &mut root_var_min_capture_list {
for capture in captures {
match capture.info.capture_kind {
ty::UpvarCapture::ByRef(_) => {
let PlaceBase::Upvar(upvar_id) = capture.place.base else {
bug!("expected upvar")
};
let origin = UpvarRegion(upvar_id, closure_span);
let upvar_region = self.next_region_var(origin);
capture.region = Some(upvar_region);
}
_ => (),
}
}
}
debug!(
"For closure={:?}, min_captures before sorting={:?}",
closure_def_id, root_var_min_capture_list
);
// Now that we have the minimized list of captures, sort the captures by field id.
// This causes the closure to capture the upvars in the same order as the fields are
// declared which is also the drop order. Thus, in situations where we capture all the
// fields of some type, the observable drop order will remain the same as it previously
// was even though we're dropping each capture individually.
// See https://github.com/rust-lang/project-rfc-2229/issues/42 and
// `tests/ui/closures/2229_closure_analysis/preserve_field_drop_order.rs`.
for (_, captures) in &mut root_var_min_capture_list {
captures.sort_by(|capture1, capture2| {
for (p1, p2) in capture1.place.projections.iter().zip(&capture2.place.projections) {
// We do not need to look at the `Projection.ty` fields here because at each
// step of the iteration, the projections will either be the same and therefore
// the types must be as well or the current projection will be different and
// we will return the result of comparing the field indexes.
match (p1.kind, p2.kind) {
// Paths are the same, continue to next loop.
(ProjectionKind::Deref, ProjectionKind::Deref) => {}
(ProjectionKind::OpaqueCast, ProjectionKind::OpaqueCast) => {}
(ProjectionKind::Field(i1, _), ProjectionKind::Field(i2, _))
if i1 == i2 => {}
// Fields are different, compare them.
(ProjectionKind::Field(i1, _), ProjectionKind::Field(i2, _)) => {
return i1.cmp(&i2);
}
// We should have either a pair of `Deref`s or a pair of `Field`s.
// Anything else is a bug.
(
l @ (ProjectionKind::Deref | ProjectionKind::Field(..)),
r @ (ProjectionKind::Deref | ProjectionKind::Field(..)),
) => bug!(
"ProjectionKinds Deref and Field were mismatched: ({:?}, {:?})",
l,
r
),
(
l @ (ProjectionKind::Index
| ProjectionKind::Subslice
| ProjectionKind::Deref
| ProjectionKind::OpaqueCast
| ProjectionKind::Field(..)),
r @ (ProjectionKind::Index
| ProjectionKind::Subslice
| ProjectionKind::Deref
| ProjectionKind::OpaqueCast
| ProjectionKind::Field(..)),
) => bug!(
"ProjectionKinds Index or Subslice were unexpected: ({:?}, {:?})",
l,
r
),
}
}
self.tcx.sess.delay_span_bug(
closure_span,
format!(
"two identical projections: ({:?}, {:?})",
capture1.place.projections, capture2.place.projections
),
);
std::cmp::Ordering::Equal
});
}
debug!(
"For closure={:?}, min_captures after sorting={:#?}",
closure_def_id, root_var_min_capture_list
);
typeck_results.closure_min_captures.insert(closure_def_id, root_var_min_capture_list);
}
/// Perform the migration analysis for RFC 2229, and emit lint
/// `disjoint_capture_drop_reorder` if needed.
fn perform_2229_migration_analysis(
&self,
closure_def_id: LocalDefId,
body_id: hir::BodyId,
capture_clause: hir::CaptureBy,
span: Span,
) {
let (need_migrations, reasons) = self.compute_2229_migrations(
closure_def_id,
span,
capture_clause,
self.typeck_results.borrow().closure_min_captures.get(&closure_def_id),
);
if !need_migrations.is_empty() {
let (migration_string, migrated_variables_concat) =
migration_suggestion_for_2229(self.tcx, &need_migrations);
let closure_hir_id = self.tcx.hir().local_def_id_to_hir_id(closure_def_id);
let closure_head_span = self.tcx.def_span(closure_def_id);
self.tcx.struct_span_lint_hir(
lint::builtin::RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES,
closure_hir_id,
closure_head_span,
reasons.migration_message(),
|lint| {
for NeededMigration { var_hir_id, diagnostics_info } in &need_migrations {
// Labels all the usage of the captured variable and why they are responsible
// for migration being needed
for lint_note in diagnostics_info.iter() {
match &lint_note.captures_info {
UpvarMigrationInfo::CapturingPrecise { source_expr: Some(capture_expr_id), var_name: captured_name } => {
let cause_span = self.tcx.hir().span(*capture_expr_id);
lint.span_label(cause_span, format!("in Rust 2018, this closure captures all of `{}`, but in Rust 2021, it will only capture `{}`",
self.tcx.hir().name(*var_hir_id),
captured_name,
));
}
UpvarMigrationInfo::CapturingNothing { use_span } => {
lint.span_label(*use_span, format!("in Rust 2018, this causes the closure to capture `{}`, but in Rust 2021, it has no effect",
self.tcx.hir().name(*var_hir_id),
));
}
_ => { }
}
// Add a label pointing to where a captured variable affected by drop order
// is dropped
if lint_note.reason.drop_order {
let drop_location_span = drop_location_span(self.tcx, closure_hir_id);
match &lint_note.captures_info {
UpvarMigrationInfo::CapturingPrecise { var_name: captured_name, .. } => {
lint.span_label(drop_location_span, format!("in Rust 2018, `{}` is dropped here, but in Rust 2021, only `{}` will be dropped here as part of the closure",
self.tcx.hir().name(*var_hir_id),
captured_name,
));
}
UpvarMigrationInfo::CapturingNothing { use_span: _ } => {
lint.span_label(drop_location_span, format!("in Rust 2018, `{v}` is dropped here along with the closure, but in Rust 2021 `{v}` is not part of the closure",
v = self.tcx.hir().name(*var_hir_id),
));
}
}
}
// Add a label explaining why a closure no longer implements a trait
for &missing_trait in &lint_note.reason.auto_traits {
// not capturing something anymore cannot cause a trait to fail to be implemented:
match &lint_note.captures_info {
UpvarMigrationInfo::CapturingPrecise { var_name: captured_name, .. } => {
let var_name = self.tcx.hir().name(*var_hir_id);
lint.span_label(closure_head_span, format!("\
in Rust 2018, this closure implements {missing_trait} \
as `{var_name}` implements {missing_trait}, but in Rust 2021, \
this closure will no longer implement {missing_trait} \
because `{var_name}` is not fully captured \
and `{captured_name}` does not implement {missing_trait}"));
}
// Cannot happen: if we don't capture a variable, we impl strictly more traits
UpvarMigrationInfo::CapturingNothing { use_span } => span_bug!(*use_span, "missing trait from not capturing something"),
}
}
}
}
lint.note("for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/disjoint-capture-in-closures.html>");
let diagnostic_msg = format!(
"add a dummy let to cause {migrated_variables_concat} to be fully captured"
);
let closure_span = self.tcx.hir().span_with_body(closure_hir_id);
let mut closure_body_span = {
// If the body was entirely expanded from a macro
// invocation, i.e. the body is not contained inside the
// closure span, then we walk up the expansion until we
// find the span before the expansion.
let s = self.tcx.hir().span_with_body(body_id.hir_id);
s.find_ancestor_inside(closure_span).unwrap_or(s)
};
if let Ok(mut s) = self.tcx.sess.source_map().span_to_snippet(closure_body_span) {
if s.starts_with('$') {
// Looks like a macro fragment. Try to find the real block.
if let Some(hir::Node::Expr(&hir::Expr {
kind: hir::ExprKind::Block(block, ..), ..
