From c6b1efb41b790f8487e6924b623d621010e878fa Mon Sep 17 00:00:00 2001
From: Guflly <145608489+Guflly@users.noreply.github.com>
Date: Sun, 2 Aug 2026 18:13:40 -0700
Subject: [PATCH] Quote multiline scalars that start with tabs

---
 internal/libyaml/node.go            |  4 ++
 internal/libyaml/serializer.go      |  4 +-
 internal/libyaml/testdata/node.yaml | 15 +++++++
 yaml_test.go                        | 67 ++++++++++++++++++++++++++---
 4 files changed, 84 insertions(+), 6 deletions(-)

diff --git a/internal/libyaml/node.go b/internal/libyaml/node.go
index 4fee73b3..761dc2c0 100644
--- a/internal/libyaml/node.go
+++ b/internal/libyaml/node.go
@@ -250,6 +250,10 @@ func shouldUseLiteralStyle(s string) bool {
 	if !strings.Contains(s, "\n") || len(s) < 2 {
 		return false
 	}
+	withoutLeadingBreaks := strings.TrimLeft(s, "\r\n\u0085\u2028\u2029")
+	if strings.HasPrefix(withoutLeadingBreaks, "\t") {
+		return false
+	}
 	// Must contain at least one non-whitespace character
 	for _, r := range s {
 		if !unicode.IsSpace(r) {
diff --git a/internal/libyaml/serializer.go b/internal/libyaml/serializer.go
index 4914dce0..db90afa1 100644
--- a/internal/libyaml/serializer.go
+++ b/internal/libyaml/serializer.go
@@ -215,8 +215,10 @@ func (s *Serializer) node(node *Node, tail string) {
 			style = LITERAL_SCALAR_STYLE
 		case node.Style&FoldedStyle != 0:
 			style = FOLDED_SCALAR_STYLE
-		case strings.Contains(value, "\n"):
+		case shouldUseLiteralStyle(value):
 			style = LITERAL_SCALAR_STYLE
+		case strings.Contains(value, "\n"):
+			style = DOUBLE_QUOTED_SCALAR_STYLE
 		case forceQuoting:
 			style = s.quotePreference.ScalarStyle()
 		}
diff --git a/internal/libyaml/testdata/node.yaml b/internal/libyaml/testdata/node.yaml
index c3cc655e..a82c794e 100644
--- a/internal/libyaml/testdata/node.yaml
+++ b/internal/libyaml/testdata/node.yaml
@@ -298,6 +298,21 @@
   from: "hello\nworld"
   want: true
 
+- name: shouldUseLiteralStyle with leading tab
+  type: should-literal
+  from: "\tcontent\nnext"
+  want: false
+
+- name: shouldUseLiteralStyle with leading break then tab
+  type: should-literal
+  from: "\n\tcontent\nnext"
+  want: false
+
+- name: shouldUseLiteralStyle with tab on later line
+  type: should-literal
+  from: "first\n\tsecond"
+  want: true
+
 - name: shouldUseLiteralStyle with single char
   type: should-literal
   from: "a"
diff --git a/yaml_test.go b/yaml_test.go
index 33319910..fe5c190d 100644
--- a/yaml_test.go
+++ b/yaml_test.go
@@ -2984,29 +2984,39 @@ func TestScalarStyleWithTabs(t *testing.T) {
 		},
 		{
 			"\tThis starts with tab\nand is long enough\nfor literal style",
-			"|-\n    \tThis starts with tab\n    and is long enough\n    for literal style\n",
+			"\"\\tThis starts with tab\\nand is long enough\\nfor literal style\"\n",
 			"Multiline starting with tab",
 		},
 		{
 			"\tB\n\tC\n",
-			"|\n    \tB\n    \tC\n",
+			"\"\\tB\\n\\tC\\n\"\n",
 			"Tab B newline tab C newline",
 		},
 		{
 			"\ta\n",
-			"|\n    \ta\n",
+			"\"\\ta\\n\"\n",
 			"Tab + char + newline",
 		},
 		{
 			"\thello\n",
-			"|\n    \thello\n",
+			"\"\\thello\\n\"\n",
 			"Tab + text + newline",
 		},
 		{
 			"\t\nhello",
-			"|-\n    \t\n    hello\n",
+			"\"\\t\\nhello\"\n",
 			"Tab + newline + text",
 		},
+		{
+			"\n\tthis\nnext",
+			"\"\\n\\tthis\\nnext\"\n",
+			"Tab after initial newline",
+		},
+		{
+			"first\n\tsecond",
+			"|-\n    first\n    \tsecond\n",
+			"Tab after content line",
+		},
 	}
 
 	for i, testCase := range testCases {
@@ -3018,6 +3028,53 @@ func TestScalarStyleWithTabs(t *testing.T) {
 	}
 }
 
+func TestLeadingTabScalarRoundTrip(t *testing.T) {
+	testCases := []struct {
+		value      string
+		mapYAML    string
+		scalarYAML string
+	}{
+		{
+			"\tthis\nis\nmultiline",
+			"text: \"\\tthis\\nis\\nmultiline\"\n",
+			"\"\\tthis\\nis\\nmultiline\"\n",
+		},
+		{
+			"\n\tthis\nnext",
+			"text: \"\\n\\tthis\\nnext\"\n",
+			"\"\\n\\tthis\\nnext\"\n",
+		},
+		{
+			"first\n\tsecond",
+			"text: |-\n    first\n    \tsecond\n",
+			"|-\n    first\n    \tsecond\n",
+		},
+	}
+
+	for _, testCase := range testCases {
+		wantMap := map[string]string{"text": testCase.value}
+		data, err := yaml.Marshal(wantMap)
+		assert.NoError(t, err)
+		assert.Equal(t, testCase.mapYAML, string(data))
+
+		var gotMap map[string]string
+		err = yaml.Unmarshal(data, &gotMap)
+		assert.NoError(t, err)
+		assert.DeepEqual(t, wantMap, gotMap)
+
+		var node yaml.Node
+		node.SetString(testCase.value)
+		data, err = yaml.Marshal(&node)
+		assert.NoError(t, err)
+		assert.Equal(t, testCase.scalarYAML, string(data))
+
+		var gotScalar string
+		err = yaml.Unmarshal(data, &gotScalar)
+		assert.NoError(t, err)
+		assert.Equal(t, testCase.value, gotScalar)
+	}
+}
+
 func TestUnicodeWhitespaceHandling(t *testing.T) {
 	// Test cases for Unicode whitespace characters that should be properly handled
 	// by the shouldUseLiteralStyle function using unicode.IsSpace()