// Interpolate uses the given mapping of variable values and uses
// those as the values to replace any variables in this raw
// configuration.
//
// Any prior calls to Interpolate are replaced with this one.
//
// If a variable key is missing, this will panic.
func (r *RawConfig) Interpolate(vs map[string]ast.Variable) error {
	config := langEvalConfig(vs)
	return r.interpolate(func(root ast.Node) (string, error) {
		// We detect the variables again and check if the value of any
		// of the variables is the computed value. If it is, then we
		// treat this entire value as computed.
		//
		// We have to do this here before the `lang.Eval` because
		// if any of the variables it depends on are computed, then
		// the interpolation can fail at runtime for other reasons. Example:
		// `${count.index+1}`: in a world where `count.index` is computed,
		// this would fail a type check since the computed placeholder is
		// a string, but realistically the whole value is just computed.
		vars, err := DetectVariables(root)
		if err != nil {
			return "", err
		}
		for _, v := range vars {
			varVal, ok := vs[v.FullKey()]
			if ok && varVal.Value == UnknownVariableValue {
				return UnknownVariableValue, nil
			}
		}

		// None of the variables we need are computed, meaning we should
		// be able to properly evaluate.
		out, _, err := lang.Eval(root, config)
		if err != nil {
			return "", err
		}

		return out.(string), nil
	})
}

func testFunction(t *testing.T, config testFunctionConfig) {
	for i, tc := range config.Cases {
		ast, err := lang.Parse(tc.Input)
		if err != nil {
			t.Fatalf("Case #%d: input: %#v\nerr: %s", i, tc.Input, err)
		}

		out, _, err := lang.Eval(ast, langEvalConfig(config.Vars))
		if err != nil != tc.Error {
			t.Fatalf("Case #%d:\ninput: %#v\nerr: %s", i, tc.Input, err)
		}

		if !reflect.DeepEqual(out, tc.Result) {
			t.Fatalf(
				"%d: bad output for input: %s\n\nOutput: %#v\nExpected: %#v",
				i, tc.Input, out, tc.Result)
		}
	}
}

// execute parses and executes a template using vars.
func execute(s string, vars map[string]interface{}) (string, error) {
	root, err := lang.Parse(s)
	if err != nil {
		return "", err
	}

	varmap := make(map[string]ast.Variable)
	for k, v := range vars {
		// As far as I can tell, v is always a string.
		// If it's not, tell the user gracefully.
		s, ok := v.(string)
		if !ok {
			return "", fmt.Errorf("unexpected type for variable %q: %T", k, v)
		}
		varmap[k] = ast.Variable{
			Value: s,
			Type:  ast.TypeString,
		}
	}

	cfg := lang.EvalConfig{
		GlobalScope: &ast.BasicScope{
			VarMap:  varmap,
			FuncMap: config.Funcs(),
		},
	}

	out, typ, err := lang.Eval(root, &cfg)
	if err != nil {
		return "", err
	}
	if typ != ast.TypeString {
		return "", fmt.Errorf("unexpected output ast.Type: %v", typ)
	}

	return out.(string), nil
}

//.........这里部分代码省略.........
	dupped = nil

	// Validate resources
	for n, r := range resources {
		// Verify count variables
		for _, v := range r.RawCount.Variables {
			switch v.(type) {
			case *CountVariable:
				errs = append(errs, fmt.Errorf(
					"%s: resource count can't reference count variable: %s",
					n,
					v.FullKey()))
			case *ModuleVariable:
				errs = append(errs, fmt.Errorf(
					"%s: resource count can't reference module variable: %s",
					n,
					v.FullKey()))
			case *ResourceVariable:
				errs = append(errs, fmt.Errorf(
					"%s: resource count can't reference resource variable: %s",
					n,
					v.FullKey()))
			case *UserVariable:
				// Good
			default:
				panic("Unknown type in count var: " + n)
			}
		}

		// Interpolate with a fixed number to verify that its a number.
		r.RawCount.interpolate(func(root ast.Node) (string, error) {
			// Execute the node but transform the AST so that it returns
			// a fixed value of "5" for all interpolations.
			out, _, err := lang.Eval(
				lang.FixedValueTransform(
					root, &ast.LiteralNode{Value: "5", Typex: ast.TypeString}),
				nil)
			if err != nil {
				return "", err
			}

			return out.(string), nil
		})
		_, err := strconv.ParseInt(r.RawCount.Value().(string), 0, 0)
		if err != nil {
			errs = append(errs, fmt.Errorf(
				"%s: resource count must be an integer",
				n))
		}
		r.RawCount.init()

		// Verify depends on points to resources that all exist
		for _, d := range r.DependsOn {
			// Check if we contain interpolations
			rc, err := NewRawConfig(map[string]interface{}{
				"value": d,
			})
			if err == nil && len(rc.Variables) > 0 {
				errs = append(errs, fmt.Errorf(
					"%s: depends on value cannot contain interpolations: %s",
					n, d))
				continue
			}

			if _, ok := resources[d]; !ok {
				errs = append(errs, fmt.Errorf(