Add writable context to Node

The variable scope in the Go templates makes it hard, if possible at all, to write templates with counter variables or similar state.

This commit fixes that by adding a writable context to Node, backed by a map: Scratch.

This context has three methods, Get, Set and Add. The Add is tailored for counter variables, but can be used for any built-in numeric values or strings.

helpers/general.go

@@ -17,10 +17,12 @@ import (
 	"bytes"
 	"crypto/md5"
 	"encoding/hex"
+	"errors"
 	"fmt"
 	"io"
 	"net"
 	"path/filepath"
+	"reflect"
 	"strings"
 
 	bp "github.com/spf13/hugo/bufferpool"
@@ -118,3 +120,124 @@ func Md5String(f string) string {
 	h.Write([]byte(f))
 	return hex.EncodeToString(h.Sum([]byte{}))
 }
+
+// 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
+		} else {
+			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
+		} else {
+			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
+		} else {
+			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
+		} else {
+			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
+		} else {
+			return nil, errors.New("Can't divide the value by 0")
+		}
+	default:
+		return nil, errors.New("There is no such an operation")
+	}
+}

helpers/general_test.go

@@ -2,6 +2,7 @@ package helpers
 
 import (
 	"github.com/stretchr/testify/assert"
+	"reflect"
 	"strings"
 	"testing"
 )
@@ -128,3 +129,91 @@ func TestMd5StringEmpty(t *testing.T) {
 		Md5String(in)
 	}
 }
+
+func TestDoArithmetic(t *testing.T) {
+	for i, this := 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},
+	} {
+		result, err := DoArithmetic(this.a, this.b, this.op)
+		if b, ok := this.expect.(bool); ok && !b {
+			if err == nil {
+				t.Errorf("[%d] doArithmetic didn't return an expected error")
+			}
+		} else {
+			if err != nil {
+				t.Errorf("[%d] failed: %s", i, err)
+				continue
+			}
+			if !reflect.DeepEqual(result, this.expect) {
+				t.Errorf("[%d] doArithmetic got %v but expected %v", i, result, this.expect)
+			}
+		}
+	}
+}

hugolib/node.go

@@ -33,6 +33,7 @@ type Node struct {
 	UrlPath
 	paginator     *pager
 	paginatorInit sync.Once
+	scratch       *Scratch
 }
 
 func (n *Node) Now() time.Time {
@@ -124,3 +125,11 @@ type UrlPath struct {
 	Slug      string
 	Section   string
 }
+
+// Scratch returns the writable context associated with this Node.
+func (n *Node) Scratch() *Scratch {
+	if n.scratch == nil {
+		n.scratch = newScratch()
+	}
+	return n.scratch
+}

hugolib/scratch.go

@@ -0,0 +1,57 @@
+// Copyright © 2013-14 Steve Francia <spf@spf13.com>.
+//
+// Licensed under the Simple Public 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://opensource.org/licenses/Simple-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 hugolib
+
+import (
+	"github.com/spf13/hugo/helpers"
+)
+
+// Scratch is a writable context used for stateful operations in Page/Node rendering.
+type Scratch struct {
+	values map[string]interface{}
+}
+
+// Add will add (using the + operator) the addend to the existing addend (if found).
+// Supports numeric values and strings.
+func (c *Scratch) Add(key string, newAddend interface{}) (string, error) {
+	var newVal interface{}
+	existingAddend, found := c.values[key]
+	if found {
+		var err error
+		newVal, err = helpers.DoArithmetic(existingAddend, newAddend, '+')
+		if err != nil {
+			return "", err
+		}
+	} else {
+		newVal = newAddend
+	}
+	c.values[key] = newVal
+	return "", nil // have to return something to make it work with the Go templates
+}
+
+// Set stores a value with the given key in the Node context.
+// This value can later be retrieved with Get.
+func (c *Scratch) Set(key string, value interface{}) string {
+	c.values[key] = value
+	return ""
+}
+
+// Get returns a value previously set by Add or Set
+func (c *Scratch) Get(key string) interface{} {
+	return c.values[key]
+}
+
+func newScratch() *Scratch {
+	return &Scratch{values: make(map[string]interface{})}
+}

hugolib/scratch_test.go

@@ -0,0 +1,49 @@
+package hugolib
+
+import (
+	"github.com/stretchr/testify/assert"
+	"testing"
+)
+
+func TestScratchAdd(t *testing.T) {
+	scratch := newScratch()
+	scratch.Add("int1", 10)
+	scratch.Add("int1", 20)
+	scratch.Add("int2", 20)
+
+	assert.Equal(t, 30, scratch.Get("int1"))
+	assert.Equal(t, 20, scratch.Get("int2"))
+
+	scratch.Add("float1", float64(10.5))
+	scratch.Add("float1", float64(20.1))
+
+	assert.Equal(t, float64(30.6), scratch.Get("float1"))
+
+	scratch.Add("string1", "Hello ")
+	scratch.Add("string1", "big ")
+	scratch.Add("string1", "World!")
+
+	assert.Equal(t, "Hello big World!", scratch.Get("string1"))
+
+	scratch.Add("scratch", scratch)
+	_, err := scratch.Add("scratch", scratch)
+
+	if err == nil {
+		t.Errorf("Expected error from invalid arithmetic")
+	}
+
+}
+
+func TestScratchSet(t *testing.T) {
+	scratch := newScratch()
+	scratch.Set("key", "val")
+	assert.Equal(t, "val", scratch.Get("key"))
+}
+
+func TestScratchGet(t *testing.T) {
+	scratch := newScratch()
+	nothing := scratch.Get("nothing")
+	if nothing != nil {
+		t.Errorf("Should not return anything, but got %v", nothing)
+	}
+}

tpl/template_test.go

@@ -101,94 +101,6 @@ func doTestCompare(t *testing.T, tp tstCompareType, funcUnderTest func(a, b inte
 	}
 }
 
-func TestDoArithmetic(t *testing.T) {
-	for i, this := 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},
-	} {
-		result, err := doArithmetic(this.a, this.b, this.op)
-		if b, ok := this.expect.(bool); ok && !b {
-			if err == nil {
-				t.Errorf("[%d] doArithmetic didn't return an expected error", i)
-			}
-		} else {
-			if err != nil {
-				t.Errorf("[%d] failed: %s", i, err)
-				continue
-			}
-			if !reflect.DeepEqual(result, this.expect) {
-				t.Errorf("[%d] doArithmetic got %v but expected %v", i, result, this.expect)
-			}
-		}
-	}
-}
-
 func TestMod(t *testing.T) {
 	for i, this := range []struct {
 		a      interface{}