fix: Cross-modular override check

Source/DafnyCore/Compilers/Compiler-js.cs

@@ -2527,9 +2527,9 @@ bool SendToNewNodeProcess(string dafnyProgramName, string targetProgramText, str
 
       var psi = new ProcessStartInfo("node", "") {
         RedirectStandardInput = true,
-        StandardInputEncoding = Encoding.UTF8,
         RedirectStandardOutput = true,
         RedirectStandardError = true,
+        StandardInputEncoding = Encoding.UTF8,
       };
 
       try {

Source/DafnyCore/Compilers/Compiler-python.cs

@@ -1752,10 +1752,7 @@ private static string FindModuleName(string externFilename) {
         }
       }
       rd.Close();
-      if (externFilename.EndsWith(".py")) {
-        return externFilename.Substring(0, externFilename.Length - 3);
-      }
-      return null;
+      return externFilename.EndsWith(".py") ? externFilename[..^3] : null;
     }
 
     static bool CopyExternLibraryIntoPlace(string externFilename, string mainProgram, TextWriter outputWriter) {

Source/DafnyCore/Substituter.cs

@@ -54,7 +54,7 @@ public virtual Expression Substitute(Expression expr) {
       } else if (expr is WildcardExpr) {
         // nothing to substitute
       } else if (expr is ThisExpr) {
-        return receiverReplacement == null ? expr : receiverReplacement;
+        return receiverReplacement ?? expr;
       } else if (expr is IdentifierExpr) {
         IdentifierExpr e = (IdentifierExpr)expr;
         Expression substExpr;

Source/DafnyCore/Verifier/FunctionCallSubstituter.cs

@@ -3,8 +3,8 @@
 namespace Microsoft.Dafny {
   public class FunctionCallSubstituter : Substituter {
     public readonly Function A, B;
-    public FunctionCallSubstituter(Expression receiverReplacement, Dictionary<IVariable, Expression/*!*/>/*!*/ substMap, Function a, Function b)
-      : base(receiverReplacement, substMap, new Dictionary<TypeParameter, Type>()) {
+    public FunctionCallSubstituter(Expression receiverReplacement, Dictionary<IVariable, Expression/*!*/>/*!*/ substMap, Dictionary<TypeParameter, Type> typeMap, Function a, Function b)
+      : base(receiverReplacement, substMap, typeMap) {
       A = a;
       B = b;
     }
@@ -21,8 +21,8 @@ public override Expression Substitute(Expression expr) {
           newFce.Function = e.Function;
           newFce.Type = e.Type;
         }
-        newFce.TypeApplication_AtEnclosingClass = e.TypeApplication_AtEnclosingClass;  // resolve here
-        newFce.TypeApplication_JustFunction = e.TypeApplication_JustFunction;  // resolve here
+        newFce.TypeApplication_AtEnclosingClass = SubstituteTypeList(e.TypeApplication_AtEnclosingClass);  // resolve here
+        newFce.TypeApplication_JustFunction = SubstituteTypeList(e.TypeApplication_JustFunction);  // resolve here
         newFce.IsByMethodCall = e.IsByMethodCall;
         return newFce;
       }

Source/DafnyCore/Verifier/Translator.ClassMembers.cs

@@ -213,7 +213,8 @@ private void AddAllocationAxiom(Boogie.Declaration fieldDeclaration, Field f, To
         AddWellformednessCheck(cf);
         if (InVerificationScope(cf)) {
           var etran = new ExpressionTranslator(this, predef, f.tok);
-          heightAntecedent = Bpl.Expr.Lt(Bpl.Expr.Literal(cf.EnclosingModule.CallGraph.GetSCCRepresentativePredecessorCount(cf)), etran.FunctionContextHeight());
+          var visibilityLevel = cf.EnclosingModule.CallGraph.GetSCCRepresentativePredecessorCount(cf);
+          heightAntecedent = Bpl.Expr.Lt(MkFunctionHeight(visibilityLevel), etran.FunctionContextHeight());
         }
       }
 
