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turn append_place_to_string from recursion into iteration #96733

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May 6, 2022
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turn append_place_to_string from recursion into iteration #96733

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210 changes: 78 additions & 132 deletions compiler/rustc_borrowck/src/diagnostics/mod.rs
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Original file line number Diff line number Diff line change
@@ -1,5 +1,6 @@
//! Borrow checker diagnostics.

use itertools::Itertools;
use rustc_const_eval::util::{call_kind, CallDesugaringKind};
use rustc_errors::{Applicability, Diagnostic};
use rustc_hir as hir;
Expand Down Expand Up @@ -161,158 +162,103 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
}

/// End-user visible description of `place` if one can be found.
/// If the place is a temporary for instance, None will be returned.
/// If the place is a temporary for instance, `None` will be returned.
pub(super) fn describe_place(&self, place_ref: PlaceRef<'tcx>) -> Option<String> {
self.describe_place_with_options(place_ref, IncludingDowncast(false))
}

/// End-user visible description of `place` if one can be found. If the
/// place is a temporary for instance, None will be returned.
/// `IncludingDowncast` parameter makes the function return `Err` if `ProjectionElem` is
/// End-user visible description of `place` if one can be found. If the place is a temporary
/// for instance, `None` will be returned.
/// `IncludingDowncast` parameter makes the function return `None` if `ProjectionElem` is
/// `Downcast` and `IncludingDowncast` is true
pub(super) fn describe_place_with_options(
&self,
place: PlaceRef<'tcx>,
including_downcast: IncludingDowncast,
) -> Option<String> {
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let local = place.local;
let mut autoderef_index = None;
let mut buf = String::new();
match self.append_place_to_string(place, &mut buf, false, &including_downcast) {
Ok(()) => Some(buf),
Err(()) => None,
}
}

/// Appends end-user visible description of `place` to `buf`.
fn append_place_to_string(
&self,
place: PlaceRef<'tcx>,
buf: &mut String,
mut autoderef: bool,
including_downcast: &IncludingDowncast,
) -> Result<(), ()> {
match place {
PlaceRef { local, projection: [] } => {
self.append_local_to_string(local, buf)?;
}
PlaceRef { local, projection: [ProjectionElem::Deref] }
if self.body.local_decls[local].is_ref_for_guard() =>
{
self.append_place_to_string(
PlaceRef { local, projection: &[] },
buf,
autoderef,
&including_downcast,
)?;
}
PlaceRef { local, projection: [ProjectionElem::Deref] }
if self.body.local_decls[local].is_ref_to_static() =>
{
let local_info = &self.body.local_decls[local].local_info;
if let Some(box LocalInfo::StaticRef { def_id, .. }) = *local_info {
buf.push_str(self.infcx.tcx.item_name(def_id).as_str());
} else {
unreachable!();
}
}
PlaceRef { local, projection: [proj_base @ .., elem] } => {
match elem {
ProjectionElem::Deref => {
let upvar_field_projection = self.is_upvar_field_projection(place);
if let Some(field) = upvar_field_projection {
let var_index = field.index();
let name = self.upvars[var_index].place.to_string(self.infcx.tcx);
if self.upvars[var_index].by_ref {
buf.push_str(&name);
} else {
buf.push('*');
buf.push_str(&name);
}
} else {
if autoderef {
// FIXME turn this recursion into iteration
self.append_place_to_string(
PlaceRef { local, projection: proj_base },
buf,
autoderef,
&including_downcast,
)?;
} else {
buf.push('*');
self.append_place_to_string(
PlaceRef { local, projection: proj_base },
buf,
autoderef,
&including_downcast,
)?;
}
let mut ok = self.append_local_to_string(local, &mut buf);

for (index, elem) in place.projection.into_iter().enumerate() {
match elem {
ProjectionElem::Deref => {
if index == 0 {
if self.body.local_decls[local].is_ref_for_guard() {
continue;
}
}
ProjectionElem::Downcast(..) => {
self.append_place_to_string(
PlaceRef { local, projection: proj_base },
buf,
autoderef,
&including_downcast,
)?;
if including_downcast.0 {
return Err(());
if let Some(box LocalInfo::StaticRef { def_id, .. }) =
&self.body.local_decls[local].local_info
{
buf.push_str(self.infcx.tcx.item_name(*def_id).as_str());
ok = Ok(());
continue;
}
}
ProjectionElem::Field(field, _ty) => {
autoderef = true;

