core: Fix interpolation tests with nested lists

Some of the tests for splat syntax were from the pre-list-and-map world,
and effectively flattened the values if interpolating a resource value
which was itself a list.

We now set the expected values correctly so that an interpolation like
`aws_instance.test.*.security_group_ids` now returns a list of lists.

We also fix the implementation to correctly deal with maps.

terraform/interpolate.go

@@ -493,7 +493,8 @@ func (i *Interpolater) computeResourceMultiVariable(
 	if module == nil || len(module.Resources) == 0 {
 		return &unknownVariable, nil
 	}
-	var values []string
+
+	var values []interface{}
 	for j := 0; j < count; j++ {
 		id := fmt.Sprintf("%s.%d", v.ResourceId(), j)
 
@@ -521,9 +522,10 @@ func (i *Interpolater) computeResourceMultiVariable(
 			continue
 		}
 
-		// computed list attribute
-		_, ok = r.Primary.Attributes[v.Field+".#"]
-		if !ok {
+		// computed list or map attribute
+		_, isList := r.Primary.Attributes[v.Field+".#"]
+		_, isMap := r.Primary.Attributes[v.Field+".%"]
+		if !(isList || isMap) {
 			continue
 		}
 		multiAttr, err := i.interpolateComplexTypeAttribute(v.Field, r.Primary.Attributes)
@@ -535,14 +537,7 @@ func (i *Interpolater) computeResourceMultiVariable(
 			return &ast.Variable{Type: ast.TypeString, Value: ""}, nil
 		}
 
-		for _, element := range multiAttr.Value.([]ast.Variable) {
-			strVal := element.Value.(string)
-			if strVal == config.UnknownVariableValue {
-				return &unknownVariable, nil
-			}
-
-			values = append(values, strVal)
-		}
+		values = append(values, multiAttr)
 	}
 
 	if len(values) == 0 {
@@ -595,7 +590,7 @@ func (i *Interpolater) interpolateComplexTypeAttribute(
 
 		keys := make([]string, 0)
 		listElementKey := regexp.MustCompile("^" + resourceID + "\\.[0-9]+$")
-		for id, _ := range attributes {
+		for id := range attributes {
 			if listElementKey.MatchString(id) {
 				keys = append(keys, id)
 			}

terraform/interpolate_test.go

@@ -449,11 +449,11 @@ func TestInterpolator_resourceMultiAttributesWithResourceCount(t *testing.T) {
 
 	// More than 1 element
 	testInterpolate(t, i, scope, "aws_route53_zone.terra.0.name_servers",
-		interfaceToVariableSwallowError(name_servers[0:4]))
+		interfaceToVariableSwallowError(name_servers[:4]))
 
 	// More than 1 element in both
 	testInterpolate(t, i, scope, "aws_route53_zone.terra.*.name_servers",
-		interfaceToVariableSwallowError(name_servers))
+		interfaceToVariableSwallowError([]interface{}{name_servers[:4], name_servers[4:]}))
 
 	// Exactly 1 element
 	testInterpolate(t, i, scope, "aws_route53_zone.terra.0.listeners",
@@ -461,7 +461,7 @@ func TestInterpolator_resourceMultiAttributesWithResourceCount(t *testing.T) {
 
 	// Exactly 1 element in both
 	testInterpolate(t, i, scope, "aws_route53_zone.terra.*.listeners",
-		interfaceToVariableSwallowError([]interface{}{"red", "blue"}))
+		interfaceToVariableSwallowError([]interface{}{[]interface{}{"red"}, []interface{}{"blue"}}))
 
 	// Zero elements
 	testInterpolate(t, i, scope, "aws_route53_zone.terra.0.nothing",
@@ -469,7 +469,7 @@ func TestInterpolator_resourceMultiAttributesWithResourceCount(t *testing.T) {
 
 	// Zero + 1 element
 	testInterpolate(t, i, scope, "aws_route53_zone.terra.*.special",
-		interfaceToVariableSwallowError([]interface{}{"extra"}))
+		interfaceToVariableSwallowError([]interface{}{[]interface{}{"extra"}}))
 
 	// Maps still need to work
 	testInterpolate(t, i, scope, "aws_route53_zone.terra.0.tags.Name", ast.Variable{