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text/template: make reflect.Value indirections more robust

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Always shadow or modify the original parameter name. With code like:

	func index(item reflect.Value, ... {
		v := indirectInterface(item)

It was possible to incorrectly use 'item' and 'v' later in the function,
which could result in subtle bugs. This is precisely the kind of mistake
that led to #36199.

Instead, don't keep both the old and new reflect.Value variables in
scope. Always shadow or modify the original variable.

While at it, simplify the signature of 'length', to receive a
reflect.Value directly and save a few redundant lines.

Change-Id: I01416636a9d49f81246d28b91aca6413b1ba1aa5
Reviewed-on: https://go-review.googlesource.com/c/go/+/212117
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Roberto Clapis <robclap8@gmail.com>
Reviewed-by: Rob Pike <r@golang.org>
This commit is contained in:
Daniel Martí 2019-12-19 14:13:59 +00:00
parent 31acdcc701
commit 218f4572f5
1 changed files with 66 additions and 72 deletions
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138
src/text/template/funcs.go
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@ -185,41 +185,41 @@ func indexArg(index reflect.Value, cap int) (int, error) {
// arguments. Thus "index x 1 2 3" is, in Go syntax, x[1][2][3]. Each // arguments. Thus "index x 1 2 3" is, in Go syntax, x[1][2][3]. Each
// indexed item must be a map, slice, or array. // indexed item must be a map, slice, or array.
func index(item reflect.Value, indexes ...reflect.Value) (reflect.Value, error) { func index(item reflect.Value, indexes ...reflect.Value) (reflect.Value, error) {
v := indirectInterface(item) item = indirectInterface(item)
if !v.IsValid() { if !item.IsValid() {
return reflect.Value{}, fmt.Errorf("index of untyped nil") return reflect.Value{}, fmt.Errorf("index of untyped nil")
} }
for _, i := range indexes { for _, index := range indexes {
index := indirectInterface(i) index = indirectInterface(index)
var isNil bool var isNil bool
if v, isNil = indirect(v); isNil { if item, isNil = indirect(item); isNil {
return reflect.Value{}, fmt.Errorf("index of nil pointer") return reflect.Value{}, fmt.Errorf("index of nil pointer")
} }
switch v.Kind() { switch item.Kind() {
case reflect.Array, reflect.Slice, reflect.String: case reflect.Array, reflect.Slice, reflect.String:
x, err := indexArg(index, v.Len()) x, err := indexArg(index, item.Len())
if err != nil { if err != nil {
return reflect.Value{}, err return reflect.Value{}, err
} }
v = v.Index(x) item = item.Index(x)
case reflect.Map: case reflect.Map:
index, err := prepareArg(index, v.Type().Key()) index, err := prepareArg(index, item.Type().Key())
if err != nil { if err != nil {
return reflect.Value{}, err return reflect.Value{}, err
} }
if x := v.MapIndex(index); x.IsValid() { if x := item.MapIndex(index); x.IsValid() {
v = x item = x
} else { } else {
v = reflect.Zero(v.Type().Elem()) item = reflect.Zero(item.Type().Elem())
} }
case reflect.Invalid: case reflect.Invalid:
// the loop holds invariant: v.IsValid() // the loop holds invariant: item.IsValid()
panic("unreachable") panic("unreachable")
default: default:
return reflect.Value{}, fmt.Errorf("can't index item of type %s", v.Type()) return reflect.Value{}, fmt.Errorf("can't index item of type %s", item.Type())
} }
} }
return v, nil return item, nil
} }
// Slicing. // Slicing.
