Move rustc_mir::borrow_check to new crate rustc_borrowck.
This commit is contained in:
Camille GILLOT
parent
8ceea01bb4
commit
31a61ccc38
64 changed files with 374 additions and 317 deletions
665
compiler/rustc_borrowck/src/diagnostics/region_errors.rs
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665
compiler/rustc_borrowck/src/diagnostics/region_errors.rs
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@ -0,0 +1,665 @@
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//! Error reporting machinery for lifetime errors.
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use rustc_errors::{Applicability, DiagnosticBuilder};
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use rustc_infer::infer::{
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error_reporting::nice_region_error::NiceRegionError,
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error_reporting::unexpected_hidden_region_diagnostic, NllRegionVariableOrigin,
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};
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use rustc_middle::mir::{ConstraintCategory, ReturnConstraint};
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use rustc_middle::ty::subst::Subst;
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use rustc_middle::ty::{self, RegionVid, Ty};
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use rustc_span::symbol::{kw, sym};
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use rustc_span::{BytePos, Span};
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use crate::borrowck_errors;
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use crate::region_infer::BlameConstraint;
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use crate::{
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nll::ConstraintDescription,
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region_infer::{values::RegionElement, TypeTest},
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universal_regions::DefiningTy,
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MirBorrowckCtxt,
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};
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use super::{OutlivesSuggestionBuilder, RegionName};
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impl ConstraintDescription for ConstraintCategory {
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fn description(&self) -> &'static str {
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// Must end with a space. Allows for empty names to be provided.
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match self {
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ConstraintCategory::Assignment => "assignment ",
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ConstraintCategory::Return(_) => "returning this value ",
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ConstraintCategory::Yield => "yielding this value ",
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ConstraintCategory::UseAsConst => "using this value as a constant ",
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ConstraintCategory::UseAsStatic => "using this value as a static ",
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ConstraintCategory::Cast => "cast ",
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ConstraintCategory::CallArgument => "argument ",
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ConstraintCategory::TypeAnnotation => "type annotation ",
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ConstraintCategory::ClosureBounds => "closure body ",
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ConstraintCategory::SizedBound => "proving this value is `Sized` ",
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ConstraintCategory::CopyBound => "copying this value ",
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ConstraintCategory::OpaqueType => "opaque type ",
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ConstraintCategory::ClosureUpvar(_) => "closure capture ",
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ConstraintCategory::Boring
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| ConstraintCategory::BoringNoLocation
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| ConstraintCategory::Internal => "",
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}
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}
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}
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/// A collection of errors encountered during region inference. This is needed to efficiently
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/// report errors after borrow checking.
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///
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/// Usually we expect this to either be empty or contain a small number of items, so we can avoid
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/// allocation most of the time.
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crate type RegionErrors<'tcx> = Vec<RegionErrorKind<'tcx>>;
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#[derive(Clone, Debug)]
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crate enum RegionErrorKind<'tcx> {
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/// A generic bound failure for a type test (`T: 'a`).
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TypeTestError { type_test: TypeTest<'tcx> },
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/// An unexpected hidden region for an opaque type.
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UnexpectedHiddenRegion {
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/// The span for the member constraint.
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span: Span,
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/// The hidden type.
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hidden_ty: Ty<'tcx>,
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/// The unexpected region.
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member_region: ty::Region<'tcx>,
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},
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/// Higher-ranked subtyping error.
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BoundUniversalRegionError {
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/// The placeholder free region.
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longer_fr: RegionVid,
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/// The region element that erroneously must be outlived by `longer_fr`.
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error_element: RegionElement,
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/// The placeholder region.
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placeholder: ty::PlaceholderRegion,
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},
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/// Any other lifetime error.
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RegionError {
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/// The origin of the region.
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fr_origin: NllRegionVariableOrigin,
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/// The region that should outlive `shorter_fr`.
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longer_fr: RegionVid,
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/// The region that should be shorter, but we can't prove it.
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shorter_fr: RegionVid,
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/// Indicates whether this is a reported error. We currently only report the first error
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/// encountered and leave the rest unreported so as not to overwhelm the user.
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is_reported: bool,
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},
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}
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/// Information about the various region constraints involved in a borrow checker error.
