arity for {|a,| } was -2 and should have been 1

core/src/main/java/org/jruby/RubyHash.java

@@ -1624,7 +1624,7 @@ public RubyHash each_pairCommon(final ThreadContext context, final Block block)
         public void visit(ThreadContext context, RubyHash self, IRubyObject key, IRubyObject value, int index, Block block) {
             if (block.type == Block.Type.LAMBDA) {
                 block.call(context, context.runtime.newArray(key, value));
-            } else if (block.getSignature().arityValue() > 1) {
+            } else if (block.getSignature().isSpreadable()) {
                 block.yieldSpecific(context, key, value);
             } else {
                 block.yield(context, context.runtime.newArray(key, value));

core/src/main/java/org/jruby/ir/runtime/IRRuntimeHelpers.java

@@ -513,7 +513,9 @@ public static IRubyObject[] convertValueIntoArgArray(ThreadContext context, IRub
                         new IRubyObject[] { value };
             case  0:
             case  1:
-                return new IRubyObject[] { value };
+                return signature.rest() == org.jruby.runtime.Signature.Rest.ANON ?
+                        IRBlockBody.toAry(context, value) :
+                        new IRubyObject[] { value };
         }
 
         return IRBlockBody.toAry(context, value);

core/src/main/java/org/jruby/runtime/IRBlockBody.java

@@ -102,14 +102,13 @@ public IRubyObject yieldSpecific(ThreadContext context, Block block, IRubyObject
     }
 
     private IRubyObject yieldSpecificMultiArgsCommon(ThreadContext context, Block block, IRubyObject... args) {
-        int blockArity = signature.arityValue();
-        if (blockArity == 1) {
+        if (signature.isOneArgument()) {
             args = new IRubyObject[] { RubyArray.newArrayMayCopy(context.runtime, args) };
         }
 
         if (canCallDirect()) return yieldDirect(context, block, args, null);
 
-        if (blockArity == 0) {
+        if (signature.arityValue() == 0) {
             args = IRubyObject.NULL_ARRAY; // discard args
         }
         if (block.type == Block.Type.LAMBDA) signature.checkArity(context.runtime, args);

core/src/main/java/org/jruby/runtime/Signature.java

@@ -85,7 +85,7 @@ public boolean restKwargs() {
      * Are there an exact (fixed) number of parameters to this signature?
      */
     public boolean isFixed() {
-        return arityValue() >= 0;
+        return arityValue() >= 0 && rest != Rest.ANON;
     }
 
     /**
@@ -135,8 +135,9 @@ public int calculateArityValue() {
         int oneForKeywords = requiredKwargs > 0 ? 1 : 0;
         int fixedValue = pre() + post() + oneForKeywords;
         boolean hasOptionalKeywords = kwargs - requiredKwargs > 0;
+        boolean optionalFromRest = rest() != Rest.NONE && rest != Rest.ANON;
 
-        if (opt() > 0 || rest() != Rest.NONE || (hasOptionalKeywords || restKwargs()) && oneForKeywords == 0) {
+        if (opt() > 0 || optionalFromRest || (hasOptionalKeywords || restKwargs()) && oneForKeywords == 0) {
             return -1 * (fixedValue + 1);
         }
 
@@ -153,7 +154,7 @@ public int arityValue() {
      * @return true if the signature expects multiple args
      */
     public boolean isSpreadable() {
-        return arityValue < -1 || arityValue > 1 || (opt > 0 && !restKwargs());
+        return arityValue < -1 || arityValue > 1 || (opt > 0 && !restKwargs()) || rest == Rest.ANON;
     }