feat(validation-gen): add FieldValidator

- Added FieldValidator interface to allow validation on field definitions.
- Implemented registration and initialization for field validators in the registry.
- Updated validation extraction logic to process field validators after tag and type validators.
- Improved error handling and validation checks in the validation generation process.

Co-authored-by: Tim Hockin <thockin@google.com>

staging/src/k8s.io/code-generator/cmd/validation-gen/validation.go

@@ -392,6 +392,9 @@ func (td *typeDiscoverer) discoverType(t *types.Type, fldPath *field.Path) (*typ
 	// are called in emitted code, just how we evaluate what to emit.
 	switch t.Kind {
 	case types.Alias, types.Struct:
+		if fldPath.String() != t.String() {
+			panic(fmt.Sprintf("path for type != the type name: %s, %s", t.String(), fldPath.String()))
+		}
 		context := validators.Context{
 			Scope:  validators.ScopeType,
 			Type:   t,
@@ -452,7 +455,7 @@ func (td *typeDiscoverer) discoverType(t *types.Type, fldPath *field.Path) (*typ
 						//
 						// Note: the first argument to Function() is really
 						// only for debugging.
-						v, err := validators.ForEachVal(fldPath, underlying.childType,
+						v, err := validators.ForEachVal(fldPath, thisNode.valueType,
 							validators.Function("iterateListValues", validators.DefaultFlags, funcName))
 						if err != nil {
 							return nil, fmt.Errorf("generating list iteration: %w", err)
@@ -576,11 +579,11 @@ func (td *typeDiscoverer) discoverStruct(thisNode *typeNode, fldPath *field.Path
 			Path:   childPath,
 		}
 
-		Tags, err := td.validator.ExtractTags(context, memb.CommentLines)
+		tags, err := td.validator.ExtractTags(context, memb.CommentLines)
 		if err != nil {
 			return fmt.Errorf("field %s: %w", childPath.String(), err)
 		}
-		if validations, err := td.validator.ExtractValidations(context, Tags...); err != nil {
+		if validations, err := td.validator.ExtractValidations(context, tags...); err != nil {
 			return fmt.Errorf("field %s: %w", childPath.String(), err)
 		} else if validations.Empty() {
 			klog.V(6).InfoS("no field-attached validations", "field", childPath)

staging/src/k8s.io/code-generator/cmd/validation-gen/validators/registry.go

@@ -42,7 +42,8 @@ type registry struct {
 	tagValidators map[string]TagValidator // keyed by tagname
 	tagIndex      []string                // all tag names
 
-	typeValidators []TypeValidator
+	typeValidators  []TypeValidator
+	fieldValidators []FieldValidator
 }
 
 func (reg *registry) addTagValidator(tv TagValidator) {
@@ -71,6 +72,17 @@ func (reg *registry) addTypeValidator(tv TypeValidator) {
 	globalRegistry.typeValidators = append(globalRegistry.typeValidators, tv)
 }
 
+func (reg *registry) addFieldValidator(fv FieldValidator) {
+	if reg.initialized.Load() {
+		panic("registry was modified after init")
+	}
+
+	reg.lock.Lock()
+	defer reg.lock.Unlock()
+
+	globalRegistry.fieldValidators = append(globalRegistry.fieldValidators, fv)
+}
+
 func (reg *registry) init(c *generator.Context) {
 	if reg.initialized.Load() {
 		panic("registry.init() was called twice")
@@ -97,6 +109,13 @@ func (reg *registry) init(c *generator.Context) {
 		return cmp.Compare(a.Name(), b.Name())
 	})
 
+	for _, fv := range reg.fieldValidators {
+		fv.Init(cfg)
+	}
+	slices.SortFunc(reg.fieldValidators, func(a, b FieldValidator) int {
+		return cmp.Compare(a.Name(), b.Name())
+	})
+
 	reg.initialized.Store(true)
 }
 
@@ -127,6 +146,8 @@ func (reg *registry) ExtractValidations(context Context, tags ...codetags.Tag) (
 		panic("registry.init() was not called")
 	}
 	validations := Validations{}
+
+	// Run tag-validators first.
 	phases := reg.sortTagsIntoPhases(tags)
 	for _, tags := range phases {
 		for _, tag := range tags {
@@ -144,6 +165,7 @@ func (reg *registry) ExtractValidations(context Context, tags ...codetags.Tag) (
 			}
 		}
 	}
+
 	// Run type-validators after tag validators are done.
 	if context.Scope == ScopeType {
 		// Run all type-validators.
@@ -156,6 +178,18 @@ func (reg *registry) ExtractValidations(context Context, tags ...codetags.Tag) (
 		}
 	}
 
+	// Run field-validators after tag and type validators are done.
+	if context.Scope == ScopeField {
+		// Run all field-validators.
+		for _, fv := range reg.fieldValidators {
+			if theseValidations, err := fv.GetValidations(context); err != nil {
+				return Validations{}, fmt.Errorf("field validator %q: %w", fv.Name(), err)
+			} else {
+				validations.Add(theseValidations)
+			}
+		}
+	}
+
 	return validations, nil
 }
 
@@ -213,18 +247,24 @@ func (reg *registry) Docs() []TagDoc {
 	return result
 }
 
-// RegisterTagValidator must be called by any validator which wants to run when
-// a specific tag is found.
+// RegisterTagValidator must be called for TagValidator to be used by
+// validation-gen. See TagValidator for more information.
 func RegisterTagValidator(tv TagValidator) {
 	globalRegistry.addTagValidator(tv)
 }
 
