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tpl/tplimpl: Fix template truth logic

Before this commit, due to a bug in Go's `text/template` package, this would print different output for typed nil interface values:

```
{{ if .AuthenticatedUser }}User is authenticated!{{ else }}{{ end }}
{{ if not .AuthenticatedUser }}{{ else }}}User is authenticated!{{ end }}
```

This commit works around this by wrapping every `if` and `with` with a custom `getif` template func with truth logic that matches `not`, `and` and `or`.

Those 3 template funcs from Go's stdlib are now pulled into Hugo's source tree and adjusted to support custom zero values, e.g. types that implement `IsZero`.

This means that you can now do:

```
{{ with .Date }}{{ . }}{{ end }}
```

And it would work as expected.

Fixes #5738
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bep committed Mar 6, 2019
1 parent bdf47e8 commit 02eaddc2fbe92c26e67d9f82dd9aabecbbf2106c
@@ -0,0 +1,91 @@
// Copyright 2019 The Hugo Authors. All rights reserved.
// Some functions in this file (see comments) is based on the Go source code,
// copyright The Go Authors and governed by a BSD-style license.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Package hreflect contains reflect helpers.
package hreflect

import (
"reflect"

"github.com/gohugoio/hugo/common/types"
)

// IsTruthful returns whether in represents a truthful value.
// See IsTruthfulValue
func IsTruthful(in interface{}) bool {
switch v := in.(type) {
case reflect.Value:
return IsTruthfulValue(v)
default:
return IsTruthfulValue(reflect.ValueOf(in))
}

}

var zeroType = reflect.TypeOf((*types.Zeroer)(nil)).Elem()

// IsTruthfulValue returns whether the given value has a meaningful truth value.
// This is based on template.IsTrue in Go's stdlib, but also considers
// IsZero and any interface value will be unwrapped before it's considered
// for truthfulness.
//
// Based on:
// https://github.com/golang/go/blob/178a2c42254166cffed1b25fb1d3c7a5727cada6/src/text/template/exec.go#L306
func IsTruthfulValue(val reflect.Value) (truth bool) {
val = indirectInterface(val)

if !val.IsValid() {
// Something like var x interface{}, never set. It's a form of nil.
return
}

if val.Type().Implements(zeroType) {
return !val.Interface().(types.Zeroer).IsZero()
}

switch val.Kind() {
case reflect.Array, reflect.Map, reflect.Slice, reflect.String:
truth = val.Len() > 0
case reflect.Bool:
truth = val.Bool()
case reflect.Complex64, reflect.Complex128:
truth = val.Complex() != 0
case reflect.Chan, reflect.Func, reflect.Ptr, reflect.Interface:
truth = !val.IsNil()
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
truth = val.Int() != 0
case reflect.Float32, reflect.Float64:
truth = val.Float() != 0
case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
truth = val.Uint() != 0
case reflect.Struct:
truth = true // Struct values are always true.
default:
return
}

return
}

// Based on: https://github.com/golang/go/blob/178a2c42254166cffed1b25fb1d3c7a5727cada6/src/text/template/exec.go#L931
func indirectInterface(v reflect.Value) reflect.Value {
if v.Kind() != reflect.Interface {
return v
}
if v.IsNil() {
return reflect.Value{}
}
return v.Elem()
}
@@ -0,0 +1,42 @@
// Copyright 2019 The Hugo Authors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package hreflect

import (
"reflect"
"testing"
"time"

"github.com/stretchr/testify/require"
)

func TestIsTruthful(t *testing.T) {
assert := require.New(t)

assert.True(IsTruthful(true))
assert.False(IsTruthful(false))
assert.True(IsTruthful(time.Now()))
assert.False(IsTruthful(time.Time{}))
}

func BenchmarkIsTruthFul(b *testing.B) {
v := reflect.ValueOf("Hugo")

b.ResetTimer()
for i := 0; i < b.N; i++ {
if !IsTruthfulValue(v) {
b.Fatal("not truthful")
}
}
}
@@ -50,3 +50,9 @@ func NewKeyValuesStrings(key string, values ...string) KeyValues {
}
return KeyValues{Key: key, Values: iv}
}

