Auto merge of rust-lang#117593 - lqd:polonius-crater, r=<try>

crater: assert_eq!(NLL, location-insensitive polonius);

Crater run to check `-Zpolonius=next`. Any differences in how NLLs and location-insensitive polonius compute scopes will cause an assert to trip and an ICE.

Depends on rust-lang#117560 to fix the last known fuzzing example where there was such a difference.

r? `@ghost`

compiler/rustc_borrowck/src/dataflow.rs

@@ -273,11 +273,10 @@ impl<'tcx> PoloniusOutOfScopePrecomputer<'_, 'tcx> {
     ) {
         let sccs = self.regioncx.constraint_sccs();
         let universal_regions = self.regioncx.universal_regions();
-        let issuing_region_scc = sccs.scc(issuing_region);
 
         // We first handle the cases where the loan doesn't go out of scope, depending on the issuing
         // region's successors.
-        for scc in sccs.depth_first_search(issuing_region_scc) {
+        for successor in self.regioncx.region_graph().depth_first_search(issuing_region) {
             // 1. Via applied member constraints
             //
             // The issuing region can flow into the choice regions, and they are either:
@@ -290,6 +289,7 @@ impl<'tcx> PoloniusOutOfScopePrecomputer<'_, 'tcx> {
             // For additional insurance via fuzzing and crater, we verify that the constraint's min
             // choice indeed escapes the function. In the future, we could e.g. turn this check into
             // a debug assert and early return as an optimization.
+            let scc = sccs.scc(successor);
             for constraint in self.regioncx.applied_member_constraints(scc) {
                 if universal_regions.is_universal_region(constraint.min_choice) {
                     return;
@@ -300,7 +300,7 @@ impl<'tcx> PoloniusOutOfScopePrecomputer<'_, 'tcx> {
             //
             // If the issuing region outlives such a region, its loan escapes the function and
             // cannot go out of scope. We can early return.
-            if self.regioncx.scc_is_live_at_all_points(scc) {
+            if self.regioncx.is_region_live_at_all_points(successor) {
                 return;
             }
         }

compiler/rustc_borrowck/src/region_infer/mod.rs

@@ -22,11 +22,10 @@ use rustc_middle::traits::ObligationCauseCode;
 use rustc_middle::ty::{self, RegionVid, Ty, TyCtxt, TypeFoldable, TypeVisitableExt};
 use rustc_span::Span;
 
+use crate::constraints::graph::{self, NormalConstraintGraph, RegionGraph};
 use crate::dataflow::BorrowIndex;
 use crate::{
-    constraints::{
-        graph::NormalConstraintGraph, ConstraintSccIndex, OutlivesConstraint, OutlivesConstraintSet,
-    },
+    constraints::{ConstraintSccIndex, OutlivesConstraint, OutlivesConstraintSet},
     diagnostics::{RegionErrorKind, RegionErrors, UniverseInfo},
     member_constraints::{MemberConstraintSet, NllMemberConstraintIndex},
     nll::PoloniusOutput,
@@ -2293,19 +2292,21 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         self.constraint_sccs.as_ref()
     }
 
-    /// Returns whether the given SCC is live at all points: whether the representative is a
+    /// Access to the region graph, built from the outlives constraints.
+    pub(crate) fn region_graph(&self) -> RegionGraph<'_, 'tcx, graph::Normal> {
+        self.constraint_graph.region_graph(&self.constraints, self.universal_regions.fr_static)
+    }
+
+    /// Returns whether the given region is considered live at all points: whether it is a
     /// placeholder or a free region.
-    pub(crate) fn scc_is_live_at_all_points(&self, scc: ConstraintSccIndex) -> bool {
+    pub(crate) fn is_region_live_at_all_points(&self, region: RegionVid) -> bool {
         // FIXME: there must be a cleaner way to find this information. At least, when
         // higher-ranked subtyping is abstracted away from the borrowck main path, we'll only
         // need to check whether this is a universal region.
-        let representative = self.scc_representatives[scc];
-        let origin = self.var_infos[representative].origin;
+        let origin = self.region_definition(region).origin;
         let live_at_all_points = matches!(
             origin,
-            RegionVariableOrigin::Nll(
-                NllRegionVariableOrigin::Placeholder(_) | NllRegionVariableOrigin::FreeRegion
-            )
+            NllRegionVariableOrigin::Placeholder(_) | NllRegionVariableOrigin::FreeRegion
         );
         live_at_all_points
     }

compiler/rustc_session/src/config.rs

@@ -3414,13 +3414,13 @@ impl DumpMonoStatsFormat {
 #[derive(Clone, Copy, PartialEq, Hash, Debug, Default)]
 pub enum Polonius {
     /// The default value: disabled.
-    #[default]
     Off,
 
     /// Legacy version, using datalog and the `polonius-engine` crate. Historical value for `-Zpolonius`.
     Legacy,
 
