adding concatlist for concatenating lists

config/interpolate_funcs.go

@@ -18,6 +18,7 @@ var Funcs map[string]ast.Function
 
 func init() {
 	Funcs = map[string]ast.Function{
+		"concatlist": interpolationFuncConcatlist(),
 		"file":       interpolationFuncFile(),
 		"format":     interpolationFuncFormat(),
 		"formatlist": interpolationFuncFormatList(),
@@ -54,6 +55,27 @@ func interpolationFuncConcat() ast.Function {
 	}
 }
 
+// interpolationFuncConcatList implements the "concatlist" function that
+// concatenates multiple lists together.
+func interpolationFuncConcatlist() ast.Function {
+	return ast.Function{
+		ArgTypes:     []ast.Type{ast.TypeAny},
+		ReturnType:   ast.TypeString,
+		Variadic:     true,
+		VariadicType: ast.TypeAny,
+		Callback: func(args []interface{}) (interface{}, error) {
+			var list []string
+			for _, arg := range args {
+				parts := strings.Split(arg.(string), InterpSplitDelim)
+				if len(parts) > 0 {
+					list = append(list, parts...)
+				}
+			}
+			return strings.Join(list, InterpSplitDelim), nil
+		},
+	}
+}
+
 // interpolationFuncFile implements the "file" function that allows
 // loading contents from a file.
 func interpolationFuncFile() ast.Function {

config/interpolate_funcs_test.go

@@ -35,6 +35,33 @@ func TestInterpolateFuncConcat(t *testing.T) {
 	})
 }
 
+func TestInterpolateFuncConcatLists(t *testing.T) {
+	testFunction(t, testFunctionConfig{
+		Cases: []testFunctionCase{
+			{
+				`${join(",", concatlist(split(",", "A,B"), split(",", "C,D")))}`,
+				"A,B,C,D",
+				false,
+			},
+			{
+				`${join(",", concatlist(split(",", "A,B"), split(",", "C,D"), split(",", "E")))}`,
+				"A,B,C,D,E",
+				false,
+			},
+			{
+				`${join(",", concatlist(split(",", "A,B"), "C"))}`,
+				"A,B,C",
+				false,
+			},
+			{
+				`${join(",", concatlist("A", "B"))}`,
+				"A,B",
+				false,
+			},
+		},
+	})
+}
+
 func TestInterpolateFuncFile(t *testing.T) {
 	tf, err := ioutil.TempFile("", "tf")
 	if err != nil {