tpl: Add template function namespaces

This commit moves almost all of the template functions into separate
packages under tpl/ and adds a namespace framework.  All changes should
be backward compatible for end users, as all existing function names in
the template funcMap are left intact.

Seq and DoArithmatic have been moved out of the helpers package and into
template namespaces.

Most of the tests involved have been refactored, and many new tests have
been written.  There's still work to do, but this is a big improvement.

I got a little overzealous and added some new functions along the way:

- strings.Contains
- strings.ContainsAny
- strings.HasSuffix
- strings.TrimPrefix
- strings.TrimSuffix

Documentation is forthcoming.

Fixes #3042

2 files changed, 427 insertions, 0 deletions

diff --git a/tpl/math/math.go b/tpl/math/math.go
new file mode 100644
index 000000000..47b7b8306
--- /dev/null
+++ b/tpl/math/math.go
@@ -0,0 +1,199 @@
+// Copyright 2017 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 math
+
+import (
+	"errors"
+	"reflect"
+)
+
+// New returns a new instance of the math-namespaced template functions.
+func New() *Namespace {
+	return &Namespace{}
+}
+
+// Namespace provides template functions for the "math" namespace.
+type Namespace struct{}
+
+// Namespace returns a pointer to the current namespace instance.
+func (ns *Namespace) Namespace() *Namespace { return ns }
+
+func (ns *Namespace) Add(a, b interface{}) (interface{}, error) {
+	return DoArithmetic(a, b, '+')
+}
+
+func (ns *Namespace) Div(a, b interface{}) (interface{}, error) {
+	return DoArithmetic(a, b, '/')
+}
+
+// Mod returns a % b.
+func (ns *Namespace) Mod(a, b interface{}) (int64, error) {
+	av := reflect.ValueOf(a)
+	bv := reflect.ValueOf(b)
+	var ai, bi int64
+
+	switch av.Kind() {
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		ai = av.Int()
+	default:
+		return 0, errors.New("Modulo operator can't be used with non integer value")
+	}
+
+	switch bv.Kind() {
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		bi = bv.Int()
+	default:
+		return 0, errors.New("Modulo operator can't be used with non integer value")
+	}
+
+	if bi == 0 {
+		return 0, errors.New("The number can't be divided by zero at modulo operation")
+	}
+
+	return ai % bi, nil
+}
+
+// ModBool returns the boolean of a % b.  If a % b == 0, return true.
+func (ns *Namespace) ModBool(a, b interface{}) (bool, error) {
+	res, err := ns.Mod(a, b)
+	if err != nil {
+		return false, err
+	}
+
+	return res == int64(0), nil
+}
+
+func (ns *Namespace) Mul(a, b interface{}) (interface{}, error) {
+	return DoArithmetic(a, b, '*')
+}
+
+func (ns *Namespace) Sub(a, b interface{}) (interface{}, error) {
+	return DoArithmetic(a, b, '-')
+}
+
+// DoArithmetic performs arithmetic operations (+,-,*,/) using reflection to
+// determine the type of the two terms.
+func DoArithmetic(a, b interface{}, op rune) (interface{}, error) {
+	av := reflect.ValueOf(a)
+	bv := reflect.ValueOf(b)
+	var ai, bi int64
+	var af, bf float64
+	var au, bu uint64
+	switch av.Kind() {
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		ai = av.Int()
+		switch bv.Kind() {
+		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+			bi = bv.Int()
+		case reflect.Float32, reflect.Float64:
+			af = float64(ai) // may overflow
+			ai = 0
+			bf = bv.Float()
+		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+			bu = bv.Uint()
+			if ai >= 0 {
+				au = uint64(ai)
+				ai = 0
+			} else {
+				bi = int64(bu) // may overflow
+				bu = 0
+			}
+		default:
+			return nil, errors.New("Can't apply the operator to the values")
+		}
+	case reflect.Float32, reflect.Float64:
+		af = av.Float()
