text/template: change IsTrue to take interface{} instead of reflect.Value.

This is a follow-up to a326c3e1 to avoid reflect being in the API.

Fixes #12801.

Change-Id: Ic4c2e592e2c35b5911f75d88f1d9c44787c80f30
Reviewed-on: https://go-review.googlesource.com/15240
Run-TryBot: David Symonds <dsymonds@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>

src/html/template/template.go

@@ -9,7 +9,6 @@ import (
 	"io"
 	"io/ioutil"
 	"path/filepath"
-	"reflect"
 	"sync"
 	"text/template"
 	"text/template/parse"
@@ -420,6 +419,6 @@ func parseGlob(t *Template, pattern string) (*Template, error) {
 // IsTrue reports whether the value is 'true', in the sense of not the zero of its type,
 // and whether the value has a meaningful truth value. This is the definition of
 // truth used by if and other such actions.
-func IsTrue(val reflect.Value) (truth, ok bool) {
+func IsTrue(val interface{}) (truth, ok bool) {
 	return template.IsTrue(val)
 }

src/text/template/exec.go

@@ -242,7 +242,7 @@ func (s *state) walk(dot reflect.Value, node parse.Node) {
 func (s *state) walkIfOrWith(typ parse.NodeType, dot reflect.Value, pipe *parse.PipeNode, list, elseList *parse.ListNode) {
 	defer s.pop(s.mark())
 	val := s.evalPipeline(dot, pipe)
-	truth, ok := IsTrue(val)
+	truth, ok := isTrue(val)
 	if !ok {
 		s.errorf("if/with can't use %v", val)
 	}
@@ -260,7 +260,11 @@ func (s *state) walkIfOrWith(typ parse.NodeType, dot reflect.Value, pipe *parse.
 // IsTrue reports whether the value is 'true', in the sense of not the zero of its type,
 // and whether the value has a meaningful truth value. This is the definition of
 // truth used by if and other such actions.
-func IsTrue(val reflect.Value) (truth, ok bool) {
+func IsTrue(val interface{}) (truth, ok bool) {
+	return isTrue(reflect.ValueOf(val))
+}
+
+func isTrue(val reflect.Value) (truth, ok bool) {
 	if !val.IsValid() {
 		// Something like var x interface{}, never set. It's a form of nil.
 		return false, true

src/text/template/funcs.go

@@ -265,7 +265,7 @@ func call(fn interface{}, args ...interface{}) (interface{}, error) {
 // Boolean logic.
 
 func truth(a interface{}) bool {
-	t, _ := IsTrue(reflect.ValueOf(a))
+	t, _ := IsTrue(a)
 	return t
 }