cue-lang/cue v0.18.0-rc.2

on GitHub

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

Language

A CUE file which belongs to no module can now declare the language version it is written for with a @version attribute, placed ahead of any other file attribute and the package clause, so that a reproducer or a standalone file written for an older version runs as written without creating a module for it. The attribute is an error in a file of a module which declares a language version, as the module file decides the version of its files. cue fix adds the attribute when it enables an experiment in such a file, recording the version the file was migrated at.

@version(v0.17.0)

package p

⚠️ The functions experiment

The experiment now follows the revised proposal on function contracts: an implementation unified with a function type must accept every argument the type admits, callbacks are checked where they are passed, and two function literals with different bodies no longer compose when unified, undoing the change announced in v0.18.0-alpha.3. Some configurations which evaluated before are now rejected; the proposal lists them and how to fix them.

Evaluator

A reference unified with a definition or with a disjunction of definitions, as in deps: [...#Node] with #Node: #Task | #Group, is now shared with the value it refers to rather than evaluated again under every path, so that a dependency graph typed this way is evaluated once per node rather than exponentially in its depth, regardless of the order in which the fields are declared (#4512, #4513).

Exporting a struct holding many unifications of empty or single-field structs no longer takes memory exponential in their number.

The != and =~ bounds and the builtin validators of a field in an inline struct or a let which is read through a reference, such as by an interpolation, are now checked, where they were silently dropped. This surfaces conflicts which earlier releases accepted, such as a let inside a definition which sets an integer on a field declared as a float with a default (#4510).

cmd/cue

The new cue mod upgrade command moves a module to a new language version, rewriting every CUE file of the module for that version, including those under cue.mod, before recording the version in cue.mod/module.cue. Files are rewritten without loading them, so a package whose import cannot be resolved is converted all the same, and a file which cannot be converted stops the upgrade before anything is written unless --force is given. cue fix without package arguments now fixes every file of the module the same way, from any directory inside it, and the explicitopen rewrite fixes several cases where it closed a value which the original left open.

The new --language-version flag of the commands which read CUE outside a module, among them cue eval, cue export, cue vet, cue fmt, cue fix, cue import, and cue get go, selects the language version for files which belong to no module, including standard input. It is only a fallback: the files of a module which declares a language version keep that version, and a file's own @version attribute takes precedence. CUE generated by cue import, cue get go, and cue get crd targets the chosen version.

cue cmd now reports the errors within a command which declares no tasks, such as a comprehension or dynamic field which failed to declare them, alongside no tasks found (#3536). Its memory use no longer grows with the number of tasks which return a result, as tools/flow now releases each earlier configuration once the tasks depending on it have completed: the peak memory of a command running 40 such tasks drops from about 500MB to about 125MB (#4509).

LSP server

The language server now understands the function literals of the functions experiment. References in a function's body, parameter constraints, defaults, and result type resolve, so go-to-definition, find references, rename, and completion work inside a function literal, and a rename of a parameter covers every literal unified with the function. The label of a labeled argument resolves to the parameter it binds, through references, imports, and partial applications, and completion at a call offers the callee's labeled parameters. Hovering a parameter or a call label shows the parameter's constraint, and a position inside a function literal is no longer treated as part of the value of the field the literal belongs to.

Encodings

The YAML decoder no longer swallows the key following a sequence which ends with an empty entry and is not indented relative to its own key.

The JSON Schema decoder no longer keeps a repeated allOf conjunct twice when merging changes it, such as a disjunction holding a nested allOf. The syntax returned by encoding/jsonschema's Extract and ExtractCRDs and by encoding/protobuf's Extract now follows the style of cue/format.Simplify, with labels unquoted where possible, so that Go API users see the same CUE that cue import prints (#4117).

Go API

cue/load.Config.LanguageVersion sets the fallback language version for input which belongs to no module, as the --language-version flag does, and the new cue/build.Instance.TargetLanguageVersion reports the version which cue.Value.Syntax targets for an instance.

Programs embedding CUE could be far larger than necessary, as the text/template builtin and cue/stats looked up methods by name, which stops the Go linker from discarding unused exported methods anywhere in the binary; one reported binary was 66MiB rather than 25MiB (#4514). cue/stats no longer does so, and building with the cuenotemplate build tag leaves the text/template package out of the standard library so that the linker discards unused methods again, at the cost of CUE code importing text/template failing.