Auto merge of rust-lang#134914 - lqd:polonius-next-episode-5, r=jackh726

A couple datalog/borrowck cleanups

As discussed on zulip, here's a chill one in between slightly more interesting PRs:
- I hadn't noticed there still were a couple of datalog-related modules outside of their dedicated `polonius` module (go to horn-clause jail, bonk!).
- there somehow was both a `diags` module and a `diagnostics` module.
- a couple other tiny things being renamed -- let me know what you think.

As requested I've tried to have somewhat granular commits to ease review, but the last two or three could be squashed together, since they're all related to the `diags` module (but moving its contents is less tedious to check in its own commit).

r? `@jackh726`

compiler/rustc_borrowck/src/consumers.rs

@@ -8,11 +8,12 @@ use rustc_middle::ty::TyCtxt;
 pub use super::borrow_set::{BorrowData, BorrowSet, TwoPhaseActivation};
 pub use super::constraints::OutlivesConstraint;
 pub use super::dataflow::{BorrowIndex, Borrows, calculate_borrows_out_of_scope_at_location};
-pub use super::facts::{AllFacts as PoloniusInput, PoloniusRegionVid, RustcFacts};
-pub use super::location::{LocationTable, RichLocation};
-pub use super::nll::PoloniusOutput;
 pub use super::place_ext::PlaceExt;
 pub use super::places_conflict::{PlaceConflictBias, places_conflict};
+pub use super::polonius::legacy::{
+    AllFacts as PoloniusInput, LocationTable, PoloniusOutput, PoloniusRegionVid, RichLocation,
+    RustcFacts,
+};
 pub use super::region_infer::RegionInferenceContext;
 
 /// Options determining the output behavior of [`get_body_with_borrowck_facts`].

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -1,6 +1,9 @@
 //! Borrow checker diagnostics.
 
+use std::collections::BTreeMap;
+
 use rustc_abi::{FieldIdx, VariantIdx};
+use rustc_data_structures::fx::FxIndexMap;
 use rustc_errors::{Applicability, Diag, MultiSpan};
 use rustc_hir::def::{CtorKind, Namespace};
 use rustc_hir::{self as hir, CoroutineKind, LangItem};
@@ -17,10 +20,10 @@ use rustc_middle::mir::{
 use rustc_middle::ty::print::Print;
 use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
 use rustc_middle::util::{CallDesugaringKind, call_kind};
-use rustc_mir_dataflow::move_paths::{InitLocation, LookupResult};
+use rustc_mir_dataflow::move_paths::{InitLocation, LookupResult, MoveOutIndex};
 use rustc_span::def_id::LocalDefId;
 use rustc_span::source_map::Spanned;
-use rustc_span::{DUMMY_SP, Span, Symbol, sym};
+use rustc_span::{DUMMY_SP, ErrorGuaranteed, Span, Symbol, sym};
 use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
 use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::traits::{
@@ -68,6 +71,126 @@ pub(super) struct DescribePlaceOpt {
 
 pub(super) struct IncludingTupleField(pub(super) bool);
 