+		switch bv.Kind() {
+		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+			bf = float64(bv.Int()) // may overflow
+		case reflect.Float32, reflect.Float64:
+			bf = bv.Float()
+		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+			bf = float64(bv.Uint()) // may overflow
+		default:
+			return nil, errors.New("Can't apply the operator to the values")
+		}
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+		au = av.Uint()
+		switch bv.Kind() {
+		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+			bi = bv.Int()
+			if bi >= 0 {
+				bu = uint64(bi)
+				bi = 0
+			} else {
+				ai = int64(au) // may overflow
+				au = 0
+			}
+		case reflect.Float32, reflect.Float64:
+			af = float64(au) // may overflow
+			au = 0
+			bf = bv.Float()
+		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+			bu = bv.Uint()
+		default:
+			return nil, errors.New("Can't apply the operator to the values")
+		}
+	case reflect.String:
+		as := av.String()
+		if bv.Kind() == reflect.String && op == '+' {
+			bs := bv.String()
+			return as + bs, nil
+		}
+		return nil, errors.New("Can't apply the operator to the values")
+	default:
+		return nil, errors.New("Can't apply the operator to the values")
+	}
+
+	switch op {
+	case '+':
+		if ai != 0 || bi != 0 {
+			return ai + bi, nil
+		} else if af != 0 || bf != 0 {
+			return af + bf, nil
+		} else if au != 0 || bu != 0 {
+			return au + bu, nil
+		}
+		return 0, nil
+	case '-':
+		if ai != 0 || bi != 0 {
+			return ai - bi, nil
+		} else if af != 0 || bf != 0 {
+			return af - bf, nil
+		} else if au != 0 || bu != 0 {
+			return au - bu, nil
+		}
+		return 0, nil
+	case '*':
+		if ai != 0 || bi != 0 {
+			return ai * bi, nil
+		} else if af != 0 || bf != 0 {
+			return af * bf, nil
+		} else if au != 0 || bu != 0 {
+			return au * bu, nil
+		}
+		return 0, nil
+	case '/':
+		if bi != 0 {
+			return ai / bi, nil
+		} else if bf != 0 {
+			return af / bf, nil
+		} else if bu != 0 {
+			return au / bu, nil
+		}
+		return nil, errors.New("Can't divide the value by 0")
+	default:
+		return nil, errors.New("There is no such an operation")
+	}
+}
diff --git a/tpl/math/math_test.go b/tpl/math/math_test.go
new file mode 100644
index 000000000..649a2756e
--- /dev/null
+++ b/tpl/math/math_test.go
@@ -0,0 +1,228 @@
+// Copyright 2017 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 math
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestNamespace(t *testing.T) {
+	t.Parallel()
+
+	ns := New()
+
+	assert.Equal(t, ns, ns.Namespace(), "object pointers should match")
+}
+
+func TestBasicNSArithmetic(t *testing.T) {
+	t.Parallel()
+
+	ns := New()
+
+	for i, test := range []struct {
+		fn     func(a, b interface{}) (interface{}, error)
+		a      interface{}
+		b      interface{}
+		expect interface{}
+	}{
+		{ns.Add, 4, 2, int64(6)},
+		{ns.Add, 1.0, "foo", false},
+		{ns.Sub, 4, 2, int64(2)},
+		{ns.Sub, 1.0, "foo", false},
+		{ns.Mul, 4, 2, int64(8)},
+		{ns.Mul, 1.0, "foo", false},
+		{ns.Div, 4, 2, int64(2)},
+		{ns.Div, 1.0, "foo", false},
+	} {
+		errMsg := fmt.Sprintf("[%d] %v", i, test)
+
+		result, err := test.fn(test.a, test.b)
+
+		if b, ok := test.expect.(bool); ok && !b {
+			require.Error(t, err, errMsg)
+			continue
+		}
+
+		require.NoError(t, err, errMsg)
+		assert.Equal(t, test.expect, result, errMsg)
+	}
+}
+
+func TestDoArithmetic(t *testing.T) {
+	t.Parallel()
+
+	for i, test := range []struct {
+		a      interface{}
+		b      interface{}
+		op     rune
+		expect interface{}
+	}{
+		{3, 2, '+', int64(5)},
+		{3, 2, '-', int64(1)},
+		{3, 2, '*', int64(6)},
+		{3, 2, '/', int64(1)},
+		{3.0, 2, '+', float64(5)},
+		{3.0, 2, '-', float64(1)},
