internal/cuegen incompatible with cuelang.org/go v0.16.0

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#404 opened on Mar 18, 2026 0 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty: 2/5
Estimated time: 1-3 hours
Newbie friendliness: 62/100

Issue type: Bug
Clarity: Clearly specified
Activity status: Stale
Tech stack: go
Domain: tooling

Research direction

Read internal/cuegen/cue.go, especially doScalarField(), and compare its ast.Field construction with the cuelang.org/go v0.16.0 API. Reproduce the issue with go build ./... or golangci-lint using CUE v0.16.0; done means the project compiles without the unknown Optional field error.

Written by the indexing model from the issue text.

Description

Overview

The internal/cuegen/cue.go file uses ast.Field.Optional (a token.Pos), which was removed in cuelang.org/go v0.16.0. The field was replaced with ast.Field.Constraint (a token.Token), where token.OPTION represents an optional field.

This causes a compilation error when a downstream project's dependency graph pulls in CUE v0.16.0:

  vendor/github.com/redpanda-data/benthos/v4/internal/cuegen/cue.go:171:3:
    unknown field Optional in struct literal of type ast.Field

Affected Code

The affected code is in doScalarField():

return &ast.Field{
    Label:    label,
    Value:    val,
    Optional: optional,  // no longer exists in cuelang.org/go v0.16.0
}, nil

The new CUE API equivalent would be:

  return &ast.Field{
      Label:      label,
      Value:      val,
      Constraint: token.OPTION,  // when the field should be optional
  }, nil

Reproduction

In a Go project that depends on benthos/v4, update cuelang.org/go to v0.16.0
Run go build ./... (or golangci-lint)
Compilation fails with the error above

Versions

cuelang.org/go v0.16.0 (breaking change)
benthos v4.68.0 (latest, still pins CUE v0.15.4)

Dominant language: Go
Stars: 571
Forks: 121
Avg merge: 2d 1h
Merged PRs (30d): 18

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