+enum BufferedDiag<'infcx> {
+    Error(Diag<'infcx>),
+    NonError(Diag<'infcx, ()>),
+}
+
+impl<'infcx> BufferedDiag<'infcx> {
+    fn sort_span(&self) -> Span {
+        match self {
+            BufferedDiag::Error(diag) => diag.sort_span,
+            BufferedDiag::NonError(diag) => diag.sort_span,
+        }
+    }
+}
+
+#[derive(Default)]
+pub(crate) struct BorrowckDiagnosticsBuffer<'infcx, 'tcx> {
+    /// This field keeps track of move errors that are to be reported for given move indices.
+    ///
+    /// There are situations where many errors can be reported for a single move out (see
+    /// #53807) and we want only the best of those errors.
+    ///
+    /// The `report_use_of_moved_or_uninitialized` function checks this map and replaces the
+    /// diagnostic (if there is one) if the `Place` of the error being reported is a prefix of
+    /// the `Place` of the previous most diagnostic. This happens instead of buffering the
+    /// error. Once all move errors have been reported, any diagnostics in this map are added
+    /// to the buffer to be emitted.
+    ///
+    /// `BTreeMap` is used to preserve the order of insertions when iterating. This is necessary
+    /// when errors in the map are being re-added to the error buffer so that errors with the
+    /// same primary span come out in a consistent order.
+    buffered_move_errors: BTreeMap<Vec<MoveOutIndex>, (PlaceRef<'tcx>, Diag<'infcx>)>,
+
+    buffered_mut_errors: FxIndexMap<Span, (Diag<'infcx>, usize)>,
+
+    /// Buffer of diagnostics to be reported. A mixture of error and non-error diagnostics.
+    buffered_diags: Vec<BufferedDiag<'infcx>>,
+}
+
+impl<'infcx, 'tcx> BorrowckDiagnosticsBuffer<'infcx, 'tcx> {
+    pub(crate) fn buffer_non_error(&mut self, diag: Diag<'infcx, ()>) {
+        self.buffered_diags.push(BufferedDiag::NonError(diag));
+    }
+}
+
+impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
+    pub(crate) fn buffer_error(&mut self, diag: Diag<'infcx>) {
+        self.diags_buffer.buffered_diags.push(BufferedDiag::Error(diag));
+    }
+
+    pub(crate) fn buffer_non_error(&mut self, diag: Diag<'infcx, ()>) {
+        self.diags_buffer.buffer_non_error(diag);
+    }
+
+    pub(crate) fn buffer_move_error(
+        &mut self,
+        move_out_indices: Vec<MoveOutIndex>,
+        place_and_err: (PlaceRef<'tcx>, Diag<'infcx>),
+    ) -> bool {
+        if let Some((_, diag)) =
+            self.diags_buffer.buffered_move_errors.insert(move_out_indices, place_and_err)
+        {
+            // Cancel the old diagnostic so we don't ICE
+            diag.cancel();
+            false
+        } else {
+            true
+        }
+    }
+
+    pub(crate) fn get_buffered_mut_error(&mut self, span: Span) -> Option<(Diag<'infcx>, usize)> {
+        // FIXME(#120456) - is `swap_remove` correct?
+        self.diags_buffer.buffered_mut_errors.swap_remove(&span)
+    }
+
+    pub(crate) fn buffer_mut_error(&mut self, span: Span, diag: Diag<'infcx>, count: usize) {
+        self.diags_buffer.buffered_mut_errors.insert(span, (diag, count));
+    }
+
+    pub(crate) fn emit_errors(&mut self) -> Option<ErrorGuaranteed> {
+        let mut res = self.infcx.tainted_by_errors();
+
+        // Buffer any move errors that we collected and de-duplicated.
+        for (_, (_, diag)) in std::mem::take(&mut self.diags_buffer.buffered_move_errors) {
+            // We have already set tainted for this error, so just buffer it.
+            self.buffer_error(diag);
+        }
+        for (_, (mut diag, count)) in std::mem::take(&mut self.diags_buffer.buffered_mut_errors) {
+            if count > 10 {
+                #[allow(rustc::diagnostic_outside_of_impl)]
+                #[allow(rustc::untranslatable_diagnostic)]
+                diag.note(format!("...and {} other attempted mutable borrows", count - 10));
+            }
+            self.buffer_error(diag);
+        }
+
+        if !self.diags_buffer.buffered_diags.is_empty() {
+            self.diags_buffer.buffered_diags.sort_by_key(|buffered_diag| buffered_diag.sort_span());
+            for buffered_diag in self.diags_buffer.buffered_diags.drain(..) {
+                match buffered_diag {
+                    BufferedDiag::Error(diag) => res = Some(diag.emit()),
+                    BufferedDiag::NonError(diag) => diag.emit(),
+                }
+            }
+        }
+
+        res
+    }
+
+    pub(crate) fn has_buffered_diags(&self) -> bool {
+        self.diags_buffer.buffered_diags.is_empty()
+    }
+
+    pub(crate) fn has_move_error(
+        &self,
+        move_out_indices: &[MoveOutIndex],
+    ) -> Option<&(PlaceRef<'tcx>, Diag<'infcx>)> {
+        self.diags_buffer.buffered_move_errors.get(move_out_indices)
+    }
+}
+
 impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
     /// Adds a suggestion when a closure is invoked twice with a moved variable or when a closure
     /// is moved after being invoked.