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Separate region inference logic from error handling better #67404

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Dec 21, 2019
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Separate region inference logic from error handling better #67404

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4c7f5af
Separate region inference logic from error handling better
mark-i-m Dec 16, 2019
90ef197
Better comment
mark-i-m Dec 20, 2019
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37 changes: 33 additions & 4 deletions src/librustc_mir/borrow_check/diagnostics/region_errors.rs
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Original file line number Diff line number Diff line change
@@ -1,10 +1,13 @@
//! Error reporting machinery for lifetime errors.

use rustc::hir::def_id::DefId;
use rustc::infer::error_reporting::nice_region_error::NiceRegionError;
use rustc::infer::InferCtxt;
use rustc::infer::NLLRegionVariableOrigin;
use rustc::mir::{ConstraintCategory, Local, Location, Body};
use rustc::infer::{
error_reporting::nice_region_error::NiceRegionError,
InferCtxt, NLLRegionVariableOrigin,
};
use rustc::mir::{
ConstraintCategory, Local, Location, Body,
};
use rustc::ty::{self, RegionVid};
use rustc_index::vec::IndexVec;
use rustc_errors::DiagnosticBuilder;
Expand Down Expand Up @@ -93,6 +96,32 @@ pub struct ErrorConstraintInfo {
}

impl<'tcx> RegionInferenceContext<'tcx> {
/// Converts a region inference variable into a `ty::Region` that
/// we can use for error reporting. If `r` is universally bound,
/// then we use the name that we have on record for it. If `r` is
/// existentially bound, then we check its inferred value and try
/// to find a good name from that. Returns `None` if we can't find
/// one (e.g., this is just some random part of the CFG).
pub fn to_error_region(&self, r: RegionVid) -> Option<ty::Region<'tcx>> {
self.to_error_region_vid(r).and_then(|r| self.definitions[r].external_name)
}

/// Returns the [RegionVid] corresponding to the region returned by
/// `to_error_region`.
pub fn to_error_region_vid(&self, r: RegionVid) -> Option<RegionVid> {
if self.universal_regions.is_universal_region(r) {
Some(r)
} else {
let r_scc = self.constraint_sccs.scc(r);
let upper_bound = self.universal_upper_bound(r);
if self.scc_values.contains(r_scc, upper_bound) {
self.to_error_region_vid(upper_bound)
} else {
None
}
}
}

/// Tries to find the best constraint to blame for the fact that
/// `R: from_region`, where `R` is some region that meets
/// `target_test`. This works by following the constraint graph,
Expand Down
147 changes: 63 additions & 84 deletions src/librustc_mir/borrow_check/region_infer/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -928,32 +928,6 @@ impl<'tcx> RegionInferenceContext<'tcx> {
}
}

/// Converts a region inference variable into a `ty::Region` that
/// we can use for error reporting. If `r` is universally bound,
/// then we use the name that we have on record for it. If `r` is
/// existentially bound, then we check its inferred value and try
/// to find a good name from that. Returns `None` if we can't find
/// one (e.g., this is just some random part of the CFG).
pub fn to_error_region(&self, r: RegionVid) -> Option<ty::Region<'tcx>> {
self.to_error_region_vid(r).and_then(|r| self.definitions[r].external_name)
}

/// Returns the [RegionVid] corresponding to the region returned by
/// `to_error_region`.
pub fn to_error_region_vid(&self, r: RegionVid) -> Option<RegionVid> {
if self.universal_regions.is_universal_region(r) {
Some(r)
} else {
let r_scc = self.constraint_sccs.scc(r);
let upper_bound = self.universal_upper_bound(r);
if self.scc_values.contains(r_scc, upper_bound) {
self.to_error_region_vid(upper_bound)
} else {
None
}
}
}

/// Invoked when we have some type-test (e.g., `T: 'X`) that we cannot
/// prove to be satisfied. If this is a closure, we will attempt to
/// "promote" this type-test into our `ClosureRegionRequirements` and
Expand Down Expand Up @@ -1164,7 +1138,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
/// include the CFG anyhow.
/// - For each `end('x)` element in `'r`, compute the mutual LUB, yielding
/// a result `'y`.
fn universal_upper_bound(&self, r: RegionVid) -> RegionVid {
pub (in crate::borrow_check) fn universal_upper_bound(&self, r: RegionVid) -> RegionVid {
debug!("universal_upper_bound(r={:?}={})", r, self.region_value_str(r));

