Merge #980

980: WIP: Iterator tracking issues r=Aurel300 a=vl0w

Some (smaller / bigger) changes needed to enable iterator support
(WIP / tracking PR)

- Moved normalization of constraint param env (for assoc types) for better logging
- Fixed a bug in `SpecGraph`: Preconditions of the base spec were copied to the constrained spec
- Ghost constraint resolving is a bit relaxed (`predicate_may_hold` instead of `predicate_must_hold_considering_regions`) to account for references in associated types. See test `associated_types_6.rs`
- `merge_generics` now also merges lifetimes to accout for lifetimes appearing in `#[refine_trait_spec]`
- Lifetimes in type models are not converted to the anonymous lifetime `'_` anymore
- Do not `#[derive(Copy, Clone]` on type models, because the derive macro "conditionally" implements it when generics are involved. That is, `#[derive(Copy)] struct Foo<T>` adds `impl<T: Copy> Copy for Foo {}`, but we do not want to implement `Copy` only if `T` is `Copy`.
- Quantified variables now support associated types: `forall(|x: Self::SomeAssocType| ...)`

Co-authored-by: Jonas Hansen <[email protected]>

docs/dev-guide/src/config/flags.md

@@ -23,6 +23,7 @@
 | [`DUMP_VIPER_PROGRAM`](#dump_viper_program) | `bool` | `false` |
 | [`ENABLE_CACHE`](#enable_cache) | `bool` | `true` |
 | [`ENABLE_GHOST_CONSTRAINTS`](#enable_ghost_constraints) | `bool` | `false` |
+| [`ENABLE_ITERATORS`](#enable_iterators) | `bool` | `false` |
 | [`ENABLE_PURIFICATION_OPTIMIZATION`](#enable_purification_optimization) | `bool` | `false` |
 | [`ENABLE_TYPE_INVARIANTS`](#enable_type_invariants) | `bool` | `false` |
 | [`ENABLE_VERIFY_ONLY_BASIC_BLOCK_PATH`](#enable_verify_only_basic_block_path) | `bool` | `false` |
@@ -175,6 +176,13 @@ on a generic type parameter) is satisfied.
 
 **This is an experimental feature**, because it is currently possible to introduce unsound verification behavior.
 
+## `ENABLE_ITERATORS`
+
+When enabled, calls to `Iterator::next` will be encoded in the Viper program.
+Otherwise, an error is thrown during the encoding.
+
+**This is an experimental feature**, iterator support is still experimental.
+
 ## `ENABLE_PURIFICATION_OPTIMIZATION`
 
 When enabled, impure methods are optimized using the purification optimization, which tries to convert heap operations to pure (snapshot-based) operations.

prusti-common/src/config.rs

@@ -127,6 +127,7 @@ lazy_static::lazy_static! {
         settings.set_default("print_hash", false).unwrap();
         settings.set_default("enable_cache", true).unwrap();
         settings.set_default("enable_ghost_constraints", false).unwrap();
+        settings.set_default("enable_iterators", false).unwrap();
 
         // Flags for testing.
         settings.set_default::<Option<i64>>("verification_deadline", None).unwrap();
@@ -847,3 +848,9 @@ pub fn enable_ghost_constraints() -> bool {
 pub fn enable_type_invariants() -> bool {
     read_setting("enable_type_invariants")
 }
+
+/// When enabled, calls to `Iterator::next` will be encoded in the Viper program.
+/// Otherwise, an error is thrown during the encoding.
+pub fn enable_iterators() -> bool {
+    read_setting("enable_iterators")
+}

prusti-contracts/src/lib.rs

@@ -351,4 +351,12 @@ pub fn exists<T, F>(_trigger_set: T, _closure: F) -> bool {
     true
 }
 
+pub fn snap<T>(_x: &T) -> T {
+    unimplemented!()
+}
+
+pub fn snapshot_equality<T>(_l: T, _r: T) -> bool {
+    true
+}
+
 pub use private::*;

prusti-interface/src/environment/mod.rs

@@ -12,6 +12,7 @@ use prusti_rustc_interface::hir::def_id::{DefId, LocalDefId};
 use prusti_rustc_interface::middle::ty::{self, TyCtxt};
 use prusti_rustc_interface::middle::ty::subst::{Subst, SubstsRef};
 use prusti_rustc_interface::trait_selection::infer::{InferCtxtExt, TyCtxtInferExt};
+use prusti_rustc_interface::middle::ty::TypeSuperFoldable;
 use std::path::PathBuf;
 use prusti_rustc_interface::errors::{DiagnosticBuilder, EmissionGuarantee, MultiSpan};
 use prusti_rustc_interface::span::{Span, symbol::Symbol};
@@ -308,7 +309,11 @@ impl<'tcx> Environment<'tcx> {
         body
             .monomorphised_bodies
             .entry(substs)
-            .or_insert_with(|| ty::EarlyBinder(body.base_body.clone()).subst(self.tcx, substs))
+            .or_insert_with(|| {
+                let param_env = self.tcx.param_env(def_id);
+                let substituted = ty::EarlyBinder(body.base_body.clone()).subst(self.tcx, substs);
+                self.resolve_assoc_types(substituted.clone(), param_env)
+            })
             .clone()
     }
 
