From c558eecdcd6444919c0314043c0f328c85ca3b22 Mon Sep 17 00:00:00 2001
From: qunyanm <unknown>
Date: Fri, 26 Feb 2016 16:50:38 -0800
Subject: Fix issue 139. Allow bound variables in nested case patterns to
 shadow variables declared outside the enclosing match.

---
 Source/Dafny/Resolver.cs      | 12 +++++++++++-
 Test/dafny4/Bug139.dfy        | 25 +++++++++++++++++++++++++
 Test/dafny4/Bug139.dfy.expect |  2 ++
 3 files changed, 38 insertions(+), 1 deletion(-)
 create mode 100644 Test/dafny4/Bug139.dfy
 create mode 100644 Test/dafny4/Bug139.dfy.expect

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
-- 
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