Compiler crash on exports.fn pattern

[mihailik]

Bug Report

🔎 Search Terms

🕗 Version & Regression Information

• This is a crash
• This changed between versions 4.0.5 and 4.1.3

⏯ Playground Link

2-line example

💻 Code

exports.fn1();
exports.fn2 = Math.min;

🙁 Actual behavior

Crashing:

TypeError: Cannot read property 'length' of undefined
    at getPropertyOfType (C:\Users\mihai\danfo\node_modules\typescript\lib\tsc.js:44083:45)
    at getTypeOfDottedName (C:\Users\mihai\danfo\node_modules\typescript\lib\tsc.js:52423:44)
    at getEffectsSignature (C:\Users\mihai\danfo\node_modules\typescript\lib\tsc.js:52436:32)
    at getTypeAtFlowCall (C:\Users\mihai\danfo\node_modules\typescript\lib\tsc.js:52755:33)
    at getTypeAtFlowNode (C:\Users\mihai\danfo\node_modules\typescript\lib\tsc.js:52636:32)
    at getFlowTypeOfReference (C:\Users\mihai\danfo\node_modules\typescript\lib\tsc.js:52593:51)      
    at checkIdentifier (C:\Users\mihai\danfo\node_modules\typescript\lib\tsc.js:53580:28)
    at checkExpressionWorker (C:\Users\mihai\danfo\node_modules\typescript\lib\tsc.js:59973:28)       
    at checkExpression (C:\Users\mihai\danfo\node_modules\typescript\lib\tsc.js:59928:38)
    at checkNonNullExpression (C:\Users\mihai\danfo\node_modules\typescript\lib\tsc.js:55612:37)      

This is running tsc.js with: node --inspect-brk node_modules\typescript\lib\tsc.js repor.js --out repor.out.js --allowJs and some state in context:

🙂 Expected behavior

Transpile, don't crash. Can produce errors/warnings, but not crash.

Background

This happened when I tried to run TypeScript over the latest CodeMirror, and stumbled upon the file runmode.node.js (see on unpkg). Then, simplified to the minimal reproduction case.

As you can see from the caught error above, resolved.callSignatures is undefined and that causes throw here.

I assume this happens because exports isn't treated as a normal global variable even in a variable position. But in variable position it should be treated as a variable.

Note: can't simplify any more, both lines are necessary. Which means it's not just bad handling of exports, but something more conspiratorial.

[mihailik]

Sorry, I think it really should be more urgent than 4.3.0.

It's not an obscure bug, TypeScript currently crashes on CodeMirror -- arguably the most basic core library on the web, everyone on here touches it daily in Sources and Console tab of DevTools.

[RyanCavanaugh]

Is the regression information accurate? 4.1 came out two months ago and this is the first we've heard of it, which would indicate this isn't as critical as you're describing.

[eventualbuddha]

I don't have much to contribute in terms of helping identify why this happens, but I ran into it while trying to move from yarn to pnpm: votingworks/vxsuite#146. Downgrading to TS 4.0.5 fixed it.

[minestarks]

Already fixed, but repro at https://github.com/microsoft/tsserverfuzzer/issues/299