tpl: Extend merge to accept multiple parameters

Fixes #7595

3 files changed, 106 insertions, 65 deletions

diff --git a/tpl/collections/init.go b/tpl/collections/init.go
index 17ca16543..1e6412610 100644
--- a/tpl/collections/init.go
+++ b/tpl/collections/init.go
@@ -116,10 +116,12 @@ func init() {
 			[][2]string{
 				{
 					`{{ (querify "foo" 1 "bar" 2 "baz" "with spaces" "qux" "this&that=those") | safeHTML }}`,
-					`bar=2&baz=with+spaces&foo=1&qux=this%26that%3Dthose`},
+					`bar=2&baz=with+spaces&foo=1&qux=this%26that%3Dthose`,
+				},
 				{
 					`<a href="https://www.google.com?{{ (querify "q" "test" "page" 3) | safeURL }}">Search</a>`,
-					`<a href="https://www.google.com?page=3&amp;q=test">Search</a>`},
+					`<a href="https://www.google.com?page=3&amp;q=test">Search</a>`,
+				},
 			},
 		)
 
@@ -186,15 +188,22 @@ func init() {
 		ns.AddMethodMapping(ctx.Merge,
 			[]string{"merge"},
 			[][2]string{
-				{`{{ dict "title" "Hugo Rocks!" | collections.Merge (dict "title" "Default Title" "description" "Yes, Hugo Rocks!") | sort }}`,
-					`[Yes, Hugo Rocks! Hugo Rocks!]`},
-				{`{{  merge (dict "title" "Default Title" "description" "Yes, Hugo Rocks!") (dict "title" "Hugo Rocks!") | sort }}`,
-					`[Yes, Hugo Rocks! Hugo Rocks!]`},
+				{
+					`{{ dict "title" "Hugo Rocks!" | collections.Merge (dict "title" "Default Title" "description" "Yes, Hugo Rocks!") | sort }}`,
+					`[Yes, Hugo Rocks! Hugo Rocks!]`,
+				},
+				{
+					`{{  merge (dict "title" "Default Title" "description" "Yes, Hugo Rocks!") (dict "title" "Hugo Rocks!") | sort }}`,
+					`[Yes, Hugo Rocks! Hugo Rocks!]`,
+				},
+				{
+					`{{  merge (dict "title" "Default Title" "description" "Yes, Hugo Rocks!") (dict "title" "Hugo Rocks!") (dict "extra" "For reals!") | sort }}`,
+					`[Yes, Hugo Rocks! For reals! Hugo Rocks!]`,
+				},
 			},
 		)
 
 		return ns
-
 	}
 
 	internal.AddTemplateFuncsNamespace(f)
diff --git a/tpl/collections/merge.go b/tpl/collections/merge.go
index c65e9dd90..029416142 100644
--- a/tpl/collections/merge.go
+++ b/tpl/collections/merge.go
@@ -17,17 +17,35 @@ import (
 	"reflect"
 	"strings"
 
-	"github.com/gohugoio/hugo/common/maps"
-
 	"github.com/gohugoio/hugo/common/hreflect"
+	"github.com/gohugoio/hugo/common/maps"
 
 	"github.com/pkg/errors"
 )
 
-// Merge creates a copy of dst and merges src into it.
-// Currently only maps supported. Key handling is case insensitive.
-func (ns *Namespace) Merge(src, dst interface{}) (interface{}, error) {
+// Merge creates a copy of the final parameter and merges the preceeding
+// parameters into it in reverse order.
+// Currently only maps are supported. Key handling is case insensitive.
+func (ns *Namespace) Merge(params ...interface{}) (interface{}, error) {
+	if len(params) < 2 {
+		return nil, errors.New("merge requires at least two parameters")
+	}
+
+	var err error
+	result := params[len(params)-1]
+
+	for i := len(params) - 2; i >= 0; i-- {
+		result, err = ns.merge(params[i], result)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return result, nil
+}
 
+// merge creates a copy of dst and merges src into it.
+func (ns *Namespace) merge(src, dst interface{}) (interface{}, error) {
 	vdst, vsrc := reflect.ValueOf(dst), reflect.ValueOf(src)
 
 	if vdst.Kind() != reflect.Map {
@@ -60,14 +78,12 @@ func caseInsensitiveLookup(m, k reflect.Value) (reflect.Value, bool) {
 		if strings.EqualFold(k.String(), key.String()) {
 			return m.MapIndex(key), true
 		}
-
 	}
 
 	return reflect.Value{}, false
 }
 
 func mergeMap(dst, src reflect.Value) reflect.Value {
-
 	out := reflect.MakeMap(dst.Type())
 