@@ -496,14 +501,18 @@ impl<'tcx> Environment<'tcx> {
         called_def_id: ProcedureDefId, // what are we calling?
         call_substs: SubstsRef<'tcx>,
     ) -> (ProcedureDefId, SubstsRef<'tcx>) {
-        use prusti_rustc_interface::middle::ty::TypeFoldable;
-
-        // avoids a compiler-internal panic
-        if call_substs.needs_infer() {
+        // Avoids a compiler-internal panic
+        // this check ignores any lifetimes/regions, which at this point would
+        // need inference. They are thus ignored.
+        if self.any_type_needs_infer(call_substs) {
             return (called_def_id, call_substs);
         }
 
         let param_env = self.tcx.param_env(caller_def_id);
+
+        // `resolve_instance` below requires normalized substs.
+        let call_substs = self.tcx.normalize_erasing_regions(param_env, call_substs);
+
         traits::resolve_instance(self.tcx, param_env.and((called_def_id, call_substs)))
             .map(|opt_instance| opt_instance
                 .map(|instance| (instance.def_id(), instance.substs))
@@ -517,6 +526,7 @@ impl<'tcx> Environment<'tcx> {
         // Normalize the type to account for associated types
         let ty = self.resolve_assoc_types(ty, param_env);
         let ty = self.tcx.erase_late_bound_regions(ty);
+        let ty = self.tcx.erase_regions(ty);
         ty.is_copy_modulo_regions(self.tcx.at(prusti_rustc_interface::span::DUMMY_SP), param_env)
     }
 
@@ -557,28 +567,86 @@ impl<'tcx> Environment<'tcx> {
         );
 
         self.tcx.infer_ctxt().enter(|infcx| {
-            infcx.predicate_must_hold_considering_regions(&obligation)
+            infcx.predicate_must_hold_modulo_regions(&obligation)
         })
     }
 
     /// Normalizes associated types in foldable types,
     /// i.e. this resolves projection types ([ty::TyKind::Projection]s)
-    /// **Important:** Regions while be erased during this process
-    pub fn resolve_assoc_types<T: ty::TypeFoldable<'tcx> + std::fmt::Debug + Copy>(&self, normalizable: T, param_env: ty::ParamEnv<'tcx>) -> T {
-        let norm_res = self.tcx.try_normalize_erasing_regions(
-            param_env,
-            normalizable
-        );
+    pub fn resolve_assoc_types<T: ty::TypeFoldable<'tcx> + std::fmt::Debug>(&self, normalizable: T, param_env: ty::ParamEnv<'tcx>) -> T {
+        struct Normalizer<'a, 'tcx> {
+            tcx: &'a ty::TyCtxt<'tcx>,
+            param_env: ty::ParamEnv<'tcx>,
+        }
+        impl<'a, 'tcx> ty::fold::TypeFolder<'tcx> for Normalizer<'a, 'tcx> {
+            fn tcx(&self) -> ty::TyCtxt<'tcx> {
+                *self.tcx
+            }
+
+            fn fold_mir_const(&mut self, c: mir::ConstantKind<'tcx>) -> mir::ConstantKind<'tcx> {
+                // rustc by default panics when we execute this TypeFolder on a mir::* type,
+                // but we want to resolve associated types when we retrieve a local mir::Body
+                c
+            }
 
-        match norm_res {
-            Ok(normalized) => {
-                debug!("Normalized {:?}: {:?}", normalizable, normalized);
-                normalized
-            },
-            Err(err) => {
-                debug!("Error while resolving associated types for {:?}: {:?}", normalizable, err);
-                normalizable
+            fn fold_ty(&mut self, ty: ty::Ty<'tcx>) -> ty::Ty<'tcx> {
+                match ty.kind() {
+                    ty::TyKind::Projection(_) => {
+                        let normalized = self.tcx.infer_ctxt().enter(|infcx| {
+                            use prusti_rustc_interface::trait_selection::traits::{fully_normalize, ObligationCause, FulfillmentContext};
+
+                            let normalization_result = fully_normalize(
+                                &infcx,
+                                FulfillmentContext::new(),
+                                ObligationCause::dummy(),
+                                self.param_env,
+                                ty
+                            );
+
+                            match normalization_result {
+                                Ok(res) => res,
+                                Err(errors) => {
+                                    debug!("Error while resolving associated types: {:?}", errors);
+                                    ty
+                                }
+                            }
+                        });
+                        normalized.super_fold_with(self)
+                    }
+                    _ => ty.super_fold_with(self)
+                }
             }
         }
+
+        normalizable.fold_with(&mut Normalizer {tcx: &self.tcx, param_env})
     }
-}
+
+    fn any_type_needs_infer<T: ty::TypeFoldable<'tcx>>(&self, t: T) -> bool {
+        // Helper
+        fn is_nested_ty(ty: ty::Ty<'_>) -> bool {
+            let mut walker = ty.walk();
+            let first = walker.next().unwrap().expect_ty();
+            assert!(ty == first);
+            walker.next().is_some()
+        }
+
+        // Visitor
+        struct NeedsInfer;
+        impl<'tcx> ty::fold::TypeVisitor<'tcx> for NeedsInfer {
+            type BreakTy = ();
+
+            fn visit_ty(&mut self, ty: ty::Ty<'tcx>) -> std::ops::ControlFlow<Self::BreakTy> {
+                use prusti_rustc_interface::middle::ty::TypeFoldable;
+                if is_nested_ty(ty) {
+                    ty.super_visit_with(self)
+                } else if ty.needs_infer() {
+                    std::ops::ControlFlow::BREAK
+                } else {
+                    std::ops::ControlFlow::CONTINUE
+                }
+            }
+        }
+
+        t.visit_with(&mut NeedsInfer).is_break()
+    }
+}

