tsc crashes with typescript@>4.0.0

[anilanar]

TypeScript Version: 4.1.0-dev.20200824

Search Terms: tsc cannot read property 'length' of undefined getResolvedMembersOrExportsOfSymbol symbol.declarations

Problem
tsc crashes after upgrading from 3.9.6 to 4.x.

Code

This problem happens after upgrading typescript on a project with 100k lines of code.
I don't have reproduction but I did my best to figure out what might be going wrong.

The crash stack trace:

TypeError: Cannot read property 'length' of undefined
    at getResolvedMembersOrExportsOfSymbol (/home/aanar/Development/Javascript/projects/Userlike/apps/umf/node_modules/typescript/lib/tsc.js:41835:68)
    at getMembersOfSymbol (/home/aanar/Development/Javascript/projects/Userlike/apps/umf/node_modules/typescript/lib/tsc.js:41868:19)
    at isEmptyAnonymousObjectType (/home/aanar/Development/Javascript/projects/Userlike/apps/umf/node_modules/typescript/lib/tsc.js:46924:60)
    at addTypeToIntersection (/home/aanar/Development/Javascript/projects/Userlike/apps/umf/node_modules/typescript/lib/tsc.js:44587:17)
    at addTypesToIntersection (/home/aanar/Development/Javascript/projects/Userlike/apps/umf/node_modules/typescript/lib/tsc.js:44611:28)
    at getIntersectionType (/home/aanar/Development/Javascript/projects/Userlike/apps/umf/node_modules/typescript/lib/tsc.js:44700:28)
    at instantiateTypeWorker (/home/aanar/Development/Javascript/projects/Userlike/apps/umf/node_modules/typescript/lib/tsc.js:46192:25)
    at instantiateType (/home/aanar/Development/Javascript/projects/Userlike/apps/umf/node_modules/typescript/lib/tsc.js:46166:26)
    at getReturnTypeOfSignature (/home/aanar/Development/Javascript/projects/Userlike/apps/umf/node_modules/typescript/lib/tsc.js:43416:47)
    at checkCallExpression (/home/aanar/Development/Javascript/projects/Userlike/apps/umf/node_modules/typescript/lib/tsc.js:56186:30)

So the crash happens in the first line of the following for loop, while trying to iterate symbol.declarations which is undefined:

  for (var _i = 0, _a = symbol.declarations; _i < _a.length; _i++) {
      var decl = _a[_i];
      var members = ts.getMembersOfDeclaration(decl);
      if (members) {
          for (var _b = 0, members_5 = members; _b < members_5.length; _b++) {
              var member = members_5[_b];
              if (isStatic === ts.hasStaticModifier(member) && hasLateBindableName(member)) {
                  lateBindMember(symbol, earlySymbols, lateSymbols, member);
              }
          }
      }
  }

I modified tsc.js to place some console.log statements. Right before the line that causes the crash:

  if (!symbol.declarations) {
    console.log(symbol);
  }

The result:

Symbol {
  flags: 33556480,
  escapedName: '__type',
  declarations: undefined,
  valueDeclaration: undefined,
  id: undefined,
  mergeId: undefined,
  parent: undefined,
  checkFlags: 0,
  type: Type {
    flags: 524288,
    id: 107,
    objectFlags: 16,
    symbol: [Circular *1],
    members: Map(1) { 'default' => [Symbol] },
    properties: [ [Symbol] ],
    callSignatures: [],
    constructSignatures: [],
    stringIndexInfo: undefined,
    numberIndexInfo: undefined
  },
  resolvedMembers: Map(0) {}
}

If I console.log(symbol.type.propertires) or symbol.type.members, I notice that it's pointing to @types/react-redux/index.d.ts.

It looks like it works when the for loop for symbol.declarations is wrapped with an if condition as below:

// The crash is due to `symbol.declarations` being undefined. So my naive workaround:
if (symbol.declarations) {
  for (var _i = 0, _a = symbol.declarations; _i < _a.length; _i++) {
      var decl = _a[_i];
      var members = ts.getMembersOfDeclaration(decl);
      if (members) {
          for (var _b = 0, members_5 = members; _b < members_5.length; _b++) {
              var member = members_5[_b];
              if (isStatic === ts.hasStaticModifier(member) && hasLateBindableName(member)) {
                  lateBindMember(symbol, earlySymbols, lateSymbols, member);
              }
          }
      }
  }
}

If there's anything more I can help with, please let me know.

[RyanCavanaugh]

Thanks for the debugging on this!

[anilanar]

Edit: Nevermind, I can reproduce this in dozens of other places.

Well, after some digging with try/catch and ts.getSourceFileOfNode, I figured out the file that causes it and created minimal (to my knowledge) reproduction.

It seems it has something to do with dynamic import and esModuleInterop.

Reproduction: https://github.com/anilanar/tscbug

"esModuleInterop": true stops the crashing.

[sandersn]

Here's a standalone repro:

// @esModuleInterop: true
// @file:empty-export.d.ts
export {}
// @file:index.ts
declare function mock<M>(_: M): {} & M;
mock(await import('./empty-export'))

Edit: For me, I had to turn ON esModuleInterop. Here's the command line I'm using:

tsc --noemit --skiplibcheck --strict --esModuleInterop ~/src/test/index.ts

This was true for the tscbug repo as well.

[sandersn]

The type is the shim type created for a module by esModuleInterop. It has an export named 'default' that's an alias for the empty-export module. However, the shim type's symbol has no declarations, is missing a bunch of other properties, but is marked with TypeLiteral flags (among others). I don't know what to make of it.

I'm not sure whether the shim type's symbol shouldn't be used anywhere, or whether the mapped type instantiation should be dereferencing or ignoring the shim, or whether the shim needs to better stand in for a real type/symbol. @weswigham any ideas?

[sandersn]

PR that introduces this crash is #38673
@ahejlsberg

[weswigham]

but is marked with TypeLiteral flags (among others)

Iirc, its marked as a literal because module objects get marked at literals so they can have inferred index signatures during assignment (since they're immutable). Honestly we should probably just err on the side of being better at handling a symbol without declarations more gracefully (the esmodule synthetic symbol is far from the only one without a declaration).

[artaommahe]

When new version with this fix will be released? Faced this crash while upgrading monorepo with angular projects to ng10 and ts 4.0.2..

[JackCA]

And FWIW, I'm still getting this on v4.0.3

[anilanar]

@artaommahe @JackCA Please try beta which is prerelease 4.1.0.