Cannot read properties of undefined (reading 'length')

Bug Report

🔎 Search Terms

Cannot read properties of undefined, tsc crash

🕗 Version & Regression Information

First noticed on 5.0.0-dev.20221118 nightly build, persists on 5.0.0-dev.20221122

⏯ Playground Link

https://www.typescriptlang.org/play?module=1&ts=5.0.0-dev.20221122#code/KYDwDg9gTgLgBDAnmYcBiEIB4AqcC8cAzjFAJYB2A5gHwFwDeAvgNwBQbA9J3AAIBmZADbAKAQwC2wAFxxBIgEwA6GEQ5kJkWIwwQmcqBAlwA5Es6UwAVxgn2bflYoBjGGQgU4AIzFRcNAApgESkKGFldAEpGNjg4KGAYKyhPAEZ2Jg4fKADUuDEidEwsCisJL2AoGkiWIA

💻 Code

// main.ts
import {Foo} from './x';

function bar<T>(element: Foo) {
  return 1;
}

bar(1 as Foo<number>);

// x.ts
export type Foo<T = string> = {};

🙁 Actual behavior

A crash:

/usr/local/lib/node_modules/typescript/lib/tsc.js:98593
      throw e;
      ^

TypeError: Cannot read properties of undefined (reading 'length')
    at inferFromTypeArguments (/usr/local/lib/node_modules/typescript/lib/tsc.js:55506:54)
    at inferFromTypes (/usr/local/lib/node_modules/typescript/lib/tsc.js:55314:11)
    at inferTypes (/usr/local/lib/node_modules/typescript/lib/tsc.js:55300:5)
    at inferTypeArguments (/usr/local/lib/node_modules/typescript/lib/tsc.js:61051:11)
    at chooseOverload (/usr/local/lib/node_modules/typescript/lib/tsc.js:61672:33)
    at resolveCall (/usr/local/lib/node_modules/typescript/lib/tsc.js:61539:16)
    at resolveCallExpression (/usr/local/lib/node_modules/typescript/lib/tsc.js:61870:12)
    at resolveSignature (/usr/local/lib/node_modules/typescript/lib/tsc.js:62215:16)
    at getResolvedSignature (/usr/local/lib/node_modules/typescript/lib/tsc.js:62235:20)
    at checkCallExpression (/usr/local/lib/node_modules/typescript/lib/tsc.js:62340:23)

🙂 Expected behavior

Success or compilation errors.

Running git bisect with this repro shows the error popped up at a3092c7 (#51152).

This particular error goes away with this patch (unfortunately, it breaks other things though):

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 92a989a2bc..394fa24674 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -14901,7 +14901,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                     const resolved = resolveAlias(aliasSymbol);
                     if (resolved && resolved.flags & SymbolFlags.TypeAlias) {
                         newAliasSymbol = resolved;
-                        aliasTypeArguments = typeArgumentsFromTypeReferenceNode(node);
+                        aliasTypeArguments = getTypeArgumentsForAliasSymbol(newAliasSymbol);
                     }
                 }
             }

I'm not entirely sure if this patch produces a correct result for this test case as I'm not entirely sure what to expect out of the .types and .symbols snapshots here. It compiles and doesn't produce any errors though.

Fix microsoft#51623

Fix #51623 (#51762)

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Cannot read properties of undefined (reading 'length') #51623

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Cannot read properties of undefined (reading 'length') #51623

Description

Bug Report

🔎 Search Terms

🕗 Version & Regression Information

⏯ Playground Link

💻 Code

🙁 Actual behavior

🙂 Expected behavior

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nicolas377 commented on Nov 22, 2022

Andarist commented on Nov 23, 2022

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