@@ -877,8 +878,8 @@ private void AddFunctionOverrideCheckImpl(Function f) {
       }
       // the procedure itself
       var req = new List<Boogie.Requires>();
-      // free requires mh == ModuleContextHeight && fh == FunctionContextHeight;
-      req.Add(Requires(f.tok, true, etran.HeightContext(f.OverriddenFunction), null, null));
+      // free requires fh == FunctionContextHeight;
+      req.Add(Requires(f.tok, true, etran.HeightContext(f.OverriddenFunction, true), null, null));
       if (f is TwoStateFunction) {
         // free requires prevHeap == Heap && HeapSucc(prevHeap, currHeap) && IsHeap(currHeap)
         var a0 = Boogie.Expr.Eq(prevHeap, ordinaryEtran.HeapExpr);
@@ -920,18 +921,16 @@ private void AddFunctionOverrideCheckImpl(Function f) {
       }
 
       var substMap = new Dictionary<IVariable, Expression>();
-      for (int i = 0; i < f.Formals.Count; i++) {
-        //get corresponsing formal in the class
-        var ie = new IdentifierExpr(f.Formals[i].tok, f.Formals[i].AssignUniqueName(f.IdGenerator));
-        ie.Var = f.Formals[i]; ie.Type = ie.Var.Type;
-        substMap.Add(f.OverriddenFunction.Formals[i], ie);
+      foreach (var (formal, overriddenFormal) in f.Formals.Zip(f.OverriddenFunction.Formals, Tuple.Create)) {
+        // get corresponding formal in the class
+        var ie = new IdentifierExpr(formal.tok, formal.AssignUniqueName(f.IdGenerator)) { Var = formal, Type = formal.Type };
+        substMap.Add(overriddenFormal, ie);
       }
 
       if (f.OverriddenFunction.Result != null) {
         Contract.Assert(pOut != null);
-        //get corresponsing formal in the class
-        var ie = new IdentifierExpr(pOut.tok, pOut.AssignUniqueName(f.IdGenerator));
-        ie.Var = pOut; ie.Type = ie.Var.Type;
+        // get corresponding formal in the class
+        var ie = new IdentifierExpr(pOut.tok, pOut.AssignUniqueName(f.IdGenerator)) { Var = pOut, Type = pOut.Type };
         substMap.Add(f.OverriddenFunction.Result, ie);
       }
 
@@ -946,8 +945,8 @@ private void AddFunctionOverrideCheckImpl(Function f) {
       //adding assert W <= Frame’
       AddFunctionOverrideSubsetChk(f, builder, etran, localVariables, substMap, typeMap);
 
-      //adding assume Q; assert Post’;
-      //adding assume J.F(ins) == C.F(ins);
+      //adding assume Q;
+      //assert Post’;
       AddFunctionOverrideEnsChk(f, builder, etran, substMap, typeMap, implInParams, implOutParams.Count == 0 ? null : implOutParams[0]);
 
       var stmts = builder.Collect(f.tok);
@@ -1134,7 +1133,7 @@ private Boogie.Axiom FunctionOverrideAxiom(Function f, Function overridingFuncti
       // The axiom
       Boogie.Expr ax = BplForall(f.tok, new List<Boogie.TypeVariable>(), forallFormals, null, tr,
         Boogie.Expr.Imp(Boogie.Expr.And(ReceiverNotNull(bvThisExpr), isOfSubtype), synonyms));
-      var activate = AxiomActivation(f, etran);
+      var activate = AxiomActivation(overridingFunction, etran, true);
       string comment = "override axiom for " + f.FullSanitizedName + " in class " + overridingFunction.EnclosingClass.FullSanitizedName;
       return new Boogie.Axiom(f.tok, Boogie.Expr.Imp(activate, ax), comment);
     }

Source/DafnyCore/Verifier/Translator.ExpressionTranslator.cs

@@ -258,12 +258,11 @@ public Boogie.IdentifierExpr FunctionContextHeight() {
         return new Boogie.IdentifierExpr(Token.NoToken, "$FunctionContextHeight", Boogie.Type.Int);
       }
 
-      public Boogie.Expr HeightContext(ICallable m) {
+      public Boogie.Expr HeightContext(ICallable m, bool reducedScope = false) {
         Contract.Requires(m != null);
         // free requires fh == FunctionContextHeight;
-        var module = m.EnclosingModule;
-        Boogie.Expr context =
-          Boogie.Expr.Eq(Boogie.Expr.Literal(module.CallGraph.GetSCCRepresentativePredecessorCount(m)), FunctionContextHeight());
+        var visibilityLevel = m.EnclosingModule.CallGraph.GetSCCRepresentativePredecessorCount(m);
+        Boogie.Expr context = Boogie.Expr.Eq(MkFunctionHeight(visibilityLevel, reducedScope), FunctionContextHeight());
         return context;
       }
 

