cue-lang/cue v0.6.0

on GitHub

The main focus of this release is the introduction of required fields, as well as fixing a number of issues and regressions introduced in the v0.5.0 release.

As a reminder: users can register their projects with unity, our regression and performance testing setup. unity is used to ensure that a project's CUE evaluations do not unexpectedly stop working, or regress in terms of performance. unity continues to catch multiple issues with each release. Adding your project to unity not only guarantees that we will not break your tests (if we do, we will work with you to fix your CUE code), but it also helps to improve the quality of each CUE release. Follow this link to learn more about Unity, install it, or get in touch with any questions.

Thank you to @4ad, @Abirdcfly, @alexandear, @chee-zaram, @eraserhd, @ghostwheel42, @joanlopez, @jpluscplusm, @kcburge, @mpvl, @mvdan, @myitcv, @rogpeppe, @toshi0607, and @zeithaste for contributing to this release!

API

CL 543335 adds arch to set of injectable system variables understood by cue/load. The text at cue help injection explains how this in more detail.

CL 552142 adds support for zero values in cue.Value.Float64, which has the effect of fixing the error when attempting to use strconv.FormatFloat with a zero value.

CL 548783 fixes a long-standing bug to make HTML escaping in JSON an opt-in. This means that cue export now respects the --escape flag when set, and encoding/json only escapes HTML when HTMLEscape is used.

Language

Required fields

The main focus of the v0.6.0 release is the introduction of required fields.

CUE already supports the “optional field constraint”, denoted foo?: value.

Required fields add a “required field constraint”, denoted foo!: value, which is like foo?: value, but requires a regular field be provided for foo (a field foo: without !: or ?:).

We refer to optional field constraints and required field constraints collectively as “field constraints”.

As a general rule, all data and data templating should be defined with regular fields, whereas schemas would be defined in terms of field constraints. Of course, CUE being CUE, mixing these two fields is allowed: this rule is not a restriction but suggested as a matter of style and proper usage.

Here are some examples of how exclamation marks can be used to express things that were previously not possible.

#Def: {
    kind!: "def"
    intList!: [...int]
}

Using required fields can also result in better error messages. Consider this schema:

#Person: {
    name: string
    age?: int
}

Note that this is non-idiomatic, because our new guidelines suggest schemas should only be defined in terms of field constraints, but we will use this for illustration purposes.

Now consider this usage of #Person:

jack: #Person & {age: 3}

In data mode, the error message here is currently jack.name: incomplete value string, which does not provide much actionable information to the user to help them fix the problem.

Now consider how #Person looks with required fields, idiomatically only using field constraints:

#Person: {
    name!: string
    age?:  int
}

jack: #Person & {age: 3}

Now the error message reads:

jack.name: field is required but not present

which more closely reflects the underlying problem..

This error could be resolved by adding jack: name: "Jack".

For more details and background on the change, please see the original required fields proposal.

Other changes

Whilst it should not be a breaking change from a CUE perspective, we have upgraded to use github.com/cockroachdb/apd/v3. We have also increased apd.Context precision from 24 to 34.

CL 551207 adds support for making dynamic fields optional or required. For example, the following is now possible:

x:	"y"
(x):  "foo"
(x)?: "foo"
(x)!: "foo"

and yields:

x: "y"
y: "foo"

CL 546886 removes support for old-style :: definitions. This also includes deprecation support. In a similar vein, CL 547011 removes the last vestiges of <foo>: T. This was once the notation for pattern constraints.

Spec

Various bug fixes, with special thanks to @nicuveo for raising many of these.

Builtins

The following four functions have been added to the net package:

• PathEscape
• PathUnescape
• QueryEscape
• QueryUnescape

Thanks to @eraserhd for this change.

CL 549087 reimplements pkg/list.Sort. The resulting reduction in the number of allocations and other work gives rise to a ~80% reduction in running time against CUE benchmarks.

cmd/cue

CL 547212 improves the documentation for the -l flag passed to cue import. This addresses a frequent point of confusion in questions to GitHub Discussions and on Slack.

CL 550616 fixes cue get go to respect the --exclude flag for constants. This makes it possible to (for example) exclude all unexported identifiers from a cue get go run.

CL 555576 fixed an important bug where cmd/cue vet was not properly consuming all input data.

CL 556526 fixed a bug where CUE files beginning with an underscore were not being loaded when explicitly given as filename arguments.

WebAssembly (Wasm)

We have added preliminary support for Wasm. Users can compile code from any language and toolchain that supports Wasm into plugins that are dynamically loaded by CUE. Users can then call and use functions from these Wasm modules, just like they can use standard library functions.

See the documentation at cuelang.org/go/cue/interpreter/wasm to learn more about Wasm and its current limitations.

Changelog