text/template: add 'nil' as a keyword in the language

The keyword reprents an untyped nil and is useful for
passing nil values to methods and functions. The
nil will be promoted to the appropriate type when
used; if a type cannot be assigned, an error results.

R=rsc, dsymonds
CC=golang-dev
https://golang.org/cl/6459056

1 files changed, 13 insertions, 2 deletions

diff --git a/src/pkg/text/template/exec_test.go b/src/pkg/text/template/exec_test.go
index 4efe2d1b38..95e0592df8 100644
--- a/src/pkg/text/template/exec_test.go
+++ b/src/pkg/text/template/exec_test.go
@@ -63,6 +63,7 @@ type T struct {
 	BinaryFunc      func(string, string) string
 	VariadicFunc    func(...string) string
 	VariadicFuncInt func(int, ...string) string
+	NilOKFunc       func(*int) bool
 	// Template to test evaluation of templates.
 	Tmpl *Template
 	// Unexported field; cannot be accessed by template.
@@ -127,6 +128,7 @@ var tVal = &T{
 	BinaryFunc:        func(a, b string) string { return fmt.Sprintf("[%s=%s]", a, b) },
 	VariadicFunc:      func(s ...string) string { return fmt.Sprint("<", strings.Join(s, "+"), ">") },
 	VariadicFuncInt:   func(a int, s ...string) string { return fmt.Sprint(a, "=<", strings.Join(s, "+"), ">") },
+	NilOKFunc:         func(s *int) bool { return s == nil },
 	Tmpl:              Must(New("x").Parse("test template")), // "x" is the value of .X
 }
 
@@ -222,6 +224,7 @@ var execTests = []execTest{
 	// Trivial cases.
 	{"empty", "", "", nil, true},
 	{"text", "some text", "some text", nil, true},
+	{"nil action", "{{nil}}", "", nil, false},
 
 	// Ideal constants.
 	{"ideal int", "{{typeOf 3}}", "int", 0, true},
@@ -230,6 +233,7 @@ var execTests = []execTest{
 	{"ideal complex", "{{typeOf 1i}}", "complex128", 0, true},
 	{"ideal int", "{{typeOf " + bigInt + "}}", "int", 0, true},
 	{"ideal too big", "{{typeOf " + bigUint + "}}", "", 0, false},
+	{"ideal nil without type", "{{nil}}", "", 0, false},
 
 	// Fields of structs.
 	{".X", "-{{.X}}-", "-x-", tVal, true},
@@ -295,7 +299,8 @@ var execTests = []execTest{
 	{".Method2(3, .X)", "-{{.Method2 3 .X}}-", "-Method2: 3 x-", tVal, true},
 	{".Method2(.U16, `str`)", "-{{.Method2 .U16 `str`}}-", "-Method2: 16 str-", tVal, true},
 	{".Method2(.U16, $x)", "{{if $x := .X}}-{{.Method2 .U16 $x}}{{end}}-", "-Method2: 16 x-", tVal, true},
-	{".Method3(nil)", "-{{.Method3 .MXI.unset}}-", "-Method3: <nil>-", tVal, true},
+	{".Method3(nil constant)", "-{{.Method3 nil}}-", "-Method3: <nil>-", tVal, true},
+	{".Method3(nil value)", "-{{.Method3 .MXI.unset}}-", "-Method3: <nil>-", tVal, true},
 	{"method on var", "{{if $x := .}}-{{$x.Method2 .U16 $x.X}}{{end}}-", "-Method2: 16 x-", tVal, true},
 	{"method on chained var",
 		"{{range .MSIone}}{{if $.U.TrueFalse $.True}}{{$.U.TrueFalse $.True}}{{else}}WRONG{{end}}{{end}}",
@@ -306,6 +311,8 @@ var execTests = []execTest{
 	{"chained method on variable",
 		"{{with $x := .}}{{with .SI}}{{$.GetU.TrueFalse $.True}}{{end}}{{end}}",
 		"true", tVal, true},
+	{".NilOKFunc not nil", "{{call .NilOKFunc .PI}}", "false", tVal, true},
+	{".NilOKFunc nil", "{{call .NilOKFunc nil}}", "true", tVal, true},
 
 	// Function call builtin.
 	{".BinaryFunc", "{{call .BinaryFunc `1` `2`}}", "[1=2]", tVal, true},
@@ -324,6 +331,7 @@ var execTests = []execTest{
 	{".VariadicFuncBad0", "{{call .VariadicFunc 3}}", "", tVal, false},
 	{".VariadicFuncIntBad0", "{{call .VariadicFuncInt}}", "", tVal, false},
 	{".VariadicFuncIntBad`", "{{call .VariadicFuncInt `x`}}", "", tVal, false},
+	{".VariadicFuncNilBad", "{{call .VariadicFunc nil}}", "", tVal, false},
 
 	// Pipelines.
 	{"pipeline", "-{{.Method0 | .Method2 .U16}}-", "-Method2: 16 M0-", tVal, true},
@@ -332,6 +340,7 @@ var execTests = []execTest{
 	// If.
 	{"if true", "{{if true}}TRUE{{end}}", "TRUE", tVal, true},
 	{"if false", "{{if false}}TRUE{{else}}FALSE{{end}}", "FALSE", tVal, true},
+	{"if nil", "{{if nil}}TRUE{{end}}", "", tVal, false},
 	{"if 1", "{{if 1}}NON-ZERO{{else}}ZERO{{end}}", "NON-ZERO", tVal, true},
 	{"if 0", "{{if 0}}NON-ZERO{{else}}ZERO{{end}}", "ZERO", tVal, true},
 	{"if 1.5", "{{if 1.5}}NON-ZERO{{else}}ZERO{{end}}", "NON-ZERO", tVal, true},
@@ -351,7 +360,8 @@ var execTests = []execTest{
 
 	// Print etc.
 	{"print", `{{print "hello, print"}}`, "hello, print", tVal, true},
-	{"print", `{{print 1 2 3}}`, "1 2 3", tVal, true},
+	{"print 123", `{{print 1 2 3}}`, "1 2 3", tVal, true},
+	{"print nil", `{{print nil}}`, "<nil>", tVal, true},
 	{"println", `{{println 1 2 3}}`, "1 2 3\n", tVal, true},
 	{"printf int", `{{printf "%04x" 127}}`, "007f", tVal, true},
 	{"printf float", `{{printf "%g" 3.5}}`, "3.5", tVal, true},
@@ -391,6 +401,7 @@ var execTests = []execTest{
 	{"map[one]", "{{index .MSI `one`}}", "1", tVal, true},
 	{"map[two]", "{{index .MSI `two`}}", "2", tVal, true},
 	{"map[NO]", "{{index .MSI `XXX`}}", "0", tVal, true},
+	{"map[nil]", "{{index .MSI nil}}", "0", tVal, true},
 	{"map[WRONG]", "{{index .MSI 10}}", "", tVal, false},
 	{"double index", "{{index .SMSI 1 `eleven`}}", "11", tVal, true},