Adding some tests

pkg/yqlib/candidate_node_test.go

@@ -106,6 +106,31 @@ func TestCreateScalarNodeScenarios(t *testing.T) {
 	}
 }
 
+type createStringScalarNodeScenario struct {
+	stringValue string
+	expectedTag string
+}
+
+var createStringScalarNodeScenarios = []createStringScalarNodeScenario{
+	{
+		stringValue: "yourKey",
+		expectedTag: "!!str",
+	},
+	{
+		stringValue: "<<",
+		expectedTag: "!!merge",
+	},
+}
+
+func TestCreateStringScalarNodeScenarios(t *testing.T) {
+	for _, tt := range createStringScalarNodeScenarios {
+		actual := createStringScalarNode(tt.stringValue)
+		test.AssertResultWithContext(t, tt.stringValue, actual.Value, fmt.Sprintf("Value for: %v", tt.stringValue))
+		test.AssertResultWithContext(t, tt.expectedTag, actual.Tag, fmt.Sprintf("Tag for: %v", tt.stringValue))
+		test.AssertResultWithContext(t, ScalarNode, actual.Kind, fmt.Sprintf("Kind for: %v", tt.stringValue))
+	}
+}
+
 func TestGetKeyForMapValue(t *testing.T) {
 	key := createStringScalarNode("yourKey")
 	n := CandidateNode{Key: key, Value: "meow", document: 3}

pkg/yqlib/doc/operators/anchor-and-alias-operators.md

@@ -2,7 +2,7 @@
 
 Use the `alias` and `anchor` operators to read and write yaml aliases and anchors. The `explode` operator normalises a yaml file (dereference (or expands) aliases and remove anchor names).
 
-`yq` supports merge aliases (like `<<: *blah`) however this is no longer in the standard yaml spec (1.2) and so `yq` will automatically add the `!!merge` tag to these nodes as it is effectively a custom tag.
+`yq` supports merge keys (like `<<: *blah`) from YAML 1.1. These are no longer part of the YAML 1.2 standard, but remain common in practice. Plain `<<:` keys are recognised as merge keys and round-trip as `<<:` without an explicit `!!merge` tag. When the source uses an explicit `!!merge` tag, that is preserved on output. Internally, when `yq` synthesises a `<<` map key (for example during merge operations), it tags the key as `!!merge` rather than `!!str`.
 
 
 ## NOTE --yaml-fix-merge-anchor-to-spec flag

pkg/yqlib/doc/operators/headers/anchor-and-alias-operators.md

@@ -2,7 +2,7 @@
 
 Use the `alias` and `anchor` operators to read and write yaml aliases and anchors. The `explode` operator normalises a yaml file (dereference (or expands) aliases and remove anchor names).
 
-`yq` supports merge aliases (like `<<: *blah`) however this is no longer in the standard yaml spec (1.2) and so `yq` will automatically add the `!!merge` tag to these nodes as it is effectively a custom tag.
+`yq` supports merge keys (like `<<: *blah`) from YAML 1.1. These are no longer part of the YAML 1.2 standard, but remain common in practice. Plain `<<:` keys are recognised as merge keys and round-trip as `<<:` without an explicit `!!merge` tag. When the source uses an explicit `!!merge` tag, that is preserved on output. Internally, when `yq` synthesises a `<<` map key (for example during merge operations), it tags the key as `!!merge` rather than `!!str`.
 
 
 ## NOTE --yaml-fix-merge-anchor-to-spec flag

pkg/yqlib/goccy_yaml_test.go

@@ -230,7 +230,7 @@ var goccyYamlFormatScenarios = []formatScenario{
 		description: "merge anchor",
 		skipDoc:     true,
 		input:       "a: &remember\n  c: mike\nb:\n  <<: *remember",
-		expected: "a: &remember\n  c: mike\nb:\n  <<: *remember\n",
+		expected:    "a: &remember\n  c: mike\nb:\n  <<: *remember\n",
 	},
 	{
 		description: "custom tag",