})) = self.tcx.hir().find(body_id.hir_id) {
// If the body is a block (with `{..}`), we use the span of that block.
// E.g. with a `|| $body` expanded from a `m!({ .. })`, we use `{ .. }`, and not `$body`.
// Since we know it's a block, we know we can insert the `let _ = ..` without
// breaking the macro syntax.
if let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(block.span) {
closure_body_span = block.span;
s = snippet;
}
}
}
let mut lines = s.lines();
let line1 = lines.next().unwrap_or_default();
if line1.trim_end() == "{" {
// This is a multi-line closure with just a `{` on the first line,
// so we put the `let` on its own line.
// We take the indentation from the next non-empty line.
let line2 = lines.find(|line| !line.is_empty()).unwrap_or_default();
let indent = line2.split_once(|c: char| !c.is_whitespace()).unwrap_or_default().0;
lint.span_suggestion(
closure_body_span.with_lo(closure_body_span.lo() + BytePos::from_usize(line1.len())).shrink_to_lo(),
diagnostic_msg,
format!("\n{indent}{migration_string};"),
Applicability::MachineApplicable,
);
} else if line1.starts_with('{') {
// This is a closure with its body wrapped in
// braces, but with more than just the opening
// brace on the first line. We put the `let`
// directly after the `{`.
lint.span_suggestion(
closure_body_span.with_lo(closure_body_span.lo() + BytePos(1)).shrink_to_lo(),
diagnostic_msg,
format!(" {migration_string};"),
Applicability::MachineApplicable,
);
} else {
// This is a closure without braces around the body.
// We add braces to add the `let` before the body.
lint.multipart_suggestion(
diagnostic_msg,
vec![
(closure_body_span.shrink_to_lo(), format!("{{ {migration_string}; ")),
(closure_body_span.shrink_to_hi(), " }".to_string()),
],
Applicability::MachineApplicable
);
}
} else {
lint.span_suggestion(
closure_span,
diagnostic_msg,
migration_string,
Applicability::HasPlaceholders
);
}
lint
},
);
}
}
/// Combines all the reasons for 2229 migrations
fn compute_2229_migrations_reasons(
&self,
auto_trait_reasons: UnordSet<&'static str>,
drop_order: bool,
) -> MigrationWarningReason {
MigrationWarningReason {
auto_traits: auto_trait_reasons.to_sorted_stable_ord(),
drop_order,
}
}
/// Figures out the list of root variables (and their types) that aren't completely
/// captured by the closure when `capture_disjoint_fields` is enabled and auto-traits
/// differ between the root variable and the captured paths.
///
/// Returns a tuple containing a HashMap of CapturesInfo that maps to a HashSet of trait names
/// if migration is needed for traits for the provided var_hir_id, otherwise returns None
fn compute_2229_migrations_for_trait(
&self,
min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
var_hir_id: hir::HirId,
closure_clause: hir::CaptureBy,
) -> Option<FxIndexMap<UpvarMigrationInfo, UnordSet<&'static str>>> {
let auto_traits_def_id = [
self.tcx.lang_items().clone_trait(),
self.tcx.lang_items().sync_trait(),
self.tcx.get_diagnostic_item(sym::Send),
self.tcx.lang_items().unpin_trait(),
self.tcx.get_diagnostic_item(sym::unwind_safe_trait),
self.tcx.get_diagnostic_item(sym::ref_unwind_safe_trait),
];
const AUTO_TRAITS: [&str; 6] =
["`Clone`", "`Sync`", "`Send`", "`Unpin`", "`UnwindSafe`", "`RefUnwindSafe`"];
let root_var_min_capture_list = min_captures.and_then(|m| m.get(&var_hir_id))?;
let ty = self.resolve_vars_if_possible(self.node_ty(var_hir_id));
let ty = match closure_clause {
hir::CaptureBy::Value { .. } => ty, // For move closure the capture kind should be by value
hir::CaptureBy::Ref => {
// For non move closure the capture kind is the max capture kind of all captures
// according to the ordering ImmBorrow < UniqueImmBorrow < MutBorrow < ByValue
let mut max_capture_info = root_var_min_capture_list.first().unwrap().info;
for capture in root_var_min_capture_list.iter() {
max_capture_info = determine_capture_info(max_capture_info, capture.info);
}
apply_capture_kind_on_capture_ty(
self.tcx,
ty,
max_capture_info.capture_kind,
Some(self.tcx.lifetimes.re_erased),
)
}
};
let mut obligations_should_hold = Vec::new();
// Checks if a root variable implements any of the auto traits
for check_trait in auto_traits_def_id.iter() {
obligations_should_hold.push(check_trait.is_some_and(|check_trait| {
self.infcx
.type_implements_trait(check_trait, [ty], self.param_env)
.must_apply_modulo_regions()
}));
}
let mut problematic_captures = FxIndexMap::default();
// Check whether captured fields also implement the trait
for capture in root_var_min_capture_list.iter() {
let ty = apply_capture_kind_on_capture_ty(
self.tcx,
capture.place.ty(),
capture.info.capture_kind,
Some(self.tcx.lifetimes.re_erased),
);
// Checks if a capture implements any of the auto traits
let mut obligations_holds_for_capture = Vec::new();
for check_trait in auto_traits_def_id.iter() {
obligations_holds_for_capture.push(check_trait.is_some_and(|check_trait| {
self.infcx
.type_implements_trait(check_trait, [ty], self.param_env)
.must_apply_modulo_regions()
}));
}
let mut capture_problems = UnordSet::default();
// Checks if for any of the auto traits, one or more trait is implemented
// by the root variable but not by the capture
for (idx, _) in obligations_should_hold.iter().enumerate() {
if !obligations_holds_for_capture[idx] && obligations_should_hold[idx] {
capture_problems.insert(AUTO_TRAITS[idx]);
}
}
if !capture_problems.is_empty() {
problematic_captures.insert(
UpvarMigrationInfo::CapturingPrecise {
source_expr: capture.info.path_expr_id,
var_name: capture.to_string(self.tcx),
},
capture_problems,
);
}
}
if !problematic_captures.is_empty() {
return Some(problematic_captures);
}
None
}
/// Figures out the list of root variables (and their types) that aren't completely
/// captured by the closure when `capture_disjoint_fields` is enabled and drop order of
/// some path starting at that root variable **might** be affected.