@ -229,29 +229,27 @@ func index(item reflect.Value, indexes ...reflect.Value) (reflect.Value, error)
// is x[:], "slice x 1" is x[1:], and "slice x 1 2 3" is x[1:2:3]. The first // is x[:], "slice x 1" is x[1:], and "slice x 1 2 3" is x[1:2:3]. The first
// argument must be a string, slice, or array. // argument must be a string, slice, or array.
func slice(item reflect.Value, indexes ...reflect.Value) (reflect.Value, error) { func slice(item reflect.Value, indexes ...reflect.Value) (reflect.Value, error) {
var ( item = indirectInterface(item)
cap int if !item.IsValid() {
v = indirectInterface(item)
)
if !v.IsValid() {
return reflect.Value{}, fmt.Errorf("slice of untyped nil") return reflect.Value{}, fmt.Errorf("slice of untyped nil")
} }
if len(indexes) > 3 { if len(indexes) > 3 {
return reflect.Value{}, fmt.Errorf("too many slice indexes: %d", len(indexes)) return reflect.Value{}, fmt.Errorf("too many slice indexes: %d", len(indexes))
} }
switch v.Kind() { var cap int
switch item.Kind() {
case reflect.String: case reflect.String:
if len(indexes) == 3 { if len(indexes) == 3 {
return reflect.Value{}, fmt.Errorf("cannot 3-index slice a string") return reflect.Value{}, fmt.Errorf("cannot 3-index slice a string")
} }
cap = v.Len() cap = item.Len()
case reflect.Array, reflect.Slice: case reflect.Array, reflect.Slice:
cap = v.Cap() cap = item.Cap()
default: default:
return reflect.Value{}, fmt.Errorf("can't slice item of type %s", v.Type()) return reflect.Value{}, fmt.Errorf("can't slice item of type %s", item.Type())
} }
// set default values for cases item[:], item[i:]. // set default values for cases item[:], item[i:].
idx := [3]int{0, v.Len()} idx := [3]int{0, item.Len()}
for i, index := range indexes { for i, index := range indexes {
x, err := indexArg(index, cap) x, err := indexArg(index, cap)
if err != nil { if err != nil {
@ -264,32 +262,28 @@ func slice(item reflect.Value, indexes ...reflect.Value) (reflect.Value, error)
return reflect.Value{}, fmt.Errorf("invalid slice index: %d > %d", idx[0], idx[1]) return reflect.Value{}, fmt.Errorf("invalid slice index: %d > %d", idx[0], idx[1])
} }
if len(indexes) < 3 { if len(indexes) < 3 {
return v.Slice(idx[0], idx[1]), nil return item.Slice(idx[0], idx[1]), nil
} }
// given item[i:j:k], make sure i <= j <= k. // given item[i:j:k], make sure i <= j <= k.
if idx[1] > idx[2] { if idx[1] > idx[2] {
return reflect.Value{}, fmt.Errorf("invalid slice index: %d > %d", idx[1], idx[2]) return reflect.Value{}, fmt.Errorf("invalid slice index: %d > %d", idx[1], idx[2])
} }
return v.Slice3(idx[0], idx[1], idx[2]), nil return item.Slice3(idx[0], idx[1], idx[2]), nil
} }
// Length // Length
// length returns the length of the item, with an error if it has no defined length. // length returns the length of the item, with an error if it has no defined length.
func length(item interface{}) (int, error) { func length(item reflect.Value) (int, error) {
v := reflect.ValueOf(item) item, isNil := indirect(item)
if !v.IsValid() {
return 0, fmt.Errorf("len of untyped nil")
}
v, isNil := indirect(v)
if isNil { if isNil {
return 0, fmt.Errorf("len of nil pointer") return 0, fmt.Errorf("len of nil pointer")
} }
switch v.Kind() { switch item.Kind() {
case reflect.Array, reflect.Chan, reflect.Map, reflect.Slice, reflect.String: case reflect.Array, reflect.Chan, reflect.Map, reflect.Slice, reflect.String:
return v.Len(), nil return item.Len(), nil
} }
return 0, fmt.Errorf("len of type %s", v.Type()) return 0, fmt.Errorf("len of type %s", item.Type())
} }
// Function invocation // Function invocation
@ -297,11 +291,11 @@ func length(item interface{}) (int, error) {
// call returns the result of evaluating the first argument as a function. // call returns the result of evaluating the first argument as a function.
