TypeError: Cannot read properties of undefined (reading 'parent')

[yf-yang]

The problem is this line

eslint-plugin-etc/source/rules/no-internal.ts

Line 64 in e04da45

return typeChecker.getFullyQualifiedName(type.symbol);

Sometimes ts.Type may have an undefined symbol property, instead the aliasSymbol is correct. At least type aliases are using this member, not symbol. Check the esample here
Here is a related stack overflow answer

[yf-yang]

I forgot to provide background, this error occurs in rule no-internal.

[axelboc]

This came up for me when attempting to upgrade to TypeScript 5.1.6.