///
/// The output list would include a root variable if:
/// - It would have been moved into the closure when `capture_disjoint_fields` wasn't
/// enabled, **and**
/// - It wasn't completely captured by the closure, **and**
/// - One of the paths starting at this root variable, that is not captured needs Drop.
///
/// This function only returns a HashSet of CapturesInfo for significant drops. If there
/// are no significant drops than None is returned
#[instrument(level = "debug", skip(self))]
fn compute_2229_migrations_for_drop(
&self,
closure_def_id: LocalDefId,
closure_span: Span,
min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
closure_clause: hir::CaptureBy,
var_hir_id: hir::HirId,
) -> Option<FxIndexSet<UpvarMigrationInfo>> {
let ty = self.resolve_vars_if_possible(self.node_ty(var_hir_id));
if !ty.has_significant_drop(self.tcx, self.tcx.param_env(closure_def_id)) {
debug!("does not have significant drop");
return None;
}
let Some(root_var_min_capture_list) = min_captures.and_then(|m| m.get(&var_hir_id)) else {
// The upvar is mentioned within the closure but no path starting from it is
// used. This occurs when you have (e.g.)
//
// ```
// let x = move || {
// let _ = y;
// });
// ```
debug!("no path starting from it is used");
match closure_clause {
// Only migrate if closure is a move closure
hir::CaptureBy::Value { .. } => {
let mut diagnostics_info = FxIndexSet::default();
let upvars =
self.tcx.upvars_mentioned(closure_def_id).expect("must be an upvar");
let upvar = upvars[&var_hir_id];
diagnostics_info
.insert(UpvarMigrationInfo::CapturingNothing { use_span: upvar.span });
return Some(diagnostics_info);
}
hir::CaptureBy::Ref => {}
}
return None;
};
debug!(?root_var_min_capture_list);
let mut projections_list = Vec::new();
let mut diagnostics_info = FxIndexSet::default();
for captured_place in root_var_min_capture_list.iter() {
match captured_place.info.capture_kind {
// Only care about captures that are moved into the closure
ty::UpvarCapture::ByValue => {
projections_list.push(captured_place.place.projections.as_slice());
diagnostics_info.insert(UpvarMigrationInfo::CapturingPrecise {
source_expr: captured_place.info.path_expr_id,
var_name: captured_place.to_string(self.tcx),
});
}
ty::UpvarCapture::ByRef(..) => {}
}
}
debug!(?projections_list);
debug!(?diagnostics_info);
let is_moved = !projections_list.is_empty();
debug!(?is_moved);
let is_not_completely_captured =
root_var_min_capture_list.iter().any(|capture| !capture.place.projections.is_empty());
debug!(?is_not_completely_captured);
if is_moved
&& is_not_completely_captured
&& self.has_significant_drop_outside_of_captures(
closure_def_id,
closure_span,
ty,
projections_list,
)
{
return Some(diagnostics_info);
}
None
}
/// Figures out the list of root variables (and their types) that aren't completely
/// captured by the closure when `capture_disjoint_fields` is enabled and either drop
/// order of some path starting at that root variable **might** be affected or auto-traits
/// differ between the root variable and the captured paths.
///
/// The output list would include a root variable if:
/// - It would have been moved into the closure when `capture_disjoint_fields` wasn't
/// enabled, **and**
/// - It wasn't completely captured by the closure, **and**
/// - One of the paths starting at this root variable, that is not captured needs Drop **or**
/// - One of the paths captured does not implement all the auto-traits its root variable
/// implements.
///
/// Returns a tuple containing a vector of MigrationDiagnosticInfo, as well as a String
/// containing the reason why root variables whose HirId is contained in the vector should
/// be captured
#[instrument(level = "debug", skip(self))]
fn compute_2229_migrations(
&self,
closure_def_id: LocalDefId,
closure_span: Span,
closure_clause: hir::CaptureBy,
min_captures: Option<&ty::RootVariableMinCaptureList<'tcx>>,
) -> (Vec<NeededMigration>, MigrationWarningReason) {
let Some(upvars) = self.tcx.upvars_mentioned(closure_def_id) else {
return (Vec::new(), MigrationWarningReason::default());
};
let mut need_migrations = Vec::new();
let mut auto_trait_migration_reasons = UnordSet::default();
let mut drop_migration_needed = false;
// Perform auto-trait analysis
for (&var_hir_id, _) in upvars.iter() {
let mut diagnostics_info = Vec::new();
let auto_trait_diagnostic = if let Some(diagnostics_info) =
self.compute_2229_migrations_for_trait(min_captures, var_hir_id, closure_clause)
{
diagnostics_info
} else {
FxIndexMap::default()
};
let drop_reorder_diagnostic = if let Some(diagnostics_info) = self
.compute_2229_migrations_for_drop(
closure_def_id,
closure_span,
min_captures,
closure_clause,
var_hir_id,
) {
drop_migration_needed = true;
diagnostics_info
} else {
FxIndexSet::default()
};
// Combine all the captures responsible for needing migrations into one HashSet
let mut capture_diagnostic = drop_reorder_diagnostic.clone();
for key in auto_trait_diagnostic.keys() {
capture_diagnostic.insert(key.clone());
}
let mut capture_diagnostic = capture_diagnostic.into_iter().collect::<Vec<_>>();
capture_diagnostic.sort();
for captures_info in capture_diagnostic {
// Get the auto trait reasons of why migration is needed because of that capture, if there are any
let capture_trait_reasons =
if let Some(reasons) = auto_trait_diagnostic.get(&captures_info) {
reasons.clone()
} else {
UnordSet::default()
};
// Check if migration is needed because of drop reorder as a result of that capture
let capture_drop_reorder_reason = drop_reorder_diagnostic.contains(&captures_info);
// Combine all the reasons of why the root variable should be captured as a result of
// auto trait implementation issues
auto_trait_migration_reasons.extend_unord(capture_trait_reasons.items().copied());
diagnostics_info.push(MigrationLintNote {
captures_info,
reason: self.compute_2229_migrations_reasons(
capture_trait_reasons,
capture_drop_reorder_reason,
),
});
}
if !diagnostics_info.is_empty() {
need_migrations.push(NeededMigration { var_hir_id, diagnostics_info });
}
}
(
need_migrations,
self.compute_2229_migrations_reasons(
auto_trait_migration_reasons,
drop_migration_needed,
),
)
}
/// This is a helper function to `compute_2229_migrations_precise_pass`. Provided the type
/// of a root variable and a list of captured paths starting at this root variable (expressed
/// using list of `Projection` slices), it returns true if there is a path that is not
/// captured starting at this root variable that implements Drop.
///
/// The way this function works is at a given call it looks at type `base_path_ty` of some base
/// path say P and then list of projection slices which represent the different captures moved
/// into the closure starting off of P.
///
/// This will make more sense with an example:
///
/// ```rust,edition2021
///
/// struct FancyInteger(i32); // This implements Drop
///
/// struct Point { x: FancyInteger, y: FancyInteger }
/// struct Color;
///
/// struct Wrapper { p: Point, c: Color }
///
/// fn f(w: Wrapper) {
/// let c = || {
/// // Closure captures w.p.x and w.c by move.
