Make ge, le etc. work with the Hugo Version number

This means that you can do something ala:

```html
{{ if ge .Hugo.Version "0.36" }}Reasonable new Hugo version!{{ end }}
```

The intented use is feature toggling, but please note that it will take some time and Hugo versions until this can be trusted. It does not work in older Hugo versions.

Fixes #4443

9 files changed, 127 insertions, 14 deletions

diff --git a/compare/eq.go b/compare/compare.go
index 6120c0bf2..19a5deaa2 100644
--- a/compare/eq.go
+++ b/compare/compare.go
@@ -19,3 +19,11 @@ package compare
 type Eqer interface {
 	Eq(other interface{}) bool
 }
+
+// Comparer can be used to compare two values.
+// This will be used when using the le, ge etc. operators in the templates.
+// Compare returns -1 if the given version is less than, 0 if equal and 1 if greater than
+// the running version.
+type Comparer interface {
+	Compare(other interface{}) int
+}
diff --git a/helpers/hugo.go b/helpers/hugo.go
index c4c3f4a76..b9b42e6cf 100644
--- a/helpers/hugo.go
+++ b/helpers/hugo.go
@@ -18,6 +18,7 @@ import (
 	"fmt"
 	"strings"
 
+	"github.com/gohugoio/hugo/compare"
 	"github.com/spf13/cast"
 )
 
@@ -34,10 +35,40 @@ type HugoVersion struct {
 	Suffix string
 }
 
+var (
+	_ compare.Eqer     = (*HugoVersionString)(nil)
+	_ compare.Comparer = (*HugoVersionString)(nil)
+)
+
+type HugoVersionString string
+
 func (v HugoVersion) String() string {
 	return hugoVersion(v.Number, v.PatchLevel, v.Suffix)
 }
 
+func (v HugoVersion) Version() HugoVersionString {
+	return HugoVersionString(v.String())
+}
+
+func (h HugoVersionString) String() string {
+	return string(h)
+}
+
+// Implements compare.Comparer
+func (h HugoVersionString) Compare(other interface{}) int {
+	v := MustParseHugoVersion(h.String())
+	return compareVersions(v.Number, v.PatchLevel, other)
+}
+
+// Implements compare.Eqer
+func (h HugoVersionString) Eq(other interface{}) bool {
+	s, err := cast.ToStringE(other)
+	if err != nil {
+		return false
+	}
+	return s == h.String()
+}
+
 // ParseHugoVersion parses a version string.
 func ParseHugoVersion(s string) (HugoVersion, error) {
 	var vv HugoVersion
diff --git a/helpers/hugo_test.go b/helpers/hugo_test.go
index 1f5e5193f..78742c705 100644
--- a/helpers/hugo_test.go
+++ b/helpers/hugo_test.go
@@ -29,6 +29,11 @@ func TestHugoVersion(t *testing.T) {
 	require.Equal(t, v.ReleaseVersion().String(), "0.21")
 	require.Equal(t, "0.21-DEV", v.String())
 	require.Equal(t, "0.22", v.Next().String())
+	nextVersionString := v.Next().Version()
+	require.Equal(t, "0.22", nextVersionString.String())
+	require.True(t, nextVersionString.Eq("0.22"))
+	require.False(t, nextVersionString.Eq("0.21"))
+	require.True(t, nextVersionString.Eq(nextVersionString))
 	require.Equal(t, "0.20.3", v.NextPatchLevel(3).String())
 }
 
diff --git a/hugolib/hugo_info.go b/hugolib/hugo_info.go
index 1e0c192e5..303231edb 100644
--- a/hugolib/hugo_info.go
+++ b/hugolib/hugo_info.go
@@ -1,4 +1,4 @@
-// Copyright 2015 The Hugo Authors. All rights reserved.
+// Copyright 2018 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.
@@ -33,7 +33,7 @@ var hugoInfo *HugoInfo
 