// Find the smallest universal region that contains all other
Expand Down Expand Up @@ -1458,19 +1432,34 @@ impl<'tcx> RegionInferenceContext<'tcx> {
debug!("check_polonius_subset_errors: subset_error longer_fr={:?},\
shorter_fr={:?}", longer_fr, shorter_fr);

self.report_or_propagate_universal_region_error(
let propagated = self.try_propagate_universal_region_error(
*longer_fr,
*shorter_fr,
infcx,
body,
local_names,
upvars,
mir_def_id,
&mut propagated_outlives_requirements,
&mut outlives_suggestion,
errors_buffer,
region_naming,
);
if !propagated {
// If we are not in a context where we can't propagate errors, or we
// could not shrink `fr` to something smaller, then just report an
// error.
//
// Note: in this case, we use the unapproximated regions to report the
// error. This gives better error messages in some cases.
let db = self.report_error(
body,
local_names,
upvars,
infcx,
mir_def_id,
*longer_fr,
NLLRegionVariableOrigin::FreeRegion,
*shorter_fr,
&mut outlives_suggestion,
region_naming,
);

db.buffer(errors_buffer);
}
}

// Handle the placeholder errors as usual, until the chalk-rustc-polonius triumvirate has
Expand Down Expand Up @@ -1594,48 +1583,59 @@ impl<'tcx> RegionInferenceContext<'tcx> {
return None;
}

self.report_or_propagate_universal_region_error(
let propagated = self.try_propagate_universal_region_error(
longer_fr,
shorter_fr,
infcx,
body,
local_names,
upvars,
mir_def_id,
propagated_outlives_requirements,
outlives_suggestion,
errors_buffer,
region_naming,
)
);

if propagated {
None
} else {
// If we are not in a context where we can't propagate errors, or we
// could not shrink `fr` to something smaller, then just report an
// error.
//
// Note: in this case, we use the unapproximated regions to report the
// error. This gives better error messages in some cases.
let db = self.report_error(
body,
local_names,
upvars,
infcx,
mir_def_id,
longer_fr,
NLLRegionVariableOrigin::FreeRegion,
shorter_fr,
outlives_suggestion,
region_naming,
);

db.buffer(errors_buffer);

Some(ErrorReported)
}
}

fn report_or_propagate_universal_region_error(
/// Attempt to propagate a region error (e.g. `'a: 'b`) that is not met to a closure's
/// creator. If we cannot, then the caller should report an error to the user.
///
/// Returns `true` if the error was propagated, and `false` otherwise.
fn try_propagate_universal_region_error(
&self,
longer_fr: RegionVid,
shorter_fr: RegionVid,
infcx: &InferCtxt<'_, 'tcx>,
body: &Body<'tcx>,
local_names: &IndexVec<Local, Option<Symbol>>,
upvars: &[Upvar],
mir_def_id: DefId,
propagated_outlives_requirements: &mut Option<&mut Vec<ClosureOutlivesRequirement<'tcx>>>,
outlives_suggestion: &mut OutlivesSuggestionBuilder<'_>,
errors_buffer: &mut Vec<Diagnostic>,
region_naming: &mut RegionErrorNamingCtx,
) -> Option<ErrorReported> {
debug!(
"report_or_propagate_universal_region_error: fr={:?} does not outlive shorter_fr={:?}",
longer_fr, shorter_fr,
);

) -> bool {
if let Some(propagated_outlives_requirements) = propagated_outlives_requirements {
// Shrink `longer_fr` until we find a non-local region (if we do).
// We'll call it `fr-` -- it's ever so slightly smaller than
// `longer_fr`.

if let Some(fr_minus) =
self.universal_region_relations.non_local_lower_bound(longer_fr) {
debug!("report_or_propagate_universal_region_error: fr_minus={:?}", fr_minus);
debug!("try_propagate_universal_region_error: fr_minus={:?}", fr_minus);

let blame_span_category =
self.find_outlives_blame_span(body, longer_fr,
Expand All @@ -1648,7 +1648,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
.universal_region_relations
.non_local_upper_bounds(&shorter_fr);
debug!(
"report_or_propagate_universal_region_error: shorter_fr_plus={:?}",
"try_propagate_universal_region_error: shorter_fr_plus={:?}",
shorter_fr_plus
);
for &&fr in &shorter_fr_plus {
Expand All @@ -1660,32 +1660,11 @@ impl<'tcx> RegionInferenceContext<'tcx> {
category: blame_span_category.0,
});
}
return None;
return true;
}
}

// If we are not in a context where we can't propagate errors, or we
// could not shrink `fr` to something smaller, then just report an
// error.
//
// Note: in this case, we use the unapproximated regions to report the
// error. This gives better error messages in some cases.
let db = self.report_error(
body,
local_names,
upvars,
infcx,
mir_def_id,
longer_fr,
NLLRegionVariableOrigin::FreeRegion,
shorter_fr,
outlives_suggestion,
region_naming,
);

db.buffer(errors_buffer);

Some(ErrorReported)
false
}

fn check_bound_universal_region(
Expand Down