/// };
///
/// c();
/// }
/// ```
///
/// If `capture_disjoint_fields` wasn't enabled the closure would've moved `w` instead of the
/// precise paths. If we look closely `w.p.y` isn't captured which implements Drop and
/// therefore Drop ordering would change and we want this function to return true.
///
/// Call stack to figure out if we need to migrate for `w` would look as follows:
///
/// Our initial base path is just `w`, and the paths captured from it are `w[p, x]` and
/// `w[c]`.
/// Notation:
/// - Ty(place): Type of place
/// - `(a, b)`: Represents the function parameters `base_path_ty` and `captured_by_move_projs`
/// respectively.
/// ```ignore (illustrative)
/// (Ty(w), [ &[p, x], &[c] ])
/// // |
/// // ----------------------------
/// // | |
/// // v v
/// (Ty(w.p), [ &[x] ]) (Ty(w.c), [ &[] ]) // I(1)
/// // | |
/// // v v
/// (Ty(w.p), [ &[x] ]) false
/// // |
/// // |
/// // -------------------------------
/// // | |
/// // v v
/// (Ty((w.p).x), [ &[] ]) (Ty((w.p).y), []) // IMP 2
/// // | |
/// // v v
/// false NeedsSignificantDrop(Ty(w.p.y))
/// // |
/// // v
/// true
/// ```
///
/// IMP 1 `(Ty(w.c), [ &[] ])`: Notice the single empty slice inside `captured_projs`.
/// This implies that the `w.c` is completely captured by the closure.
/// Since drop for this path will be called when the closure is
/// dropped we don't need to migrate for it.
///
/// IMP 2 `(Ty((w.p).y), [])`: Notice that `captured_projs` is empty. This implies that this
/// path wasn't captured by the closure. Also note that even
/// though we didn't capture this path, the function visits it,
/// which is kind of the point of this function. We then return
/// if the type of `w.p.y` implements Drop, which in this case is
/// true.
///
/// Consider another example:
///
/// ```ignore (pseudo-rust)
/// struct X;
/// impl Drop for X {}
///
/// struct Y(X);
/// impl Drop for Y {}
///
/// fn foo() {
/// let y = Y(X);
/// let c = || move(y.0);
/// }
/// ```
///
/// Note that `y.0` is captured by the closure. When this function is called for `y`, it will
/// return true, because even though all paths starting at `y` are captured, `y` itself
/// implements Drop which will be affected since `y` isn't completely captured.
fn has_significant_drop_outside_of_captures(
&self,
closure_def_id: LocalDefId,
closure_span: Span,
base_path_ty: Ty<'tcx>,
captured_by_move_projs: Vec<&[Projection<'tcx>]>,
) -> bool {
let needs_drop =
|ty: Ty<'tcx>| ty.has_significant_drop(self.tcx, self.tcx.param_env(closure_def_id));
let is_drop_defined_for_ty = |ty: Ty<'tcx>| {
let drop_trait = self.tcx.require_lang_item(hir::LangItem::Drop, Some(closure_span));
self.infcx
.type_implements_trait(drop_trait, [ty], self.tcx.param_env(closure_def_id))
.must_apply_modulo_regions()
};
let is_drop_defined_for_ty = is_drop_defined_for_ty(base_path_ty);
// If there is a case where no projection is applied on top of current place
// then there must be exactly one capture corresponding to such a case. Note that this
// represents the case of the path being completely captured by the variable.
//
// eg. If `a.b` is captured and we are processing `a.b`, then we can't have the closure also
// capture `a.b.c`, because that violates min capture.
let is_completely_captured = captured_by_move_projs.iter().any(|projs| projs.is_empty());
assert!(!is_completely_captured || (captured_by_move_projs.len() == 1));
if is_completely_captured {
// The place is captured entirely, so doesn't matter if needs dtor, it will be drop
// when the closure is dropped.
return false;
}
if captured_by_move_projs.is_empty() {
return needs_drop(base_path_ty);
}
if is_drop_defined_for_ty {
// If drop is implemented for this type then we need it to be fully captured,
// and we know it is not completely captured because of the previous checks.
// Note that this is a bug in the user code that will be reported by the
// borrow checker, since we can't move out of drop types.
// The bug exists in the user's code pre-migration, and we don't migrate here.
return false;
}
match base_path_ty.kind() {
// Observations:
// - `captured_by_move_projs` is not empty. Therefore we can call
// `captured_by_move_projs.first().unwrap()` safely.
// - All entries in `captured_by_move_projs` have at least one projection.
// Therefore we can call `captured_by_move_projs.first().unwrap().first().unwrap()` safely.
// We don't capture derefs in case of move captures, which would have be applied to
// access any further paths.
ty::Adt(def, _) if def.is_box() => unreachable!(),
ty::Ref(..) => unreachable!(),
ty::RawPtr(..) => unreachable!(),
ty::Adt(def, args) => {
// Multi-variant enums are captured in entirety,
// which would've been handled in the case of single empty slice in `captured_by_move_projs`.
assert_eq!(def.variants().len(), 1);
// Only Field projections can be applied to a non-box Adt.
assert!(
captured_by_move_projs.iter().all(|projs| matches!(
projs.first().unwrap().kind,
ProjectionKind::Field(..)
))
);
def.variants().get(FIRST_VARIANT).unwrap().fields.iter_enumerated().any(
|(i, field)| {
let paths_using_field = captured_by_move_projs
.iter()
.filter_map(|projs| {
if let ProjectionKind::Field(field_idx, _) =
projs.first().unwrap().kind
{
if field_idx == i { Some(&projs[1..]) } else { None }
} else {
unreachable!();
}
})
.collect();
let after_field_ty = field.ty(self.tcx, args);
self.has_significant_drop_outside_of_captures(
closure_def_id,
closure_span,
after_field_ty,
paths_using_field,
)
},
)
}
ty::Tuple(fields) => {
// Only Field projections can be applied to a tuple.
assert!(
captured_by_move_projs.iter().all(|projs| matches!(
projs.first().unwrap().kind,
ProjectionKind::Field(..)
))
);
fields.iter().enumerate().any(|(i, element_ty)| {
let paths_using_field = captured_by_move_projs
.iter()
.filter_map(|projs| {
if let ProjectionKind::Field(field_idx, _) = projs.first().unwrap().kind
{
if field_idx.index() == i { Some(&projs[1..]) } else { None }
} else {
unreachable!();
}
})
.collect();
self.has_significant_drop_outside_of_captures(
closure_def_id,
closure_span,
element_ty,
paths_using_field,
)
})
}
// Anything else would be completely captured and therefore handled already.
_ => unreachable!(),
}
}
fn init_capture_kind_for_place(
&self,
place: &Place<'tcx>,
capture_clause: hir::CaptureBy,
) -> ty::UpvarCapture {
match capture_clause {
// In case of a move closure if the data is accessed through a reference we
// want to capture by ref to allow precise capture using reborrows.
