TypeError: Cannot read properties of undefined (reading '0') - weird errors

[rubiesonthesky]

🐛 Bug Report

• TypeStat version: 0.7.2
• TypeScript version: 4.9.5
• Node version: 20.10.0

Actual Behavior

There are a lot errors like this when I try to run the tool

Error in <project_path>/<path>/<file>.ts at node 'export interface ApiResponse {
  deleted: number;
  errors: string[];
}' (position 1652):
	TypeError: Cannot read properties of undefined (reading '0')
	    at Object.expandReferencesForGenericTypes (<project_path>/node_modules/typestat/src/mutators/builtIn/fixIncompleteTypes/fixIncompleteInterfaceOrTypeLiteralGenerics/collectGenericNodeReferences.js:79:77)
	    at Object.collectGenericNodeReferences (<project_path>/node_modules/typestat/src/mutators/builtIn/fixIncompleteTypes/fixIncompleteInterfaceOrTypeLiteralGenerics/collectGenericNodeReferences.js:35:20)
	    at visitInterfaceOrTypeLiteral (<project_path>/node_modules/typestat/src/mutators/builtIn/fixIncompleteTypes/fixIncompleteInterfaceOrTypeLiteralGenerics/index.js:35:66)
	    at tryGetMutation (<project_path>/node_modules/typestat/src/mutators/collectMutationsFromNodes.js:46:16)
	    at visitNode (<project_path>/node_modules/typestat/src/mutators/collectMutationsFromNodes.js:33:30)
	    at visitNodes (<project_path>/node_modules/typescript/lib/typescript.js:31216:30)
	    at forEachChildInSourceFile (<project_path>/node_modules/typescript/lib/typescript.js:31575:20)
	    at Object.forEachChild (<project_path>/node_modules/typescript/lib/typescript.js:31990:47)
	    at Object.collectMutationsFromNodes (<project_path>/node_modules/typestat/src/mutators/collectMutationsFromNodes.js:40:8)
	    at fixIncompleteInterfaceOrTypeLiteralGenerics (<project_path>/node_modules/typestat/src/mutators/builtIn/fixIncompleteTypes/fixIncompleteInterfaceOrTypeLiteralGenerics/index.js:30:94)

Also, some places imports are overwritten like this. Not sure if these are connected. They do not seem to, but you never know.

-import {SearchApiService} from '../services/search-api.service';
+import {SearchApiService} from '../service | List<T>s/search-api.service';

Expected Behavior

Not throw weirds errors without explanation.

Reproduction

I have been trying with few different setups, but here is latest

{
  "include": [
    "src/**/*.ts"
  ],
  "filters": [
    "CallExpression[expression.text=suiteTeardown]",
    "CallExpression[expression.text=teardown]",
    "MethodDeclaration[name.text=dispose]"
  ],
  "fixes": {
    "incompleteTypes": true
  },
  "types": {
    "matching": [
      "^(null|undefined)$"
    ],
    "onlyPrimitives": true,
    "strictNullChecks": true
  }
}

Unfortunately, this is not a repo I can share straight away. It's Angular project, so there are legacy/experimental decorators for example. Strict options look like this

    "experimentalDecorators": true,
    "alwaysStrict": true,
    "noImplicitAny": false,
    "noImplicitOverride": false,
    "noImplicitReturns": true,
    "noImplicitThis": true,
    "strictBindCallApply": true,
    "strictFunctionTypes": true,
    "strictNullChecks": false,
    "strictPropertyInitialization": false,
    "useUnknownInCatchVariables": true

I think this code that the error points to this.

        // Find the index of the corresponding type argument in the instantation of the node,
        // and finally use that to grab the node for the template parameter from the type argument's index
        const typeArgumentIndex = templatedParentInstantiation.typeArguments.indexOf(referencingNode);
        const templateDeclaredTypeNode = templatedDeclaration.typeParameters[typeArgumentIndex];

---

I have tried to restrict to run only on some files, and I suspect that Angular decorators are one culprit here.

[JoshuaKGoldberg]

Thanks for posting! I tried playing a bit with experimental decorators locally but couldn't figure out how to reproduce this error. 😕

@rubiesonthesky I'd be happy to sign an NDA and take a look at the code privately. Otherwise, without a reproduction, I'm stuck here.

[rubiesonthesky]

I think, version 0.7.3 fixed the problem where with messing up imports.

I'm still getting a lot errors in the console though with same message TypeError: Cannot read properties of undefined (reading '0'). But I feel we are getting closer to the problem.