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#[derive(Clone, Debug)]
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pub struct ErrorConstraintInfo {
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// fr: outlived_fr
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pub(super) fr: RegionVid,
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pub(super) fr_is_local: bool,
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pub(super) outlived_fr: RegionVid,
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pub(super) outlived_fr_is_local: bool,
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// Category and span for best blame constraint
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pub(super) category: ConstraintCategory,
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pub(super) span: Span,
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}
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impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
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/// Converts a region inference variable into a `ty::Region` that
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/// we can use for error reporting. If `r` is universally bound,
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/// then we use the name that we have on record for it. If `r` is
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/// existentially bound, then we check its inferred value and try
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/// to find a good name from that. Returns `None` if we can't find
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/// one (e.g., this is just some random part of the CFG).
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pub(super) fn to_error_region(&self, r: RegionVid) -> Option<ty::Region<'tcx>> {
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self.to_error_region_vid(r).and_then(|r| self.regioncx.region_definition(r).external_name)
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}
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/// Returns the `RegionVid` corresponding to the region returned by
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/// `to_error_region`.
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pub(super) fn to_error_region_vid(&self, r: RegionVid) -> Option<RegionVid> {
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if self.regioncx.universal_regions().is_universal_region(r) {
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Some(r)
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} else {
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// We just want something nameable, even if it's not
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// actually an upper bound.
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let upper_bound = self.regioncx.approx_universal_upper_bound(r);
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if self.regioncx.upper_bound_in_region_scc(r, upper_bound) {
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self.to_error_region_vid(upper_bound)
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} else {
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None
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}
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}
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}
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/// Returns `true` if a closure is inferred to be an `FnMut` closure.
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fn is_closure_fn_mut(&self, fr: RegionVid) -> bool {
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if let Some(ty::ReFree(free_region)) = self.to_error_region(fr) {
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if let ty::BoundRegionKind::BrEnv = free_region.bound_region {
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if let DefiningTy::Closure(_, substs) =
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self.regioncx.universal_regions().defining_ty
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{
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return substs.as_closure().kind() == ty::ClosureKind::FnMut;
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}
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}
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}
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false
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}
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/// Produces nice borrowck error diagnostics for all the errors collected in `nll_errors`.
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pub(crate) fn report_region_errors(&mut self, nll_errors: RegionErrors<'tcx>) {
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// Iterate through all the errors, producing a diagnostic for each one. The diagnostics are
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// buffered in the `MirBorrowckCtxt`.
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let mut outlives_suggestion = OutlivesSuggestionBuilder::default();
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for nll_error in nll_errors.into_iter() {
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match nll_error {
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RegionErrorKind::TypeTestError { type_test } => {
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// Try to convert the lower-bound region into something named we can print for the user.
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let lower_bound_region = self.to_error_region(type_test.lower_bound);
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let type_test_span = type_test.locations.span(&self.body);
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if let Some(lower_bound_region) = lower_bound_region {
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self.infcx
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.construct_generic_bound_failure(
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type_test_span,
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None,
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type_test.generic_kind,
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lower_bound_region,
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)
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.buffer(&mut self.errors_buffer);
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} else {
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// FIXME. We should handle this case better. It
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// indicates that we have e.g., some region variable
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// whose value is like `'a+'b` where `'a` and `'b` are
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// distinct unrelated univesal regions that are not
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// known to outlive one another. It'd be nice to have
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// some examples where this arises to decide how best
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// to report it; we could probably handle it by
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// iterating over the universal regions and reporting
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// an error that multiple bounds are required.
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self.infcx
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.tcx
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.sess
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.struct_span_err(
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type_test_span,
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&format!("`{}` does not live long enough", type_test.generic_kind),
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)
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.buffer(&mut self.errors_buffer);
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}
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}
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RegionErrorKind::UnexpectedHiddenRegion { span, hidden_ty, member_region } => {
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let named_ty = self.regioncx.name_regions(self.infcx.tcx, hidden_ty);
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let named_region = self.regioncx.name_regions(self.infcx.tcx, member_region);
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unexpected_hidden_region_diagnostic(
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self.infcx.tcx,
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span,
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named_ty,
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named_region,
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)
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.buffer(&mut self.errors_buffer);
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}
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RegionErrorKind::BoundUniversalRegionError {
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longer_fr,
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placeholder,
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error_element,
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} => {
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let error_vid = self.regioncx.region_from_element(longer_fr, &error_element);
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// Find the code to blame for the fact that `longer_fr` outlives `error_fr`.