//
// If the data will be moved out of this place, then the place will be truncated
// at the first Deref in `adjust_upvar_borrow_kind_for_consume` and then moved into
// the closure.
hir::CaptureBy::Value { .. } if !place.deref_tys().any(Ty::is_ref) => {
ty::UpvarCapture::ByValue
}
hir::CaptureBy::Value { .. } | hir::CaptureBy::Ref => {
ty::UpvarCapture::ByRef(ty::ImmBorrow)
}
}
}
fn place_for_root_variable(
&self,
closure_def_id: LocalDefId,
var_hir_id: hir::HirId,
) -> Place<'tcx> {
let upvar_id = ty::UpvarId::new(var_hir_id, closure_def_id);
Place {
base_ty: self.node_ty(var_hir_id),
base: PlaceBase::Upvar(upvar_id),
projections: Default::default(),
}
}
fn should_log_capture_analysis(&self, closure_def_id: LocalDefId) -> bool {
self.tcx.has_attr(closure_def_id, sym::rustc_capture_analysis)
}
fn log_capture_analysis_first_pass(
&self,
closure_def_id: LocalDefId,
capture_information: &InferredCaptureInformation<'tcx>,
closure_span: Span,
) {
if self.should_log_capture_analysis(closure_def_id) {
let mut diag =
self.tcx.sess.struct_span_err(closure_span, "First Pass analysis includes:");
for (place, capture_info) in capture_information {
let capture_str = construct_capture_info_string(self.tcx, place, capture_info);
let output_str = format!("Capturing {capture_str}");
let span =
capture_info.path_expr_id.map_or(closure_span, |e| self.tcx.hir().span(e));
diag.span_note(span, output_str);
}
diag.emit();
}
}
fn log_closure_min_capture_info(&self, closure_def_id: LocalDefId, closure_span: Span) {
if self.should_log_capture_analysis(closure_def_id) {
if let Some(min_captures) =
self.typeck_results.borrow().closure_min_captures.get(&closure_def_id)
{
let mut diag =
self.tcx.sess.struct_span_err(closure_span, "Min Capture analysis includes:");
for (_, min_captures_for_var) in min_captures {
for capture in min_captures_for_var {
let place = &capture.place;
let capture_info = &capture.info;
let capture_str =
construct_capture_info_string(self.tcx, place, capture_info);
let output_str = format!("Min Capture {capture_str}");
if capture.info.path_expr_id != capture.info.capture_kind_expr_id {
let path_span = capture_info
.path_expr_id
.map_or(closure_span, |e| self.tcx.hir().span(e));
let capture_kind_span = capture_info
.capture_kind_expr_id
.map_or(closure_span, |e| self.tcx.hir().span(e));
let mut multi_span: MultiSpan =
MultiSpan::from_spans(vec![path_span, capture_kind_span]);
let capture_kind_label =
construct_capture_kind_reason_string(self.tcx, place, capture_info);
let path_label = construct_path_string(self.tcx, place);
multi_span.push_span_label(path_span, path_label);
multi_span.push_span_label(capture_kind_span, capture_kind_label);
diag.span_note(multi_span, output_str);
} else {
let span = capture_info
.path_expr_id
.map_or(closure_span, |e| self.tcx.hir().span(e));
diag.span_note(span, output_str);
};
}
}
diag.emit();
}
}
}
/// A captured place is mutable if
/// 1. Projections don't include a Deref of an immut-borrow, **and**
/// 2. PlaceBase is mut or projections include a Deref of a mut-borrow.
fn determine_capture_mutability(
&self,
typeck_results: &'a TypeckResults<'tcx>,
place: &Place<'tcx>,
) -> hir::Mutability {
let var_hir_id = match place.base {
PlaceBase::Upvar(upvar_id) => upvar_id.var_path.hir_id,
_ => unreachable!(),
};
let bm = *typeck_results.pat_binding_modes().get(var_hir_id).expect("missing binding mode");
let mut is_mutbl = match bm {
ty::BindByValue(mutability) => mutability,
ty::BindByReference(_) => hir::Mutability::Not,
};
for pointer_ty in place.deref_tys() {
match pointer_ty.kind() {
// We don't capture derefs of raw ptrs
ty::RawPtr(_) => unreachable!(),
// Dereferencing a mut-ref allows us to mut the Place if we don't deref
// an immut-ref after on top of this.
ty::Ref(.., hir::Mutability::Mut) => is_mutbl = hir::Mutability::Mut,
// The place isn't mutable once we dereference an immutable reference.
ty::Ref(.., hir::Mutability::Not) => return hir::Mutability::Not,
// Dereferencing a box doesn't change mutability
ty::Adt(def, ..) if def.is_box() => {}
unexpected_ty => bug!("deref of unexpected pointer type {:?}", unexpected_ty),
}
}
is_mutbl
}
}
/// Truncate the capture so that the place being borrowed is in accordance with RFC 1240,
/// which states that it's unsafe to take a reference into a struct marked `repr(packed)`.
fn restrict_repr_packed_field_ref_capture<'tcx>(
mut place: Place<'tcx>,
mut curr_borrow_kind: ty::UpvarCapture,
) -> (Place<'tcx>, ty::UpvarCapture) {
let pos = place.projections.iter().enumerate().position(|(i, p)| {
let ty = place.ty_before_projection(i);
// Return true for fields of packed structs.
match p.kind {
ProjectionKind::Field(..) => match ty.kind() {
ty::Adt(def, _) if def.repr().packed() => {
// We stop here regardless of field alignment. Field alignment can change as
// types change, including the types of private fields in other crates, and that
// shouldn't affect how we compute our captures.
true
}
_ => false,
},
_ => false,
}
});
if let Some(pos) = pos {
truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_borrow_kind, pos);
}
(place, curr_borrow_kind)
}
/// Returns a Ty that applies the specified capture kind on the provided capture Ty
fn apply_capture_kind_on_capture_ty<'tcx>(
tcx: TyCtxt<'tcx>,
ty: Ty<'tcx>,
capture_kind: UpvarCapture,
region: Option<ty::Region<'tcx>>,
) -> Ty<'tcx> {
match capture_kind {
ty::UpvarCapture::ByValue => ty,
ty::UpvarCapture::ByRef(kind) => Ty::new_ref(
tcx,
region.unwrap(),
ty::TypeAndMut { ty: ty, mutbl: kind.to_mutbl_lossy() },
),
}
}
/// Returns the Span of where the value with the provided HirId would be dropped
fn drop_location_span(tcx: TyCtxt<'_>, hir_id: hir::HirId) -> Span {
let owner_id = tcx.hir().get_enclosing_scope(hir_id).unwrap();
let owner_node = tcx.hir().get(owner_id);
let owner_span = match owner_node {
hir::Node::Item(item) => match item.kind {
hir::ItemKind::Fn(_, _, owner_id) => tcx.hir().span(owner_id.hir_id),
_ => {
bug!("Drop location span error: need to handle more ItemKind '{:?}'", item.kind);
}
},
hir::Node::Block(block) => tcx.hir().span(block.hir_id),
hir::Node::TraitItem(item) => tcx.hir().span(item.hir_id()),
hir::Node::ImplItem(item) => tcx.hir().span(item.hir_id()),
_ => {
bug!("Drop location span error: need to handle more Node '{:?}'", owner_node);
}
};
tcx.sess.source_map().end_point(owner_span)
}
struct InferBorrowKind<'tcx> {
// The def-id of the closure whose kind and upvar accesses are being inferred.
closure_def_id: LocalDefId,
/// For each Place that is captured by the closure, we track the minimal kind of
/// access we need (ref, ref mut, move, etc) and the expression that resulted in such access.