Source/DafnyCore/Verifier/Translator.cs

@@ -2053,7 +2053,7 @@ void AddFunctionConsequenceAxiom(Boogie.Function boogieFunction, Function f, Lis
       //   (mh == ModuleContextHeight && fh <= FunctionContextHeight)
       //
       // USE_VIA_CONTEXT
-      //   (mh != ModuleContextHeight || fh != FunctionContextHeight) &&
+      //   fh < FunctionContextHeight &&
       //   GOOD_PARAMETERS
       // where GOOD_PARAMETERS means:
       //   $IsGoodHeap($Heap) && this != null && formals-have-the-expected-types &&
@@ -2156,10 +2156,9 @@ void AddFunctionConsequenceAxiom(Boogie.Function boogieFunction, Function f, Lis
       foreach (AttributedExpression req in f.Req) {
         pre = BplAnd(pre, etran.TrExpr(Substitute(req.E, null, substMap)));
       }
-      // useViaContext: (mh != ModuleContextHeight || fh != FunctionContextHeight)
-      var mod = f.EnclosingClass.EnclosingModuleDefinition;
-      Bpl.Expr useViaContext = !InVerificationScope(f) ? Bpl.Expr.True :
-        (Bpl.Expr)Bpl.Expr.Neq(Bpl.Expr.Literal(mod.CallGraph.GetSCCRepresentativePredecessorCount(f)), etran.FunctionContextHeight());
+      // useViaContext: fh < FunctionContextHeight
+      var visibilityLevel = f.EnclosingClass.EnclosingModuleDefinition.CallGraph.GetSCCRepresentativePredecessorCount(f);
+      Expr useViaContext = !InVerificationScope(f) ? Bpl.Expr.True : Expr.Lt(MkFunctionHeight(visibilityLevel), etran.FunctionContextHeight());
       // useViaCanCall: f#canCall(args)
       Bpl.IdentifierExpr canCallFuncID = new Bpl.IdentifierExpr(f.tok, f.FullSanitizedName + "#canCall", Bpl.Type.Bool);
       Bpl.Expr useViaCanCall = new Bpl.NAryExpr(f.tok, new Bpl.FunctionCall(canCallFuncID), Concat(tyargs, args));
@@ -2254,15 +2253,14 @@ void AddFunctionConsequenceAxiom(Boogie.Function boogieFunction, Function f, Lis
       return (olderParameterCount, olderCondition);
     }
 
-    Bpl.Expr AxiomActivation(Function f, ExpressionTranslator etran) {
+    Bpl.Expr AxiomActivation(Function f, ExpressionTranslator etran, bool requiresFullScope = false) {
       Contract.Requires(f != null);
       Contract.Requires(etran != null);
       Contract.Requires(VisibleInScope(f));
-      var module = f.EnclosingClass.EnclosingModuleDefinition;
 
       if (InVerificationScope(f)) {
-        return
-          Bpl.Expr.Le(Bpl.Expr.Literal(module.CallGraph.GetSCCRepresentativePredecessorCount(f)), etran.FunctionContextHeight());
+        var visibilityLevel = f.EnclosingClass.EnclosingModuleDefinition.CallGraph.GetSCCRepresentativePredecessorCount(f);
+        return Expr.Le(MkFunctionHeight(visibilityLevel, !requiresFullScope), etran.FunctionContextHeight());
       } else {
         return Bpl.Expr.True;
       }
@@ -2302,7 +2300,7 @@ private Axiom GetFunctionAxiom(Function f, Expression body, List<Formal> lits) {
       // for visibility==ForeignModuleOnly, means:
       //   GOOD_PARAMETERS
       // for visibility==IntraModuleOnly, means:
-      //   fh != FunctionContextHeight &&
+      //   fh < FunctionContextHeight &&
       //   GOOD_PARAMETERS
       // where GOOD_PARAMETERS means:
       //   $IsGoodHeap($Heap) && this != null && formals-have-the-expected-types &&
@@ -2507,12 +2505,11 @@ private Axiom GetFunctionAxiom(Function f, Expression body, List<Formal> lits) {
         return null;
       }
 