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let (_, span) = self.regioncx.find_outlives_blame_span(
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&self.body,
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longer_fr,
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NllRegionVariableOrigin::Placeholder(placeholder),
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error_vid,
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);
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let universe = placeholder.universe;
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let universe_info = self.regioncx.universe_info(universe);
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universe_info.report_error(self, placeholder, error_element, span);
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}
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RegionErrorKind::RegionError { fr_origin, longer_fr, shorter_fr, is_reported } => {
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if is_reported {
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self.report_region_error(
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longer_fr,
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fr_origin,
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shorter_fr,
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&mut outlives_suggestion,
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);
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} else {
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// We only report the first error, so as not to overwhelm the user. See
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// `RegRegionErrorKind` docs.
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//
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// FIXME: currently we do nothing with these, but perhaps we can do better?
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// FIXME: try collecting these constraints on the outlives suggestion
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// builder. Does it make the suggestions any better?
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debug!(
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"Unreported region error: can't prove that {:?}: {:?}",
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longer_fr, shorter_fr
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);
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}
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}
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}
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}
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// Emit one outlives suggestions for each MIR def we borrowck
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outlives_suggestion.add_suggestion(self);
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}
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/// Report an error because the universal region `fr` was required to outlive
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/// `outlived_fr` but it is not known to do so. For example:
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///
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/// ```
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/// fn foo<'a, 'b>(x: &'a u32) -> &'b u32 { x }
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/// ```
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///
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/// Here we would be invoked with `fr = 'a` and `outlived_fr = `'b`.
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pub(crate) fn report_region_error(
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&mut self,
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fr: RegionVid,
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fr_origin: NllRegionVariableOrigin,
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outlived_fr: RegionVid,
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outlives_suggestion: &mut OutlivesSuggestionBuilder,
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) {
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debug!("report_region_error(fr={:?}, outlived_fr={:?})", fr, outlived_fr);
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let BlameConstraint { category, span, variance_info, from_closure: _ } =
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self.regioncx.best_blame_constraint(&self.body, fr, fr_origin, |r| {
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self.regioncx.provides_universal_region(r, fr, outlived_fr)
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});
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debug!("report_region_error: category={:?} {:?} {:?}", category, span, variance_info);
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// Check if we can use one of the "nice region errors".
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if let (Some(f), Some(o)) = (self.to_error_region(fr), self.to_error_region(outlived_fr)) {
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let nice = NiceRegionError::new_from_span(self.infcx, span, o, f);
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if let Some(diag) = nice.try_report_from_nll() {
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diag.buffer(&mut self.errors_buffer);
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return;
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}
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}
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let (fr_is_local, outlived_fr_is_local): (bool, bool) = (
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self.regioncx.universal_regions().is_local_free_region(fr),
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self.regioncx.universal_regions().is_local_free_region(outlived_fr),
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);
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debug!(
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"report_region_error: fr_is_local={:?} outlived_fr_is_local={:?} category={:?}",
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fr_is_local, outlived_fr_is_local, category
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);
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let errci = ErrorConstraintInfo {
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fr,
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outlived_fr,
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fr_is_local,
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outlived_fr_is_local,
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category,
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span,
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};
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let mut diag = match (category, fr_is_local, outlived_fr_is_local) {
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(ConstraintCategory::Return(kind), true, false) if self.is_closure_fn_mut(fr) => {
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self.report_fnmut_error(&errci, kind)
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}
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(ConstraintCategory::Assignment, true, false)
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| (ConstraintCategory::CallArgument, true, false) => {
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let mut db = self.report_escaping_data_error(&errci);
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outlives_suggestion.intermediate_suggestion(self, &errci, &mut db);
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outlives_suggestion.collect_constraint(fr, outlived_fr);
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db
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}
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_ => {
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let mut db = self.report_general_error(&errci);
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outlives_suggestion.intermediate_suggestion(self, &errci, &mut db);
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outlives_suggestion.collect_constraint(fr, outlived_fr);
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db
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}
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};
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match variance_info {
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ty::VarianceDiagInfo::None => {}
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ty::VarianceDiagInfo::Mut { kind, ty } => {
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let kind_name = match kind {
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ty::VarianceDiagMutKind::Ref => "reference",
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ty::VarianceDiagMutKind::RawPtr => "pointer",
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};
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diag.note(&format!("requirement occurs because of a mutable {kind_name} to {ty}",));
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diag.note(&format!("mutable {kind_name}s are invariant over their type parameter"));
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diag.help("see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance");
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}
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}
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diag.buffer(&mut self.errors_buffer);
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}
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/// Report a specialized error when `FnMut` closures return a reference to a captured variable.
