Make lifetimes in constants live at the point of use

Author: matthewjasper

src/librustc_mir/borrow_check/nll/type_check/mod.rs

@@ -276,7 +276,17 @@ impl<'a, 'b, 'tcx> Visitor<'tcx> for TypeVerifier<'a, 'b, 'tcx> {
 
     fn visit_constant(&mut self, constant: &Constant<'tcx>, location: Location) {
         self.super_constant(constant, location);
-        self.sanitize_type(constant, constant.literal.ty);
+        let ty = self.sanitize_type(constant, constant.literal.ty);
+
+        self.cx.infcx.tcx.for_each_free_region(&ty, |live_region| {
+            let live_region_vid =
+                self.cx.borrowck_context.universal_regions.to_region_vid(live_region);
+            self.cx
+                .borrowck_context
+                .constraints
+                .liveness_constraints
+                .add_element(live_region_vid, location);
+        });
 
         if let Some(annotation_index) = constant.user_ty {
             if let Err(terr) = self.cx.relate_type_and_user_type(
@@ -528,56 +538,64 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
 
         let parent_body = mem::replace(&mut self.body, promoted_body);
 
+        // Use new sets of constraints and closure bounds so that we can
+        // modify their locations.
         let all_facts = &mut None;
         let mut constraints = Default::default();
         let mut closure_bounds = Default::default();
+        let mut liveness_constraints = LivenessValues::new(
+            Rc::new(RegionValueElements::new(promoted_body)),
+        );
         // Don't try to add borrow_region facts for the promoted MIR
-        mem::swap(self.cx.borrowck_context.all_facts, all_facts);
 
-        // Use a new sets of constraints and closure bounds so that we can
-        // modify their locations.
-        mem::swap(
-            &mut self.cx.borrowck_context.constraints.outlives_constraints,
-            &mut constraints
-        );
-        mem::swap(
-            &mut self.cx.borrowck_context.constraints.closure_bounds_mapping,
-            &mut closure_bounds
-        );
+        let mut swap_constraints = |this: &mut Self| {
+            mem::swap(this.cx.borrowck_context.all_facts, all_facts);
+            mem::swap(
+                &mut this.cx.borrowck_context.constraints.outlives_constraints,
+                &mut constraints
+            );
+            mem::swap(
+                &mut this.cx.borrowck_context.constraints.closure_bounds_mapping,
+                &mut closure_bounds
+            );
+            mem::swap(
+                &mut this.cx.borrowck_context.constraints.liveness_constraints,
+                &mut liveness_constraints
+            );
+        };
+
+        swap_constraints(self);
 
         self.visit_body(promoted_body);
 
+
         if !self.errors_reported {
             // if verifier failed, don't do further checks to avoid ICEs
             self.cx.typeck_mir(promoted_body);
         }
 
         self.body = parent_body;
         // Merge the outlives constraints back in, at the given location.
-        mem::swap(self.cx.borrowck_context.all_facts, all_facts);
-        mem::swap(
-            &mut self.cx.borrowck_context.constraints.outlives_constraints,
-            &mut constraints
-        );
-        mem::swap(
-            &mut self.cx.borrowck_context.constraints.closure_bounds_mapping,
-            &mut closure_bounds
-        );
+        swap_constraints(self);
 
         let locations = location.to_locations();
         for constraint in constraints.outlives().iter() {
             let mut constraint = *constraint;
             constraint.locations = locations;
             if let ConstraintCategory::Return
-                | ConstraintCategory::UseAsConst
-                | ConstraintCategory::UseAsStatic = constraint.category
+            | ConstraintCategory::UseAsConst
+            | ConstraintCategory::UseAsStatic = constraint.category
             {
                 // "Returning" from a promoted is an assigment to a
                 // temporary from the user's point of view.
                 constraint.category = ConstraintCategory::Boring;
             }
             self.cx.borrowck_context.constraints.outlives_constraints.push(constraint)
         }
+        for live_region in liveness_constraints.rows() {
+            self.cx.borrowck_context.constraints.liveness_constraints
+                .add_element(live_region, location);
+        }
 
         if !closure_bounds.is_empty() {
             let combined_bounds_mapping = closure_bounds

src/test/ui/hrtb/due-to-where-clause.nll.stderr

@@ -0,0 +1,8 @@
+error: higher-ranked subtype error
+  --> $DIR/due-to-where-clause.rs:2:5
+   |
+LL |     test::<FooS>(&mut 42);
+   |     ^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+

src/test/ui/hrtb/due-to-where-clause.rs

@@ -1,6 +1,3 @@
-// ignore-compare-mode-nll
-// ^ This code works in nll mode.
-
 fn main() {
     test::<FooS>(&mut 42); //~ ERROR implementation of `Foo` is not general enough
 }

src/test/ui/hrtb/due-to-where-clause.stderr

@@ -1,5 +1,5 @@
 error: implementation of `Foo` is not general enough
-  --> $DIR/due-to-where-clause.rs:5:5
+  --> $DIR/due-to-where-clause.rs:2:5
    |
 LL |     test::<FooS>(&mut 42);
    |     ^^^^^^^^^^^^ implementation of `Foo` is not general enough

src/test/ui/nll/promoted-liveness.rs

@@ -0,0 +1,8 @@
+// Test that promoted that have larger mir bodies than their containing function
+// don't cause an ICE.
+
+// check-pass
+
+fn main() {
+    &["0", "1", "2", "3", "4", "5", "6", "7"];
+}