-      // useViaContext: (mh != ModuleContextHeight || fh != FunctionContextHeight)
-      ModuleDefinition mod = f.EnclosingClass.EnclosingModuleDefinition;
+      // useViaContext: fh < FunctionContextHeight
+      var visibilityLevel = f.EnclosingClass.EnclosingModuleDefinition.CallGraph.GetSCCRepresentativePredecessorCount(f);
       Bpl.Expr useViaContext = !InVerificationScope(f)
-        ? (Bpl.Expr)Bpl.Expr.True
-        : Bpl.Expr.Neq(Bpl.Expr.Literal(mod.CallGraph.GetSCCRepresentativePredecessorCount(f)),
-          etran.FunctionContextHeight());
+        ? Bpl.Expr.True
+        : Bpl.Expr.Lt(MkFunctionHeight(visibilityLevel), etran.FunctionContextHeight());
       // ante := (useViaContext && typeAnte && pre)
       ante = BplAnd(useViaContext, BplAnd(ante, pre));
 
@@ -3486,65 +3483,41 @@ private void AddFunctionOverrideEnsChk(Function f, BoogieStmtListBuilder builder
         builder.Add(TrAssumeCmd(f.tok, etran.TrExpr(en.E)));
       }
 
-      //generating assume J.F(ins) == C.F(ins)
-      Bpl.FunctionCall funcIdC = new Bpl.FunctionCall(new Bpl.IdentifierExpr(f.tok, f.FullSanitizedName, TrType(f.ResultType)));
-      Bpl.FunctionCall funcIdT = new Bpl.FunctionCall(new Bpl.IdentifierExpr(f.OverriddenFunction.tok, f.OverriddenFunction.FullSanitizedName, TrType(f.OverriddenFunction.ResultType)));
-      List<Bpl.Expr> argsC = new List<Bpl.Expr>();
-      List<Bpl.Expr> argsT = new List<Bpl.Expr>();
-      // add type arguments
-      argsT.AddRange(GetTypeArguments(f.OverriddenFunction, f).ConvertAll(TypeToTy));
-      argsC.AddRange(GetTypeArguments(f, null).ConvertAll(TypeToTy));
-      // add fuel arguments
-      if (f.IsFuelAware()) {
-        argsC.Add(etran.layerInterCluster.GetFunctionFuel(f));
-      }
-      if (f.OverriddenFunction.IsFuelAware()) {
-        argsT.Add(etran.layerInterCluster.GetFunctionFuel(f));
-      }
-      // add heap arguments
-      if (f is TwoStateFunction) {
-        argsC.Add(etran.Old.HeapExpr);
-        argsT.Add(etran.Old.HeapExpr);
-      }
-      if (AlwaysUseHeap || f.ReadsHeap) {
-        argsC.Add(etran.HeapExpr);
-      }
-      if (AlwaysUseHeap || f.OverriddenFunction.ReadsHeap) {
-        argsT.Add(etran.HeapExpr);
-      }
-      // add "ordinary" parameters (including "this", if any)
-      var prefixCount = implInParams.Count - f.Formals.Count;
-      for (var i = 0; i < implInParams.Count; i++) {
-        Bpl.Expr cParam = new Bpl.IdentifierExpr(f.tok, implInParams[i]);
-        Bpl.Expr tParam = new Bpl.IdentifierExpr(f.OverriddenFunction.tok, implInParams[i]);
-        if (prefixCount <= i && ModeledAsBoxType(f.OverriddenFunction.Formals[i - prefixCount].Type)) {
-          tParam = BoxIfNecessary(f.tok, tParam, f.Formals[i - prefixCount].Type);
-        }
-        argsC.Add(cParam);
-        argsT.Add(tParam);
-      }
-      Bpl.Expr funcExpC = new Bpl.NAryExpr(f.tok, funcIdC, argsC);
-      Bpl.Expr funcExpT = new Bpl.NAryExpr(f.OverriddenFunction.tok, funcIdT, argsT);
-      var funcExpCPossiblyBoxed = funcExpC;
-      if (ModeledAsBoxType(f.OverriddenFunction.ResultType)) {
-        funcExpCPossiblyBoxed = BoxIfUnboxed(funcExpCPossiblyBoxed, f.ResultType);
-      }
-      builder.Add(TrAssumeCmd(f.tok, Bpl.Expr.Eq(funcExpCPossiblyBoxed, funcExpT)));
-
       //generating assume C.F(ins) == out, if a result variable was given
       if (resultVariable != null) {
+        var funcIdC = new FunctionCall(new Bpl.IdentifierExpr(f.tok, f.FullSanitizedName, TrType(f.ResultType)));
+        var argsC = new List<Bpl.Expr>();
+
+        // add type arguments
+        argsC.AddRange(GetTypeArguments(f, null).ConvertAll(TypeToTy));
+
+        // add fuel arguments
+        if (f.IsFuelAware()) {
+          argsC.Add(etran.layerInterCluster.GetFunctionFuel(f));
+        }
+
+        // add heap arguments
+        if (f is TwoStateFunction) {
+          argsC.Add(etran.Old.HeapExpr);
+        }
+        if (AlwaysUseHeap || f.ReadsHeap) {
+          argsC.Add(etran.HeapExpr);
+        }
+
+        argsC.AddRange(implInParams.Select(var => new Bpl.IdentifierExpr(f.tok, var)));
+
+        var funcExpC = new Bpl.NAryExpr(f.tok, funcIdC, argsC);
         var resultVar = new Bpl.IdentifierExpr(resultVariable.tok, resultVariable);
         builder.Add(TrAssumeCmd(f.tok, Bpl.Expr.Eq(funcExpC, resultVar)));
       }
 