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/// This function expects `fr` to be local and `outlived_fr` to not be local.
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///
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/// ```text
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/// error: captured variable cannot escape `FnMut` closure body
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/// --> $DIR/issue-53040.rs:15:8
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/// |
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/// LL | || &mut v;
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/// | -- ^^^^^^ creates a reference to a captured variable which escapes the closure body
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/// | |
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/// | inferred to be a `FnMut` closure
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/// |
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/// = note: `FnMut` closures only have access to their captured variables while they are
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/// executing...
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/// = note: ...therefore, returned references to captured variables will escape the closure
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/// ```
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fn report_fnmut_error(
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&self,
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errci: &ErrorConstraintInfo,
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kind: ReturnConstraint,
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) -> DiagnosticBuilder<'tcx> {
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let ErrorConstraintInfo { outlived_fr, span, .. } = errci;
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let mut diag = self
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.infcx
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.tcx
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.sess
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.struct_span_err(*span, "captured variable cannot escape `FnMut` closure body");
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let mut output_ty = self.regioncx.universal_regions().unnormalized_output_ty;
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if let ty::Opaque(def_id, _) = *output_ty.kind() {
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output_ty = self.infcx.tcx.type_of(def_id)
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};
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debug!("report_fnmut_error: output_ty={:?}", output_ty);
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let message = match output_ty.kind() {
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ty::Closure(_, _) => {
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"returns a closure that contains a reference to a captured variable, which then \
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escapes the closure body"
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}
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ty::Adt(def, _) if self.infcx.tcx.is_diagnostic_item(sym::gen_future, def.did) => {
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"returns an `async` block that contains a reference to a captured variable, which then \
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escapes the closure body"
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}
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_ => "returns a reference to a captured variable which escapes the closure body",
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};
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diag.span_label(*span, message);
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// FIXME(project-rfc-2229#48): This should store a captured_place not a hir id
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if let ReturnConstraint::ClosureUpvar(upvar) = kind {
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let def_id = match self.regioncx.universal_regions().defining_ty {
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DefiningTy::Closure(def_id, _) => def_id,
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ty => bug!("unexpected DefiningTy {:?}", ty),
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};
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let upvar_def_span = self.infcx.tcx.hir().span(upvar);
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let upvar_span = self.infcx.tcx.upvars_mentioned(def_id).unwrap()[&upvar].span;
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diag.span_label(upvar_def_span, "variable defined here");
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diag.span_label(upvar_span, "variable captured here");
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}
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if let Some(fr_span) = self.give_region_a_name(*outlived_fr).unwrap().span() {
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diag.span_label(fr_span, "inferred to be a `FnMut` closure");
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}
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diag.note(
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"`FnMut` closures only have access to their captured variables while they are \
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executing...",
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);
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diag.note("...therefore, they cannot allow references to captured variables to escape");
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diag
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}
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/// Reports an error specifically for when data is escaping a closure.
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///
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/// ```text
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/// error: borrowed data escapes outside of function
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/// --> $DIR/lifetime-bound-will-change-warning.rs:44:5
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/// |
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/// LL | fn test2<'a>(x: &'a Box<Fn()+'a>) {
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/// | - `x` is a reference that is only valid in the function body
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/// LL | // but ref_obj will not, so warn.
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/// LL | ref_obj(x)
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/// | ^^^^^^^^^^ `x` escapes the function body here
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/// ```
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fn report_escaping_data_error(&self, errci: &ErrorConstraintInfo) -> DiagnosticBuilder<'tcx> {
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let ErrorConstraintInfo { span, category, .. } = errci;
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let fr_name_and_span = self.regioncx.get_var_name_and_span_for_region(
|
||||
self.infcx.tcx,
|
||||
&self.body,
|
||||
&self.local_names,
|
||||
&self.upvars,
|
||||
errci.fr,
|
||||
);
|
||||
let outlived_fr_name_and_span = self.regioncx.get_var_name_and_span_for_region(
|
||||
self.infcx.tcx,
|
||||
&self.body,
|
||||
&self.local_names,
|
||||
&self.upvars,
|
||||
errci.outlived_fr,
|
||||
);
|
||||
|
||||
let (_, escapes_from) = self
|
||||
.infcx
|
||||
.tcx
|
||||
.article_and_description(self.regioncx.universal_regions().defining_ty.def_id());
|
||||
|
||||
// Revert to the normal error in these cases.