// The function must return 1 result, or 2 results, the second of which is an error. // The function must return 1 result, or 2 results, the second of which is an error.
func call(fn reflect.Value, args ...reflect.Value) (reflect.Value, error) { func call(fn reflect.Value, args ...reflect.Value) (reflect.Value, error) {
v := indirectInterface(fn) fn = indirectInterface(fn)
if !v.IsValid() { if !fn.IsValid() {
return reflect.Value{}, fmt.Errorf("call of nil") return reflect.Value{}, fmt.Errorf("call of nil")
} }
typ := v.Type() typ := fn.Type()
if typ.Kind() != reflect.Func { if typ.Kind() != reflect.Func {
return reflect.Value{}, fmt.Errorf("non-function of type %s", typ) return reflect.Value{}, fmt.Errorf("non-function of type %s", typ)
} }
@ -322,7 +316,7 @@ func call(fn reflect.Value, args ...reflect.Value) (reflect.Value, error) {
} }
argv := make([]reflect.Value, len(args)) argv := make([]reflect.Value, len(args))
for i, arg := range args { for i, arg := range args {
value := indirectInterface(arg) arg = indirectInterface(arg)
// Compute the expected type. Clumsy because of variadics. // Compute the expected type. Clumsy because of variadics.
argType := dddType argType := dddType
if !typ.IsVariadic() || i < numIn-1 { if !typ.IsVariadic() || i < numIn-1 {
@ -330,11 +324,11 @@ func call(fn reflect.Value, args ...reflect.Value) (reflect.Value, error) {
} }
var err error var err error
if argv[i], err = prepareArg(value, argType); err != nil { if argv[i], err = prepareArg(arg, argType); err != nil {
return reflect.Value{}, fmt.Errorf("arg %d: %s", i, err) return reflect.Value{}, fmt.Errorf("arg %d: %s", i, err)
} }
} }
return safeCall(v, argv) return safeCall(fn, argv)
} }
// safeCall runs fun.Call(args), and returns the resulting value and error, if // safeCall runs fun.Call(args), and returns the resulting value and error, if
@ -440,52 +434,52 @@ func basicKind(v reflect.Value) (kind, error) {
// eq evaluates the comparison a == b || a == c || ... // eq evaluates the comparison a == b || a == c || ...
func eq(arg1 reflect.Value, arg2 ...reflect.Value) (bool, error) { func eq(arg1 reflect.Value, arg2 ...reflect.Value) (bool, error) {
v1 := indirectInterface(arg1) arg1 = indirectInterface(arg1)
if v1 != zero { if arg1 != zero {
if t1 := v1.Type(); !t1.Comparable() { if t1 := arg1.Type(); !t1.Comparable() {
return false, fmt.Errorf("uncomparable type %s: %v", t1, v1) return false, fmt.Errorf("uncomparable type %s: %v", t1, arg1)
} }
} }
if len(arg2) == 0 { if len(arg2) == 0 {
return false, errNoComparison return false, errNoComparison
} }
k1, _ := basicKind(v1) k1, _ := basicKind(arg1)
for _, arg := range arg2 { for _, arg := range arg2 {
v2 := indirectInterface(arg) arg = indirectInterface(arg)
k2, _ := basicKind(v2) k2, _ := basicKind(arg)
truth := false truth := false
if k1 != k2 { if k1 != k2 {
// Special case: Can compare integer values regardless of type's sign. // Special case: Can compare integer values regardless of type's sign.