// Zeroer, as implemented by time.Time, will be used by the truth template
// funcs in Hugo (if, with, not, and, or).
type Zeroer interface {
IsZero() bool
}
1 go.sum
@@ -76,6 +76,7 @@ github.com/magefile/mage v1.4.0 h1:RI7B1CgnPAuu2O9lWszwya61RLmfL0KCdo+QyyI/Bhk=
github.com/magefile/mage v1.4.0/go.mod h1:IUDi13rsHje59lecXokTfGX0QIzO45uVPlXnJYsXepA=
github.com/magiconair/properties v1.8.0 h1:LLgXmsheXeRoUOBOjtwPQCWIYqM/LU1ayDtDePerRcY=
github.com/magiconair/properties v1.8.0/go.mod h1:PppfXfuXeibc/6YijjN8zIbojt8czPbwD3XqdrwzmxQ=
github.com/markbates/inflect v0.0.0-20171215194931-a12c3aec81a6 h1:LZhVjIISSbj8qLf2qDPP0D8z0uvOWAW5C85ly5mJW6c=
github.com/markbates/inflect v0.0.0-20171215194931-a12c3aec81a6/go.mod h1:oTeZL2KHA7CUX6X+fovmK9OvIOFuqu0TwdQrZjLTh88=
github.com/matryer/try v0.0.0-20161228173917-9ac251b645a2/go.mod h1:0KeJpeMD6o+O4hW7qJOT7vyQPKrWmj26uf5wMc/IiIs=
github.com/mattn/go-colorable v0.0.9/go.mod h1:9vuHe8Xs5qXnSaW/c/ABM9alt+Vo+STaOChaDxuIBZU=
@@ -71,6 +71,27 @@ func init() {
[][2]string{},
)

ns.AddMethodMapping(ctx.And,
[]string{"and"},
[][2]string{},
)

ns.AddMethodMapping(ctx.Or,
[]string{"or"},
[][2]string{},
)

// getif is used internally by Hugo. Do not document.
ns.AddMethodMapping(ctx.getIf,
[]string{"getif"},
[][2]string{},
)

ns.AddMethodMapping(ctx.Not,
[]string{"not"},
[][2]string{},
)

ns.AddMethodMapping(ctx.Conditional,
[]string{"cond"},
[][2]string{
@@ -0,0 +1,73 @@
// Copyright 2019 The Hugo Authors. All rights reserved.
// The functions in this file is based on the Go source code, copyright
// The Go Authors and governed by a BSD-style license.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Package compare provides template functions for comparing values.
package compare

import (
"reflect"

"github.com/gohugoio/hugo/common/hreflect"
)

// Boolean logic, based on:
// https://github.com/golang/go/blob/178a2c42254166cffed1b25fb1d3c7a5727cada6/src/text/template/funcs.go#L302

func truth(arg reflect.Value) bool {
return hreflect.IsTruthfulValue(arg)
}

// getIf will return the given arg if it is considered truthful, else an empty string.
func (*Namespace) getIf(arg reflect.Value) reflect.Value {
if truth(arg) {
return arg
}
return reflect.ValueOf("")
}

// And computes the Boolean AND of its arguments, returning
// the first false argument it encounters, or the last argument.
func (*Namespace) And(arg0 reflect.Value, args ...reflect.Value) reflect.Value {
if !truth(arg0) {
return arg0
}
for i := range args {
arg0 = args[i]
if !truth(arg0) {
break
}
}
return arg0
}

// Or computes the Boolean OR of its arguments, returning
// the first true argument it encounters, or the last argument.
func (*Namespace) Or(arg0 reflect.Value, args ...reflect.Value) reflect.Value {
if truth(arg0) {
return arg0
}
for i := range args {
arg0 = args[i]
if truth(arg0) {
break
}
}
return arg0
}

// Not returns the Boolean negation of its argument.
func (*Namespace) Not(arg reflect.Value) bool {
return !truth(arg)
}
@@ -0,0 +1,60 @@
// Copyright 2019 The Hugo Authors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package compare

import (
"reflect"
"testing"
"time"

"github.com/gohugoio/hugo/common/hreflect"
"github.com/stretchr/testify/require"
)

func TestTruth(t *testing.T) {
n := New()

truthv, falsev := reflect.ValueOf(time.Now()), reflect.ValueOf(false)

assertTruth := func(t *testing.T, v reflect.Value, expected bool) {
if hreflect.IsTruthfulValue(v) != expected {
t.Fatal("truth mismatch")
}
}

t.Run("And", func(t *testing.T) {
assertTruth(t, n.And(truthv, truthv), true)
assertTruth(t, n.And(truthv, falsev), false)

})

t.Run("Or", func(t *testing.T) {
assertTruth(t, n.Or(truthv, truthv), true)
assertTruth(t, n.Or(falsev, truthv, falsev), true)
assertTruth(t, n.Or(falsev, falsev), false)
})

t.Run("Not", func(t *testing.T) {
assert := require.New(t)
assert.True(n.Not(falsev))
assert.False(n.Not(truthv))
})

t.Run("getIf", func(t *testing.T) {
assert := require.New(t)
assertTruth(t, n.getIf(reflect.ValueOf(nil)), false)
s := reflect.ValueOf("Hugo")
assert.Equal(s, n.getIf(s))
})
}
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