+++ /dev/null
-//! Contains utilities for generating suggestions for borrowck errors related to unsatisfied
-//! outlives constraints.
-
-use std::collections::BTreeMap;
-
-use rustc_data_structures::fx::FxHashSet;
-use rustc_errors::DiagnosticBuilder;
-use rustc_middle::ty::RegionVid;
-use tracing::debug;
-
-use smallvec::SmallVec;
-
-use crate::borrow_check::MirBorrowckCtxt;
-
-use super::{ErrorConstraintInfo, RegionName, RegionNameSource};
-
-/// The different things we could suggest.
-enum SuggestedConstraint {
- /// Outlives(a, [b, c, d, ...]) => 'a: 'b + 'c + 'd + ...
- Outlives(RegionName, SmallVec<[RegionName; 2]>),
-
- /// 'a = 'b
- Equal(RegionName, RegionName),
-
- /// 'a: 'static i.e. 'a = 'static and the user should just use 'static
- Static(RegionName),
-}
-
-/// Collects information about outlives constraints that needed to be added for a given MIR node
-/// corresponding to a function definition.
-///
-/// Adds a help note suggesting adding a where clause with the needed constraints.
-#[derive(Default)]
-pub struct OutlivesSuggestionBuilder {
- /// The list of outlives constraints that need to be added. Specifically, we map each free
- /// region to all other regions that it must outlive. I will use the shorthand `fr:
- /// outlived_frs`. Not all of these regions will already have names necessarily. Some could be
- /// implicit free regions that we inferred. These will need to be given names in the final
- /// suggestion message.
- constraints_to_add: BTreeMap<RegionVid, Vec<RegionVid>>,
-}
-
-impl OutlivesSuggestionBuilder {
- /// Returns `true` iff the `RegionNameSource` is a valid source for an outlives
- /// suggestion.
- //
- // FIXME: Currently, we only report suggestions if the `RegionNameSource` is an early-bound
- // region or a named region, avoiding using regions with synthetic names altogether. This
- // allows us to avoid giving impossible suggestions (e.g. adding bounds to closure args).
- // We can probably be less conservative, since some inferred free regions are namable (e.g.
- // the user can explicitly name them. To do this, we would allow some regions whose names
- // come from `MatchedAdtAndSegment`, being careful to filter out bad suggestions, such as
- // naming the `'self` lifetime in methods, etc.
- fn region_name_is_suggestable(name: &RegionName) -> bool {
- match name.source {
- RegionNameSource::NamedEarlyBoundRegion(..)
- | RegionNameSource::NamedFreeRegion(..)
- | RegionNameSource::Static => true,
-
- // Don't give suggestions for upvars, closure return types, or other unnamable
- // regions.
- RegionNameSource::SynthesizedFreeEnvRegion(..)
- | RegionNameSource::AnonRegionFromArgument(..)
- | RegionNameSource::AnonRegionFromUpvar(..)
- | RegionNameSource::AnonRegionFromOutput(..)
- | RegionNameSource::AnonRegionFromYieldTy(..)
- | RegionNameSource::AnonRegionFromAsyncFn(..) => {
- debug!("Region {:?} is NOT suggestable", name);
- false
- }
- }
- }
-
- /// Returns a name for the region if it is suggestable. See `region_name_is_suggestable`.
- fn region_vid_to_name(
- &self,
- mbcx: &MirBorrowckCtxt<'_, '_>,
- region: RegionVid,
- ) -> Option<RegionName> {
- mbcx.give_region_a_name(region).filter(Self::region_name_is_suggestable)
- }
-
- /// Compiles a list of all suggestions to be printed in the final big suggestion.
- fn compile_all_suggestions(
- &self,
- mbcx: &MirBorrowckCtxt<'_, '_>,
- ) -> SmallVec<[SuggestedConstraint; 2]> {
- let mut suggested = SmallVec::new();
-
- // Keep track of variables that we have already suggested unifying so that we don't print
- // out silly duplicate messages.
- let mut unified_already = FxHashSet::default();
-
- for (fr, outlived) in &self.constraints_to_add {
- let fr_name = if let Some(fr_name) = self.region_vid_to_name(mbcx, *fr) {
- fr_name
- } else {
- continue;
- };
-
- let outlived = outlived
- .iter()
- // if there is a `None`, we will just omit that constraint
- .filter_map(|fr| self.region_vid_to_name(mbcx, *fr).map(|rname| (fr, rname)))
- .collect::<Vec<_>>();
-
- // No suggestable outlived lifetimes.
- if outlived.is_empty() {
- continue;
- }
-
- // There are three types of suggestions we can make:
- // 1) Suggest a bound: 'a: 'b
- // 2) Suggest replacing 'a with 'static. If any of `outlived` is `'static`, then we
- // should just replace 'a with 'static.
- // 3) Suggest unifying 'a with 'b if we have both 'a: 'b and 'b: 'a
-
- if outlived
- .iter()
- .any(|(_, outlived_name)| matches!(outlived_name.source, RegionNameSource::Static))
- {
- suggested.push(SuggestedConstraint::Static(fr_name));
- } else {
- // We want to isolate out all lifetimes that should be unified and print out
- // separate messages for them.