 // HugoInfo contains information about the current Hugo environment
 type HugoInfo struct {
-	Version    string
+	Version    helpers.HugoVersionString
 	Generator  template.HTML
 	CommitHash string
 	BuildDate  string
@@ -41,7 +41,7 @@ type HugoInfo struct {
 
 func init() {
 	hugoInfo = &HugoInfo{
-		Version:    helpers.CurrentHugoVersion.String(),
+		Version:    helpers.CurrentHugoVersion.Version(),
 		CommitHash: CommitHash,
 		BuildDate:  BuildDate,
 		Generator:  template.HTML(fmt.Sprintf(`<meta name="generator" content="Hugo %s" />`, helpers.CurrentHugoVersion.String())),
diff --git a/hugolib/hugo_info_test.go b/hugolib/hugo_info_test.go
new file mode 100644
index 000000000..0a34330ac
--- /dev/null
+++ b/hugolib/hugo_info_test.go
@@ -0,0 +1,33 @@
+// Copyright 2018 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 hugolib
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/gohugoio/hugo/helpers"
+	"github.com/stretchr/testify/require"
+)
+
+func TestHugoInfo(t *testing.T) {
+	assert := require.New(t)
+
+	assert.Equal(helpers.CurrentHugoVersion.Version(), hugoInfo.Version)
+	assert.IsType(helpers.HugoVersionString(""), hugoInfo.Version)
+	assert.Equal(CommitHash, hugoInfo.CommitHash)
+	assert.Equal(BuildDate, hugoInfo.BuildDate)
+	assert.Contains(hugoInfo.Generator, fmt.Sprintf("Hugo %s", hugoInfo.Version))
+
+}
diff --git a/tpl/compare/compare.go b/tpl/compare/compare.go
index 65228da99..b228040cd 100644
--- a/tpl/compare/compare.go
+++ b/tpl/compare/compare.go
@@ -88,11 +88,12 @@ func (*Namespace) Default(dflt interface{}, given ...interface{}) (interface{},
 // Eq returns the boolean truth of arg1 == arg2.
 func (*Namespace) Eq(x, y interface{}) bool {
 
-	// hugolib.Page implements compare.Eqer to make Page and PageOutput comparable.
-	if e1, ok := x.(compare.Eqer); ok {
-		if e2, ok := y.(compare.Eqer); ok {
-			return e1.Eq(e2)
-		}
+	if e, ok := x.(compare.Eqer); ok {
+		return e.Eq(y)
+	}
+
+	if e, ok := y.(compare.Eqer); ok {
+		return e.Eq(x)
 	}
 
 	normalize := func(v interface{}) interface{} {
@@ -120,25 +121,25 @@ func (n *Namespace) Ne(x, y interface{}) bool {
 
 // Ge returns the boolean truth of arg1 >= arg2.
 func (n *Namespace) Ge(a, b interface{}) bool {
-	left, right := n.compareGetFloat(a, b)
+	left, right := n.compareGet(a, b)
 	return left >= right
 }
 
 // Gt returns the boolean truth of arg1 > arg2.
 func (n *Namespace) Gt(a, b interface{}) bool {
-	left, right := n.compareGetFloat(a, b)
+	left, right := n.compareGet(a, b)
 	return left > right
 }
 
 // Le returns the boolean truth of arg1 <= arg2.
 func (n *Namespace) Le(a, b interface{}) bool {
-	left, right := n.compareGetFloat(a, b)
+	left, right := n.compareGet(a, b)
 	return left <= right
 }
 
 // Lt returns the boolean truth of arg1 < arg2.
 func (n *Namespace) Lt(a, b interface{}) bool {
-	left, right := n.compareGetFloat(a, b)
+	left, right := n.compareGet(a, b)
 	return left < right
 }
 
@@ -151,7 +152,29 @@ func (n *Namespace) Conditional(condition bool, a, b interface{}) interface{} {
 	return b
 }
 
