Port TypeScript PR #60303: Fix template string escaping for control characters

internal/printer/utilities.go

@@ -103,7 +103,7 @@ func escapeStringWorker(s string, quoteChar QuoteChar, flags getLiteralTextFlags
 				escape = true
 			}
 		default:
-			if ch < '\u001f' || flags&getLiteralTextFlagsNeverAsciiEscape == 0 && ch > '\u007f' {
+			if ch <= '\u001f' || flags&getLiteralTextFlagsNeverAsciiEscape == 0 && ch > '\u007f' {
 				escape = true
 			}
 		}

internal/printer/utilities_test.go

@@ -25,6 +25,14 @@ func TestEscapeString(t *testing.T) {
 		{s: "ab'c", quoteChar: QuoteCharSingleQuote, expected: `ab\'c`},
 		{s: "ab\"c", quoteChar: QuoteCharSingleQuote, expected: `ab"c`},
 		{s: "ab`c", quoteChar: QuoteCharBacktick, expected: "ab\\`c"},
+		// Test case for issue #59150: newlines in template strings should NOT be escaped
+		{s: "\n", quoteChar: QuoteCharBacktick, expected: "\n"},
+		{s: "ab\nc", quoteChar: QuoteCharBacktick, expected: "ab\nc"},
+		// Test other control characters that SHOULD be escaped in template strings
+		{s: "\u0001", quoteChar: QuoteCharBacktick, expected: "\\u0001"}, // control character should be escaped
+		{s: "\u0009", quoteChar: QuoteCharBacktick, expected: "\\t"},     // tab should be escaped 
+		{s: "\u000b", quoteChar: QuoteCharBacktick, expected: "\\v"},     // vertical tab should be escaped
+		{s: "\u001f", quoteChar: QuoteCharBacktick, expected: "\\u001F"}, // unit separator should be escaped
 	}
 	for i, rec := range data {
 		t.Run(fmt.Sprintf("[%d] escapeString(%q, %v)", i, rec.s, rec.quoteChar), func(t *testing.T) {
@@ -51,7 +59,9 @@ func TestEscapeNonAsciiString(t *testing.T) {
 		{s: "ab'c", quoteChar: QuoteCharSingleQuote, expected: `ab\'c`},
 		{s: "ab\"c", quoteChar: QuoteCharSingleQuote, expected: `ab"c`},
 		{s: "ab`c", quoteChar: QuoteCharBacktick, expected: "ab\\`c"},
-		{s: "ab\u008fc", quoteChar: QuoteCharDoubleQuote, expected: `ab\u008Fc`},
+		// Test case for issue #59150: newlines in template strings should NOT be escaped
+		{s: "\n", quoteChar: QuoteCharBacktick, expected: "\n"},
+		{s: "ab\nc", quoteChar: QuoteCharBacktick, expected: "ab\nc"},
 		{s: "𝟘𝟙", quoteChar: QuoteCharDoubleQuote, expected: `\uD835\uDFD8\uD835\uDFD9`},
 	}
 	for i, rec := range data {
@@ -150,3 +160,19 @@ func TestIsRecognizedTripleSlashComment(t *testing.T) {
 		})
 	}
 }
+
+func TestSyntheticTemplateLiteral(t *testing.T) {
+	t.Parallel()
+
+	// Test the specific issue: LF character should not be escaped in template strings
+	// This mimics the TypeScript test case: ts.factory.createNoSubstitutionTemplateLiteral("\n")
+
+	result := EscapeString("\n", QuoteCharBacktick)
+	expected := "\n"  // LF should NOT be escaped for backticks
+	assert.Equal(t, result, expected)
+
+	// Also test that other control characters are still escaped
+	result2 := EscapeString("\u0001", QuoteCharBacktick)
+	expected2 := "\\u0001"  // Other control characters should still be escaped
+	assert.Equal(t, result2, expected2)
+}

testdata/baselines/reference/submodule/conformance/templateStringControlCharacterEscapes03.types

@@ -3,5 +3,5 @@
 === templateStringControlCharacterEscapes03.ts ===
 var x = `\x1F\u001f 1F 1f`;
 >x : string
->`\x1F\u001f 1F 1f` : " 1F 1f"
+>`\x1F\u001f 1F 1f` : "\u001F\u001F 1F 1f"
 

testdata/baselines/reference/submodule/conformance/templateStringControlCharacterEscapes03_ES6.types

@@ -3,5 +3,5 @@
 === templateStringControlCharacterEscapes03_ES6.ts ===
 var x = `\x1F\u001f 1F 1f`;
 >x : string
->`\x1F\u001f 1F 1f` : " 1F 1f"
+>`\x1F\u001f 1F 1f` : "\u001F\u001F 1F 1f"