///
/// Consider closure where s.str1 is captured via an ImmutableBorrow and
/// s.str2 via a MutableBorrow
///
/// ```rust,no_run
/// struct SomeStruct { str1: String, str2: String };
///
/// // Assume that the HirId for the variable definition is `V1`
/// let mut s = SomeStruct { str1: format!("s1"), str2: format!("s2") };
///
/// let fix_s = |new_s2| {
/// // Assume that the HirId for the expression `s.str1` is `E1`
/// println!("Updating SomeStruct with str1={0}", s.str1);
/// // Assume that the HirId for the expression `*s.str2` is `E2`
/// s.str2 = new_s2;
/// };
/// ```
///
/// For closure `fix_s`, (at a high level) the map contains
///
/// ```ignore (illustrative)
/// Place { V1, [ProjectionKind::Field(Index=0, Variant=0)] } : CaptureKind { E1, ImmutableBorrow }
/// Place { V1, [ProjectionKind::Field(Index=1, Variant=0)] } : CaptureKind { E2, MutableBorrow }
/// ```
capture_information: InferredCaptureInformation<'tcx>,
fake_reads: Vec<(Place<'tcx>, FakeReadCause, hir::HirId)>,
}
impl<'tcx> euv::Delegate<'tcx> for InferBorrowKind<'tcx> {
fn fake_read(
&mut self,
place: &PlaceWithHirId<'tcx>,
cause: FakeReadCause,
diag_expr_id: hir::HirId,
) {
let PlaceBase::Upvar(_) = place.place.base else { return };
// We need to restrict Fake Read precision to avoid fake reading unsafe code,
// such as deref of a raw pointer.
let dummy_capture_kind = ty::UpvarCapture::ByRef(ty::BorrowKind::ImmBorrow);
let (place, _) = restrict_capture_precision(place.place.clone(), dummy_capture_kind);
let (place, _) = restrict_repr_packed_field_ref_capture(place, dummy_capture_kind);
self.fake_reads.push((place, cause, diag_expr_id));
}
#[instrument(skip(self), level = "debug")]
fn consume(&mut self, place_with_id: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) {
let PlaceBase::Upvar(upvar_id) = place_with_id.place.base else { return };
assert_eq!(self.closure_def_id, upvar_id.closure_expr_id);
self.capture_information.push((
place_with_id.place.clone(),
ty::CaptureInfo {
capture_kind_expr_id: Some(diag_expr_id),
path_expr_id: Some(diag_expr_id),
capture_kind: ty::UpvarCapture::ByValue,
},
));
}
#[instrument(skip(self), level = "debug")]
fn borrow(
&mut self,
place_with_id: &PlaceWithHirId<'tcx>,
diag_expr_id: hir::HirId,
bk: ty::BorrowKind,
) {
let PlaceBase::Upvar(upvar_id) = place_with_id.place.base else { return };
assert_eq!(self.closure_def_id, upvar_id.closure_expr_id);
// The region here will get discarded/ignored
let capture_kind = ty::UpvarCapture::ByRef(bk);
// We only want repr packed restriction to be applied to reading references into a packed
// struct, and not when the data is being moved. Therefore we call this method here instead
// of in `restrict_capture_precision`.
let (place, mut capture_kind) =
restrict_repr_packed_field_ref_capture(place_with_id.place.clone(), capture_kind);
// Raw pointers don't inherit mutability
if place_with_id.place.deref_tys().any(Ty::is_unsafe_ptr) {
capture_kind = ty::UpvarCapture::ByRef(ty::BorrowKind::ImmBorrow);
}
self.capture_information.push((
place,
ty::CaptureInfo {
capture_kind_expr_id: Some(diag_expr_id),
path_expr_id: Some(diag_expr_id),
capture_kind,
},
));
}
#[instrument(skip(self), level = "debug")]
fn mutate(&mut self, assignee_place: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) {
self.borrow(assignee_place, diag_expr_id, ty::BorrowKind::MutBorrow);
}
}
/// Rust doesn't permit moving fields out of a type that implements drop
fn restrict_precision_for_drop_types<'a, 'tcx>(
fcx: &'a FnCtxt<'a, 'tcx>,
mut place: Place<'tcx>,
mut curr_mode: ty::UpvarCapture,
) -> (Place<'tcx>, ty::UpvarCapture) {
let is_copy_type = fcx.infcx.type_is_copy_modulo_regions(fcx.param_env, place.ty());
if let (false, UpvarCapture::ByValue) = (is_copy_type, curr_mode) {
for i in 0..place.projections.len() {
match place.ty_before_projection(i).kind() {
ty::Adt(def, _) if def.destructor(fcx.tcx).is_some() => {
truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i);
break;
}
_ => {}
}
}
}
(place, curr_mode)
}
/// Truncate `place` so that an `unsafe` block isn't required to capture it.
/// - No projections are applied to raw pointers, since these require unsafe blocks. We capture
/// them completely.
/// - No projections are applied on top of Union ADTs, since these require unsafe blocks.
fn restrict_precision_for_unsafe(
mut place: Place<'_>,
mut curr_mode: ty::UpvarCapture,
) -> (Place<'_>, ty::UpvarCapture) {
if place.base_ty.is_unsafe_ptr() {
truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, 0);
}
if place.base_ty.is_union() {
truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, 0);
}
for (i, proj) in place.projections.iter().enumerate() {
if proj.ty.is_unsafe_ptr() {
// Don't apply any projections on top of an unsafe ptr.
truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i + 1);
break;
}
if proj.ty.is_union() {
// Don't capture precise fields of a union.
truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i + 1);
break;
}
}
(place, curr_mode)
}
/// Truncate projections so that following rules are obeyed by the captured `place`:
/// - No Index projections are captured, since arrays are captured completely.