+		{3.0, 2, '*', float64(6)},
+		{3.0, 2, '/', float64(1.5)},
+		{3, 2.0, '+', float64(5)},
+		{3, 2.0, '-', float64(1)},
+		{3, 2.0, '*', float64(6)},
+		{3, 2.0, '/', float64(1.5)},
+		{3.0, 2.0, '+', float64(5)},
+		{3.0, 2.0, '-', float64(1)},
+		{3.0, 2.0, '*', float64(6)},
+		{3.0, 2.0, '/', float64(1.5)},
+		{uint(3), uint(2), '+', uint64(5)},
+		{uint(3), uint(2), '-', uint64(1)},
+		{uint(3), uint(2), '*', uint64(6)},
+		{uint(3), uint(2), '/', uint64(1)},
+		{uint(3), 2, '+', uint64(5)},
+		{uint(3), 2, '-', uint64(1)},
+		{uint(3), 2, '*', uint64(6)},
+		{uint(3), 2, '/', uint64(1)},
+		{3, uint(2), '+', uint64(5)},
+		{3, uint(2), '-', uint64(1)},
+		{3, uint(2), '*', uint64(6)},
+		{3, uint(2), '/', uint64(1)},
+		{uint(3), -2, '+', int64(1)},
+		{uint(3), -2, '-', int64(5)},
+		{uint(3), -2, '*', int64(-6)},
+		{uint(3), -2, '/', int64(-1)},
+		{-3, uint(2), '+', int64(-1)},
+		{-3, uint(2), '-', int64(-5)},
+		{-3, uint(2), '*', int64(-6)},
+		{-3, uint(2), '/', int64(-1)},
+		{uint(3), 2.0, '+', float64(5)},
+		{uint(3), 2.0, '-', float64(1)},
+		{uint(3), 2.0, '*', float64(6)},
+		{uint(3), 2.0, '/', float64(1.5)},
+		{3.0, uint(2), '+', float64(5)},
+		{3.0, uint(2), '-', float64(1)},
+		{3.0, uint(2), '*', float64(6)},
+		{3.0, uint(2), '/', float64(1.5)},
+		{0, 0, '+', 0},
+		{0, 0, '-', 0},
+		{0, 0, '*', 0},
+		{"foo", "bar", '+', "foobar"},
+		{3, 0, '/', false},
+		{3.0, 0, '/', false},
+		{3, 0.0, '/', false},
+		{uint(3), uint(0), '/', false},
+		{3, uint(0), '/', false},
+		{-3, uint(0), '/', false},
+		{uint(3), 0, '/', false},
+		{3.0, uint(0), '/', false},
+		{uint(3), 0.0, '/', false},
+		{3, "foo", '+', false},
+		{3.0, "foo", '+', false},
+		{uint(3), "foo", '+', false},
+		{"foo", 3, '+', false},
+		{"foo", "bar", '-', false},
+		{3, 2, '%', false},
+	} {
+		errMsg := fmt.Sprintf("[%d] %v", i, test)
+
+		result, err := DoArithmetic(test.a, test.b, test.op)
+
+		if b, ok := test.expect.(bool); ok && !b {
+			require.Error(t, err, errMsg)
+			continue
+		}
+
+		require.NoError(t, err, errMsg)
+		assert.Equal(t, test.expect, result, errMsg)
+	}
+}
+
+func TestMod(t *testing.T) {
+	t.Parallel()
+
+	ns := New()
+
+	for i, test := range []struct {
+		a      interface{}
+		b      interface{}
+		expect interface{}
+	}{
+		{3, 2, int64(1)},
+		{3, 1, int64(0)},
+		{3, 0, false},
+		{0, 3, int64(0)},
+		{3.1, 2, false},
+		{3, 2.1, false},
+		{3.1, 2.1, false},
+		{int8(3), int8(2), int64(1)},
+		{int16(3), int16(2), int64(1)},
+		{int32(3), int32(2), int64(1)},
+		{int64(3), int64(2), int64(1)},
+	} {
+		errMsg := fmt.Sprintf("[%d] %v", i, test)
+
+		result, err := ns.Mod(test.a, test.b)
+
+		if b, ok := test.expect.(bool); ok && !b {
+			require.Error(t, err, errMsg)
+			continue
+		}
+
+		require.NoError(t, err, errMsg)
+		assert.Equal(t, test.expect, result, errMsg)
+	}
+}
+
+func TestModBool(t *testing.T) {
+	t.Parallel()
+
+	ns := New()
+
+	for i, test := range []struct {
+		a      interface{}
+		b      interface{}
+		expect interface{}
+	}{
+		{3, 3, true},
+		{3, 2, false},
+		{3, 1, true},
+		{3, 0, nil},
+		{0, 3, true},
+		{3.1, 2, nil},
+		{3, 2.1, nil},
+		{3.1, 2.1, nil},
+		{int8(3), int8(3), true},
+		{int8(3), int8(2), false},
+		{int16(3), int16(3), true},
+		{int16(3), int16(2), false},
+		{int32(3), int32(3), true},
+		{int32(3), int32(2), false},
+		{int64(3), int64(3), true},
+		{int64(3), int64(2), false},
+	} {
+		errMsg := fmt.Sprintf("[%d] %v", i, test)
+
+		result, err := ns.ModBool(test.a, test.b)
+
+		if test.expect == nil {
+			require.Error(t, err, errMsg)
+			continue
+		}
+
+		require.NoError(t, err, errMsg)
+		assert.Equal(t, test.expect, result, errMsg)
+	}
+}