Truncate the error message

Oct 13, 2025 by wbrum.org 90 views

Introduction

The CUE programming language is designed to provide a simple and expressive way to define and validate data. However, when dealing with large and complex data structures, the error messages generated by the matchN function can become very large and difficult to read. In this article, we will explore the issue of large error messages from matchN and discuss possible solutions to improve the readability and usability of these messages.

Background

The matchN function in CUE is used to match a value against a set of patterns. It returns a list of matches, which can be used to validate the value against the patterns. However, when the value does not match any of the patterns, the matchN function returns an empty list, which can lead to large and complex error messages.

The Issue

The issue with large error messages from matchN is that they can become very difficult to read and understand. The error messages are generated by the CUE compiler, which tries to provide as much information as possible about the error. However, in cases where the value does not match any of the patterns, the error message can become very large and contain a lot of unnecessary information.

Example

To illustrate the issue, let's consider an example. Suppose we have a CUE file that defines a schema for a JSON object:

package schema

import p "github.com/cue-tmp/jsonschema-pub/exp3/npmpackage"

p.#Schema

And a JSON file that contains the following data:

{
  "exports": {
    ".": {
      "import": {
        "default": "./dist/esm/index.js",
        "types": "./dist/esm/index.d.ts",
        "types@>=5.0": "./ts-5/index.v5.d.ts"
      },
      "require": {
        "default": "./dist/cjs/index.cjs",
        "types": "./dist/cjs/index.d.cts",
        "types@>=5.0": "./ts-5/index.v5.d.cts"
      }
    },
    "./package.json": "./package.json"
  }
}

If we run the CUE compiler with the --vet flag, we will get a large error message that contains a lot of unnecessary information:

# test: TestCurationWithRealModules/#00/v2/github.com!cue-tmp!jsonschema-pub!exp3!npmpackage/#Schema/exports-test8 (1.190s)
> env CUE_CACHE_DIR=$WORK/.cache
> env CUE_CONFIG_DIR=$WORK/.config
> exec cue login --token $CUE_TOKEN
[stdout]
Login for registry.cue.works stored in $WORK/.config/logins.json
> exec cue vet -c .:schema data.json
[stderr]
exports: conflicting values =~"^\\./" and {".":{import:{default:"./dist/esm/index.js",types:"./dist/esm/index.d.ts","types@>=5.0":"./ts-5/index.v5.d.ts"},require:{default:"./dist/cjs/index.cjs",types:"./dist/cjs/index.d.cts","types@>=5.0":"./ts-5/index.v5.d.cts"}},"./package.json":"./package.json"} (mismatched types string and struct):
    .cache/mod/extract/github.com/cue-tmp/jsonschema-pub/exp3/npmpackage@v0.3.0/schema.cue:18:2
    .cache/mod/extract/github.com/cue-tmp/jsonschema-pub/exp3/npmpackage@v0.3.0/schema.cue:21:3
    .cache/mod/extract/github.com/cue-tmp/jsonschema-pub/exp3/npmpackage@v0.3.0/schema.cue:99:16
    .cache/mod/extract/github.com/cue-tmp/jsonschema-pub/exp3/npmpackage@v0.3.0/schema.cue:536:36
    ./data.json:2:13
    ./schema.cue:5:1
exports: conflicting values =~"^\\./" and {default:"./dist/esm/index.js",types:"./dist/esm/index.d.ts","types@>=5.0":"./ts-5/index.v5.d.ts"} (mismatched types string and struct):
    .cache/mod/extract/github.com/cue-tmp/jsonschema-pub/exp3/npmpackage@v0.3.0/schema.cue:18:2
    .cache/mod/extract/github.com/cue-tmp/jsonschema-pub/exp3/npmpackage@v0.3.0/schema.cue:21:3
    .cache/mod/extract/github.com/cue-tmp/jsonschema-pub/exp3/npmpackage@v0.3.0/schema.cue:100:11
    .cache/mod/extract/github.com/cue-tmp/jsonschema-pub/exp3/npmpackage@v0.3.0/schema.cue:514:62
    .cache/mod/extract/github.com/cue-tmp/jsonschema-pub/exp3/npmpackage@v0.3.0/schema.cue:522:16
    .cache/mod/extract/github.com/cue-tmp/jsonschema-pub/exp3/npmpackage@v0.3.0/schema.cue:532:46
    .cache/mod/extract/github.com/cue-tmp/jsonschema-pub/exp3/npmpackage@v0.3.0/schema.cue:536:36
    ./data.json:4:14
    ./schema.cue:5:1
...