// FIXME(project-rfc_2229#36): print capture precisely here.
let upvar_field_projection = self.is_upvar_field_projection(place);
if let Some(field) = upvar_field_projection {
let var_index = field.index();
let name = self.upvars[var_index].place.to_string(self.infcx.tcx);
buf.push_str(&name);
} else {
let field_name = self
.describe_field(PlaceRef { local, projection: proj_base }, *field);
self.append_place_to_string(
PlaceRef { local, projection: proj_base },
buf,
autoderef,
&including_downcast,
)?;
buf.push('.');
buf.push_str(&field_name);
if let Some(field) = self.is_upvar_field_projection(PlaceRef {
local,
projection: place.projection.split_at(index + 1).0,
}) {
let var_index = field.index();
buf = self.upvars[var_index].place.to_string(self.infcx.tcx);
ok = Ok(());
if !self.upvars[var_index].by_ref {
buf.insert(0, '*');
}
}
ProjectionElem::Index(index) => {
autoderef = true;

self.append_place_to_string(
PlaceRef { local, projection: proj_base },
buf,
autoderef,
&including_downcast,
)?;
buf.push('[');
if self.append_local_to_string(*index, buf).is_err() {
buf.push('_');
} else {
if autoderef_index.is_none() {
autoderef_index =
match place.projection.into_iter().rev().find_position(|elem| {
!matches!(
elem,
ProjectionElem::Deref | ProjectionElem::Downcast(..)
)
}) {
Some((index, _)) => Some(place.projection.len() - index),
None => Some(0),
};
}
if index >= autoderef_index.unwrap() {
buf.insert(0, '*');
}
buf.push(']');
}
ProjectionElem::ConstantIndex { .. } | ProjectionElem::Subslice { .. } => {
autoderef = true;
// Since it isn't possible to borrow an element on a particular index and
// then use another while the borrow is held, don't output indices details
// to avoid confusing the end-user
self.append_place_to_string(
PlaceRef { local, projection: proj_base },
buf,
autoderef,
&including_downcast,
)?;
buf.push_str("[..]");
}
ProjectionElem::Downcast(..) if including_downcast.0 => return None,
ProjectionElem::Downcast(..) => (),
ProjectionElem::Field(field, _ty) => {
// FIXME(project-rfc_2229#36): print capture precisely here.
if let Some(field) = self.is_upvar_field_projection(PlaceRef {
local,
projection: place.projection.split_at(index + 1).0,
}) {
buf = self.upvars[field.index()].place.to_string(self.infcx.tcx);
ok = Ok(());
} else {
let field_name = self.describe_field(
PlaceRef { local, projection: place.projection.split_at(index).0 },
*field,
);
buf.push('.');
buf.push_str(&field_name);
}
};
}
ProjectionElem::Index(index) => {
buf.push('[');
if self.append_local_to_string(*index, &mut buf).is_err() {
buf.push('_');
}
buf.push(']');
}
ProjectionElem::ConstantIndex { .. } | ProjectionElem::Subslice { .. } => {
// Since it isn't possible to borrow an element on a particular index and
// then use another while the borrow is held, don't output indices details
// to avoid confusing the end-user
buf.push_str("[..]");
}
}
}

Ok(())
ok.ok().map(|_| buf)
}

/// Appends end-user visible description of the `local` place to `buf`. If `local` doesn't have
Expand Down