map: Fix bug with result container type (#4860)

Fix bug in map where the result container type was getting set
of the incorrect value.

Closes #4855

runtime/expr/map.go

@@ -22,16 +22,16 @@ func NewMapCall(zctx *zed.Context, e, inner Evaluator) Evaluator {
 }
 
 func (a *mapCall) Eval(ectx Context, in *zed.Value) *zed.Value {
-	v := a.eval.Eval(ectx, in)
-	if v.IsError() {
-		return v
+	val := a.eval.Eval(ectx, in)
+	if val.IsError() {
+		return val
 	}
-	elems, err := v.Elements()
+	elems, err := val.Elements()
 	if err != nil {
 		return ectx.CopyValue(*a.zctx.WrapError(err.Error(), in))
 	}
 	if len(elems) == 0 {
-		return v
+		return val
 	}
 	a.vals = a.vals[:0]
 	a.types = a.types[:0]
@@ -42,7 +42,7 @@ func (a *mapCall) Eval(ectx Context, in *zed.Value) *zed.Value {
 	}
 	inner := a.innerType(a.types)
 	bytes := a.buildVal(inner, a.vals)
-	if _, ok := zed.TypeUnder(in.Type).(*zed.TypeSet); ok {
+	if _, ok := zed.TypeUnder(val.Type).(*zed.TypeSet); ok {
 		return ectx.NewValue(a.zctx.LookupTypeSet(inner), zed.NormalizeSet(bytes))
 	}
 	return ectx.NewValue(a.zctx.LookupTypeArray(inner), bytes)

runtime/expr/ztests/map.yaml

@@ -1,5 +1,6 @@
 script: |
   echo '{a:["foo","bar","baz"]}' | zq -z 'a := map(a,upper)' -
+  echo '{a:|["foo","bar","baz"]|}' | zq -z 'a := map(a,upper)' -
   echo '["1","2","3"]' | zq -z 'yield map(this,int64)' -
   echo '[1,2,3]' | zq -z -I udf.zed -
 
@@ -13,5 +14,6 @@ outputs:
   - name: stdout
     data: |
       {a:["FOO","BAR","BAZ"]}
+      {a:|["BAR","BAZ","FOO"]|}
       [1,2,3]
       ["1","2","3"]