html/template: handle nils during indirection

Fixes #5982.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/12387043

diff --git a/src/pkg/html/template/content.go b/src/pkg/html/template/content.go
index 9d1f74f6f01772ae17a63ed0e6b724746a845cce..41b1116a661cb0d81022722b3a8553fbbec9576c 100644 (file)
--- a/src/pkg/html/template/content.go
+++ b/src/pkg/html/template/content.go
@@ -74,6 +74,9 @@ const (
 // indirect returns the value, after dereferencing as many times
 // as necessary to reach the base type (or nil).
 func indirect(a interface{}) interface{} {
+       if a == nil {
+               return nil
+       }
        if t := reflect.TypeOf(a); t.Kind() != reflect.Ptr {
                // Avoid creating a reflect.Value if it's not a pointer.
                return a
@@ -94,6 +97,9 @@ var (
 // as necessary to reach the base type (or nil) or an implementation of fmt.Stringer
 // or error,
 func indirectToStringerOrError(a interface{}) interface{} {
+       if a == nil {
+               return nil
+       }
        v := reflect.ValueOf(a)
        for !v.Type().Implements(fmtStringerType) && !v.Type().Implements(errorType) && v.Kind() == reflect.Ptr && !v.IsNil() {
                v = v.Elem()

diff --git a/src/pkg/html/template/content_test.go b/src/pkg/html/template/content_test.go
index 3c32e5e89cfac3e524e70d5dbcac75f6bf993030..da1eb5c376864c0adea99321988c6044bf7731ed 100644 (file)
--- a/src/pkg/html/template/content_test.go
+++ b/src/pkg/html/template/content_test.go
@@ -259,3 +259,28 @@ func TestStringer(t *testing.T) {
                t.Errorf("expected %q got %q", expect, b.String())
        }
 }
+
+// https://code.google.com/p/go/issues/detail?id=5982
+func TestEscapingNilNonemptyInterfaces(t *testing.T) {
+       tmpl := Must(New("x").Parse("{{.E}}"))
+
+       defer func() {
+               if r := recover(); r != nil {
+                       t.Errorf("panic during template execution: %v", r)
+               }
+       }()
+
+       got := new(bytes.Buffer)
+       testData := struct{ E error }{} // any non-empty interface here will do; error is just ready at hand
+       tmpl.Execute(got, testData)
+
+       // Use this data instead of just hard-coding "<nil>" to avoid
+       // dependencies on the html escaper and the behavior of fmt w.r.t. nil.
+       want := new(bytes.Buffer)
+       data := struct{ E string }{E: fmt.Sprint(nil)}
+       tmpl.Execute(want, data)
+
+       if !bytes.Equal(want.Bytes(), got.Bytes()) {
+               t.Errorf("expected %q got %q", string(want.Bytes()), string(got.Bytes()))
+       }
+}