Merge pull request #1096 from hashicorp/f-sprintf

config: add "format' function [GH-758]

config/interpolate_funcs.go

@@ -17,6 +17,7 @@ var Funcs map[string]ast.Function
 func init() {
 	Funcs = map[string]ast.Function{
 		"file":    interpolationFuncFile(),
+		"format":  interpolationFuncFormat(),
 		"join":    interpolationFuncJoin(),
 		"element": interpolationFuncElement(),
 		"replace": interpolationFuncReplace(),
@@ -66,6 +67,21 @@ func interpolationFuncFile() ast.Function {
 	}
 }
 
+// interpolationFuncFormat implements the "replace" function that does
+// string replacement.
+func interpolationFuncFormat() ast.Function {
+	return ast.Function{
+		ArgTypes:     []ast.Type{ast.TypeString},
+		Variadic:     true,
+		VariadicType: ast.TypeAny,
+		ReturnType:   ast.TypeString,
+		Callback: func(args []interface{}) (interface{}, error) {
+			format := args[0].(string)
+			return fmt.Sprintf(format, args[1:]...), nil
+		},
+	}
+}
+
 // interpolationFuncJoin implements the "join" function that allows
 // multi-variable values to be joined by some character.
 func interpolationFuncJoin() ast.Function {

config/interpolate_funcs_test.go

@@ -70,6 +70,42 @@ func TestInterpolateFuncFile(t *testing.T) {
 	})
 }
 
+func TestInterpolateFuncFormat(t *testing.T) {
+	testFunction(t, testFunctionConfig{
+		Cases: []testFunctionCase{
+			{
+				`${format("hello")}`,
+				"hello",
+				false,
+			},
+
+			{
+				`${format("hello %s", "world")}`,
+				"hello world",
+				false,
+			},
+
+			{
+				`${format("hello %d", 42)}`,
+				"hello 42",
+				false,
+			},
+
+			{
+				`${format("hello %05d", 42)}`,
+				"hello 00042",
+				false,
+			},
+
+			{
+				`${format("hello %05d", 12345)}`,
+				"hello 12345",
+				false,
+			},
+		},
+	})
+}
+
 func TestInterpolateFuncJoin(t *testing.T) {
 	testFunction(t, testFunctionConfig{
 		Cases: []testFunctionCase{

config/lang/ast/ast.go

@@ -48,7 +48,8 @@ type Type uint32
 
 const (
 	TypeInvalid Type = 0
-	TypeString  Type = 1 << iota
+	TypeAny     Type = 1 << iota
+	TypeString
 	TypeInt
 	TypeFloat
 )

config/lang/ast/type_string.go

@@ -6,16 +6,18 @@ import "fmt"
 
 const (
 	_Type_name_0 = "TypeInvalid"
-	_Type_name_1 = "TypeString"
-	_Type_name_2 = "TypeInt"
-	_Type_name_3 = "TypeFloat"
+	_Type_name_1 = "TypeAny"
+	_Type_name_2 = "TypeString"
+	_Type_name_3 = "TypeInt"
+	_Type_name_4 = "TypeFloat"
 )
 
 var (
 	_Type_index_0 = [...]uint8{0, 11}
-	_Type_index_1 = [...]uint8{0, 10}
-	_Type_index_2 = [...]uint8{0, 7}
-	_Type_index_3 = [...]uint8{0, 9}
+	_Type_index_1 = [...]uint8{0, 7}
+	_Type_index_2 = [...]uint8{0, 10}
+	_Type_index_3 = [...]uint8{0, 7}
+	_Type_index_4 = [...]uint8{0, 9}
 )
 
 func (i Type) String() string {
@@ -28,6 +30,8 @@ func (i Type) String() string {
 		return _Type_name_2
 	case i == 8:
 		return _Type_name_3
+	case i == 16:
+		return _Type_name_4
 	default:
 		return fmt.Sprintf("Type(%d)", i)
 	}

config/lang/check_types.go

@@ -174,6 +174,10 @@ func (tc *typeCheckCall) TypeCheck(v *TypeCheck) (ast.Node, error) {
 
 	// Verify the args
 	for i, expected := range function.ArgTypes {
+		if expected == ast.TypeAny {
+			continue
+		}
+
 		if args[i] != expected {
 			cn := v.ImplicitConversion(args[i], expected, tc.n.Args[i])
 			if cn != nil {
@@ -188,7 +192,7 @@ func (tc *typeCheckCall) TypeCheck(v *TypeCheck) (ast.Node, error) {
 	}
 
 	// If we're variadic, then verify the types there
-	if function.Variadic {
+	if function.Variadic && function.VariadicType != ast.TypeAny {
 		args = args[len(function.ArgTypes):]
 		for i, t := range args {
 			if t != function.VariadicType {

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

@@ -80,6 +80,12 @@ The supported built-in functions are:
       in this file are _not_ interpolated. The contents of the file are
       read as-is.
 
+  * `format(format, args...)` - Formats a string according to the given
+      format. The syntax for the format is standard `sprintf` syntax.
+      Good documentation for the syntax can be [found here](http://golang.org/pkg/fmt/).
+      Example to zero-prefix a count, used commonly for naming servers:
+      `format("web-%03d", count.index+1)`.
+
   * `join(delim, list)` - Joins the list with the delimiter. A list is
       only possible with splat variables from resources with a count
       greater than one. Example: `join(",", aws_instance.foo.*.id)`