In which we implement illegal subset relations errors using Polonius

Cargo.lock

@@ -2575,9 +2575,9 @@ checksum = "676e8eb2b1b4c9043511a9b7bea0915320d7e502b0a079fb03f9635a5252b18c"
 
 [[package]]
 name = "polonius-engine"
-version = "0.10.0"
+version = "0.11.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "50fa9dbfd0d3d60594da338cfe6f94028433eecae4b11b7e83fd99759227bbfe"
+checksum = "1e478d7c38eb785c6416cbe58df12aa55d7aefa3759b6d3e044b2ed03f423cec"
 dependencies = [
  "datafrog",
  "log",

src/librustc/Cargo.toml

@@ -20,7 +20,7 @@ scoped-tls = "1.0"
 log = { version = "0.4", features = ["release_max_level_info", "std"] }
 rustc-rayon = "0.3.0"
 rustc-rayon-core = "0.3.0"
-polonius-engine  = "0.10.0"
+polonius-engine = "0.11.0"
 rustc_apfloat = { path = "../librustc_apfloat" }
 rustc_feature = { path = "../librustc_feature" }
 rustc_target = { path = "../librustc_target" }

src/librustc_data_structures/transitive_relation.rs

@@ -373,6 +373,14 @@ impl<T: Clone + Debug + Eq + Hash> TransitiveRelation<T> {
         }
         matrix
     }
+
+    /// Lists all the base edges in the graph: the initial _non-transitive_ set of element
+    /// relations, which will be later used as the basis for the transitive closure computation.
+    pub fn base_edges(&self) -> impl Iterator<Item=(&T, &T)> {
+        self.edges
+            .iter()
+            .map(move |edge| (&self.elements[edge.source.0], &self.elements[edge.target.0]))
+    }
 }
 
 /// Pare down is used as a step in the LUB computation. It edits the

src/librustc_mir/Cargo.toml

@@ -16,7 +16,7 @@ dot = { path = "../libgraphviz", package = "graphviz" }
 itertools = "0.8"
 log = "0.4"
 log_settings = "0.1.1"
-polonius-engine  = "0.10.0"
+polonius-engine = "0.11.0"
 rustc = { path = "../librustc" }
 rustc_target = { path = "../librustc_target" }
 rustc_data_structures = { path = "../librustc_data_structures" }

src/librustc_mir/borrow_check/flows.rs

@@ -3,16 +3,15 @@
 //! FIXME: this might be better as a "generic" fixed-point combinator,
 //! but is not as ugly as it is right now.
 
-use rustc::mir::{BasicBlock, Local, Location};
-use rustc::ty::RegionVid;
+use rustc::mir::{BasicBlock, Location};
 use rustc_index::bit_set::BitIter;
 
 use crate::borrow_check::location::LocationIndex;
 
-use polonius_engine::Output;
+use crate::borrow_check::nll::PoloniusOutput;
 
 use crate::dataflow::indexes::BorrowIndex;
-use crate::dataflow::move_paths::{HasMoveData, MovePathIndex};
+use crate::dataflow::move_paths::HasMoveData;
 use crate::dataflow::Borrows;
 use crate::dataflow::EverInitializedPlaces;
 use crate::dataflow::MaybeUninitializedPlaces;
@@ -21,8 +20,6 @@ use either::Either;
 use std::fmt;
 use std::rc::Rc;
 
-crate type PoloniusOutput = Output<RegionVid, BorrowIndex, LocationIndex, Local, MovePathIndex>;
-
 crate struct Flows<'b, 'tcx> {
     borrows: FlowAtLocation<'tcx, Borrows<'b, 'tcx>>,
     pub uninits: FlowAtLocation<'tcx, MaybeUninitializedPlaces<'b, 'tcx>>,

src/librustc_mir/borrow_check/nll/facts.rs

@@ -1,6 +1,6 @@
 use crate::borrow_check::location::{LocationIndex, LocationTable};
 use crate::dataflow::indexes::{BorrowIndex, MovePathIndex};
-use polonius_engine::AllFacts as PoloniusAllFacts;
+use polonius_engine::AllFacts as PoloniusFacts;
 use polonius_engine::Atom;
 use rustc::mir::Local;
 use rustc::ty::{RegionVid, TyCtxt};
@@ -11,7 +11,18 @@ use std::fs::{self, File};
 use std::io::Write;
 use std::path::Path;
 
-crate type AllFacts = PoloniusAllFacts<RegionVid, BorrowIndex, LocationIndex, Local, MovePathIndex>;
+#[derive(Copy, Clone, Debug)]
+crate struct RustcFacts;
+
+impl polonius_engine::FactTypes for RustcFacts {
+    type Origin = RegionVid;
+    type Loan = BorrowIndex;
+    type Point = LocationIndex;
+    type Variable = Local;
+    type Path = MovePathIndex;
+}
+
+crate type AllFacts = PoloniusFacts<RustcFacts>;
 
 crate trait AllFactsExt {
     /// Returns `true` if there is a need to gather `AllFacts` given the
@@ -55,6 +66,7 @@ impl AllFactsExt for AllFacts {
             wr.write_facts_to_path(self.[
                 borrow_region,
                 universal_region,
+                placeholder,
                 cfg_edge,
                 killed,
                 outlives,
@@ -69,6 +81,7 @@ impl AllFactsExt for AllFacts {
                 initialized_at,
                 moved_out_at,
                 path_accessed_at,
+                known_subset,
             ])
         }
         Ok(())

