Fix issue 139. Allow bound variables in nested case patterns to shadow variables

declared outside the enclosing match.

3 files changed, 38 insertions, 1 deletions

diff --git a/Source/Dafny/Resolver.cs b/Source/Dafny/Resolver.cs
index 5a63b4e3..d3b59b51 100644
--- a/Source/Dafny/Resolver.cs
+++ b/Source/Dafny/Resolver.cs
@@ -6376,7 +6376,12 @@ namespace Microsoft.Dafny
         if (topLevel) {

           ScopePushAndReport(scope, v, "parameter");

         } else {

-          if (scope.Find(v.Name) != null) {

+          // For cons(a, const(b, c)):

+          // this handles check to see if 'b' or 'c' is duplicate with 'a',

+          // the duplication check between 'b' and 'c' is handled in the desugared

+          // form (to avoid reporting the same error twice), that is why we don't 

+          // push 'b' and 'c' onto the scope, only find.

+          if (scope.FindInCurrentScope(v.Name) != null) {

             reporter.Error(MessageSource.Resolver, v, "Duplicate parameter name: {0}", v.Name);

           }

         }

@@ -11069,6 +11074,11 @@ namespace Microsoft.Dafny
       return Find(name, false);

     }

 

+    public Thing FindInCurrentScope(string name) {

+      Contract.Requires(name != null);

+      return Find(name, true);

+    }

+

     public bool ContainsDecl(Thing t) {

       return things.Exists(thing => thing == t);

     }

diff --git a/Test/dafny4/Bug139.dfy b/Test/dafny4/Bug139.dfy
new file mode 100644
index 00000000..bd4ded73
--- /dev/null
+++ b/Test/dafny4/Bug139.dfy
@@ -0,0 +1,25 @@
+// RUN: %dafny /compile:0  "%s" > "%t"

+// RUN: %diff "%s.expect" "%t"

+

+datatype List = Nil | Cons(int, List)

+

+method R(xs: List)

+{

+  var a: int;

+  var b: int;

+  match xs

+  case Nil =>

+  case Cons(a, Nil()) =>  // this 'a' is allowed

+  case Cons(x, Cons(b, tail)) =>  // this 'b' (which is in a nested position) generates an error

+}

+

+function F(xs: List): int

+{

+  var a := 4;

+  var b := 7;

+  match xs

+  case Nil => 0

+  case Cons(a, Nil()) => 1

+  case Cons(x, Cons(b, tail)) => 2

+}

+

diff --git a/Test/dafny4/Bug139.dfy.expect b/Test/dafny4/Bug139.dfy.expect
new file mode 100644
index 00000000..52595bf9
--- /dev/null
+++ b/Test/dafny4/Bug139.dfy.expect
@@ -0,0 +1,2 @@
+

+Dafny program verifier finished with 3 verified, 0 errors