From 9e0c5fd3c9980dad9cd982be1fcf15130468054c Mon Sep 17 00:00:00 2001
From: Mike Farah <mikefarah@gmail.com>
Date: Tue, 25 Nov 2025 10:15:08 +1100
Subject: [PATCH] Fixing escape charaters again :cry: #2517

---
 pkg/yqlib/lib.go      |  72 +++++++++++++++++++++----
 pkg/yqlib/lib_test.go | 119 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 182 insertions(+), 9 deletions(-)

diff --git a/pkg/yqlib/lib.go b/pkg/yqlib/lib.go
index c31724af..5a32665e 100644
--- a/pkg/yqlib/lib.go
+++ b/pkg/yqlib/lib.go
@@ -187,15 +187,69 @@ func parseInt(numberString string) (int, error) {
 }
 
 func processEscapeCharacters(original string) string {
-	value := original
-	value = strings.ReplaceAll(value, "\\\"", "\"")
-	value = strings.ReplaceAll(value, "\\n", "\n")
-	value = strings.ReplaceAll(value, "\\t", "\t")
-	value = strings.ReplaceAll(value, "\\r", "\r")
-	value = strings.ReplaceAll(value, "\\f", "\f")
-	value = strings.ReplaceAll(value, "\\v", "\v")
-	value = strings.ReplaceAll(value, "\\b", "\b")
-	value = strings.ReplaceAll(value, "\\a", "\a")
+	if original == "" {
+		return original
+	}
+
+	var result strings.Builder
+	runes := []rune(original)
+
+	for i := 0; i < len(runes); i++ {
+		if runes[i] == '\\' && i < len(runes)-1 {
+			next := runes[i+1]
+			switch next {
+			case '\\':
+				// Check if followed by opening bracket - if so, preserve both backslashes
+				// this is required for string interpolation to work correctly.
+				if i+2 < len(runes) && runes[i+2] == '(' {
+					// Preserve \\ when followed by (
+					result.WriteRune('\\')
+					result.WriteRune('\\')
+					i++ // Skip the next backslash (we'll process the ( normally on next iteration)
+					continue
+				}
+				// Escaped backslash: \\ -> \
+				result.WriteRune('\\')
+				i++ // Skip the next backslash
+				continue
+			case '"':
+				result.WriteRune('"')
+				i++ // Skip the quote
+				continue
+			case 'n':
+				result.WriteRune('\n')
+				i++ // Skip the 'n'
+				continue
+			case 't':
+				result.WriteRune('\t')
+				i++ // Skip the 't'
+				continue
+			case 'r':
+				result.WriteRune('\r')
+				i++ // Skip the 'r'
+				continue
+			case 'f':
+				result.WriteRune('\f')
+				i++ // Skip the 'f'
+				continue
+			case 'v':
+				result.WriteRune('\v')
+				i++ // Skip the 'v'
+				continue
+			case 'b':
+				result.WriteRune('\b')
+				i++ // Skip the 'b'
+				continue
+			case 'a':
+				result.WriteRune('\a')
+				i++ // Skip the 'a'
+				continue
+			}
+		}
+		result.WriteRune(runes[i])
+	}
+
+	value := result.String()
 	if value != original {
 		log.Debug("processEscapeCharacters from [%v] to [%v]", original, value)
 	}
diff --git a/pkg/yqlib/lib_test.go b/pkg/yqlib/lib_test.go
index a9aada14..a6ad5786 100644
--- a/pkg/yqlib/lib_test.go
+++ b/pkg/yqlib/lib_test.go
@@ -408,3 +408,122 @@ func TestKindString(t *testing.T) {
 	test.AssertResult(t, "AliasNode", KindString(AliasNode))
 	test.AssertResult(t, "unknown!", KindString(Kind(999))) // Invalid kind
 }
+
+type processEscapeCharactersScenario struct {
+	input    string
+	expected string
+}
+
+var processEscapeCharactersScenarios = []processEscapeCharactersScenario{
+	{
+		input:    "",
+		expected: "",
+	},
+	{
+		input:    "hello",
+		expected: "hello",
+	},
+	{
+		input:    "\\\"",
+		expected: "\"",
+	},
+	{
+		input:    "hello\\\"world",
+		expected: "hello\"world",
+	},
+	{
+		input:    "\\n",
+		expected: "\n",
+	},
+	{
+		input:    "line1\\nline2",
+		expected: "line1\nline2",
+	},
+	{
+		input:    "\\t",
+		expected: "\t",
+	},
+	{
+		input:    "hello\\tworld",
+		expected: "hello\tworld",
+	},
+	{
+		input:    "\\r",
+		expected: "\r",
+	},
+	{
+		input:    "hello\\rworld",
+		expected: "hello\rworld",
+	},
+	{
+		input:    "\\f",
+		expected: "\f",
+	},
+	{
+		input:    "hello\\fworld",
+		expected: "hello\fworld",
+	},
+	{
+		input:    "\\v",
+		expected: "\v",
+	},
+	{
+		input:    "hello\\vworld",
+		expected: "hello\vworld",
+	},
+	{
+		input:    "\\b",
+		expected: "\b",
+	},
+	{
+		input:    "hello\\bworld",
+		expected: "hello\bworld",
+	},
+	{
+		input:    "\\a",
+		expected: "\a",
+	},
+	{
+		input:    "hello\\aworld",
+		expected: "hello\aworld",
+	},
+	{
+		input:    "\\\"\\n\\t\\r\\f\\v\\b\\a",
+		expected: "\"\n\t\r\f\v\b\a",
+	},
+	{
+		input:    "multiple\\nlines\\twith\\ttabs",
+		expected: "multiple\nlines\twith\ttabs",
+	},
+	{
+		input:    "quote\\\"here",
+		expected: "quote\"here",
+	},
+	{
+		input:    "\\\\",
+		expected: "\\", // Backslash is processed: "\\\\" becomes "\\"
+	},
+	{
+		input:    "\\\"test\\\"",
+		expected: "\"test\"",
+	},
+	{
+		input:    "a\\\\b",
+		expected: "a\\b", // Tests roundtrip: "a\\\\b" should become "a\\b"
+	},
+	{
+		input:    "Hi \\\\(.value)",
+		expected: "Hi \\\\(.value)",
+	},
+	{
+		input:    `a\\b`,
+		expected: "a\\b",
+	},
+}
+
+func TestProcessEscapeCharacters(t *testing.T) {
+	for _, tt := range processEscapeCharactersScenarios {
+		actual := processEscapeCharacters(tt.input)
+		test.AssertResultComplexWithContext(t, tt.expected, actual, fmt.Sprintf("Input: %q", tt.input))
+	}
+}