Fix template string escaping per TypeScript PR #60303

Co-authored-by: andrewbranch <3277153+andrewbranch@users.noreply.github.com>

Author: Copilot

internal/printer/printer_test.go

@@ -28,6 +28,7 @@ func TestEmit(t *testing.T) {
 		{title: "BooleanLiteral#1", input: `true`, output: `true;`},
 		{title: "BooleanLiteral#2", input: `false`, output: `false;`},
 		{title: "NoSubstitutionTemplateLiteral", input: "``", output: "``;"},
+		{title: "NoSubstitutionTemplateLiteral#2", input: "`\n`", output: "`\n`;"},
 		{title: "RegularExpressionLiteral#1", input: `/a/`, output: `/a/;`},
 		{title: "RegularExpressionLiteral#2", input: `/a/g`, output: `/a/g;`},
 		{title: "NullLiteral", input: `null`, output: `null;`},

internal/printer/template_escaping_test.go

@@ -0,0 +1,40 @@
+package printer_test
+
+import (
+	"testing"
+
+	"github.com/microsoft/typescript-go/internal/ast"
+	"github.com/microsoft/typescript-go/internal/testutil/emittestutil"
+	"github.com/microsoft/typescript-go/internal/testutil/parsetestutil"
+)
+
+// TestTemplateStringEscapingFix tests the fix for TypeScript issue #59150
+// This test mirrors the test case added in TypeScript PR #60303
+func TestTemplateStringEscapingFix(t *testing.T) {
+	t.Parallel()
+
+	// https://github.com/microsoft/TypeScript/issues/59150
+	// Replicates: printsCorrectly("template string", {}, printer =>
+	//   printer.printNode(
+	//     ts.EmitHint.Unspecified,
+	//     ts.factory.createNoSubstitutionTemplateLiteral("\n"),
+	//     ts.createSourceFile("source.ts", "", ts.ScriptTarget.ESNext),
+	//   ));
+
+	var factory ast.NodeFactory
+
+	// Create a synthetic NoSubstitutionTemplateLiteral with just a newline character
+	templateLiteral := factory.NewNoSubstitutionTemplateLiteral("\n")
+
+	// Create a synthetic source file 
+	file := factory.NewSourceFile("/source.ts", "/source.ts", "/source.ts", factory.NewNodeList([]*ast.Node{
+		factory.NewExpressionStatement(templateLiteral),
+	}))
+	ast.SetParentInChildren(file)
+	parsetestutil.MarkSyntheticRecursive(file)
+
+	// The fix ensures that LF newlines are NOT escaped in template literals
+	// Expected: `\n` (with literal newline character, not escaped)
+	// Bug would produce: `\\n` (with escaped newline)
+	emittestutil.CheckEmit(t, nil, file.AsSourceFile(), "`\n`;")
+}

internal/printer/template_string_fix_test.go

@@ -103,8 +103,18 @@ func escapeStringWorker(s string, quoteChar QuoteChar, flags getLiteralTextFlags
 				escape = true
 			}
 		default:
-			if ch < '\u001f' || flags&getLiteralTextFlagsNeverAsciiEscape == 0 && ch > '\u007f' {
-				escape = true
+			// For template strings, exclude \u000a (LF/newline) from the character range that gets escaped
+			// This matches the TypeScript fix in PR #60303 that changed the regex from \u0000-\u001f to \u0000-\u0009\u000b-\u001f
+			if quoteChar == QuoteCharBacktick {
+				// For template strings: escape \u0000-\u0009 and \u000b-\u001f (excluding \u000a which is LF)
+				if (ch >= '\u0000' && ch <= '\u0009') || (ch >= '\u000b' && ch <= '\u001f') || flags&getLiteralTextFlagsNeverAsciiEscape == 0 && ch > '\u007f' {
+					escape = true
+				}
+			} else {
+				// For regular strings: escape \u0000-\u001f as before
+				if ch < '\u001f' || flags&getLiteralTextFlagsNeverAsciiEscape == 0 && ch > '\u007f' {
+					escape = true
+				}
 			}
 		}