bug(Printer): LF newline in template strings is escaped when it shouldn't be

[maxpatiiuk]

🔎 Search Terms

template strings new line newline escape LF backslash emit print

🕗 Version & Regression Information

• This changed in commit 635f5bd. PR: Some tweaks for backtick strings #45099

⏯ Playground Link

https://github.com/maxpatiiuk/typescript-bug-needless-lf-escaping/tree/main

💻 Code

import ts from 'typescript';

const expression = ts.factory.createNoSubstitutionTemplateLiteral('\n');

const printer = ts.createPrinter();
// LF new line gets escaped by the printer:
const printed = printer.printNode(
  ts.EmitHint.Unspecified,
  expression,
  ts.createSourceFile('index.ts', '', ts.ScriptTarget.Latest)
);

// Expected \n
// Received \\n
console.log(printed);
if (printed === '`\n`') console.log('Correct');
else if (printed === '`\\n`') console.error('Incorrect');

🙁 Actual behavior

LF new lines in template literal strings are escaped

🙂 Expected behavior

As the comment in TypeScript's source code states, LF new lines in backticks should not be escaped:

// Template strings preserve simple LF newlines, still encode CRLF (or CR)
const backtickQuoteEscapedCharsRegExp = /\r\n|[\\`\u0000-\u001f\t\v\f\b\r\u2028\u2029\u0085]/g;

https://github.com/microsoft/TypeScript/blame/3163fe7e3898c1f48cd9bc097b96e3426cd2a453/src/compiler/utilities.ts#L5925-L5926

However, that RegExp has a bug - the regex has a \u0000-\u001f character range, which includes the LF character (\u000a)

/[\u0000-\u001f]/.test('\n')
// -> true

The RegExp should be modified to not match \u000a (\n). Potentially like so:

- const backtickQuoteEscapedCharsRegExp = /\r\n|[\\`\u0000-\u001f\t\v\f\b\r\u2028\u2029\u0085]/g;
+ const backtickQuoteEscapedCharsRegExp = /\r\n|[\\`\u0000-\u0009\u000b-\u001f\t\v\f\b\r\u2028\u2029\u0085]/g;

Additional information about the issue

No response