prusti-interface/src/specs/typed.rs

@@ -318,7 +318,16 @@ impl SpecGraph<ProcedureSpecification> {
     ) -> &mut ProcedureSpecification {
         self.specs_with_constraints
             .entry(constraint)
-            .or_insert_with(|| self.base_spec.clone())
+            .or_insert_with(|| {
+                let mut base = self.base_spec.clone();
+
+                // Preconditions of the base spec do not appear in the constrained spec
+                // Any preconditions that exist on the base spec are thus pruned
+                // (see comment on impl block)
+                base.pres = SpecificationItem::Empty;
+
+                base
+            })
     }
 
     /// Gets the constraint of a spec function `spec`.
@@ -462,24 +471,6 @@ pub enum ProcedureSpecificationKindError {
 }
 
 impl SpecificationItem<ProcedureSpecificationKind> {
-    pub fn is_pure(&self) -> Result<bool, ProcedureSpecificationKindError> {
-        self.validate()?;
-
-        Ok(matches!(
-            self.extract_with_selective_replacement(),
-            Some(ProcedureSpecificationKind::Pure) | Some(ProcedureSpecificationKind::Predicate(_))
-        ))
-    }
-
-    pub fn is_impure(&self) -> Result<bool, ProcedureSpecificationKindError> {
-        self.validate()?;
-
-        Ok(match self.extract_with_selective_replacement() {
-            Some(refined) => matches!(refined, ProcedureSpecificationKind::Impure),
-            _ => true,
-        })
-    }
-
     pub fn get_predicate_body(
         &self,
     ) -> Result<Option<&LocalDefId>, ProcedureSpecificationKindError> {
@@ -806,69 +797,5 @@ mod tests {
                 ));
             }
         }
-
-        mod is_impure {
-            use super::*;
-
-            macro_rules! impure_checks {
-                    ($($name:ident: $value:expr,)*) => {
-                        $(
-                            #[test]
-                            fn $name() {
-                                let (item, expected) = $value;
-                                let item: SpecificationItem<ProcedureSpecificationKind> = item;
-                                let result = item.is_impure().expect("Expected impure");
-                                assert_eq!(result, expected);
-                            }
-                        )*
-                    }
-                }
-
-            impure_checks!(
-                    empty: (Empty, true),
-                    inherent_impure: (Inherent(Impure), true),
-                    inherent_pure: (Inherent(Pure), false),
-                    inherent_predicate: (Inherent(Predicate(None)), false),
-                    inherited_impure: (Inherited(Impure), true),
-                    inherited_pure: (Inherited(Pure), false),
-                    inherited_predicate: (Inherited(Predicate(None)), false),
-                    refined_impure_parent_impure_child: (Refined(Impure, Impure), true),
-                    refined_impure_parent_pure_child: (Refined(Impure, Pure), false),
-                    refined_pure_parent_with_pure_child: (Refined(Pure, Pure), false),
-                    refined_predicate_parent_with_predicate_child: (Refined(Predicate(None), Predicate(None)), false),
-            );
-        }
-
-        mod is_pure {
-            use super::*;
-
-            macro_rules! pure_checks {
-                    ($($name:ident: $value:expr,)*) => {
-                        $(
-                            #[test]
-                            fn $name() {
-                                let (item, expected) = $value;
-                                let item: SpecificationItem<ProcedureSpecificationKind> = item;
-                                let result = item.is_pure().expect("Expected pure");
-                                assert_eq!(result, expected);
-                            }
-                        )*
-                    }
-                }
-
-            pure_checks!(
-                    empty: (Empty, false),
-                    inherent_impure: (Inherent(Impure), false),
-                    inherent_pure: (Inherent(Pure), true),
-                    inherent_predicate: (Inherent(Predicate(None)), true),
-                    inherited_impure: (Inherited(Impure), false),
-                    inherited_pure: (Inherited(Pure), true),
-                    inherited_predicate: (Inherited(Predicate(None)), true),
-                    refined_impure_parent_impure_child: (Refined(Impure, Impure), false),
-                    refined_impure_parent_pure_child: (Refined(Impure, Pure), true),
-                    refined_pure_parent_with_pure: (Refined(Pure, Pure), true),
-                    refined_predicate_parent_with_predicate_child: (Refined(Predicate(None), Predicate(None)), true),
-            );
-        }
     }
 }