attempt 2 at porting clj-1279-3.patch to clr (cf. https://dev.clojure.org/jira/browse/CLJ-1279)

gistfile1.txt

diff --git a/Clojure/Clojure.Tests/clojure/test_clojure/errors.clj b/Clojure/Clojure.Tests/clojure/test_clojure/errors.clj
index 0ae6dfb1..8e1493de 100644
--- a/Clojure/Clojure.Tests/clojure/test_clojure/errors.clj
+++ b/Clojure/Clojure.Tests/clojure/test_clojure/errors.clj
@@ -23,6 +23,8 @@
 
 (defmacro m1 [a] `(inc ~a))
 
+(defmacro m2 [] (assoc))
+
 (deftest arity-exception
   ;; IllegalArgumentException is pre-1.3
   (is (thrown-with-msg? ArgumentException #"Wrong number of args \(1\) passed to"  ;;; IllegalArgumentException
@@ -35,7 +37,17 @@
         (macroexpand `(m1 1 2))))
   (is (thrown-with-msg? ArityException  (System.Text.RegularExpressions.Regex. (System.Text.RegularExpressions.Regex/Escape "f2:+>
<->!#%&*b"))       ;;;  We don't have \Q... \E :  #"\Q/f2:+><->!#%&*|b\E"
         (f2:+><->!#%&*b 1 2))                                                                                                     
                   ;;; f2:+><->!#%&*|b  
-        "ArityException messages should demunge function names"))
+        "ArityException messages should demunge function names")
+  (is (try
+        (macroexpand `(m2))
+        (throw (RuntimeException. "fail"))
+        (catch ArityException e
+          (is (= 0 (.-actual e))))))
+  (is (try
+        (macroexpand `(m2 5))
+        (throw (RuntimeException. "fail"))
+        (catch ArityException e
+          (is (= 1 (.-actual e)))))))
 
 (deftest assert-arg-messages
   ; used to ensure that error messages properly use local names for macros
diff --git a/Clojure/Clojure/CljCompiler/Compiler.cs b/Clojure/Clojure/CljCompiler/Compiler.cs
index 39bbece4..e783e1b4 100644
--- a/Clojure/Clojure/CljCompiler/Compiler.cs
+++ b/Clojure/Clojure/CljCompiler/Compiler.cs
@@ -1224,7 +1224,11 @@ namespace clojure.lang
                 catch (ArityException e)
                 {
                     // hide the 2 extra params for a macro
-                    throw new ArityException(e.Actual - 2, e.Name);
+                    if (e.Name.Equals(munge(v.ns.Name.Name) + "$" + munge(v.sym.Name))) {
+                        throw new ArityException(e.Actual - 2, e.Name);
+                    } else {
+                        throw e;
+                    }
                 }
             }
             else
diff --git a/Clojure/Clojure/Lib/AFn.cs b/Clojure/Clojure/Lib/AFn.cs
index d60d86e6..91d2bdf5 100644
--- a/Clojure/Clojure/Lib/AFn.cs
+++ b/Clojure/Clojure/Lib/AFn.cs
@@ -467,7 +467,7 @@ namespace clojure.lang
             string name = this is Var.Unbound ? (this as Var.Unbound).ToString() : Util.NameForType(GetType()); 
             return new ArityException(
                 reqArity,
-                Compiler.demunge(name));
+                name);
         }
 
         #endregion
diff --git a/Clojure/Clojure/Lib/ArityException.cs b/Clojure/Clojure/Lib/ArityException.cs
index b2d67bbd..d17193c0 100644
--- a/Clojure/Clojure/Lib/ArityException.cs
+++ b/Clojure/Clojure/Lib/ArityException.cs
@@ -46,7 +46,7 @@ namespace clojure.lang
         }
 
         public ArityException(int actual, string name, Exception cause)
-            : base("Wrong number of args (" + actual + ") passed to: " + name, cause)
+            : base("Wrong number of args (" + actual + ") passed to: " + Compiler.demunge(name), cause)
         {
             _actual = actual;
             _name = name;