5 files changed, 44 insertions, 13 deletions
diff --git a/src/pkg/text/template/doc.go b/src/pkg/text/template/doc.go
index f622ac7dc..7c6efd59c 100644
--- a/src/pkg/text/template/doc.go
+++ b/src/pkg/text/template/doc.go
@@ -20,7 +20,7 @@ The input text for a template is UTF-8-encoded text in any format.
 "{{" and "}}"; all text outside actions is copied to the output unchanged.
 Actions may not span newlines, although comments can.
 
-Once constructed, a template may be executed safely in parallel.
+Once parsed, a template may be executed safely in parallel.
 
 Here is a trivial example that prints "17 items are made of wool".
 
diff --git a/src/pkg/text/template/exec.go b/src/pkg/text/template/exec.go
index 43b0b266e..2f3231264 100644
--- a/src/pkg/text/template/exec.go
+++ b/src/pkg/text/template/exec.go
@@ -108,6 +108,10 @@ func errRecover(errp *error) {
 
 // ExecuteTemplate applies the template associated with t that has the given name
 // to the specified data object and writes the output to wr.
+// If an error occurs executing the template or writing its output,
+// execution stops, but partial results may already have been written to
+// the output writer.
+// A template may be executed safely in parallel.
 func (t *Template) ExecuteTemplate(wr io.Writer, name string, data interface{}) error {
 	tmpl := t.tmpl[name]
 	if tmpl == nil {
@@ -118,6 +122,10 @@ func (t *Template) ExecuteTemplate(wr io.Writer, name string, data interface{})
 
 // Execute applies a parsed template to the specified data object,
 // and writes the output to wr.
+// If an error occurs executing the template or writing its output,
+// execution stops, but partial results may already have been written to
+// the output writer.
+// A template may be executed safely in parallel.
 func (t *Template) Execute(wr io.Writer, data interface{}) (err error) {
 	defer errRecover(&err)
 	value := reflect.ValueOf(data)
@@ -594,6 +602,9 @@ func (s *state) validateType(value reflect.Value, typ reflect.Type) reflect.Valu
 		switch {
 		case value.Kind() == reflect.Ptr && value.Type().Elem().AssignableTo(typ):
 			value = value.Elem()
+			if !value.IsValid() {
+				s.errorf("dereference of nil pointer of type %s", typ)
+			}
 		case reflect.PtrTo(value.Type()).AssignableTo(typ) && value.CanAddr():
 			value = value.Addr()
 		default:
diff --git a/src/pkg/text/template/exec_test.go b/src/pkg/text/template/exec_test.go
index f60702de8..868f2cb94 100644
--- a/src/pkg/text/template/exec_test.go
+++ b/src/pkg/text/template/exec_test.go
@@ -512,6 +512,8 @@ var execTests = []execTest{
 	{"bug9", "{{.cause}}", "neglect", map[string]string{"cause": "neglect"}, true},
 	// Field chain starting with function did not work.
 	{"bug10", "{{mapOfThree.three}}-{{(mapOfThree).three}}", "3-3", 0, true},
+	// Dereferencing nil pointer while evaluating function arguments should not panic. Issue 7333.
+	{"bug11", "{{valueString .PS}}", "", T{}, false},
 }
 
 func zeroArgs() string {
@@ -546,6 +548,11 @@ func vfunc(V, *V) string {
 	return "vfunc"
 }
 
+// valueString takes a string, not a pointer.
+func valueString(v string) string {
+	return "value is ignored"
+}
+
 func add(args ...int) int {
 	sum := 0
 	for _, x := range args {
@@ -580,17 +587,18 @@ func mapOfThree() interface{} {
 func testExecute(execTests []execTest, template *Template, t *testing.T) {
 	b := new(bytes.Buffer)
 	funcs := FuncMap{
-		"add":        add,
-		"count":      count,
-		"dddArg":     dddArg,
-		"echo":       echo,
-		"makemap":    makemap,
-		"mapOfThree": mapOfThree,
-		"oneArg":     oneArg,
-		"stringer":   stringer,
-		"typeOf":     typeOf,
-		"vfunc":      vfunc,
-		"zeroArgs":   zeroArgs,
+		"add":         add,
+		"count":       count,
+		"dddArg":      dddArg,
+		"echo":        echo,
+		"makemap":     makemap,
+		"mapOfThree":  mapOfThree,
+		"oneArg":      oneArg,
+		"stringer":    stringer,
+		"typeOf":      typeOf,
+		"valueString": valueString,
+		"vfunc":       vfunc,
+		"zeroArgs":    zeroArgs,
 	}
 	for _, test := range execTests {
 		var tmpl *Template
diff --git a/src/pkg/text/template/multi_test.go b/src/pkg/text/template/multi_test.go
index 1f6ed5d8e..e4e804880 100644
--- a/src/pkg/text/template/multi_test.go
+++ b/src/pkg/text/template/multi_test.go
@@ -259,6 +259,18 @@ func TestAddParseTree(t *testing.T) {
 	}
 }
 
+// Issue 7032
+func TestAddParseTreeToUnparsedTemplate(t *testing.T) {
+	master := "{{define \"master\"}}{{end}}"
+	tmpl := New("master")
+	tree, err := parse.Parse("master", master, "", "", nil)
+	if err != nil {
+		t.Fatalf("unexpected parse err: %v", err)
+	}
+	masterTree := tree["master"]
+	tmpl.AddParseTree("master", masterTree) // used to panic
+}
+
 func TestRedefinition(t *testing.T) {
 	var tmpl *Template
 	var err error
diff --git a/src/pkg/text/template/template.go b/src/pkg/text/template/template.go
index a2b9062ad..249d0cbfb 100644
--- a/src/pkg/text/template/template.go
+++ b/src/pkg/text/template/template.go
@@ -105,7 +105,7 @@ func (t *Template) copy(c *common) *Template {
 // AddParseTree creates a new template with the name and parse tree
 // and associates it with t.
 func (t *Template) AddParseTree(name string, tree *parse.Tree) (*Template, error) {
-	if t.tmpl[name] != nil {
+	if t.common != nil && t.tmpl[name] != nil {
 		return nil, fmt.Errorf("template: redefinition of template %q", name)
 	}
 	nt := t.New(name)