provisioner: add dict template function

Add dict template function inspired by
https://stackoverflow.com/questions/18276173/calling-a-template-with-several-pipeline-parameters/18276968#18276968

Compared to stackoverflow version it additionally checks for duplicate keys.

Also decided not to use `dict` from github.com/Masterminds/sprig/v3
as it allows non-string keys, uneven number of arguments and
does not check for duplicate keys.

Signed-off-by: Alexander Yastrebov <alexander.yastrebov@zalando.de>

provisioner/template.go

@@ -144,6 +144,7 @@ func renderTemplate(context *templateContext, file string) (string, error) {
 		"sumQuantities":                         sumQuantities,
 		"awsValidID":                            awsValidID,
 		"indent":                                sprig.GenericFuncMap()["indent"],
+		"dict":                                  dict,
 	}
 
 	content, ok := context.fileData[file]
@@ -285,6 +286,27 @@ func split(s string, d string) []string {
 	return strings.Split(s, d)
 }
 
+// dict is a template function that constructs a map out of its arguments.
+// Argument list is treated as a sequence of key-value pairs and must have even length.
+// Key arguments must be unique and have string type.
+func dict(args ...interface{}) (map[string]interface{}, error) {
+	if len(args) == 0 || len(args)%2 != 0 {
+		return nil, fmt.Errorf("dict: invalid number of arguments: %d", len(args))
+	}
+	dict := make(map[string]interface{}, len(args)/2)
+	for i := 0; i < len(args); i += 2 {
+		key, ok := args[i].(string)
+		if !ok {
+			return nil, fmt.Errorf("dict: key argument %d must be string", i)
+		}
+		if _, ok := dict[key]; ok {
+			return nil, fmt.Errorf("dict: duplicate key %s", key)
+		}
+		dict[key] = args[i+1]
+	}
+	return dict, nil
+}
+
 // accountID returns just the ID part of an account
 func accountID(account string) (string, error) {
 	items := strings.Split(account, ":")

provisioner/template_test.go

@@ -1164,3 +1164,40 @@ func TestNodePoolGroupsProfile(t *testing.T) {
 		})
 	}
 }
+
+func TestDict(t *testing.T) {
+	result, err := renderSingle(
+		t,
+		`{{ define "a-template" -}}
+name: {{ .name }}
+version: {{ .version }}
+{{ end }}
+
+{{ template "a-template" dict "name" "foo" "version" .Values.data }}
+`,
+		"1")
+
+	require.NoError(t, err)
+	require.EqualValues(t, `
+
+name: foo
+version: 1
+
+`, result)
+}
+
+func TestDictInvalidArgs(t *testing.T) {
+	for i, tc := range []struct {
+		args []interface{}
+	}{
+		{args: []interface{}{}},
+		{args: []interface{}{"foo"}},
+		{args: []interface{}{1, "foo"}},
+		{args: []interface{}{"foo", "bar", "foo", "baz"}},
+	} {
+		t.Run(fmt.Sprintf("%d: %v", i, tc.args), func(t *testing.T) {
+			_, err := dict(tc.args...)
+			require.Error(t, err)
+		})
+	}
+}