-func (*Namespace) compareGetFloat(a interface{}, b interface{}) (float64, float64) {
+func (*Namespace) compareGet(a interface{}, b interface{}) (float64, float64) {
+	if ac, ok := a.(compare.Comparer); ok {
+		c := ac.Compare(b)
+		if c < 0 {
+			return 1, 0
+		} else if c == 0 {
+			return 0, 0
+		} else {
+			return 0, 1
+		}
+	}
+
+	if bc, ok := b.(compare.Comparer); ok {
+		c := bc.Compare(a)
+		if c < 0 {
+			return 0, 1
+		} else if c == 0 {
+			return 0, 0
+		} else {
+			return 1, 0
+		}
+	}
+
 	var left, right float64
 	var leftStr, rightStr *string
 	av := reflect.ValueOf(a)
diff --git a/tpl/compare/compare_test.go b/tpl/compare/compare_test.go
index c9bc2ffe9..d201c995b 100644
--- a/tpl/compare/compare_test.go
+++ b/tpl/compare/compare_test.go
@@ -21,6 +21,8 @@ import (
 	"testing"
 	"time"
 
+	"github.com/gohugoio/hugo/helpers"
+
 	"github.com/spf13/cast"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -171,6 +173,13 @@ func doTestCompare(t *testing.T, tp tstCompareType, funcUnderTest func(a, b inte
 		{tstEqerType1("a"), tstEqerType2("a"), 0},
 		{tstEqerType2("a"), tstEqerType1("a"), 0},
 		{tstEqerType2("a"), tstEqerType1("b"), -1},
+		{helpers.MustParseHugoVersion("0.32.1").Version(), helpers.MustParseHugoVersion("0.32").Version(), 1},
+		{helpers.MustParseHugoVersion("0.35").Version(), helpers.MustParseHugoVersion("0.32").Version(), 1},
+		{helpers.MustParseHugoVersion("0.36").Version(), helpers.MustParseHugoVersion("0.36").Version(), 0},
+		{helpers.MustParseHugoVersion("0.32").Version(), helpers.MustParseHugoVersion("0.36").Version(), -1},
+		{helpers.MustParseHugoVersion("0.32").Version(), "0.36", -1},
+		{"0.36", helpers.MustParseHugoVersion("0.32").Version(), 1},
+		{"0.36", helpers.MustParseHugoVersion("0.36").Version(), 0},
 	} {
 		result := funcUnderTest(test.left, test.right)
 		success := false
diff --git a/tpl/compare/init.go b/tpl/compare/init.go
index 7d58cf9ab..f766ef890 100644
--- a/tpl/compare/init.go
+++ b/tpl/compare/init.go
@@ -46,7 +46,9 @@ func init() {
 
 		ns.AddMethodMapping(ctx.Ge,
 			[]string{"ge"},
-			[][2]string{},
+			[][2]string{
+				{`{{ if ge .Hugo.Version "0.36" }}Reasonable new Hugo version!{{ end }}`, `Reasonable new Hugo version!`},
+			},
 		)
 
 		ns.AddMethodMapping(ctx.Gt,
diff --git a/tpl/tplimpl/template_funcs_test.go b/tpl/tplimpl/template_funcs_test.go
index 32f1a1a71..b8390c5b9 100644
--- a/tpl/tplimpl/template_funcs_test.go
+++ b/tpl/tplimpl/template_funcs_test.go
@@ -80,12 +80,14 @@ func TestTemplateFuncsExamples(t *testing.T) {
 	var data struct {
 		Title   string
 		Section string
+		Hugo    map[string]interface{}
 		Params  map[string]interface{}
 	}
 
 	data.Title = "**BatMan**"
 	data.Section = "blog"
 	data.Params = map[string]interface{}{"langCode": "en"}
+	data.Hugo = map[string]interface{}{"Version": helpers.MustParseHugoVersion("0.36.1").Version()}
 
 	for _, nsf := range internal.TemplateFuncsNamespaceRegistry {
 		ns := nsf(d)