       //generating trait post-conditions with class variables
       foreach (var en in f.OverriddenFunction.Ens) {
-        Expression postcond = Substitute(en.E, null, substMap, typeMap);
-        bool splitHappened;  // we don't actually care
-        foreach (var s in TrSplitExpr(postcond, etran, false, out splitHappened)) {
-          if (s.IsChecked) {
-            builder.Add(Assert(f.tok, s.E, new PODesc.FunctionContractOverride(true)));
-          }
+        var receiver = new ImplicitThisExpr(f.tok) { Type = Resolver.GetThisType(f.tok, (TopLevelDeclWithMembers)f.EnclosingClass) };
+        var sub = new FunctionCallSubstituter(receiver, substMap, typeMap, f.OverriddenFunction, f);
+        Expression postcond = sub.Substitute(en.E);
+        foreach (var s in TrSplitExpr(postcond, etran, false, out _).Where(s => s.IsChecked)) {
+          builder.Add(Assert(f.tok, s.E, new PODesc.FunctionContractOverride(true)));
         }
       }
     }
@@ -4768,7 +4741,7 @@ Bpl.Expr CanCallAssumption(Expression expr, ExpressionTranslator etran) {
       Contract.Requires(predef != null);
       Contract.Ensures(Contract.Result<Bpl.Expr>() != null);
 
-      if (expr is LiteralExpr || expr is ThisExpr || expr is IdentifierExpr || expr is WildcardExpr || expr is BoogieWrapper) {
+      if (expr is LiteralExpr or ThisExpr or IdentifierExpr or WildcardExpr or BoogieWrapper) {
         return Bpl.Expr.True;
       } else if (expr is DisplayExpression) {
         DisplayExpression e = (DisplayExpression)expr;
@@ -10747,6 +10720,14 @@ List<Variable> MkTyParamFormals(List<TypeParameter> args, bool includeWhereClaus
       return null;
     }
 
+    // We use the $FunctionContextHeight to restrict the applicability of certain axioms. The entity at the end of a
+    // dependency chain has the highest number. To get more granular control over the visibility, we extend every
+    // visibility level by a precursory intermediate level. This additional level is helpful for proofs that would be
+    // disturbed by axioms that are visible the the final level.
+    static Bpl.Expr MkFunctionHeight(int visibilityLevel, bool intermediateScope = false) {
+      return Expr.Literal(visibilityLevel * 2 + (intermediateScope ? 0 : 1));
+    }
+
     public static void MapM<A>(IEnumerable<A> xs, Action<A> K) {
       Contract.Requires(xs != null);
       Contract.Requires(K != null);

Test/git-issues/git-issue-2500.dfy

@@ -0,0 +1,22 @@
+// RUN: %dafny_0 /compile:0 "%s" > "%t"
+// RUN: %diff "%s.expect" "%t"
+
+module A {
+  trait {:termination false} Trait {
+    function TotallyNotZero() : (ret: int)
+      ensures ret != 0
+  }
+}
+
+module B {
+  import opened A
+
+  class Class extends Trait {
+    constructor() {}
+    function TotallyNotZero() : (ret: int)
+      // Missing: ensures ret != 0
+    { 
+      0 
+    }
+  }
+}

Test/git-issues/git-issue-2500.dfy.expect

@@ -0,0 +1,3 @@
+git-issue-2500.dfy(16,13): Error: the function must provide an equal or more detailed postcondition than in its parent trait
+
+Dafny program verifier finished with 1 verified, 1 error

docs/dev/news/3223.fix

@@ -0,0 +1 @@
+To ensure that a `class` correctly implements a `trait`, we perform an override check. This check was previously faulty across `module`s, but works unconditionally now.