cue-lang/cue v0.17.0-alpha.1

on GitHub

Changes which may break some users are marked below with: ⚠️

Language

The active try experiment renames the new fallback keyword, used with for comprehensions, to otherwise. fallback continues to be accepted for now, but is rewritten to the new form.

The active aliasv2 experiment now allows ~(X) as an alternative to ~X for the single postfix alias form. ~X is also rewritten as ~(X) for the sake of consistency and clarity.

Language versions v0.17.0 and later allow omitting commas in multi-line lists. Just like a newline after a struct field implies a comma, a newline after a list element now implies a comma as well.

The language spec is tweaked to make $ a valid identifier, which was already allowed by the parser and evaluator.

⚠️ Support for the infix div, mod, quo, and rem operators has been removed. Since late 2020, these infix forms have been undocumented and rewritten by cue fix to the new function calls.

The new shortcircuit experiment

This release introduces the shortcircuit experiment, which changes the && and || operators to not evaluate the right operand if the left operand alone determines the result.

This matches the behavior already documented in the CUE spec and is consistent with most mainstream languages, but for the sake of a smooth transition for end users, we are rolling out this change via an experiment.

You can try this experiment via the @experiment(shortcircuit) file attribute. To mimic the old behavior with the experiment, you can use a hidden field:

_y: Y
if X && _y {}

Evaluator

Fix a number of issues where cue def could produce invalid CUE output, such as due to name conflicts.

Fix an evaluator regression where embedded disjunctions across packages may not correctly apply closedness.

Fix an evaluator bug where cue.Context.BuildExpr of close({}) did not actually result in a closed struct.

Fix a bug where some calls to standard library functions or validators did not include the "error in call to pkg.Func" error context, or included it twice.

A few changes to the evaluator should reduce allocated objects by up to 16%, reducing GC overhead and memory usage.

cmd/cue

The new global -C or --chdir flag runs cue from the given working directory.

cue import --path now skips over null values in an input stream, such as empty documents in a YAML file.

The new cue exp gengotypes --outfile flag controls the output file path when generating a single package.

LSP server

Add an initial version of organize-imports, which sorts the existing imports and removes unneeded imports. It is not yet capable of suggesting missing imports.

Wait for a short period of inactivity before sending diagnostics to the editor. This "debounce" means that a user typing incomplete CUE syntax will not be distracted with syntax errors as much.

The aliasv2 experiment is now fully supported.

The rename function is fixed to distinguish between field names and aliases.

Improve field name analysis in general so that fields with multiple aliases (e.g. v=[k=string]: _) are properly supported.

Improve attribute handling for file-level embedded attributes, and to attach attributes within expressions to the correct struct.

Treat conjunctions (&) and disjunctions (|) the same way for goto-definition. With the cursor on a path, it returns all results that the path MAY resolve to. With the cursor on a field declaration name, it returns all results that the path constructed from the field's name, and its field's name (and so on) MAY resolve to.

Special-case close function calls so that paths can resolve through fields within the argument to close.

Encodings

The JSON Schema decoder is improved to better handle the prefixItems keyword.

The JSON Schema encoder is improved to support list.UniqueItems and standalone validators, to use maxItems and minItems instead of maxLength and minLength for lists with prefix elements, and to generate description keywords for doc comments.

Standard library

The net IP APIs now consistently return an error on invalid input types.

strconv.FormatFloat now accepts a string format parameter, like FormatFloat(3.14, "e", 4, 64).

list.MatchN now shows what expected value it's matching against when it fails.

Go API

Using cue.Values concurrently is now fully supported, which required deprecating cue.Value.Context. If you encounter any races or bugs, please report them.

cue/load now supports loading from an io/fs.FS, as outlined in proposal #4285. Loading file embeds through Config.Overlay and Config.FS is supported now as well.

cue/ast/astutil deprecates Sanitize in favor of the new SanitizeFiles API, given that Sanitize on a single file cannot know if another file in the same package shadows builtin names like self.

Clarify that cue/format indents with a tab width of 4 by default.

A new fuzzer has been introduced in the cue package, checking that the parser doesn't crash and that its results are consistent with the rest of the Go APIs like cue/literal. So far, it has already resulted in seventeen bug fixes.

The cue.Interpreter option API has been deprecated in favor of cue.WithInjection, which is a better name going forward.

⚠️ cue/ast.File.Imports, deprecated in mid 2025 in favor of cue/ast.File.ImportSpecs, is now removed.

⚠️ The long-deprecated and hidden cue.Instance methods Lookup, LookupDef, LookupField, and Fill are now removed.