-
- let (unified, other): (Vec<_>, Vec<_>) = outlived.into_iter().partition(
- // Do we have both 'fr: 'r and 'r: 'fr?
- |(r, _)| {
- self.constraints_to_add
- .get(r)
- .map(|r_outlived| r_outlived.as_slice().contains(fr))
- .unwrap_or(false)
- },
- );
-
- for (r, bound) in unified.into_iter() {
- if !unified_already.contains(fr) {
- suggested.push(SuggestedConstraint::Equal(fr_name.clone(), bound));
- unified_already.insert(r);
- }
- }
-
- if !other.is_empty() {
- let other =
- other.iter().map(|(_, rname)| rname.clone()).collect::<SmallVec<_>>();
- suggested.push(SuggestedConstraint::Outlives(fr_name, other))
- }
- }
- }
-
- suggested
- }
-
- /// Add the outlives constraint `fr: outlived_fr` to the set of constraints we need to suggest.
- crate fn collect_constraint(&mut self, fr: RegionVid, outlived_fr: RegionVid) {
- debug!("Collected {:?}: {:?}", fr, outlived_fr);
-
- // Add to set of constraints for final help note.
- self.constraints_to_add.entry(fr).or_default().push(outlived_fr);
- }
-
- /// Emit an intermediate note on the given `Diagnostic` if the involved regions are
- /// suggestable.
- crate fn intermediate_suggestion(
- &mut self,
- mbcx: &MirBorrowckCtxt<'_, '_>,
- errci: &ErrorConstraintInfo,
- diag: &mut DiagnosticBuilder<'_>,
- ) {
- // Emit an intermediate note.
- let fr_name = self.region_vid_to_name(mbcx, errci.fr);
- let outlived_fr_name = self.region_vid_to_name(mbcx, errci.outlived_fr);
-
- if let (Some(fr_name), Some(outlived_fr_name)) = (fr_name, outlived_fr_name) {
- if let RegionNameSource::Static = outlived_fr_name.source {
- diag.help(&format!("consider replacing `{}` with `'static`", fr_name));
- } else {
- diag.help(&format!(
- "consider adding the following bound: `{}: {}`",
- fr_name, outlived_fr_name
- ));
- }
- }
- }
-
- /// If there is a suggestion to emit, add a diagnostic to the buffer. This is the final
- /// suggestion including all collected constraints.
- crate fn add_suggestion(&self, mbcx: &mut MirBorrowckCtxt<'_, '_>) {
- // No constraints to add? Done.
- if self.constraints_to_add.is_empty() {
- debug!("No constraints to suggest.");
- return;
- }
-
- // If there is only one constraint to suggest, then we already suggested it in the
- // intermediate suggestion above.
- if self.constraints_to_add.len() == 1
- && self.constraints_to_add.values().next().unwrap().len() == 1
- {
- debug!("Only 1 suggestion. Skipping.");
- return;
- }
-
- // Get all suggestable constraints.
- let suggested = self.compile_all_suggestions(mbcx);
-
- // If there are no suggestable constraints...
- if suggested.is_empty() {
- debug!("Only 1 suggestable constraint. Skipping.");
- return;
- }
-
- // If there is exactly one suggestable constraints, then just suggest it. Otherwise, emit a
- // list of diagnostics.
- let mut diag = if suggested.len() == 1 {
- mbcx.infcx.tcx.sess.diagnostic().struct_help(&match suggested.last().unwrap() {
- SuggestedConstraint::Outlives(a, bs) => {
- let bs: SmallVec<[String; 2]> = bs.iter().map(|r| format!("{}", r)).collect();
- format!("add bound `{}: {}`", a, bs.join(" + "))
- }
-
- SuggestedConstraint::Equal(a, b) => {
- format!("`{}` and `{}` must be the same: replace one with the other", a, b)
- }
- SuggestedConstraint::Static(a) => format!("replace `{}` with `'static`", a),
- })
- } else {
- // Create a new diagnostic.
- let mut diag = mbcx
- .infcx
- .tcx
- .sess
- .diagnostic()
- .struct_help("the following changes may resolve your lifetime errors");
-
- // Add suggestions.
- for constraint in suggested {
- match constraint {
- SuggestedConstraint::Outlives(a, bs) => {
- let bs: SmallVec<[String; 2]> =
- bs.iter().map(|r| format!("{}", r)).collect();
- diag.help(&format!("add bound `{}: {}`", a, bs.join(" + ")));
- }
- SuggestedConstraint::Equal(a, b) => {
- diag.help(&format!(
- "`{}` and `{}` must be the same: replace one with the other",
- a, b
- ));
- }
- SuggestedConstraint::Static(a) => {
- diag.help(&format!("replace `{}` with `'static`", a));
- }
- }
- }
-
- diag
- };
-
- // We want this message to appear after other messages on the mir def.
- let mir_span = mbcx.body.span;
- diag.sort_span = mir_span.shrink_to_hi();
-
- // Buffer the diagnostic
- diag.buffer(&mut mbcx.errors_buffer);
- }
-}
projects / rustc.git / blobdiff