     /// In-tree prototype, extending the NLL infrastructure.
+    #[default]
     Next,
 }
 

tests/ui/nll/polonius/location-insensitive-scopes-issue-117146.nll.stderr

@@ -0,0 +1,40 @@
+error[E0597]: `a` does not live long enough
+  --> $DIR/location-insensitive-scopes-issue-117146.rs:10:18
+   |
+LL |     let b = |_| &a;
+   |             --- -^
+   |             |   ||
+   |             |   |borrowed value does not live long enough
+   |             |   returning this value requires that `a` is borrowed for `'static`
+   |             value captured here
+...
+LL | }
+   | - `a` dropped here while still borrowed
+   |
+note: due to current limitations in the borrow checker, this implies a `'static` lifetime
+  --> $DIR/location-insensitive-scopes-issue-117146.rs:20:22
+   |
+LL | fn bad<F: Fn(&()) -> &()>(_: F) {}
+   |                      ^^^
+
+error: implementation of `Fn` is not general enough
+  --> $DIR/location-insensitive-scopes-issue-117146.rs:13:5
+   |
+LL |     bad(&b);
+   |     ^^^^^^^ implementation of `Fn` is not general enough
+   |
+   = note: closure with signature `fn(&'2 ()) -> &()` must implement `Fn<(&'1 (),)>`, for any lifetime `'1`...
+   = note: ...but it actually implements `Fn<(&'2 (),)>`, for some specific lifetime `'2`
+
+error: implementation of `FnOnce` is not general enough
+  --> $DIR/location-insensitive-scopes-issue-117146.rs:13:5
+   |
+LL |     bad(&b);
+   |     ^^^^^^^ implementation of `FnOnce` is not general enough
+   |
+   = note: closure with signature `fn(&'2 ()) -> &()` must implement `FnOnce<(&'1 (),)>`, for any lifetime `'1`...
+   = note: ...but it actually implements `FnOnce<(&'2 (),)>`, for some specific lifetime `'2`
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0597`.

tests/ui/nll/polonius/location-insensitive-scopes-issue-117146.polonius.stderr

@@ -0,0 +1,40 @@
+error[E0597]: `a` does not live long enough
+  --> $DIR/location-insensitive-scopes-issue-117146.rs:10:18
+   |
+LL |     let b = |_| &a;
+   |             --- -^
+   |             |   ||
+   |             |   |borrowed value does not live long enough
+   |             |   returning this value requires that `a` is borrowed for `'static`
+   |             value captured here
+...
+LL | }
+   | - `a` dropped here while still borrowed
+   |
+note: due to current limitations in the borrow checker, this implies a `'static` lifetime
+  --> $DIR/location-insensitive-scopes-issue-117146.rs:20:22
+   |
+LL | fn bad<F: Fn(&()) -> &()>(_: F) {}
+   |                      ^^^
+
+error: implementation of `Fn` is not general enough
+  --> $DIR/location-insensitive-scopes-issue-117146.rs:13:5
+   |
+LL |     bad(&b);
+   |     ^^^^^^^ implementation of `Fn` is not general enough
+   |
+   = note: closure with signature `fn(&'2 ()) -> &()` must implement `Fn<(&'1 (),)>`, for any lifetime `'1`...
+   = note: ...but it actually implements `Fn<(&'2 (),)>`, for some specific lifetime `'2`
+
+error: implementation of `FnOnce` is not general enough
+  --> $DIR/location-insensitive-scopes-issue-117146.rs:13:5
+   |
+LL |     bad(&b);
+   |     ^^^^^^^ implementation of `FnOnce` is not general enough
+   |
+   = note: closure with signature `fn(&'2 ()) -> &()` must implement `FnOnce<(&'1 (),)>`, for any lifetime `'1`...
+   = note: ...but it actually implements `FnOnce<(&'2 (),)>`, for some specific lifetime `'2`
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0597`.

tests/ui/nll/polonius/location-insensitive-scopes-issue-117146.rs

@@ -0,0 +1,20 @@
+// This is a non-regression test for issue #117146, where NLL and `-Zpolonius=next` computed
+// different loan scopes when a region flowed into an SCC whose representative was an existential
+// region.
+
+// revisions: nll polonius
+// [polonius] compile-flags: -Zpolonius=next
+
+fn main() {
+    let a = ();
+    let b = |_| &a;
+    //[nll]~^ ERROR `a` does not live long enough
+    //[polonius]~^^ ERROR `a` does not live long enough
+    bad(&b);
+    //[nll]~^ ERROR implementation of `Fn`
+    //[nll]~| ERROR implementation of `FnOnce`
+    //[polonius]~^^^ ERROR implementation of `Fn`
+    //[polonius]~| ERROR implementation of `FnOnce`
+}
+
+fn bad<F: Fn(&()) -> &()>(_: F) {}