/// - No unsafe block is required to capture `place`
/// Returns the truncated place and updated capture mode.
fn restrict_capture_precision(
place: Place<'_>,
curr_mode: ty::UpvarCapture,
) -> (Place<'_>, ty::UpvarCapture) {
let (mut place, mut curr_mode) = restrict_precision_for_unsafe(place, curr_mode);
if place.projections.is_empty() {
// Nothing to do here
return (place, curr_mode);
}
for (i, proj) in place.projections.iter().enumerate() {
match proj.kind {
ProjectionKind::Index | ProjectionKind::Subslice => {
// Arrays are completely captured, so we drop Index and Subslice projections
truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, i);
return (place, curr_mode);
}
ProjectionKind::Deref => {}
ProjectionKind::OpaqueCast => {}
ProjectionKind::Field(..) => {} // ignore
}
}
(place, curr_mode)
}
/// Truncate deref of any reference.
fn adjust_for_move_closure(
mut place: Place<'_>,
mut kind: ty::UpvarCapture,
) -> (Place<'_>, ty::UpvarCapture) {
let first_deref = place.projections.iter().position(|proj| proj.kind == ProjectionKind::Deref);
if let Some(idx) = first_deref {
truncate_place_to_len_and_update_capture_kind(&mut place, &mut kind, idx);
}
(place, ty::UpvarCapture::ByValue)
}
/// Adjust closure capture just that if taking ownership of data, only move data
/// from enclosing stack frame.
fn adjust_for_non_move_closure(
mut place: Place<'_>,
mut kind: ty::UpvarCapture,
) -> (Place<'_>, ty::UpvarCapture) {
let contains_deref =
place.projections.iter().position(|proj| proj.kind == ProjectionKind::Deref);
match kind {
ty::UpvarCapture::ByValue => {
if let Some(idx) = contains_deref {
truncate_place_to_len_and_update_capture_kind(&mut place, &mut kind, idx);
}
}
ty::UpvarCapture::ByRef(..) => {}
}
(place, kind)
}
fn construct_place_string<'tcx>(tcx: TyCtxt<'_>, place: &Place<'tcx>) -> String {
let variable_name = match place.base {
PlaceBase::Upvar(upvar_id) => var_name(tcx, upvar_id.var_path.hir_id).to_string(),
_ => bug!("Capture_information should only contain upvars"),
};
let mut projections_str = String::new();
for (i, item) in place.projections.iter().enumerate() {
let proj = match item.kind {
ProjectionKind::Field(a, b) => format!("({a:?}, {b:?})"),
ProjectionKind::Deref => String::from("Deref"),
ProjectionKind::Index => String::from("Index"),
ProjectionKind::Subslice => String::from("Subslice"),
ProjectionKind::OpaqueCast => String::from("OpaqueCast"),
};
if i != 0 {
projections_str.push(',');
}
projections_str.push_str(proj.as_str());
}
format!("{variable_name}[{projections_str}]")
}
fn construct_capture_kind_reason_string<'tcx>(
tcx: TyCtxt<'_>,
place: &Place<'tcx>,
capture_info: &ty::CaptureInfo,
) -> String {
let place_str = construct_place_string(tcx, place);
let capture_kind_str = match capture_info.capture_kind {
ty::UpvarCapture::ByValue => "ByValue".into(),
ty::UpvarCapture::ByRef(kind) => format!("{kind:?}"),
};
format!("{place_str} captured as {capture_kind_str} here")
}
fn construct_path_string<'tcx>(tcx: TyCtxt<'_>, place: &Place<'tcx>) -> String {
let place_str = construct_place_string(tcx, place);
format!("{place_str} used here")
}
fn construct_capture_info_string<'tcx>(
tcx: TyCtxt<'_>,
place: &Place<'tcx>,
capture_info: &ty::CaptureInfo,
) -> String {
let place_str = construct_place_string(tcx, place);
let capture_kind_str = match capture_info.capture_kind {
ty::UpvarCapture::ByValue => "ByValue".into(),
ty::UpvarCapture::ByRef(kind) => format!("{kind:?}"),
};
format!("{place_str} -> {capture_kind_str}")
}
fn var_name(tcx: TyCtxt<'_>, var_hir_id: hir::HirId) -> Symbol {
tcx.hir().name(var_hir_id)
}
#[instrument(level = "debug", skip(tcx))]
fn should_do_rust_2021_incompatible_closure_captures_analysis(
tcx: TyCtxt<'_>,
closure_id: hir::HirId,
) -> bool {
if tcx.sess.at_least_rust_2021() {
return false;
}
let (level, _) =
tcx.lint_level_at_node(lint::builtin::RUST_2021_INCOMPATIBLE_CLOSURE_CAPTURES, closure_id);
!matches!(level, lint::Level::Allow)
}
/// Return a two string tuple (s1, s2)
/// - s1: Line of code that is needed for the migration: eg: `let _ = (&x, ...)`.
/// - s2: Comma separated names of the variables being migrated.
fn migration_suggestion_for_2229(
tcx: TyCtxt<'_>,
need_migrations: &[NeededMigration],
) -> (String, String) {
let need_migrations_variables = need_migrations
.iter()
.map(|NeededMigration { var_hir_id: v, .. }| var_name(tcx, *v))
.collect::<Vec<_>>();
let migration_ref_concat =
need_migrations_variables.iter().map(|v| format!("&{v}")).collect::<Vec<_>>().join(", ");
let migration_string = if 1 == need_migrations.len() {
format!("let _ = {migration_ref_concat}")
} else {
format!("let _ = ({migration_ref_concat})")
};
let migrated_variables_concat =
need_migrations_variables.iter().map(|v| format!("`{v}`")).collect::<Vec<_>>().join(", ");
(migration_string, migrated_variables_concat)
}
/// Helper function to determine if we need to escalate CaptureKind from
/// CaptureInfo A to B and returns the escalated CaptureInfo.
/// (Note: CaptureInfo contains CaptureKind and an expression that led to capture it in that way)
///
/// If both `CaptureKind`s are considered equivalent, then the CaptureInfo is selected based
/// on the `CaptureInfo` containing an associated `capture_kind_expr_id`.
///
/// It is the caller's duty to figure out which path_expr_id to use.
///
/// If both the CaptureKind and Expression are considered to be equivalent,
/// then `CaptureInfo` A is preferred. This can be useful in cases where we want to prioritize
/// expressions reported back to the user as part of diagnostics based on which appears earlier
/// in the closure. This can be achieved simply by calling
/// `determine_capture_info(existing_info, current_info)`. This works out because the
/// expressions that occur earlier in the closure body than the current expression are processed before.
/// Consider the following example
/// ```rust,no_run
/// struct Point { x: i32, y: i32 }
/// let mut p = Point { x: 10, y: 10 };
///
/// let c = || {
/// p.x += 10;
/// // ^ E1 ^
/// // ...
/// // More code
/// // ...
/// p.x += 10; // E2
/// // ^ E2 ^
/// };
/// ```
/// `CaptureKind` associated with both `E1` and `E2` will be ByRef(MutBorrow),
/// and both have an expression associated, however for diagnostics we prefer reporting
/// `E1` since it appears earlier in the closure body. When `E2` is being processed we
/// would've already handled `E1`, and have an existing capture_information for it.
