Unexpected circularity error when variable is initialized from a class member

🔎 Search Terms

loss of type, for loop, for-loop, class field

🕗 Version & Regression Information

This changed between versions ______ and _______
This changed in commit or PR _______
This is the behavior in every version I tried, and I reviewed the FAQ for entries about _________
I was unable to test this on prior versions because _______

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/JYOwLgpgTgZghgYwgAgIIAd0BtgLmYAexGQG8AoZK5YAEwC5kBnMKUAcwG5zLq9J2hKAE9GFahJoNmrDtwkBfckvIIscJkzSYc-IiC3jq6AK4AjXcgBioWhmy58+gBQBHE9FEy2IdgEpGe10nYmQAH2QQEywsMl5JZCgIMBMoEiiY+WolFTUNLQAVCBY4iQBlCCwIBEg7HUcCYiZGCrAAHhYfdgA+ZABeSIgAd2RW5z8sqiCG-WbtBz0m8Mjo2IGMrEnkdmTRyura6cWDACFhAGF8CEERccYABTgoAjgsNoAlaqFaDtlfABo9u1OhxumDlhtSglkAB6GHIADqQgA1k9CCYQLRkABGRgAW0IADcUGAABbALQWQgIZE0Ax0FAwITILCEQjoeKSOGIlFojFYgBMLTgxOQAAMyRSAHRHEIGMXIMCEZBwZAIJpgRWkiAkExMEmk-CciTAGDIZySpgy+rHLR9e0rGJ+KHQ6hJFJpR2bY3ZHiu9UGTVJJjRMAPJ4vN6fdVQH4ggFA35dMG9AakBTcH1UJlQc0BkpwG1ygCSABFkIQzZapRUqjUIHUFnKmM6jK6qPnNYWm40SANq7Le1abJjBy5u8Fe2WJlnJKbzROZqF7etVq3Z-7iAQohAtq6VO2+Bq1VcbsIy-0VUXe1L+NchMIpXQ99DO1ee7NL8HQwBtO9nssAF1kAAfhAwYRlaJNQXGF8EkXW0pTgWhaGcBC5SfWgZ0PKhuXOQg8TxHUwBhDF1UI4itUZQgYkIIYOBZUASWVfUUGATUzCSOBkVIkBOIgbiNzdYpf3-B8gMvdChzg5AD2hd1UhIb8sDALYciAA

💻 Code

interface Application {
    id: string;

    category: {
        id: string;
    }
}

class Applications {
    public FindApplication(query: string): Application | null {
        return null;
    }
}

class Test {
    SelectedApplications: Set<string> = new Set();
    Applications: Applications | null = null;
    get SelectedApplicationsByCategory(): Partial<Record<string, Set<string>>> | null {
        // Workaround 1: move this block inside for loop
        // Workaround 2: Save this.Applications to a const then use that
        if (this.Applications === null) {
            return null;
        }

        const result: Partial<Record<string, Set<string>>> = {};

        for (const applicationID of this.SelectedApplications) {
            const application = this.Applications.FindApplication(applicationID);
            if (application === null) {
                continue;
            }

            const categoryID = application.category.id;
            const applications = result[categoryID] ?? new Set<string>();
            applications.add(application.id);
            // Comment/uncomment the following line to see it break/unbreak
            result[categoryID] = applications;
        }

        return result;
    }
}

🙁 Actual behavior

application has type: any. FindApplication returns Application | null, but that gets lost somewhere.

🙂 Expected behavior

type for application should be Application | null.

Additional information about the issue

See comments in code for workarounds and to see another line break type inference.

Smallest repro I could find. Very weird.

interface Application {
    id: number;
}

const result: boolean[] = [];

class Test {
    appArray: Application[] | null = null;

    foo(): void {
        if (this.appArray === null) {
            return;
        }

        for (const idx of [0, 1]) {
            const app = this.appArray[idx];
            const categoryID = app.id;
            result[categoryID] = true;
        }
    }
}

Bisects to #45974

Shorter, looking at the PR

const result: boolean[] = [];
class Test {
    appArray: number[] | null = null;
    foo(): void {
        if (this.appArray === null) {
            return;
        }
        for (let i = 0; i < 1; i++) {
            const app = this.appArray[0];
            const appRef = app;
            result[appRef] = true;
        }
    }
}

Check target equivalence in isMatchingReference before computing prop…

Another workaround is to add the type annotation.

const result: boolean[] = [];
class Test {
    appArray: number[] | null = null;
    foo(): void {
        if (this.appArray === null) {
            return;
        }
        for (let i = 0; i < 1; i++) {
            const app: number = this.appArray[0]; // <- like this
            const appRef = app;
            result[appRef] = true;
        }
    }
}

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Unexpected circularity error when variable is initialized from a class member #61606

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Unexpected circularity error when variable is initialized from a class member #61606

Description

🔎 Search Terms

🕗 Version & Regression Information

⏯ Playground Link

💻 Code

🙁 Actual behavior

🙂 Expected behavior

Additional information about the issue

Activity

RyanCavanaugh commented on Apr 22, 2025

RyanCavanaugh commented on Apr 22, 2025

RyanCavanaugh commented on Apr 22, 2025

carlosalmonte04 commented on Jul 7, 2025

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