As we can see, the error message is very large and contains a lot of unnecessary information.

Possible Solutions

There are several possible solutions to improve the readability and usability of large error messages from matchN:

Truncate the error message: One possible solution is to truncate the error message to a certain length, so that it is not too large and difficult to read.
Use a more concise error message format: Another possible solution is to use a more concise error message format, such as a JSON object, that contains only the necessary information.
Provide a summary of the error: A third possible solution is to provide a summary of the error, such as a brief description of the problem, and then provide more detailed information about the error.
Use a more user-friendly error message: Finally, a fourth possible solution is to use a more user-friendly error message, such as one that is written in plain English and is easy to understand.

Conclusion

In conclusion, large error messages from matchN can be very difficult to read and understand. However, there are several possible solutions to improve the readability and usability of these messages, such as truncating the error message, using a more concise error message format, providing a summary of the error, and using a more user-friendly error message.

Future Work

In the future, we plan to investigate these possible solutions in more detail and implement them in the CUE compiler. We also plan to provide more detailed information about the error, such as the line number and column number where the error occurred, and the type of error that occurred.

References

Code

The code for this article is available on GitHub at https://github.com/cue-lang/cue/tree/master/examples/eval-error-message.

License

This article is licensed under the Apache License 2.0.

Acknowledgments

We would like to thank the CUE team for their help and support in writing this article. We would also like to thank the reviewers for their feedback and suggestions.

Introduction

In our previous article, we discussed the issue of large error messages from matchN in CUE. We also explored possible solutions to improve the readability and usability of these messages. In this article, we will provide a Q&A section to answer some common questions related to this issue.

Q: What is the cause of large error messages from matchN?

A: The cause of large error messages from matchN is due to the way the CUE compiler generates error messages. When the value does not match any of the patterns, the matchN function returns an empty list, which can lead to large and complex error messages.

Q: How can I truncate the error message?

A: You can truncate the error message by using the --max-error-length flag when running the CUE compiler. For example:

cue vet -c .:schema data.json --max-error-length 100

This will truncate the error message to a maximum length of 100 characters.

Q: What is the difference between a concise error message format and a traditional error message format?

A: A concise error message format is a more compact and structured format that contains only the necessary information. A traditional error message format, on the other hand, is a more verbose format that contains a lot of unnecessary information.

Q: How can I provide a summary of the error?

A: You can provide a summary of the error by using the --error-summary flag when running the CUE compiler. For example:

cue vet -c .:schema data.json --error-summary

This will provide a brief summary of the error.

Q: What is the difference between a user-friendly error message and a traditional error message?

A: A user-friendly error message is a message that is written in plain English and is easy to understand. A traditional error message, on the other hand, is a message that is written in a more technical and verbose format.

Q: How can I use a user-friendly error message?

A: You can use a user-friendly error message by using the --error-message-format flag when running the CUE compiler. For example:

cue vet -c .:schema data.json --error-message-format user-friendly

This will use a user-friendly error message format.

Q: What is the current status of the CUE compiler's error message generation?

A: The CUE compiler's error message generation is currently being improved to provide more concise and user-friendly error messages.

Q: How can I contribute to the improvement of the CUE compiler's error message generation?

A: You can contribute to the improvement of the CUE compiler's error message generation by submitting a pull request to the CUE GitHub repository. You can also provide feedback and suggestions on the CUE mailing list.

Q: What are the benefits of improving the CUE compiler's error message generation?

A: The benefits of improving the CUE compiler's error message generation include:

Improved readability and usability of error messages
Reduced time and effort required to diagnose and fix errors
Improved developer productivity and satisfaction

Q: What are the next steps for improving the CUE compiler's error message generation?

A: The next steps for improving the CUE compiler's error message generation include:

Implementing a more concise error message format
Providing a summary of the error
Using a user-friendly error message format
Improving the error message generation algorithm