Declared but its Value is Never Read

Oct 13, 2025 by leolavanderia.com.br 57 views

Declared but its Value is Never Read

In the world of programming, it's essential to keep track of variables and their usage. However, sometimes, the editor may not accurately report unused local variables, leading to confusion and potential bugs. This article delves into the issue of unreliably reported unused local variables in the editor, exploring the problem, its causes, and the expected behavior.

The Problem

The problem arises when the editor fails to reliably report unused local variables. This can be frustrating, especially when working on complex projects. The issue is not limited to a specific version of the editor, as it has been observed in every version tried. The FAQ has been reviewed for common misconceptions, but none seem to address this specific issue.

Reproducing the Issue

To reproduce the issue, a simple code snippet can be used:

function hi() {
  let { offsetWidth = 1 } = { offsetWidth: 0 };

  offsetWidth = 1;
}

This code declares a variable offsetWidth but never reads its value. However, when the noUnusedLocals flag is set to true, the editor fails to report the unused variable. This can be observed in the TypeScript Playground:

https://www.typescriptlang.org/play/?noUnusedLocals=true#code/GYVwdgxgLglg9mABACxgCgJSIN4CgCQANgKZQ6JzDADOpA6jACZTKIC8iAjIgL7vmUa9JiwBciAAy8A3LgKDaUBs1YdOsvriA

Actual Behavior

The actual behavior is that the hint about unused local variables is not reliably reported in the editor. This can be confusing, especially when working on complex projects. The issue seems to be related to a race condition where Symbol.isReferenced is populated in another language feature before typecheck. This can cause the hint to be hidden, making it difficult to identify unused variables.

Semantic Highlight as a Reproduction Method

Semantic highlight is the most reliable way to reproduce the issue. To do this:

Open VSCode with a color theme that supports semantic highlight, such as the default dark+.
Paste the code to a ts file and observe the hint not being reported.
Restart TSServer, and the hint is now reported. However, editing the file hides the hint again.

Expected Behavior

The expected behavior is that the hint about unused local variables is reliably reported in the editor, regardless of other features checking the variable. This would make it easier to identify and remove unused variables, improving code quality and reducing the risk of bugs.

Additional Information about the Issue

Unfortunately, there is no additional information available about the issue, as there has been no response to the report.

Conclusion

Frequently Asked Questions

In this article, we'll address some of the most common questions related to the issue of unreliably reported unused local variables in the editor.

Q: What is the cause of the issue?

A: The cause of the issue seems to be related to a race condition where Symbol.isReferenced is populated in another language feature before typecheck.

Q: How can I reproduce the issue?

A: To reproduce the issue, you can use the following steps:

Open VSCode with a color theme that supports semantic highlight, such as the default dark+.
Paste the code to a ts file and observe the hint not being reported.
Restart TSServer, and the hint is now reported. However, editing the file hides the hint again.

Q: Why is the hint not being reported?

A: The hint is not being reported because of the race condition mentioned earlier. This can cause the hint to be hidden, making it difficult to identify unused variables.

Q: Is this issue specific to a particular version of the editor?

A: No, this issue has been observed in every version of the editor tried.

Q: Can I report this issue to the editor's developers?

A: Yes, you can report this issue to the editor's developers. However, please note that there has been no response to the report so far.

Q: What is the expected behavior?

A: The expected behavior is that the hint about unused local variables is reliably reported in the editor, regardless of other features checking the variable.

Q: How can I improve the editor's behavior in this regard?

A: To improve the editor's behavior, you can try the following:

Report the issue to the editor's developers.
Provide more information about the issue, such as the code snippet that reproduces the issue.
Try to identify the root cause of the issue and provide a solution.

Q: Is there any workaround for this issue?

A: Yes, one workaround for this issue is to use semantic highlight to identify unused variables. However, this may not be a reliable solution, as the hint may still be hidden in some cases.

Q: Can I get help from the community to resolve this issue?

A: Yes, you can get help from the community to resolve this issue. You can post about the issue on forums, social media, or other online platforms to get more information and potential solutions.

Q: What is the next step in resolving this issue?

A: The next step in resolving this issue is to report it to the editor's developers and provide more information about the issue. This will help the developers to identify the root cause of the issue and provide a solution.

Conclusion

In conclusion, the issue of unreliably reported unused local variables in the editor is a significant problem that can cause confusion and potential bugs. By understanding the cause of the issue, reproducing it, and reporting it to the editor's developers, we can work towards resolving this issue and improving the editor's behavior.