 	// If the destination is Params, we must lower case all keys.
diff --git a/tpl/collections/merge_test.go b/tpl/collections/merge_test.go
index c18664e25..dbe92d8b2 100644
--- a/tpl/collections/merge_test.go
+++ b/tpl/collections/merge_test.go
@@ -15,82 +15,108 @@ package collections
 
 import (
 	"bytes"
-	"fmt"
 	"reflect"
-	"runtime"
-	"strings"
 	"testing"
 
 	"github.com/gohugoio/hugo/common/maps"
-
+	"github.com/gohugoio/hugo/deps"
 	"github.com/gohugoio/hugo/parser"
-
 	"github.com/gohugoio/hugo/parser/metadecoders"
 
 	qt "github.com/frankban/quicktest"
-	"github.com/gohugoio/hugo/deps"
 )
 
 func TestMerge(t *testing.T) {
-
 	ns := New(&deps.Deps{})
 
 	simpleMap := map[string]interface{}{"a": 1, "b": 2}
 
 	for i, test := range []struct {
 		name   string
-		dst    interface{}
-		src    interface{}
+		params []interface{}
 		expect interface{}
 		isErr  bool
 	}{
 		{
 			"basic",
-			map[string]interface{}{"a": 1, "b": 2},
-			map[string]interface{}{"a": 42, "c": 3},
-			map[string]interface{}{"a": 1, "b": 2, "c": 3}, false},
+			[]interface{}{
+				map[string]interface{}{"a": 42, "c": 3},
+				map[string]interface{}{"a": 1, "b": 2},
+			},
+			map[string]interface{}{"a": 1, "b": 2, "c": 3}, false,
+		},
+		{
+			"multi",
+			[]interface{}{
+				map[string]interface{}{"a": 42, "c": 3, "e": 11},
+				map[string]interface{}{"a": 1, "b": 2},
+				map[string]interface{}{"a": 9, "c": 4, "d": 7},
+			},
+			map[string]interface{}{"a": 9, "b": 2, "c": 4, "d": 7, "e": 11}, false,
+		},
 		{
 			"basic case insensitive",
-			map[string]interface{}{"a": 1, "b": 2},
-			map[string]interface{}{"A": 42, "c": 3},
-			map[string]interface{}{"a": 1, "b": 2, "c": 3}, false},
+			[]interface{}{
+				map[string]interface{}{"A": 42, "c": 3},
+				map[string]interface{}{"a": 1, "b": 2},
+			},
+			map[string]interface{}{"a": 1, "b": 2, "c": 3}, false,
+		},
 		{
 			"nested",
-			map[string]interface{}{"a": 1, "b": map[string]interface{}{"d": 1, "e": 2}},
-			map[string]interface{}{"a": 42, "c": 3, "b": map[string]interface{}{"d": 55, "e": 66, "f": 3}},
-			map[string]interface{}{"a": 1, "b": map[string]interface{}{"d": 1, "e": 2, "f": 3}, "c": 3}, false},
+			[]interface{}{
+				map[string]interface{}{"a": 42, "c": 3, "b": map[string]interface{}{"d": 55, "e": 66, "f": 3}},
+				map[string]interface{}{"a": 1, "b": map[string]interface{}{"d": 1, "e": 2}},
+			},
+			map[string]interface{}{"a": 1, "b": map[string]interface{}{"d": 1, "e": 2, "f": 3}, "c": 3}, false,
+		},
 		{
 			// https://github.com/gohugoio/hugo/issues/6633
 			"params dst",
-			maps.Params{"a": 1, "b": 2},
-			map[string]interface{}{"a": 42, "c": 3},
-			maps.Params{"a": int(1), "b": int(2), "c": int(3)}, false},
+			[]interface{}{
+				map[string]interface{}{"a": 42, "c": 3},
+				maps.Params{"a": 1, "b": 2},
+			},
+			maps.Params{"a": int(1), "b": int(2), "c": int(3)}, false,
+		},
 		{
 			"params dst, upper case src",
-			maps.Params{"a": 1, "b": 2},
-			map[string]interface{}{"a": 42, "C": 3},
-			maps.Params{"a": int(1), "b": int(2), "c": int(3)}, false},
+			[]interface{}{
+				map[string]interface{}{"a": 42, "C": 3},
+				maps.Params{"a": 1, "b": 2},
+			},
+			maps.Params{"a": int(1), "b": int(2), "c": int(3)}, false,
+		},
 		{
 			"params src",
-			map[string]interface{}{"a": 1, "c": 2},
-			maps.Params{"a": 42, "c": 3},
-			map[string]interface{}{"a": int(1), "c": int(2)}, false},
+			[]interface{}{
+				maps.Params{"a": 42, "c": 3},
+				map[string]interface{}{"a": 1, "c": 2},
+			},
+			map[string]interface{}{"a": int(1), "c": int(2)}, false,
+		},
 		{
 			"params src, upper case dst",
-			map[string]interface{}{"a": 1, "C": 2},
-			maps.Params{"a": 42, "c": 3},
-			map[string]interface{}{"a": int(1), "C": int(2)}, false},
+			[]interface{}{
+				maps.Params{"a": 42, "c": 3},
+				map[string]interface{}{"a": 1, "C": 2},
+			},
+			map[string]interface{}{"a": int(1), "C": int(2)}, false,
+		},
 		{
 			"nested, params dst",
-			maps.Params{"a": 1, "b": maps.Params{"d": 1, "e": 2}},
-			map[string]interface{}{"a": 42, "c": 3, "b": map[string]interface{}{"d": 55, "e": 66, "f": 3}},
-			maps.Params{"a": 1, "b": maps.Params{"d": 1, "e": 2, "f": 3}, "c": 3}, false},
-		{"src nil", simpleMap, nil, simpleMap, false},
+			[]interface{}{
+				map[string]interface{}{"a": 42, "c": 3, "b": map[string]interface{}{"d": 55, "e": 66, "f": 3}},
+				maps.Params{"a": 1, "b": maps.Params{"d": 1, "e": 2}},
+			},
+			maps.Params{"a": 1, "b": maps.Params{"d": 1, "e": 2, "f": 3}, "c": 3}, false,
+		},
+		{"src nil", []interface{}{nil, simpleMap}, simpleMap, false},
 		// Error cases.
-		{"dst not a map", "not a map", nil, nil, true},
-		{"src not a map", simpleMap, "not a map", nil, true},
-		{"different map types", simpleMap, map[int]interface{}{32: "a"}, nil, true},
-		{"all nil", nil, nil, nil, true},
+		{"dst not a map", []interface{}{nil, "not a map"}, nil, true},
+		{"src not a map", []interface{}{"not a map", simpleMap}, nil, true},
+		{"different map types", []interface{}{map[int]interface{}{32: "a"}, simpleMap}, nil, true},
+		{"all nil", []interface{}{nil, nil}, nil, true},
 	} {
 
