config: support lists and maps in jsonencode

config/interpolate_funcs.go

@@ -409,16 +409,54 @@ func interpolationFuncJoin() ast.Function {
 }
 
 // interpolationFuncJSONEncode implements the "jsonencode" function that encodes
-// a string as its JSON representation.
+// a string, list, or map as its JSON representation. For now, values in the
+// list or map may only be strings.
 func interpolationFuncJSONEncode() ast.Function {
 	return ast.Function{
-		ArgTypes:   []ast.Type{ast.TypeString},
+		ArgTypes:   []ast.Type{ast.TypeAny},
 		ReturnType: ast.TypeString,
 		Callback: func(args []interface{}) (interface{}, error) {
-			s := args[0].(string)
-			jEnc, err := json.Marshal(s)
+			var toEncode interface{}
+
+			switch typedArg := args[0].(type) {
+			case string:
+				toEncode = typedArg
+
+			case []ast.Variable:
+				// We preallocate the list here. Note that it's important that in
+				// the length 0 case, we have an empty list rather than nil, as
+				// they encode differently.
+				// XXX It would be nice to support arbitrarily nested data here. Is
+				// there an inverse of hil.InterfaceToVariable?
+				strings := make([]string, len(typedArg))
+
+				for i, v := range typedArg {
+					if v.Type != ast.TypeString {
+						return "", fmt.Errorf("list elements must be strings")
+					}
+					strings[i] = v.Value.(string)
+				}
+				toEncode = strings
+
+			case map[string]ast.Variable:
+				// XXX It would be nice to support arbitrarily nested data here. Is
+				// there an inverse of hil.InterfaceToVariable?
+				stringMap := make(map[string]string)
+				for k, v := range typedArg {
+					if v.Type != ast.TypeString {
+						return "", fmt.Errorf("map values must be strings")
+					}
+					stringMap[k] = v.Value.(string)
+				}
+				toEncode = stringMap
+
+			default:
+				return "", fmt.Errorf("unknown type for JSON encoding: %T", args[0])
+			}
+
+			jEnc, err := json.Marshal(toEncode)
 			if err != nil {
-				return "", fmt.Errorf("failed to encode JSON data '%s'", s)
+				return "", fmt.Errorf("failed to encode JSON data '%s'", toEncode)
 			}
 			return string(jEnc), nil
 		},

config/interpolate_funcs_test.go

@@ -419,6 +419,22 @@ func TestInterpolateFuncJSONEncode(t *testing.T) {
 				Value: " foo \\ \n \t \" bar ",
 				Type:  ast.TypeString,
 			},
+			"list": interfaceToVariableSwallowError([]string{"foo", "bar\tbaz"}),
+			// XXX can't use InterfaceToVariable as it converts empty slice into empty
+			// map.
+			"emptylist": ast.Variable{
+				Value: []ast.Variable{},
+				Type:  ast.TypeList,
+			},
+			"map": interfaceToVariableSwallowError(map[string]string{
+				"foo":     "bar",
+				"ba \n z": "q\\x",
+			}),
+			"emptymap": interfaceToVariableSwallowError(map[string]string{}),
+
+			// Not yet supported (but it would be nice)
+			"nestedlist": interfaceToVariableSwallowError([][]string{{"foo"}}),
+			"nestedmap":  interfaceToVariableSwallowError(map[string][]string{"foo": {"bar"}}),
 		},
 		Cases: []testFunctionCase{
 			{
@@ -446,6 +462,36 @@ func TestInterpolateFuncJSONEncode(t *testing.T) {
 				nil,
 				true,
 			},
+			{
+				`${jsonencode(list)}`,
+				`["foo","bar\tbaz"]`,
+				false,
+			},
+			{
+				`${jsonencode(emptylist)}`,
+				`[]`,
+				false,
+			},
+			{
+				`${jsonencode(map)}`,
+				`{"ba \n z":"q\\x","foo":"bar"}`,
+				false,
+			},
+			{
+				`${jsonencode(emptymap)}`,
+				`{}`,
+				false,
+			},
+			{
+				`${jsonencode(nestedlist)}`,
+				nil,
+				true,
+			},
+			{
+				`${jsonencode(nestedmap)}`,
+				nil,
+				true,
+			},
 		},
 	})
 }

website/source/docs/configuration/interpolation.html.md

@@ -150,8 +150,10 @@ The supported built-in functions are:
       only possible with splat variables from resources with a count
       greater than one. Example: `join(",", aws_instance.foo.*.id)`
 
-  * `jsonencode(string)` - Returns a JSON-encoded representation of the given
-    string (including double quotes).
+  * `jsonencode(item)` - Returns a JSON-encoded representation of the given
+    item, which may be a string, list of strings, or map from string to string.
+    Note that if the item is a string, the return value includes the double
+    quotes.
 
   * `length(list)` - Returns a number of members in a given list
       or a number of characters in a given string.