Pkg/list: Contains Causes Evaluation Failure Inside A Definition

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Introduction

CUE is a powerful configuration language that allows developers to define and validate data structures. However, like any complex system, it can sometimes exhibit unexpected behavior. In this article, we will explore a specific issue that arises when using the list.Contains function inside a definition.

Issue Description

The issue at hand is that the list.Contains function causes an evaluation failure when used inside a definition. This is demonstrated by the following code snippet:

# file.cue --
package p
import "list"

#Foo: {
        bar: [...int]
        bar: list.Contains(1)
}

When we run the cue vet command on this file, we expect it to pass without any issues. However, the actual output is:

> exec cue vet -c file.cue -d '#Foo' data-good.yml
[stderr]
#Foo.bar: invalid value [] (does not satisfy list.Contains(1)):
    ./file.cue:6:14
    ./file.cue:5:14
    ./file.cue:6:28
[exit status 1]
FAIL: foo.txtar:5: unexpected command failure
failed run

As we can see, the cue vet command fails with an error message indicating that the list.Contains function is not satisfied.

Reproduction Steps

To reproduce this issue, we can use the following steps:

  1. Create a new file called file.cue with the following contents:
# file.cue --
package p
import "list"

#Foo: {
        bar: [...int]
        bar: list.Contains(1)
}
  1. Create two new files called data-bad.yml and data-good.yml with the following contents:
# data-bad.yml --
bar:
  - 2
  - 3

# data-good.yml --
bar:
  - 1
  - 2
  - 3
  1. Run the following command:
exec cue vet -c file.cue -d '#Foo' data-bad.yml
  1. Observe the output, which should indicate that the cue vet command fails with an error message.

Expected Behavior

We expect the cue vet command to pass without any issues, as the list.Contains function is satisfied in both the data-bad.yml and data-good.yml files.

Actual Behavior

However, the actual behavior is that the cue vet command fails with an error message indicating that the list.Contains function is not satisfied.

Possible Causes

There are several possible causes for this issue:

  1. Incorrect usage of list.Contains: The list.Contains function may be used incorrectly, leading to the evaluation failure.
  2. Bug in CUE: There may be a bug in the CUE language or the cue vet command that causes the evaluation failure.
  3. Dependency issues: There may be dependency issues between the list package and other packages that cause the evaluation failure.

Workarounds

To work around this issue, we can try the following:

  1. Use a different function: Instead of using the list.Contains function, we can use a different function that achieves the same result.
  2. Modify the list package: We can modify the list package to fix the issue.
  3. Upgrade CUE: We can upgrade to a newer version of CUE that fixes the issue.

Conclusion

In conclusion, the list.Contains function causes an evaluation failure when used inside a definition in CUE. This issue can be reproduced by using the cue vet command on a file that contains a definition with a list.Contains function. To work around this issue, we can try using a different function, modifying the list package, or upgrading to a newer version of CUE.

Related Issues

This issue may be related to the following issues:

Additional Information

  • CUE version: The CUE version used in this example is v0.13.0-alpha.4.0.20250514105820-c456d085e0c1.
  • Go version: The Go version used in this example is go1.24.0.
  • CUE language version: The CUE language version used in this example is v0.13.0.
    pkg/list: Contains causes evaluation failure inside a definition - Q&A ====================================================================

Q: What is the issue with the list.Contains function in CUE?

A: The list.Contains function causes an evaluation failure when used inside a definition in CUE.

Q: What is the expected behavior of the cue vet command?

A: The expected behavior of the cue vet command is to pass without any issues, as the list.Contains function is satisfied in both the data-bad.yml and data-good.yml files.

Q: What is the actual behavior of the cue vet command?

A: The actual behavior of the cue vet command is that it fails with an error message indicating that the list.Contains function is not satisfied.

Q: What are the possible causes of this issue?

A: There are several possible causes of this issue, including:

  1. Incorrect usage of list.Contains: The list.Contains function may be used incorrectly, leading to the evaluation failure.
  2. Bug in CUE: There may be a bug in the CUE language or the cue vet command that causes the evaluation failure.
  3. Dependency issues: There may be dependency issues between the list package and other packages that cause the evaluation failure.

Q: What are some workarounds for this issue?

A: Some workarounds for this issue include:

  1. Use a different function: Instead of using the list.Contains function, we can use a different function that achieves the same result.
  2. Modify the list package: We can modify the list package to fix the issue.
  3. Upgrade CUE: We can upgrade to a newer version of CUE that fixes the issue.

Q: Is this issue related to any other issues in CUE?

A: Yes, this issue may be related to the following issue:

Q: What is the CUE version used in this example?

A: The CUE version used in this example is v0.13.0-alpha.4.0.20250514105820-c456d085e0c1.

Q: What is the Go version used in this example?

A: The Go version used in this example is go1.24.0.

Q: What is the CUE language version used in this example?

A: The CUE language version used in this example is v0.13.0.

Q: How can I reproduce this issue?

A: To reproduce this issue, you can follow the steps outlined in the "Reproduction Steps" section of this article.

Q: What are some additional resources that may be helpful in resolving this issue?

A: Some additional resources that may be helpful in resolving this issue include:

  • The CUE documentation
  • The CUE issue tracker
  • The CUE community forums

Q: Can I get help from the CUE community if I am experiencing issues with this feature?

A: Yes, you can get help from the CUE community by posting a question on the CUE community forums or by opening an issue on the CUE issue tracker.