use self::values::{LivenessValues, RegionValueElements, RegionValues};
use super::universal_regions::UniversalRegions;
-use super::ToRegionVid;
+use super::{PoloniusOutput, ToRegionVid};
mod dump_mir;
mod graphviz;
upvars: &[Upvar],
mir_def_id: DefId,
errors_buffer: &mut Vec<Diagnostic>,
+ polonius_output: Option<Rc<PoloniusOutput>>,
) -> Option<ClosureRegionRequirements<'tcx>> {
self.propagate_constraints(body);
// multiple problems.
let mut region_naming = RegionErrorNamingCtx::new();
- self.check_universal_regions(
- infcx,
- body,
- local_names,
- upvars,
- mir_def_id,
- outlives_requirements.as_mut(),
- errors_buffer,
- &mut region_naming,
- );
+ // In Polonius mode, the errors about missing universal region relations are in the output
+ // and need to be emitted or propagated. Otherwise, we need to check whether the
+ // constraints were too strong, and if so, emit or propagate those errors.
+ if infcx.tcx.sess.opts.debugging_opts.polonius {
+ self.check_polonius_subset_errors(
+ infcx,
+ body,
+ local_names,
+ upvars,
+ mir_def_id,
+ outlives_requirements.as_mut(),
+ errors_buffer,
+ &mut region_naming,
+ polonius_output.expect("Polonius output is unavailable despite `-Z polonius`"),
+ );
+ } else {
+ self.check_universal_regions(
+ infcx,
+ body,
+ local_names,
+ upvars,
+ mir_def_id,
+ outlives_requirements.as_mut(),
+ errors_buffer,
+ &mut region_naming,
+ );
+ }
self.check_member_constraints(infcx, mir_def_id, errors_buffer);
outlives_suggestion.add_suggestion(body, self, infcx, errors_buffer, region_naming);
}
+ /// Checks if Polonius has found any unexpected free region relations.
+ ///
+ /// In Polonius terms, a "subset error" (or "illegal subset relation error") is the equivalent
+ /// of NLL's "checking if any region constraints were too strong": a placeholder origin `'a`
+ /// was unexpectedly found to be a subset of another placeholder origin `'b`, and means in NLL
+ /// terms that the "longer free region" `'a` outlived the "shorter free region" `'b`.
+ ///
+ /// More details can be found in this blog post by Niko:
+ /// http://smallcultfollowing.com/babysteps/blog/2019/01/17/polonius-and-region-errors/
+ ///
+ /// In the canonical example
+ ///
+ /// fn foo<'a, 'b>(x: &'a u32) -> &'b u32 { x }
+ ///
+ /// returning `x` requires `&'a u32 <: &'b u32` and hence we establish (transitively) a
+ /// constraint that `'a: 'b`. It is an error that we have no evidence that this
+ /// constraint holds.
+ ///
+ /// If `propagated_outlives_requirements` is `Some`, then we will
+ /// push unsatisfied obligations into there. Otherwise, we'll
+ /// report them as errors.
+ fn check_polonius_subset_errors(
+ &self,
+ infcx: &InferCtxt<'_, 'tcx>,
+ body: &Body<'tcx>,
+ local_names: &IndexVec<Local, Option<Symbol>>,
+ upvars: &[Upvar],
+ mir_def_id: DefId,
+ mut propagated_outlives_requirements: Option<&mut Vec<ClosureOutlivesRequirement<'tcx>>>,
+ errors_buffer: &mut Vec<Diagnostic>,
+ region_naming: &mut RegionErrorNamingCtx,
+ polonius_output: Rc<PoloniusOutput>,
+ ) {
+ debug!("check_polonius_subset_errors: {} subset_errors", polonius_output.subset_errors.len());
+
+ let mut outlives_suggestion = OutlivesSuggestionBuilder::new(mir_def_id, local_names);
+
+ // Similarly to `check_universal_regions`: a free region relation, which was not explicitly
+ // declared ("known") was found by Polonius, so emit an error, or propagate the
+ // requirements for our caller into the `propagated_outlives_requirements` vector.
+ //
+ // Polonius doesn't model regions ("origins") as CFG-subsets or durations, but the
+ // `longer_fr` and `shorter_fr` terminology will still be used here, for consistency with
+ // the rest of the NLL infrastructure. The "subset origin" is the "longer free region",
+ // and the "superset origin" is the outlived "shorter free region".
+ //
+ // Note: Polonius will produce a subset error at every point where the unexpected
+ // `longer_fr`'s "placeholder loan" is contained in the `shorter_fr`. This can be helpful
+ // for diagnostics in the future, e.g. to point more precisely at the key locations
+ // requiring this constraint to hold. However, the error and diagnostics code downstream
+ // expects that these errors are not duplicated (and that they are in a certain order).
+ // Otherwise, diagnostics messages such as the ones giving names like `'1` to elided or
+ // anonymous lifetimes for example, could give these names differently, while others like
+ // the outlives suggestions or the debug output from `#[rustc_regions]` would be
+ // duplicated. The polonius subset errors are deduplicated here, while keeping the
+ // CFG-location ordering.
+ let mut subset_errors: Vec<_> = polonius_output
+ .subset_errors
+ .iter()
+ .flat_map(|(_location, subset_errors)| subset_errors.iter())
+ .collect();
+ subset_errors.sort();
+ subset_errors.dedup();
+
+ for (longer_fr, shorter_fr) in subset_errors.into_iter() {
+ debug!("check_polonius_subset_errors: subset_error longer_fr={:?},\
+ shorter_fr={:?}", longer_fr, shorter_fr);
+
+ self.report_or_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,
+ );
+ }
+
+ // Handle the placeholder errors as usual, until the chalk-rustc-polonius triumvirate has
+ // a more complete picture on how to separate this responsibility.
+ for (fr, fr_definition) in self.definitions.iter_enumerated() {
+ match fr_definition.origin {
+ NLLRegionVariableOrigin::FreeRegion => {
+ // handled by polonius above
+ }
+
+ NLLRegionVariableOrigin::Placeholder(placeholder) => {
+ self.check_bound_universal_region(infcx, body, mir_def_id, fr, placeholder);
+ }
+
+ NLLRegionVariableOrigin::Existential { .. } => {
+ // nothing to check here
+ }
+ }
+ }
+
+ // Emit outlives suggestions
+ outlives_suggestion.add_suggestion(body, self, infcx, errors_buffer, region_naming);
+ }
+
/// Checks the final value for the free region `fr` to see if it
/// grew too large. In particular, examine what `end(X)` points
/// wound up in `fr`'s final value; for each `end(X)` where `X !=
return None;
}
+ self.report_or_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,
+ )
+ }
+
+ fn report_or_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!(
- "check_universal_region_relation: fr={:?} does not outlive shorter_fr={:?}",
+ "report_or_propagate_universal_region_error: fr={:?} does not outlive shorter_fr={:?}",
longer_fr, shorter_fr,
);
// 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!("check_universal_region: fr_minus={:?}", fr_minus);
+ 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);
let blame_span_category =
self.find_outlives_blame_span(body, longer_fr,
// so slightly larger than `shorter_fr`.
let shorter_fr_plus =
self.universal_region_relations.non_local_upper_bounds(&shorter_fr);
- debug!("check_universal_region: shorter_fr_plus={:?}", shorter_fr_plus);
+ debug!(
+ "report_or_propagate_universal_region_error: shorter_fr_plus={:?}", shorter_fr_plus
+ );
for &&fr in &shorter_fr_plus {
// Push the constraint `fr-: shorter_fr+`
propagated_outlives_requirements.push(ClosureOutlivesRequirement {
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