text/template: support indexing into *int* maps

Ensure that we can index maps whose key types are:
* int
* uint
* int32
* uint32
* int64
* uint64
* uintptr

Fixes #20439

Change-Id: I8fa96b14073c8af72786482ff4ffc3508064ea86
Reviewed-on: https://go-review.googlesource.com/43850
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
Run-TryBot: Rob Pike <r@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/text/template/exec_test.go

@@ -44,6 +44,12 @@ type T struct {
 	MSIEmpty map[string]int
 	MXI      map[interface{}]int
 	MII      map[int]int
+	MI32S    map[int32]string
+	MI64S    map[int64]string
+	MUI32S   map[uint32]string
+	MUI64S   map[uint64]string
+	MI8S     map[int8]string
+	MUI8S    map[uint8]string
 	SMSI     []map[string]int
 	// Empty interfaces; used to see if we can dig inside one.
 	Empty0 interface{} // nil
@@ -124,6 +130,12 @@ var tVal = &T{
 	MSIone: map[string]int{"one": 1},
 	MXI:    map[interface{}]int{"one": 1},
 	MII:    map[int]int{1: 1},
+	MI32S:  map[int32]string{1: "one", 2: "two"},
+	MI64S:  map[int64]string{2: "i642", 3: "i643"},
+	MUI32S: map[uint32]string{2: "u322", 3: "u323"},
+	MUI64S: map[uint64]string{2: "ui642", 3: "ui643"},
+	MI8S:   map[int8]string{2: "i82", 3: "i83"},
+	MUI8S:  map[uint8]string{2: "u82", 3: "u83"},
 	SMSI: []map[string]int{
 		{"one": 1, "two": 2},
 		{"eleven": 11, "twelve": 12},
@@ -448,6 +460,11 @@ var execTests = []execTest{
 	{"map[WRONG]", "{{index .MSI 10}}", "", tVal, false},
 	{"double index", "{{index .SMSI 1 `eleven`}}", "11", tVal, true},
 	{"nil[1]", "{{index nil 1}}", "", tVal, false},
+	{"map MI64S", "{{index .MI64S 2}}", "i642", tVal, true},
+	{"map MI32S", "{{index .MI32S 2}}", "two", tVal, true},
+	{"map MUI64S", "{{index .MUI64S 3}}", "ui643", tVal, true},
+	{"map MI8S", "{{index .MI8S 3}}", "i83", tVal, true},
+	{"map MUI8S", "{{index .MUI8S 2}}", "u82", tVal, true},
 
 	// Len.
 	{"slice", "{{len .SI}}", "3", tVal, true},

src/text/template/funcs.go

@@ -139,10 +139,24 @@ func prepareArg(value reflect.Value, argType reflect.Type) (reflect.Value, error
 		}
 		value = reflect.Zero(argType)
 	}
-	if !value.Type().AssignableTo(argType) {
-		return reflect.Value{}, fmt.Errorf("value has type %s; should be %s", value.Type(), argType)
+	if value.Type().AssignableTo(argType) {
+		return value, nil
 	}
+	if intLike(value.Kind()) && intLike(argType.Kind()) && value.Type().ConvertibleTo(argType) {
+		value = value.Convert(argType)
 		return value, nil
+	}
+	return reflect.Value{}, fmt.Errorf("value has type %s; should be %s", value.Type(), argType)
+}
+
+func intLike(typ reflect.Kind) bool {
+	switch typ {
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		return true
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
+		return true
+	}
+	return false
 }
 
 // Indexing.