TypeScript's code formatting corrupts code containing a numeric literal

[evanw]

Bug Report

🔎 Search Terms

formatter number tostring

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

Playground link with relevant code

💻 Code

1+ 2 .toString() +3

🙁 Actual behavior

When you run "Format Document" the code is changed to 1 + 2.toString() + 3, which is invalid JavaScript.

🙂 Expected behavior

Several valid formatting outputs include the following:

1 + 2 .toString() + 3
1 + 2..toString() + 3
1 + (2).toString() + 3

This is a problem for VSCode users because it means that saving a file in VSCode corrupts the file (if you have format-on-save enabled). And it's a problem for me as the author of esbuild because people are running VSCode's formatter on esbuild's output and then reporting the corrupted code as a bug in esbuild: evanw/esbuild#2528.

Side note: How to run TypeScript's formatter yourself

I had to manually run TypeScript's formatter to confirm that the problem was with the code in this repo. Running TypeScript's formatter on a string was unexpectedly difficult because the API is not exposed and is only available through the language server protocol, which seemed way too complicated to invoke manually. I instead used a hack that loads the code in tsserver.js to get to the formatter. Posting the hack here for posterity:

const input = '1+ 2 .toString() +3'
const process = undefined
const addEventListener = () => {}
var ts = {}
const serverFile = require.resolve('typescript/lib/tsserver')
const serverCode = require('fs').readFileSync(serverFile, 'utf8')
eval(serverCode.replace('\n"use strict";\n', ''))
const sourceFile = ts.createSourceFile('in.js', input)
const options = ts.getDefaultFormatCodeSettings()
const context = ts.formatting.getFormatContext(options, {})
const changes = ts.formatting.formatDocument(sourceFile, context)
console.log('before:', input)
console.log('after:', ts.textChanges.applyChanges(input, changes))

[fatcerberus]

TIL 2 .toString() is not a syntax error (I thought you either had to put the literal in parens or else write 2..toString()).