src/librustc_mir/borrow_check/nll/mod.rs

@@ -1,10 +1,9 @@
 use crate::borrow_check::borrow_set::BorrowSet;
-use crate::borrow_check::location::{LocationIndex, LocationTable};
+use crate::borrow_check::location::LocationTable;
 use crate::borrow_check::nll::facts::AllFactsExt;
 use crate::borrow_check::nll::type_check::{MirTypeckResults, MirTypeckRegionConstraints};
 use crate::borrow_check::nll::region_infer::values::RegionValueElements;
-use crate::dataflow::indexes::BorrowIndex;
-use crate::dataflow::move_paths::{InitLocation, MoveData, MovePathIndex, InitKind};
+use crate::dataflow::move_paths::{InitLocation, MoveData, InitKind};
 use crate::dataflow::FlowAtLocation;
 use crate::dataflow::MaybeInitializedPlaces;
 use crate::transform::MirSource;
@@ -43,10 +42,12 @@ crate mod universal_regions;
 crate mod type_check;
 crate mod region_infer;
 
-use self::facts::AllFacts;
+use self::facts::{AllFacts, RustcFacts};
 use self::region_infer::RegionInferenceContext;
 use self::universal_regions::UniversalRegions;
 
+crate type PoloniusOutput = Output<RustcFacts>;
+
 /// Rewrites the regions in the MIR to use NLL variables, also
 /// scraping out the set of universal regions (e.g., region parameters)
 /// declared on the function. That set will need to be given to
@@ -170,7 +171,7 @@ pub(in crate::borrow_check) fn compute_regions<'cx, 'tcx>(
     errors_buffer: &mut Vec<Diagnostic>,
 ) -> (
     RegionInferenceContext<'tcx>,
-    Option<Rc<Output<RegionVid, BorrowIndex, LocationIndex, Local, MovePathIndex>>>,
+    Option<Rc<PoloniusOutput>>,
     Option<ClosureRegionRequirements<'tcx>>,
 ) {
     let mut all_facts = if AllFacts::enabled(infcx.tcx) {
@@ -208,6 +209,39 @@ pub(in crate::borrow_check) fn compute_regions<'cx, 'tcx>(
             .universal_region
             .extend(universal_regions.universal_regions());
         populate_polonius_move_facts(all_facts, move_data, location_table, &body);
+
+        // Emit universal regions facts, and their relations, for Polonius.
+        //
+        // 1: universal regions are modeled in Polonius as a pair:
+        // - the universal region vid itself.
+        // - a "placeholder loan" associated to this universal region. Since they don't exist in
+        //   the `borrow_set`, their `BorrowIndex` are synthesized as the universal region index
+        //   added to the existing number of loans, as if they succeeded them in the set.
+        //
+        let borrow_count = borrow_set.borrows.len();
+        debug!(
+            "compute_regions: polonius placeholders, num_universals={}, borrow_count={}",
+            universal_regions.len(),
+            borrow_count
+        );
+
+        for universal_region in universal_regions.universal_regions() {
+            let universal_region_idx = universal_region.index();
+            let placeholder_loan_idx = borrow_count + universal_region_idx;
+            all_facts.placeholder.push((universal_region, placeholder_loan_idx.into()));
+        }
+
+        // 2: the universal region relations `outlives` constraints are emitted as
+        //  `known_subset` facts.
+        for (fr1, fr2) in universal_region_relations.known_outlives() {
+            if fr1 != fr2 {
+                debug!(
+                    "compute_regions: emitting polonius `known_subset` fr1={:?}, fr2={:?}",
+                    fr1, fr2
+                );
+                all_facts.known_subset.push((*fr1, *fr2));
+            }
+        }
     }
 
     // Create the region inference context, taking ownership of the
@@ -269,7 +303,7 @@ pub(in crate::borrow_check) fn compute_regions<'cx, 'tcx>(
 
         if infcx.tcx.sess.opts.debugging_opts.polonius {
             let algorithm = env::var("POLONIUS_ALGORITHM")
-                .unwrap_or_else(|_| String::from("Hybrid"));
+                .unwrap_or_else(|_| String::from("Naive"));
             let algorithm = Algorithm::from_str(&algorithm).unwrap();
             debug!("compute_regions: using polonius algorithm {:?}", algorithm);
             Some(Rc::new(Output::compute(
@@ -283,8 +317,15 @@ pub(in crate::borrow_check) fn compute_regions<'cx, 'tcx>(
     });
 
     // Solve the region constraints.
-    let closure_region_requirements =
-        regioncx.solve(infcx, &body, local_names, upvars, def_id, errors_buffer);
+    let closure_region_requirements = regioncx.solve(
+        infcx,
+        &body,
+        local_names,
+        upvars,
+        def_id,
+        errors_buffer,
+        polonius_output.clone(),
+    );
 
     // Dump MIR results into a file, if that is enabled. This let us
     // write unit-tests, as well as helping with debugging.