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Merge borrowck permission checks #106451

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Jan 5, 2023
Merged

Merge borrowck permission checks #106451

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48 changes: 11 additions & 37 deletions compiler/rustc_borrowck/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -863,7 +863,6 @@ enum WriteKind {
/// local place can be mutated.
//
// FIXME: @nikomatsakis suggested that this flag could be removed with the following modifications:
// - Merge `check_access_permissions()` and `check_if_reassignment_to_immutable_state()`.
// - Split `is_mutable()` into `is_assignable()` (can be directly assigned) and
// `is_declared_mutable()`.
// - Take flow state into consideration in `is_assignable()` for local variables.
Expand Down Expand Up @@ -1132,20 +1131,6 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
// Write of P[i] or *P requires P init'd.
self.check_if_assigned_path_is_moved(location, place_span, flow_state);

// Special case: you can assign an immutable local variable
// (e.g., `x = ...`) so long as it has never been initialized
// before (at this point in the flow).
if let Some(local) = place_span.0.as_local() {
if let Mutability::Not = self.body.local_decls[local].mutability {
// check for reassignments to immutable local variables
self.check_if_reassignment_to_immutable_state(
location, local, place_span, flow_state,
);
return;
}
}

// Otherwise, use the normal access permission rules.
self.access_place(
location,
place_span,
Expand Down Expand Up @@ -1554,24 +1539,6 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
}
}

fn check_if_reassignment_to_immutable_state(
&mut self,
location: Location,
local: Local,
place_span: (Place<'tcx>, Span),
flow_state: &Flows<'cx, 'tcx>,
) {
debug!("check_if_reassignment_to_immutable_state({:?})", local);

// Check if any of the initializations of `local` have happened yet:
if let Some(init_index) = self.is_local_ever_initialized(local, flow_state) {
// And, if so, report an error.
let init = &self.move_data.inits[init_index];
let span = init.span(&self.body);
self.report_illegal_reassignment(location, place_span, span, place_span.0);
}
}

fn check_if_full_path_is_moved(
&mut self,
location: Location,
Expand Down Expand Up @@ -2037,12 +2004,19 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
// partial initialization, do not complain about mutability
// errors except for actual mutation (as opposed to an attempt
// to do a partial initialization).
let previously_initialized =
self.is_local_ever_initialized(place.local, flow_state).is_some();
let previously_initialized = self.is_local_ever_initialized(place.local, flow_state);

// at this point, we have set up the error reporting state.
if previously_initialized {
self.report_mutability_error(place, span, the_place_err, error_access, location);
if let Some(init_index) = previously_initialized {
if let (AccessKind::Mutate, Some(_)) = (error_access, place.as_local()) {
// If this is a mutate access to an immutable local variable with no projections
// report the error as an illegal reassignment
let init = &self.move_data.inits[init_index];
let assigned_span = init.span(&self.body);
self.report_illegal_reassignment(location, (place, span), assigned_span, place);
} else {
self.report_mutability_error(place, span, the_place_err, error_access, location)
}
true
} else {
false
Expand Down