1 files changed, 124 insertions, 0 deletions
diff --git a/compiler/rustc_borrowck/src/constraints/mod.rs b/compiler/rustc_borrowck/src/constraints/mod.rs
new file mode 100644
index 000000000..a504d0c91
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+++ b/compiler/rustc_borrowck/src/constraints/mod.rs
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+use rustc_data_structures::graph::scc::Sccs;
+use rustc_index::vec::IndexVec;
+use rustc_middle::mir::ConstraintCategory;
+use rustc_middle::ty::{RegionVid, VarianceDiagInfo};
+use rustc_span::Span;
+use std::fmt;
+use std::ops::Index;
+
+use crate::type_check::Locations;
+
+pub(crate) mod graph;
+
+/// A set of NLL region constraints. These include "outlives"
+/// constraints of the form `R1: R2`. Each constraint is identified by
+/// a unique `OutlivesConstraintIndex` and you can index into the set
+/// (`constraint_set[i]`) to access the constraint details.
+#[derive(Clone, Default)]
+pub(crate) struct OutlivesConstraintSet<'tcx> {
+    outlives: IndexVec<OutlivesConstraintIndex, OutlivesConstraint<'tcx>>,
+}
+
+impl<'tcx> OutlivesConstraintSet<'tcx> {
+    pub(crate) fn push(&mut self, constraint: OutlivesConstraint<'tcx>) {
+        debug!(
+            "OutlivesConstraintSet::push({:?}: {:?} @ {:?}",
+            constraint.sup, constraint.sub, constraint.locations
+        );
+        if constraint.sup == constraint.sub {
+            // 'a: 'a is pretty uninteresting
+            return;
+        }
+        self.outlives.push(constraint);
+    }
+
+    /// Constructs a "normal" graph from the constraint set; the graph makes it
+    /// easy to find the constraints affecting a particular region.
+    ///
+    /// N.B., this graph contains a "frozen" view of the current
+    /// constraints. Any new constraints added to the `OutlivesConstraintSet`
+    /// after the graph is built will not be present in the graph.
+    pub(crate) fn graph(&self, num_region_vars: usize) -> graph::NormalConstraintGraph {
+        graph::ConstraintGraph::new(graph::Normal, self, num_region_vars)
+    }
+
+    /// Like `graph`, but constraints a reverse graph where `R1: R2`
+    /// represents an edge `R2 -> R1`.
+    pub(crate) fn reverse_graph(&self, num_region_vars: usize) -> graph::ReverseConstraintGraph {
+        graph::ConstraintGraph::new(graph::Reverse, self, num_region_vars)
+    }
+
+    /// Computes cycles (SCCs) in the graph of regions. In particular,
+    /// find all regions R1, R2 such that R1: R2 and R2: R1 and group
+    /// them into an SCC, and find the relationships between SCCs.
+    pub(crate) fn compute_sccs(
+        &self,
+        constraint_graph: &graph::NormalConstraintGraph,
+        static_region: RegionVid,
+    ) -> Sccs<RegionVid, ConstraintSccIndex> {
+        let region_graph = &constraint_graph.region_graph(self, static_region);
+        Sccs::new(region_graph)
+    }
+
+    pub(crate) fn outlives(&self) -> &IndexVec<OutlivesConstraintIndex, OutlivesConstraint<'tcx>> {
+        &self.outlives
+    }
+}
+
+impl<'tcx> Index<OutlivesConstraintIndex> for OutlivesConstraintSet<'tcx> {
+    type Output = OutlivesConstraint<'tcx>;
+
+    fn index(&self, i: OutlivesConstraintIndex) -> &Self::Output {
+        &self.outlives[i]
+    }
+}
+
+#[derive(Clone, PartialEq, Eq)]
+pub struct OutlivesConstraint<'tcx> {
+    // NB. The ordering here is not significant for correctness, but
+    // it is for convenience. Before we dump the constraints in the
+    // debugging logs, we sort them, and we'd like the "super region"
+    // to be first, etc. (In particular, span should remain last.)
+    /// The region SUP must outlive SUB...
+    pub sup: RegionVid,
+
+    /// Region that must be outlived.
+    pub sub: RegionVid,
+
+    /// Where did this constraint arise?
+    pub locations: Locations,
+
+    /// The `Span` associated with the creation of this constraint.
+    /// This should be used in preference to obtaining the span from
+    /// `locations`, since the `locations` may give a poor span
+    /// in some cases (e.g. converting a constraint from a promoted).
+    pub span: Span,
+
+    /// What caused this constraint?
+    pub category: ConstraintCategory<'tcx>,
+
+    /// Variance diagnostic information
+    pub variance_info: VarianceDiagInfo<'tcx>,
+}
+
+impl<'tcx> fmt::Debug for OutlivesConstraint<'tcx> {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(
+            formatter,
+            "({:?}: {:?}) due to {:?} ({:?})",
+            self.sup, self.sub, self.locations, self.variance_info
+        )
+    }
+}
+
+rustc_index::newtype_index! {
+    pub struct OutlivesConstraintIndex {
+        DEBUG_FORMAT = "OutlivesConstraintIndex({})"
+    }
+}
+
+rustc_index::newtype_index! {
+    pub struct ConstraintSccIndex {
+        DEBUG_FORMAT = "ConstraintSccIndex({})"
+    }
+}