|
||||
// Assignments aren't "escapes" in function items.
|
||||
if (fr_name_and_span.is_none() && outlived_fr_name_and_span.is_none())
|
||||
|| (*category == ConstraintCategory::Assignment
|
||||
&& self.regioncx.universal_regions().defining_ty.is_fn_def())
|
||||
|| self.regioncx.universal_regions().defining_ty.is_const()
|
||||
{
|
||||
return self.report_general_error(&ErrorConstraintInfo {
|
||||
fr_is_local: true,
|
||||
outlived_fr_is_local: false,
|
||||
..*errci
|
||||
});
|
||||
}
|
||||
|
||||
let mut diag =
|
||||
borrowck_errors::borrowed_data_escapes_closure(self.infcx.tcx, *span, escapes_from);
|
||||
|
||||
if let Some((Some(outlived_fr_name), outlived_fr_span)) = outlived_fr_name_and_span {
|
||||
diag.span_label(
|
||||
outlived_fr_span,
|
||||
format!(
|
||||
"`{}` declared here, outside of the {} body",
|
||||
outlived_fr_name, escapes_from
|
||||
),
|
||||
);
|
||||
}
|
||||
|
||||
if let Some((Some(fr_name), fr_span)) = fr_name_and_span {
|
||||
diag.span_label(
|
||||
fr_span,
|
||||
format!(
|
||||
"`{}` is a reference that is only valid in the {} body",
|
||||
fr_name, escapes_from
|
||||
),
|
||||
);
|
||||
|
||||
diag.span_label(*span, format!("`{}` escapes the {} body here", fr_name, escapes_from));
|
||||
}
|
||||
|
||||
diag
|
||||
}
|
||||
|
||||
/// Reports a region inference error for the general case with named/synthesized lifetimes to
|
||||
/// explain what is happening.
|
||||
///
|
||||
/// ```text
|
||||
/// error: unsatisfied lifetime constraints
|
||||
/// --> $DIR/regions-creating-enums3.rs:17:5
|
||||
/// |
|
||||
/// LL | fn mk_add_bad1<'a,'b>(x: &'a ast<'a>, y: &'b ast<'b>) -> ast<'a> {
|
||||
/// | -- -- lifetime `'b` defined here
|
||||
/// | |
|
||||
/// | lifetime `'a` defined here
|
||||
/// LL | ast::add(x, y)
|
||||
/// | ^^^^^^^^^^^^^^ function was supposed to return data with lifetime `'a` but it
|
||||
/// | is returning data with lifetime `'b`
|
||||
/// ```
|
||||
fn report_general_error(&self, errci: &ErrorConstraintInfo) -> DiagnosticBuilder<'tcx> {
|
||||
let ErrorConstraintInfo {
|
||||
fr,
|
||||
fr_is_local,
|
||||
outlived_fr,
|
||||
outlived_fr_is_local,
|
||||
span,
|
||||
category,
|
||||
..
|
||||
} = errci;
|
||||
|
||||
let mut diag =
|
||||
self.infcx.tcx.sess.struct_span_err(*span, "lifetime may not live long enough");
|
||||
|
||||
let (_, mir_def_name) =
|
||||
self.infcx.tcx.article_and_description(self.mir_def_id().to_def_id());
|
||||
|
||||
let fr_name = self.give_region_a_name(*fr).unwrap();
|
||||
fr_name.highlight_region_name(&mut diag);
|
||||
let outlived_fr_name = self.give_region_a_name(*outlived_fr).unwrap();
|
||||
outlived_fr_name.highlight_region_name(&mut diag);
|
||||
|
||||
match (category, outlived_fr_is_local, fr_is_local) {
|
||||
(ConstraintCategory::Return(_), true, _) => {
|
||||
diag.span_label(
|
||||
*span,
|
||||
format!(
|
||||
"{} was supposed to return data with lifetime `{}` but it is returning \
|
||||
data with lifetime `{}`",
|
||||
mir_def_name, outlived_fr_name, fr_name
|
||||
),
|
||||
);
|
||||
}
|
||||
_ => {
|
||||
diag.span_label(
|
||||
*span,
|
||||
format!(
|
||||
"{}requires that `{}` must outlive `{}`",
|
||||
category.description(),
|
||||
fr_name,
|
||||
outlived_fr_name,
|
||||
),
|
||||
);
|
||||
}
|
||||
}
|
||||
|
||||
self.add_static_impl_trait_suggestion(&mut diag, *fr, fr_name, *outlived_fr);
|
||||
|
||||
diag
|
||||
}
|
||||
|
||||
/// Adds a suggestion to errors where an `impl Trait` is returned.
