fix: backport comparable check to <1.20

Signed-off-by: Mark Sagi-Kazar <mark.sagikazar@gmail.com>

mapstructure.go

@@ -1163,7 +1163,7 @@ func (d *Decoder) decodeArray(name string, data interface{}, val reflect.Value)
 
 	valArray := val
 
-	if valArray.Comparable() && valArray.Interface() == reflect.Zero(valArray.Type()).Interface() || d.config.ZeroFields {
+	if isComparable(valArray) && valArray.Interface() == reflect.Zero(valArray.Type()).Interface() || d.config.ZeroFields {
 		// Check input type
 		if dataValKind != reflect.Array && dataValKind != reflect.Slice {
 			if d.config.WeaklyTypedInput {

reflect.go

@@ -0,0 +1,7 @@
+package mapstructure
+
+import "reflect"
+
+func isComparable(v reflect.Value) bool {
+	return v.Comparable()
+}

reflect_go1_19.go

@@ -0,0 +1,9 @@
+//go:build !go1.20
+
+package mapstructure
+
+import "reflect"
+
+func isComparable(v reflect.Value) bool {
+	return true
+}