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

3 files changed, 45 insertions, 11 deletions

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,