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cmd/cue: detect kubernetes semantics for get go #4191

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3a2f680
cmd/cue: add kubernetes semantics test
fionera Nov 24, 2025
d7f763b
cmd/cue: detect kubernetes semantics for `get go`
fionera Nov 24, 2025
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83 changes: 54 additions & 29 deletions cmd/cue/cmd/get_go.go
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Original file line number Diff line number Diff line change
Expand Up @@ -254,10 +254,11 @@ type extractor struct {
done map[string]bool

// per package
pkg *packages.Package
orig map[types.Type]*ast.StructType
usedPkgs map[string]bool
consts map[string][]string
pkg *packages.Package
orig map[types.Type]*ast.StructType
usedPkgs map[string]bool
consts map[string][]string
k8sSemantic bool

// per file
cmap ast.CommentMap
Expand Down Expand Up @@ -446,7 +447,18 @@ func (e *extractor) recordTypeInfo(p *packages.Package) {

func (e *extractor) extractPkg(root string, p *packages.Package) error {
e.pkg = p
e.logf("--- Package %s", p.PkgPath)
e.k8sSemantic = false

outer:
for _, f := range p.Syntax {
for _, c := range f.Comments {
if strings.Contains(c.Text(), "+k8s:openapi-gen=true") {
e.k8sSemantic = true
break outer
}
}
}
e.logf("--- Package %s - Kubernetes semantics: %t", p.PkgPath, e.k8sSemantic)

e.recordTypeInfo(p)

Expand Down Expand Up @@ -857,7 +869,7 @@ func (e *extractor) reportDecl(x *ast.GenDecl) (a []cueast.Decl) {
if basic, ok := typ.(*types.Basic); ok && basic.Info()&types.IsUntyped != 0 {
break // untyped basic types do not make valid identifiers
}
cv = cueast.NewBinExpr(cuetoken.AND, e.makeType(typ), cv)
cv = cueast.NewBinExpr(cuetoken.AND, e.makeType(typ, regular), cv)
}

f.Value = cv
Expand Down Expand Up @@ -1047,7 +1059,7 @@ const (
)

func (e *extractor) makeField(name string, kind fieldKind, expr types.Type, doc *ast.CommentGroup, newline bool) (f *cueast.Field, typename string) {
typ := e.makeType(expr)
typ := e.makeType(expr, kind)
var label cueast.Label
if kind == definition {
label = e.ident(name, true)
Expand Down Expand Up @@ -1075,7 +1087,7 @@ func (e *extractor) makeField(name string, kind fieldKind, expr types.Type, doc
return f, string(b)
}

func (e *extractor) makeType(typ types.Type) (result cueast.Expr) {
func (e *extractor) makeType(typ types.Type, kind fieldKind) (result cueast.Expr) {
switch typ := types.Unalias(typ).(type) {
case *types.Named:
obj := typ.Obj()
Expand Down Expand Up @@ -1209,10 +1221,14 @@ func (e *extractor) makeType(typ types.Type) (result cueast.Expr) {

return result
case *types.Pointer:
// In K8s, a field is only nullable if explicitly marked as such.
if e.k8sSemantic && kind == optional {
return e.makeType(typ.Elem(), kind)
}
return &cueast.BinaryExpr{
X: cueast.NewNull(),
Op: cuetoken.OR,
Y: e.makeType(typ.Elem()),
Y: e.makeType(typ.Elem(), kind),
}

case *types.Struct:
Expand All @@ -1231,7 +1247,7 @@ func (e *extractor) makeType(typ types.Type) (result cueast.Expr) {
if typ.Elem() == typeByte {
return e.ident("bytes", false)
}
return cueast.NewList(&cueast.Ellipsis{Type: e.makeType(typ.Elem())})
return cueast.NewList(&cueast.Ellipsis{Type: e.makeType(typ.Elem(), kind)})

case *types.Array:
if typ.Elem() == typeByte {
Expand All @@ -1248,7 +1264,7 @@ func (e *extractor) makeType(typ types.Type) (result cueast.Expr) {
Value: strconv.Itoa(int(typ.Len())),
},
Op: cuetoken.MUL,
Y: cueast.NewList(e.makeType(typ.Elem())),
Y: cueast.NewList(e.makeType(typ.Elem(), kind)),
}
}

Expand All @@ -1259,7 +1275,7 @@ func (e *extractor) makeType(typ types.Type) (result cueast.Expr) {

f := &cueast.Field{
Label: cueast.NewList(e.ident("string", false)),
Value: e.makeType(typ.Elem()),
Value: e.makeType(typ.Elem(), kind),
}
cueast.SetRelPos(f, cuetoken.Blank)
return &cueast.StructLit{
Expand All @@ -1282,7 +1298,7 @@ func (e *extractor) makeType(typ types.Type) (result cueast.Expr) {
case *types.Union:
var exprs []cueast.Expr
for term := range typ.Terms() {
exprs = append(exprs, e.makeType(term.Type()))
exprs = append(exprs, e.makeType(term.Type(), kind))
}
return cueast.NewBinExpr(cuetoken.OR, exprs...)