-// RegisterTypeValidator must be called by any validator which wants to run
-// against every type definition.
+// RegisterTypeValidator must be called for a TypeValidator to be used by
+// validation-gen. See TypeValidator for more information.
 func RegisterTypeValidator(tv TypeValidator) {
 	globalRegistry.addTypeValidator(tv)
 }
 
+// RegisterFieldValidator must be called for a FieldValidator to be used by
+// validation-gen. See FieldValidator for more information.
+func RegisterFieldValidator(fv FieldValidator) {
+	globalRegistry.addFieldValidator(fv)
+}
+
 // Validator represents an aggregation of validator plugins.
 type Validator interface {
 

staging/src/k8s.io/code-generator/cmd/validation-gen/validators/validators.go

@@ -26,7 +26,21 @@ import (
 	"k8s.io/gengo/v2/types"
 )
 
-// TagValidator describes a single validation tag and how to use it.
+// TagValidator describes a single validation tag and how to use it. To be
+// findable by validation-gen, a TagValidator must be registered - see
+// RegisterTagValidator.
+//
+// TagValidators are always evaluated before TypeValidators and
+// FieldValidators. In general, TagValidators should not depend on other
+// TagValidators having been run already because users might specify tags in
+// the any order. The one exception to this rule is that some TagValidators may
+// be designated as "late" validators (see LateTagValidator), which means they
+// will be run after all non-late TagValidators.
+//
+// No other guarantees are made about the order of execution of TagValidators
+// or LateTagValidators. Instead of relying on tag ordering, TagValidators can
+// accumulate information internally and use a TypeValidator and/or
+// FieldValidator to finish the work.
 type TagValidator interface {
 	// Init initializes the implementation.  This will be called exactly once.
 	Init(cfg Config)
@@ -53,6 +67,16 @@ type LateTagValidator interface {
 }
 
 // TypeValidator describes a validator which runs on every type definition.
+// To be findable by validation-gen, a TypeValidator must be registered - see
+// RegisterTypeValidator.
+//
+// TypeValidators are always processed after TagValidators, and after the type
+// has been fully processed (including all child fields and their types). This
+// means that they can "finish" work with data that was collected by
+// TagValidators.
+//
+// TypeValidators MUST NOT depend on other TypeValidators having been run
+// already.
 type TypeValidator interface {
 	// Init initializes the implementation.  This will be called exactly once.
 	Init(cfg Config)
@@ -73,6 +97,37 @@ type TypeValidator interface {
 	GetValidations(context Context) (Validations, error)
 }
 
+// FieldValidator describes a validator which runs on every field definition.
+// To be findable by validation-gen, a FieldValidator must be registered - see
+// RegisterFieldValidator.
+//
+// FieldValidators are always processed after TagValidators and TypeValidators,
+// and after the field has been fully processed (including all child fields).
+// This means that they can "finish" work with data that was collected by
+// TagValidators.
+//
+// FieldValidators MUST NOT depend on other FieldValidators having been run
+// already.
+type FieldValidator interface {
+	// Init initializes the implementation.  This will be called exactly once.
+	Init(cfg Config)
+
+	// Name returns a unique name for this validator.  This is used for sorting
+	// and logging.
+	Name() string
+
+	// GetValidations returns any validations imposed by this validator for the
+	// given context.
+	//
+	// The way gengo handles type definitions varies between structs and other
+	// types.  For struct definitions (e.g. `type Foo struct {}`), the realType
+	// is the struct itself (the Kind field will be `types.Struct`) and the
+	// parentType will be nil.  For other types (e.g. `type Bar string`), the
+	// realType will be the underlying type and the parentType will be the
+	// newly defined type (the Kind field will be `types.Alias`).
+	GetValidations(context Context) (Validations, error)
+}
+
 // Config carries optional configuration information for use by validators.
 type Config struct {
 	// GengoContext provides gengo's generator Context.  This allows validators
@@ -182,6 +237,8 @@ type TagDoc struct {
 	PayloadsType codetags.ValueType
 	// PayloadsRequired is true if a payload is required.
 	PayloadsRequired bool
+	// AcceptsUnknownArgs is true if unknown args are accepted
+	AcceptsUnknownArgs bool
 }
 
 func (td TagDoc) Arg(name string) (TagArgDoc, bool) {
@@ -476,14 +533,16 @@ func typeCheck(tag codetags.Tag, doc TagDoc) error {
 
 	for _, tagArg := range tag.Args {
 		if _, ok := doc.Arg(tagArg.Name); !ok {
-			return fmt.Errorf("unrecognized named argument %q", tagArg)
+			if !doc.AcceptsUnknownArgs {
+				return fmt.Errorf("unrecognized named argument %q", tagArg)
+			}
 		}
 	}
 	if tag.ValueType == codetags.ValueTypeNone {
 		if doc.PayloadsRequired {
 			return fmt.Errorf("missing required tag value of type %s", doc.PayloadsType)
 		}
-	} else if tag.ValueType != doc.PayloadsType {
+	} else if doc.PayloadsType != codetags.ValueTypeRaw && tag.ValueType != doc.PayloadsType {
 		return fmt.Errorf("tag value has wrong type: got %s, want %s", tag.ValueType, doc.PayloadsType)
 	}
 	return nil