Support numeric sort in ByParam

With this commit ByParam takes into account a type of a value under a
key. If both values are numeric then they're coerced into float64 and
then get compared.
If any value isn't numeric, for example it's nil or string, then both
values coerced into string and get compared as strings
(lexicographicaly)

Nil values are always sent to the end.

Numeric values confirm to any type listed below:
uint8, uint16, uint32, uint64, int, int8, int16, int32, int64, float32, float64

Closes #5305

2 files changed, 63 insertions, 6 deletions

diff --git a/hugolib/pageSort.go b/hugolib/pageSort.go
index c7766e2a6..454beb473 100644
--- a/hugolib/pageSort.go
+++ b/hugolib/pageSort.go
@@ -291,7 +291,6 @@ func (p Pages) Reverse() Pages {
 // Adjacent invocations on the same receiver with the same paramsKey will return a cached result.
 //
 // This may safely be executed  in parallel.
-
 func (p Pages) ByParam(paramsKey interface{}) Pages {
 	paramsKeyStr := cast.ToString(paramsKey)
 	key := "pageSort.ByParam." + paramsKeyStr
@@ -299,16 +298,31 @@ func (p Pages) ByParam(paramsKey interface{}) Pages {
 	paramsKeyComparator := func(p1, p2 *Page) bool {
 		v1, _ := p1.Param(paramsKeyStr)
 		v2, _ := p2.Param(paramsKeyStr)
-		s1 := cast.ToString(v1)
-		s2 := cast.ToString(v2)
 
-		// Sort nils last.
-		if s1 == "" {
+		if v1 == nil {
 			return false
-		} else if s2 == "" {
+		}
+
+		if v2 == nil {
 			return true
 		}
 
+		isNumeric := func(v interface{}) bool {
+			switch v.(type) {
+			case uint8, uint16, uint32, uint64, int, int8, int16, int32, int64, float32, float64:
+				return true
+			default:
+				return false
+			}
+		}
+
+		if isNumeric(v1) && isNumeric(v2) {
+			return cast.ToFloat64(v1) < cast.ToFloat64(v2)
+		}
+
+		s1 := cast.ToString(v1)
+		s2 := cast.ToString(v2)
+
 		return s1 < s2
 	}
 
diff --git a/hugolib/pageSort_test.go b/hugolib/pageSort_test.go
index 695045ff1..915947fd3 100644
--- a/hugolib/pageSort_test.go
+++ b/hugolib/pageSort_test.go
@@ -179,6 +179,49 @@ func TestPageSortByParam(t *testing.T) {
 	assert.Equal(t, unsetValue, unsetSortedValue)
 }
 
+func TestPageSortByParamNumeric(t *testing.T) {
+	t.Parallel()
+	var k interface{} = "arbitrarily.nested"
+	s := newTestSite(t)
+
+	n := 10
+	unsorted := createSortTestPages(s, n)
+	for i := 0; i < n; i++ {
+		v := 100 - i
+		if i%2 == 0 {
+			v = 100.0 - i
+		}
+
+		unsorted[i].params = map[string]interface{}{
+			"arbitrarily": map[string]interface{}{
+				"nested": v,
+			},
+		}
+	}
+	delete(unsorted[9].params, "arbitrarily")
+
+	firstSetValue, _ := unsorted[0].Param(k)
+	secondSetValue, _ := unsorted[1].Param(k)
+	lastSetValue, _ := unsorted[8].Param(k)
+	unsetValue, _ := unsorted[9].Param(k)
+
+	assert.Equal(t, 100, firstSetValue)
+	assert.Equal(t, 99, secondSetValue)
+	assert.Equal(t, 92, lastSetValue)
+	assert.Equal(t, nil, unsetValue)
+
+	sorted := unsorted.ByParam("arbitrarily.nested")
+	firstSetSortedValue, _ := sorted[0].Param(k)
+	secondSetSortedValue, _ := sorted[1].Param(k)
+	lastSetSortedValue, _ := sorted[8].Param(k)
+	unsetSortedValue, _ := sorted[9].Param(k)
+
+	assert.Equal(t, 92, firstSetSortedValue)
+	assert.Equal(t, 93, secondSetSortedValue)
+	assert.Equal(t, 100, lastSetSortedValue)
+	assert.Equal(t, unsetValue, unsetSortedValue)
+}
+
 func BenchmarkSortByWeightAndReverse(b *testing.B) {
 	s := newTestSite(b)
 	p := createSortTestPages(s, 300)