[rubiesonthesky]

I found a way to reproduce this! :D

Use typestat in this repo with npx -g typestat and with typestat.json

{
    "fixes": {
        "incompleteTypes": true
    },
    "include": [
        "src/**/*.{ts,tsx}"
    ],
    "projectPath": "tsconfig.json"
}

Error

Error in //TypeStat/src/mutators/builtIn/fixIncompleteTypes/fixIncompleteReactTypes/fixReactPropFunctionsFromCalls/createFunctionCallTypesMutation.ts at node 'interface CombinedFunctionType {
        parameters: ts.Type[][];
        returnValue?: ts.Type[];
}' (position 413):
        TypeError: Cannot read properties of undefined (reading '0')
            at expandReferencesForGenericTypes (/.npm/_npx/42ab35185b79194c/node_modules/typestat/src/mutators/builtIn/fixIncompleteTypes/fixIncompleteInterfaceOrTypeLiteralGenerics/collectGenericNodeReferences.js:83:77)
            at collectGenericNodeReferences (/.npm/_npx/42ab35185b79194c/node_modules/typestat/src/mutators/builtIn/fixIncompleteTypes/fixIncompleteInterfaceOrTypeLiteralGenerics/collectGenericNodeReferences.js:39:56)
            at visitInterfaceOrTypeLiteral (/.npm/_npx/42ab35185b79194c/node_modules/typestat/src/mutators/builtIn/fixIncompleteTypes/fixIncompleteInterfaceOrTypeLiteralGenerics/index.js:39:99)
            at tryGetMutation (/.npm/_npx/42ab35185b79194c/node_modules/typestat/src/mutators/collectMutationsFromNodes.js:50:16)
            at visitNode (/.npm/_npx/42ab35185b79194c/node_modules/typestat/src/mutators/collectMutationsFromNodes.js:37:30)
            at visitNodes (/.npm/_npx/42ab35185b79194c/node_modules/typestat/node_modules/typescript/lib/typescript.js:28303:24)
            at forEachChildInSourceFile (/.npm/_npx/42ab35185b79194c/node_modules/typestat/node_modules/typescript/lib/typescript.js:28946:18)
            at Object.forEachChild (/.npm/_npx/42ab35185b79194c/node_modules/typestat/node_modules/typescript/lib/typescript.js:28388:37)
            at collectMutationsFromNodes (/.npm/_npx/42ab35185b79194c/node_modules/typestat/src/mutators/collectMutationsFromNodes.js:44:8)
            at fixIncompleteInterfaceOrTypeLiteralGenerics (/.npm/_npx/42ab35185b79194c/node_modules/typestat/src/mutators/builtIn/fixIncompleteTypes/fixIncompleteInterfaceOrTypeLiteralGenerics/index.js:34:124)

[rubiesonthesky]

I'm seeing this also in mutation tests.

original.ts:

import ts from "typescript";

(function () {
	interface FunctionCallType {
		parameters?: (ts.Type | undefined)[];
		returnValue?: ts.Type;
	}
	interface CombinedFunctionType {
		parameters: ts.Type[][];
		returnValue?: ts.Type[];
	}

	const functionCallTypes: FunctionCallType[] = [];
	const combinedType = functionCallTypes.reduce<CombinedFunctionType>(
		(accumulator, functionCallType) => {
			return {
				parameters: combineParameters(
					undefined,
					accumulator.parameters,
					functionCallType.parameters,
				),
				returnValue: collectOptionals(accumulator.returnValue, [
					functionCallType.returnValue,
				]).filter(isNotUndefined),
			};
		},
		{
			parameters: [],
			returnValue: [],
		},
	);

	const combineParameters = (
		request: unknown,
		previous: ts.Type[][],
		next: (ts.Type | undefined)[] | undefined,
	) => {
		if (next === undefined) {
			return previous;
		}

		const combined: ts.Type[][] = [];
		let i: number;

		for (i = 0; i < previous.length; i += 1) {
			combined.push([...previous[i]]);

			if (i < next.length && next[i] !== undefined) {
				// eslint-disable-next-line @typescript-eslint/no-non-null-assertion
				combined[i].push(next[i]!);
			}
		}

		for (i; i < next.length; i += 1) {
			if (next[i] !== undefined) {
				// eslint-disable-next-line @typescript-eslint/no-non-null-assertion
				combined.push([next[i]!]);
			}
		}

		return combined;
	};

	const collectOptionals = <T>(
		...arrays: (readonly T[] | undefined)[]
	): T[] => {
		const results: T[] = [];

		for (const array of arrays) {
			if (array !== undefined) {
				results.push(...array);
			}
		}

		return results;
	};

	const isNotUndefined = <T>(item: T | undefined): item is T =>
		item !== undefined;
})();

This could probably be simplified a lot from this.