 		test := test
@@ -101,9 +127,7 @@ func TestMerge(t *testing.T) {
 
 			c := qt.New(t)
 
-			srcStr, dstStr := fmt.Sprint(test.src), fmt.Sprint(test.dst)
-
-			result, err := ns.Merge(test.src, test.dst)
+			result, err := ns.Merge(test.params...)
 
 			if test.isErr {
 				c.Assert(err, qt.Not(qt.IsNil), errMsg)
@@ -112,14 +136,6 @@ func TestMerge(t *testing.T) {
 
 			c.Assert(err, qt.IsNil)
 			c.Assert(result, qt.DeepEquals, test.expect, errMsg)
-
-			// map sort in fmt was fixed in go 1.12.
-			if !strings.HasPrefix(runtime.Version(), "go1.11") {
-				// Verify that the original maps are preserved.
-				c.Assert(fmt.Sprint(test.src), qt.Equals, srcStr)
-				c.Assert(fmt.Sprint(test.dst), qt.Equals, dstStr)
-			}
-
 		})
 	}
 }
@@ -172,9 +188,9 @@ V22 = "v22_2"
 			qt.DeepEquals,
 			map[string]interface{}{
 				"V1": "v1_1", "V2": "v2_2",
-				"V2s": map[string]interface{}{"V21": "v21_1", "V22": "v22_2"}})
+				"V2s": map[string]interface{}{"V21": "v21_1", "V22": "v22_2"},
+			})
 	}
-
 }
 
 func TestCaseInsensitiveMapLookup(t *testing.T) {