|
||||
///
|
||||
/// ```text
|
||||
/// help: to allow this `impl Trait` to capture borrowed data with lifetime `'1`, add `'_` as
|
||||
/// a constraint
|
||||
/// |
|
||||
/// LL | fn iter_values_anon(&self) -> impl Iterator<Item=u32> + 'a {
|
||||
/// | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
||||
/// ```
|
||||
fn add_static_impl_trait_suggestion(
|
||||
&self,
|
||||
diag: &mut DiagnosticBuilder<'tcx>,
|
||||
fr: RegionVid,
|
||||
// We need to pass `fr_name` - computing it again will label it twice.
|
||||
fr_name: RegionName,
|
||||
outlived_fr: RegionVid,
|
||||
) {
|
||||
if let (Some(f), Some(ty::RegionKind::ReStatic)) =
|
||||
(self.to_error_region(fr), self.to_error_region(outlived_fr))
|
||||
{
|
||||
if let Some(&ty::Opaque(did, substs)) = self
|
||||
.infcx
|
||||
.tcx
|
||||
.is_suitable_region(f)
|
||||
.map(|r| r.def_id)
|
||||
.and_then(|id| self.infcx.tcx.return_type_impl_trait(id))
|
||||
.map(|(ty, _)| ty.kind())
|
||||
{
|
||||
// Check whether or not the impl trait return type is intended to capture
|
||||
// data with the static lifetime.
|
||||
//
|
||||
// eg. check for `impl Trait + 'static` instead of `impl Trait`.
|
||||
let has_static_predicate = {
|
||||
let bounds = self.infcx.tcx.explicit_item_bounds(did);
|
||||
|
||||
let mut found = false;
|
||||
for (bound, _) in bounds {
|
||||
if let ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(_, r)) =
|
||||
bound.kind().skip_binder()
|
||||
{
|
||||
let r = r.subst(self.infcx.tcx, substs);
|
||||
if let ty::RegionKind::ReStatic = r {
|
||||
found = true;
|
||||
break;
|
||||
} else {
|
||||
// If there's already a lifetime bound, don't
|
||||
// suggest anything.
|
||||
return;
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
found
|
||||
};
|
||||
|
||||
debug!(
|
||||
"add_static_impl_trait_suggestion: has_static_predicate={:?}",
|
||||
has_static_predicate
|
||||
);
|
||||
let static_str = kw::StaticLifetime;
|
||||
// If there is a static predicate, then the only sensible suggestion is to replace
|
||||
// fr with `'static`.
|
||||
if has_static_predicate {
|
||||
diag.help(&format!("consider replacing `{}` with `{}`", fr_name, static_str));
|
||||
} else {
|
||||
// Otherwise, we should suggest adding a constraint on the return type.
|
||||
let span = self.infcx.tcx.def_span(did);
|
||||
if let Ok(snippet) = self.infcx.tcx.sess.source_map().span_to_snippet(span) {
|
||||
let suggestable_fr_name = if fr_name.was_named() {
|
||||
fr_name.to_string()
|
||||
} else {
|
||||
"'_".to_string()
|
||||
};
|
||||
let span = if snippet.ends_with(';') {
|
||||
// `type X = impl Trait;`
|
||||
span.with_hi(span.hi() - BytePos(1))
|
||||
} else {
|
||||
span
|
||||
};
|
||||
let suggestion = format!(" + {}", suggestable_fr_name);
|
||||
let span = span.shrink_to_hi();
|
||||
diag.span_suggestion(
|
||||
span,
|
||||
&format!(
|
||||
"to allow this `impl Trait` to capture borrowed data with lifetime \
|
||||
`{}`, add `{}` as a bound",
|
||||
fr_name, suggestable_fr_name,
|
||||
),
|
||||
suggestion,
|
||||
Applicability::MachineApplicable,
|
||||
);
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
Loading…
Add table
Add a link
Reference in a new issue