switch { switch {
case k1 == intKind && k2 == uintKind: case k1 == intKind && k2 == uintKind:
truth = v1.Int() >= 0 && uint64(v1.Int()) == v2.Uint() truth = arg1.Int() >= 0 && uint64(arg1.Int()) == arg.Uint()
case k1 == uintKind && k2 == intKind: case k1 == uintKind && k2 == intKind:
truth = v2.Int() >= 0 && v1.Uint() == uint64(v2.Int()) truth = arg.Int() >= 0 && arg1.Uint() == uint64(arg.Int())
default: default:
return false, errBadComparison return false, errBadComparison
} }
} else { } else {
switch k1 { switch k1 {
case boolKind: case boolKind:
truth = v1.Bool() == v2.Bool() truth = arg1.Bool() == arg.Bool()
case complexKind: case complexKind:
truth = v1.Complex() == v2.Complex() truth = arg1.Complex() == arg.Complex()
case floatKind: case floatKind:
truth = v1.Float() == v2.Float() truth = arg1.Float() == arg.Float()
case intKind: case intKind:
truth = v1.Int() == v2.Int() truth = arg1.Int() == arg.Int()
case stringKind: case stringKind:
truth = v1.String() == v2.String() truth = arg1.String() == arg.String()
case uintKind: case uintKind:
truth = v1.Uint() == v2.Uint() truth = arg1.Uint() == arg.Uint()
default: default:
if v2 == zero { if arg == zero {
truth = v1 == v2 truth = arg1 == arg
} else { } else {
if t2 := v2.Type(); !t2.Comparable() { if t2 := arg.Type(); !t2.Comparable() {
return false, fmt.Errorf("uncomparable type %s: %v", t2, v2) return false, fmt.Errorf("uncomparable type %s: %v", t2, arg)
} }
truth = v1.Interface() == v2.Interface() truth = arg1.Interface() == arg.Interface()
} }
} }
} }
@ -505,13 +499,13 @@ func ne(arg1, arg2 reflect.Value) (bool, error) {
// lt evaluates the comparison a < b. // lt evaluates the comparison a < b.
func lt(arg1, arg2 reflect.Value) (bool, error) { func lt(arg1, arg2 reflect.Value) (bool, error) {
v1 := indirectInterface(arg1) arg1 = indirectInterface(arg1)
k1, err := basicKind(v1) k1, err := basicKind(arg1)
if err != nil { if err != nil {
return false, err return false, err
} }
v2 := indirectInterface(arg2) arg2 = indirectInterface(arg2)
k2, err := basicKind(v2) k2, err := basicKind(arg2)
if err != nil { if err != nil {
return false, err return false, err
} }
@ -520,9 +514,9 @@ func lt(arg1, arg2 reflect.Value) (bool, error) {
// Special case: Can compare integer values regardless of type's sign. // Special case: Can compare integer values regardless of type's sign.
switch { switch {
case k1 == intKind && k2 == uintKind: case k1 == intKind && k2 == uintKind:
truth = v1.Int() < 0 || uint64(v1.Int()) < v2.Uint() truth = arg1.Int() < 0 || uint64(arg1.Int()) < arg2.Uint()
case k1 == uintKind && k2 == intKind: case k1 == uintKind && k2 == intKind:
truth = v2.Int() >= 0 && v1.Uint() < uint64(v2.Int()) truth = arg2.Int() >= 0 && arg1.Uint() < uint64(arg2.Int())
default: default:
return false, errBadComparison return false, errBadComparison
} }
@ -531,13 +525,13 @@ func lt(arg1, arg2 reflect.Value) (bool, error) {
case boolKind, complexKind: case boolKind, complexKind:
return false, errBadComparisonType return false, errBadComparisonType
case floatKind: case floatKind:
truth = v1.Float() < v2.Float() truth = arg1.Float() < arg2.Float()
case intKind: case intKind:
truth = v1.Int() < v2.Int() truth = arg1.Int() < arg2.Int()
case stringKind: case stringKind:
truth = v1.String() < v2.String() truth = arg1.String() < arg2.String()
case uintKind: case uintKind:
truth = v1.Uint() < v2.Uint() truth = arg1.Uint() < arg2.Uint()
default: default:
panic("invalid kind") panic("invalid kind")
} }