Expand All @@ -1305,12 +1321,12 @@ func (e *extractor) makeType(typ types.Type) (result cueast.Expr) {
//
var exprs []cueast.Expr
for etyp := range typ.EmbeddedTypes() {
exprs = append(exprs, e.makeType(etyp))
exprs = append(exprs, e.makeType(etyp, kind))
}
return cueast.NewBinExpr(cuetoken.OR, exprs...)

case *types.TypeParam:
return e.makeType(typ.Constraint())
return e.makeType(typ.Constraint(), kind)

default:
// record error
Expand Down Expand Up @@ -1360,7 +1376,7 @@ func (e *extractor) addFields(x *types.Struct, st *cueast.StructLit) {
}
switch typ := types.Unalias(typ).(type) {
case *types.Named:
embed := &cueast.EmbedDecl{Expr: e.makeType(typ)}
embed := &cueast.EmbedDecl{Expr: e.makeType(typ, regular)}
if i > 0 {
cueast.SetRelPos(embed, cuetoken.NewSection)
}
Expand All @@ -1381,10 +1397,7 @@ func (e *extractor) addFields(x *types.Struct, st *cueast.StructLit) {
doc := docs[i]

// TODO: check referrers
kind := regular
if e.isOptional(f, doc, tag) {
kind = optional
}
kind := e.detectFieldKind(f, doc, tag)
field, cueType := e.makeField(name, kind, f.Type(), doc, count > 0)
add(field)

Expand Down Expand Up @@ -1480,24 +1493,36 @@ func (e *extractor) isInline(tag string) bool {
hasFlag(tag, "yaml", "inline", 1)
}

func (e *extractor) isOptional(f *types.Var, doc *ast.CommentGroup, tag string) bool {
if _, ok := f.Type().(*types.Pointer); ok {
return true
}

func (e *extractor) detectFieldKind(f *types.Var, doc *ast.CommentGroup, tag string) fieldKind {
// From k8s docs (https://github.com/kubernetes/community/blob/master/contributors/devel/sig-architecture/api-conventions.md):
// - a map field marked with `+nullable` would accept either `foo: null` or `foo: {}`.
// - Using the `+optional` or the `omitempty` tag means that the field is optional.
// Note that for backward compatibility, any field that has the `omitempty` struct
// tag, and is not explicitly marked as `+required`, will be considered to be optional.
for line := range strings.SplitSeq(doc.Text(), "\n") {
before, _, _ := strings.Cut(strings.TrimSpace(line), "=")
if before == "+optional" {
return true
switch before {
case "+nullable":
return regular
case "+optional":
return optional
}
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@mvdan mvdan Nov 25, 2025

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I think that the way this loops over the doc lines, and returns at the first hit, will not work well when a field is marked as BOTH optional and nullable. You might need to make fieldKind a bit set, so that we can track that a field was marked as either or both optional/nullable?

If this is not common and you want to leave this tweak for a future PR, that's fine, but then we'd need a TODO.

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@fionera fionera Nov 29, 2025 •
edited
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I actually changed the whole PR 😅 I am gonna close this one and push it to gerrit as its probably a better review platform

}

if _, ok := f.Type().(*types.Pointer); ok {
return optional
}

// Go 1.24 added the "omitzero" option to encoding/json, an improvement over "omitempty".
// Note that, as of mid 2025, YAML libraries don't seem to have picked up "omitzero" yet.
// TODO: also when the type is a list or other kind of pointer.
return hasFlag(tag, "json", "omitempty", 1) ||
if hasFlag(tag, "json", "omitempty", 1) ||
hasFlag(tag, "json", "omitzero", 1) ||
hasFlag(tag, "yaml", "omitempty", 1)
hasFlag(tag, "yaml", "omitempty", 1) {
return optional
}

return regular
}

func hasFlag(tag, key, flag string, offset int) bool {
Expand Down
52 changes: 52 additions & 0 deletions cmd/cue/cmd/testdata/script/get_go_types_kubernetes.txtar
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Original file line number Diff line number Diff line change
@@ -0,0 +1,52 @@
# Test that a get go works for kubernetes types,
# including those special cases that result in _ and string
# that are specifically mentioned in help get go.

exec cue get go --local ./...
cmp ./file2_go_gen.cue ./file2_go_gen.cue.golden

-- go.mod --
module mod.test

go 1.21
-- cue.mod/module.cue --
module: "mod.test"
-- file1.go --
package pkg1

// +k8s:openapi-gen=true
-- file2.go --
package pkg1

type Foo struct {
Required string `json:"required"`
Pointer *string `json:"pointer"`
OmitEmptyPointer *string `json:"omitEmptyPointer,omitempty"`
// +optional
OptionalComment string `json:"optionalComment"`
// +optional
OptionalCommentPointer *string `json:"optionalCommentPointer"`
// +nullable
NullableCommentPointer *string `json:"nullableCommentPointer"`
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@mvdan mvdan Nov 25, 2025

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I just realised - we need to include a field which is both optional and nullable. it should generate as...

foo?: null | string

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@fionera fionera Nov 29, 2025

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Turns out that should be the default behavior:

Optional fields have the following properties:

They have the +optional comment tag in Go.
They are a pointer type in the Go definition (e.g. AwesomeFlag *SomeFlag) or have a built-in nil value (e.g. maps and slices).
They are marked with the omitempty json struct tag in the Go definition.
The API server should allow POSTing and PUTing a resource with this field unset.

}
-- file2_go_gen.cue.golden --
// Code generated by cue get go. DO NOT EDIT.

//cue:generate cue get go mod.test

package pkg1

#Foo: {
required: string @go(Required)
pointer?: string @go(Pointer,*string)
omitEmptyPointer?: string @go(OmitEmptyPointer,*string)

// +optional
optionalComment?: string @go(OptionalComment)

// +optional
optionalCommentPointer?: string @go(OptionalCommentPointer,*string)

// +nullable
nullableCommentPointer: null | string @go(NullableCommentPointer,*string)
}