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1. Ryan Cavanaugh (RyanCavanaugh)

   added

   Needs InvestigationThis issue needs a team member to investigate its status.This issue needs a team member to investigate its status.

   on Feb 17, 2023
2. Ryan Cavanaugh (RyanCavanaugh)

   assigned

   Gabriela Araujo Britto (gabritto)

   on Feb 17, 2023
3. Ryan Cavanaugh (RyanCavanaugh)

   added this to the TypeScript 5.1.0 milestone on Feb 17, 2023
4. gabritto commented on Feb 23, 2023

   

   Gabriela Araujo Britto (gabritto)

   on Feb 23, 2023

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   Hi Frank Weindel (@frank-weindel), I have been trying to reproduce this using the instructions you left, but so far I wasn't able to. If you're still able to repro this, could you repro it with logging enabled on tsserver, and post the tsserver logs here? That would help me investigate this issue. Thank you.

   In case you don't already know how to do get a tsserver log:
   (1) You can enable logging on vscode by going to your settings and looking for "Tsserver: log" setting, and setting it to "verbose".
   

   (2) Once you have logging enabled, and you manage to reproduce the issue, you can then open the log by running the "TypeScript: Open TS Server log" command on vscode:
   
5. frank-weindel commented on Feb 23, 2023

   

   Frank Weindel (frank-weindel)

   on Feb 23, 2023

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   As requested!

   • tsserver-issue-52813.log

   Specifically what I did to reproduce was:

   • Open Stepper.ts in a tab
   • Restart TS Server to clear error
   • Use Cmd+P to open ProgressStepper.ts
   • Remove the unnecessary trailing comma on line 9 of ProgressStepper.ts
   • Without needing to even save, Stepper.ts lights up with the error

   👍React with 👍1Reacted by Gabriela Araujo Britto
6. gabritto commented on Mar 3, 2023

   

   Gabriela Araujo Britto (gabritto)

   on Mar 3, 2023

   Last edited by gabritto

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   I think the following program captures the essence of this issue:

   interface Some {}
   
   class Foo<T=Some> {
       num: number = 0;
       Field: number = (this as Foo).num;
       Value = (this as Foo).num; // Ok
   }

   You don't get the circularity error reported on the above program, but you do get the error if you swap the Field and Value declarations:

   interface Some {}
   
   class Foo<T=Some> {
       num: number = 0;
       Value = (this as Foo).num; // Error
       Field: number = (this as Foo).num;
   }

   Playground link

   Essentially, what is happening is that, if we type check property Field first, we succeed and we cache some types and variances, so that when we then type check Value, we don't run into a circularity and everything works. If we start by type checking Value instead, we run into a circularity. So whether we get the circularity error or not depends on the order in which we check those properties.

   Translating that to the original reported issue, what happens is that, when we run the checker via tsc, we type check file Stepper.ts and then we check file ProgressStepper.ts. In an editor context, we sometimes check ProgressStepper.ts and then we check Stepper.ts, and when that happens, the circularity error is reported.
7. RyanCavanaugh commented on Mar 3, 2023

   

   Ryan Cavanaugh (RyanCavanaugh)

   on Mar 3, 2023

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   Does adding variance annotation(s) to Stepper fix the issue?
8. gabritto commented on Mar 3, 2023

   

   Gabriela Araujo Britto (gabritto)

   on Mar 3, 2023

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   Does adding variance annotation(s) to Stepper fix the issue?

   Yes, computing variance for Stepper is how we run into the circularity when type checking Value.
9. RyanCavanaugh commented on Mar 3, 2023

   

   Ryan Cavanaugh (RyanCavanaugh)

   on Mar 3, 2023

   Last edited by RyanCavanaugh

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   Here's a variant repro I was trying out

   function f() {
       const b = new Bar();
       // Uncomment to create error
       // console.log(b.Value);
   }
   
   class Bar<T> {
       num!: number;
       // Or swap these two lines
       Field: number = (this as Bar<any>).num;
       Value = (this as Bar<any>).num;
   }

   👍React with 👍1Reacted by Gabriela Araujo Britto
10. TypeScript Bot (typescript-bot)

    added

    Fix AvailableA PR has been opened for this issueA PR has been opened for this issue

    on Mar 20, 2023
11. Gabriela Araujo Britto (gabritto)

    closed this as completedin #53261on Mar 23, 2023
12. Kirk Ouimet (kirkouimet)

    added a commit that references this issue on Oct 6, 2026

    checker: a circular generic type's variances no longer depend on wher…

    ...

    740c377