/// Calling `determine_capture_info(existing_info_e1, current_info_e2)` will return
/// `existing_info_e1` in this case, allowing us to point to `E1` in case of diagnostics.
fn determine_capture_info(
capture_info_a: ty::CaptureInfo,
capture_info_b: ty::CaptureInfo,
) -> ty::CaptureInfo {
// If the capture kind is equivalent then, we don't need to escalate and can compare the
// expressions.
let eq_capture_kind = match (capture_info_a.capture_kind, capture_info_b.capture_kind) {
(ty::UpvarCapture::ByValue, ty::UpvarCapture::ByValue) => true,
(ty::UpvarCapture::ByRef(ref_a), ty::UpvarCapture::ByRef(ref_b)) => ref_a == ref_b,
(ty::UpvarCapture::ByValue, _) | (ty::UpvarCapture::ByRef(_), _) => false,
};
if eq_capture_kind {
match (capture_info_a.capture_kind_expr_id, capture_info_b.capture_kind_expr_id) {
(Some(_), _) | (None, None) => capture_info_a,
(None, Some(_)) => capture_info_b,
}
} else {
// We select the CaptureKind which ranks higher based the following priority order:
// ByValue > MutBorrow > UniqueImmBorrow > ImmBorrow
match (capture_info_a.capture_kind, capture_info_b.capture_kind) {
(ty::UpvarCapture::ByValue, _) => capture_info_a,
(_, ty::UpvarCapture::ByValue) => capture_info_b,
(ty::UpvarCapture::ByRef(ref_a), ty::UpvarCapture::ByRef(ref_b)) => {
match (ref_a, ref_b) {
// Take LHS:
(ty::UniqueImmBorrow | ty::MutBorrow, ty::ImmBorrow)
| (ty::MutBorrow, ty::UniqueImmBorrow) => capture_info_a,
// Take RHS:
(ty::ImmBorrow, ty::UniqueImmBorrow | ty::MutBorrow)
| (ty::UniqueImmBorrow, ty::MutBorrow) => capture_info_b,
(ty::ImmBorrow, ty::ImmBorrow)
| (ty::UniqueImmBorrow, ty::UniqueImmBorrow)
| (ty::MutBorrow, ty::MutBorrow) => {
bug!("Expected unequal capture kinds");
}
}
}
}
}
}
/// Truncates `place` to have up to `len` projections.
/// `curr_mode` is the current required capture kind for the place.
/// Returns the truncated `place` and the updated required capture kind.
///
/// Note: Capture kind changes from `MutBorrow` to `UniqueImmBorrow` if the truncated part of the `place`
/// contained `Deref` of `&mut`.
fn truncate_place_to_len_and_update_capture_kind<'tcx>(
place: &mut Place<'tcx>,
curr_mode: &mut ty::UpvarCapture,
len: usize,
) {
let is_mut_ref = |ty: Ty<'_>| matches!(ty.kind(), ty::Ref(.., hir::Mutability::Mut));
// If the truncated part of the place contains `Deref` of a `&mut` then convert MutBorrow ->
// UniqueImmBorrow
// Note that if the place contained Deref of a raw pointer it would've not been MutBorrow, so
// we don't need to worry about that case here.
match curr_mode {
ty::UpvarCapture::ByRef(ty::BorrowKind::MutBorrow) => {
for i in len..place.projections.len() {
if place.projections[i].kind == ProjectionKind::Deref
&& is_mut_ref(place.ty_before_projection(i))
{
*curr_mode = ty::UpvarCapture::ByRef(ty::BorrowKind::UniqueImmBorrow);
break;
}
}
}
ty::UpvarCapture::ByRef(..) => {}
ty::UpvarCapture::ByValue => {}
}
place.projections.truncate(len);
}
/// Determines the Ancestry relationship of Place A relative to Place B
///
/// `PlaceAncestryRelation::Ancestor` implies Place A is ancestor of Place B
/// `PlaceAncestryRelation::Descendant` implies Place A is descendant of Place B
/// `PlaceAncestryRelation::Divergent` implies neither of them is the ancestor of the other.
fn determine_place_ancestry_relation<'tcx>(
place_a: &Place<'tcx>,
place_b: &Place<'tcx>,
) -> PlaceAncestryRelation {
// If Place A and Place B don't start off from the same root variable, they are divergent.
if place_a.base != place_b.base {
return PlaceAncestryRelation::Divergent;
}
// Assume of length of projections_a = n
let projections_a = &place_a.projections;
// Assume of length of projections_b = m
let projections_b = &place_b.projections;
let same_initial_projections =
iter::zip(projections_a, projections_b).all(|(proj_a, proj_b)| proj_a.kind == proj_b.kind);
if same_initial_projections {
use std::cmp::Ordering;
// First min(n, m) projections are the same
// Select Ancestor/Descendant
match projections_b.len().cmp(&projections_a.len()) {
Ordering::Greater => PlaceAncestryRelation::Ancestor,
Ordering::Equal => PlaceAncestryRelation::SamePlace,
Ordering::Less => PlaceAncestryRelation::Descendant,
}
} else {
PlaceAncestryRelation::Divergent
}
}
/// Reduces the precision of the captured place when the precision doesn't yield any benefit from
/// borrow checking perspective, allowing us to save us on the size of the capture.
///
///
/// Fields that are read through a shared reference will always be read via a shared ref or a copy,
/// and therefore capturing precise paths yields no benefit. This optimization truncates the
/// rightmost deref of the capture if the deref is applied to a shared ref.
///
/// Reason we only drop the last deref is because of the following edge case:
///
/// ```
/// # struct A { field_of_a: Box<i32> }
/// # struct B {}
/// # struct C<'a>(&'a i32);
/// struct MyStruct<'a> {
/// a: &'static A,
/// b: B,
/// c: C<'a>,
/// }
///
/// fn foo<'a, 'b>(m: &'a MyStruct<'b>) -> impl FnMut() + 'static {
/// || drop(&*m.a.field_of_a)
/// // Here we really do want to capture `*m.a` because that outlives `'static`
///
/// // If we capture `m`, then the closure no longer outlives `'static`
/// // it is constrained to `'a`
/// }
/// ```
fn truncate_capture_for_optimization(
mut place: Place<'_>,
mut curr_mode: ty::UpvarCapture,
) -> (Place<'_>, ty::UpvarCapture) {
let is_shared_ref = |ty: Ty<'_>| matches!(ty.kind(), ty::Ref(.., hir::Mutability::Not));
// Find the right-most deref (if any). All the projections that come after this
// are fields or other "in-place pointer adjustments"; these refer therefore to
// data owned by whatever pointer is being dereferenced here.
let idx = place.projections.iter().rposition(|proj| ProjectionKind::Deref == proj.kind);
match idx {
// If that pointer is a shared reference, then we don't need those fields.
Some(idx) if is_shared_ref(place.ty_before_projection(idx)) => {
truncate_place_to_len_and_update_capture_kind(&mut place, &mut curr_mode, idx + 1)
}
None | Some(_) => {}
}
(place, curr_mode)
}
/// Precise capture is enabled if user is using Rust Edition 2021 or higher.
/// `span` is the span of the closure.
fn enable_precise_capture(span: Span) -> bool {
// We use span here to ensure that if the closure was generated by a macro with a different
// edition.
span.at_least_rust_2021()
}