Concat func.

interpolation/lists.go

@@ -25,3 +25,20 @@ func interpolationFuncList() ast.Function {
 		},
 	}
 }
+
+// interpolationFuncConcat will concat multiple lists into a single list
+func interpolationFuncConcat() ast.Function {
+	return ast.Function{
+		ArgTypes:     []ast.Type{},
+		ReturnType:   ast.TypeList,
+		Variadic:     true,
+		VariadicType: ast.TypeList,
+		Callback: func(inputs []interface{}) (interface{}, error) {
+			result := make([]ast.Variable, 0)
+			for _, input := range inputs {
+				result = append(result, input.([]ast.Variable)...)
+			}
+			return result, nil
+		},
+	}
+}

interpolation/lists_test.go

@@ -1,6 +1,10 @@
 package interpolation
 
-import "testing"
+import (
+	"testing"
+
+	"github.com/hashicorp/hil/ast"
+)
 
 func TestInterpolationFuncList(t *testing.T) {
 	testCases := []functionTestCase{
@@ -29,3 +33,41 @@ func TestInterpolationFuncList(t *testing.T) {
 		})
 	}
 }
+
+func TestInterpoloationFuncConcat(t *testing.T) {
+	testCases := []functionTestCase{
+		{
+			description: "Two lists combine",
+			text:        `${concat(foo, bar)}`,
+			expectation: []interface{}{"test1", "test2"},
+			vars: map[string]ast.Variable{
+				"foo": ast.Variable{
+					Type: ast.TypeList,
+					Value: []ast.Variable{
+						{
+							Type:  ast.TypeString,
+							Value: "test1",
+						},
+					},
+				},
+				"bar": ast.Variable{
+					Type: ast.TypeList,
+					Value: []ast.Variable{
+						{
+							Type:  ast.TypeString,
+							Value: "test2",
+						},
+					},
+				},
+			},
+		},
+	}
+
+	concatTestFunc := testInterpolationFunc("concat", interpolationFuncConcat)
+
+	for _, tc := range testCases {
+		t.Run(tc.description, func(t *testing.T) {
+			concatTestFunc(t, tc)
+		})
+	}
+}