fix: promote variable defaultValue to a named oneOf component

The list variable defaultValue was an inline string | []string oneOf,
which downstream codegen can't canonicalize: tfplugingen-openapi rejects
the inline scalar-or-array multi-type, and oapi-codegen has no named type
to attach the union's Marshal/UnmarshalJSON to.

Shape the vendored variable.DefaultValue as the named VariableDefaultValue
oneOf via a reflector InterceptSchema hook and let defaultValue $ref it,
instead of overriding the property inline. Regenerate the OpenAPI spec and
frontend client accordingly.

docs/api/openapi.yml

@@ -2971,11 +2971,7 @@ components:
         customAllValue:
           type: string
         defaultValue:
-          oneOf:
-          - type: string
-          - items:
-              type: string
-            type: array
+          $ref: '#/components/schemas/VariableDefaultValue'
         display:
           $ref: '#/components/schemas/DashboardtypesDisplay'
         name:
@@ -7895,7 +7891,11 @@ components:
       - id
       type: object
     VariableDefaultValue:
-      type: object
+      oneOf:
+      - type: string
+      - items:
+          type: string
+        type: array
     ZeustypesGettableHost:
       properties:
         hosts:

frontend/src/api/generated/services/sigNoz.schemas.ts

@@ -4564,6 +4564,8 @@ export type DashboardtypesLayoutDTO =
 export enum DashboardtypesVariableEnvelopeGithubComSigNozSignozPkgTypesDashboardtypesListVariableSpecDTOKind {
 	ListVariable = 'ListVariable',
 }
+export type VariableDefaultValueDTO = string | string[];
+
 export enum DashboardtypesVariablePluginVariantGithubComSigNozSignozPkgTypesDashboardtypesDynamicVariableSpecDTOKind {
 	'signoz/DynamicVariable' = 'signoz/DynamicVariable',
 }
@@ -4629,8 +4631,6 @@ export enum DashboardtypesListVariableSpecSortDTO {
 	'alphabetical-ci-asc' = 'alphabetical-ci-asc',
 	'alphabetical-ci-desc' = 'alphabetical-ci-desc',
 }
-export type DashboardtypesListVariableSpecDTODefaultValue = string | string[];
-
 export interface DashboardtypesListVariableSpecDTO {
 	/**
 	 * @type boolean
@@ -4648,7 +4648,7 @@ export interface DashboardtypesListVariableSpecDTO {
 	 * @type string
 	 */
 	customAllValue?: string;
-	defaultValue?: DashboardtypesListVariableSpecDTODefaultValue;
+	defaultValue?: VariableDefaultValueDTO;
 	display: DashboardtypesDisplayDTO;
 	/**
 	 * @type string
@@ -9023,10 +9023,6 @@ export interface TypesUserDTO {
 	updatedAt?: string;
 }
 
-export interface VariableDefaultValueDTO {
-	[key: string]: unknown;
-}
-
 export interface ZeustypesHostDTO {
 	/**
 	 * @type boolean

frontend/src/pages/DashboardPageV2/DashboardContainer/DashboardSettings/Variables/variableFormModel.ts

@@ -2,7 +2,7 @@ import {
 	DashboardtypesListVariableSpecSortDTO,
 	TelemetrytypesSignalDTO,
 } from 'api/generated/services/sigNoz.schemas';
-import type { DashboardtypesListVariableSpecDTODefaultValue } from 'api/generated/services/sigNoz.schemas';
+import type { VariableDefaultValueDTO } from 'api/generated/services/sigNoz.schemas';
 import { sortBy } from 'lodash-es';
 
 /**
@@ -136,7 +136,7 @@ export interface VariableFormModel {
 	 * Runtime-selected default, not editable in the management tab yet; carried
 	 * through edits so saving a definition doesn't clobber it.
 	 */
-	defaultValue?: DashboardtypesListVariableSpecDTODefaultValue;
+	defaultValue?: VariableDefaultValueDTO;
 }
 
 export function emptyVariableFormModel(): VariableFormModel {

pkg/signoz/openapi.go

@@ -39,6 +39,7 @@ import (
 	"github.com/SigNoz/signoz/pkg/statsreporter"
 	"github.com/SigNoz/signoz/pkg/types/authtypes"
 	"github.com/SigNoz/signoz/pkg/zeus"
+	"github.com/perses/spec/go/dashboard/variable"
 	"github.com/swaggest/jsonschema-go"
 	"github.com/swaggest/openapi-go"
 	"github.com/swaggest/openapi-go/openapi3"
@@ -104,6 +105,41 @@ func NewOpenAPI(ctx context.Context, instrumentation instrumentation.Instrumenta
 		return defaultDefName
 	}))
 
+	// variable.DefaultValue (perses) is the string | []string union used by a
+	// list variable's defaultValue. It marshals as a scalar-or-array, so its
+	// reflected struct shape (a bare object) is wrong. Emit it as a named oneOf
+	// component (VariableDefaultValue) and let defaultValue $ref it, instead of
+	// inlining the union onto the property: a named component gives downstream
+	// codegen a hook to canonicalize — oapi-codegen generates the union's
+	// Marshal/UnmarshalJSON and skaff's scalar-union pre-pass flattens it to a
+	// string attribute. An inline oneOf has no such component to hook.
+	reflector.JSONSchemaReflector().DefaultOptions = append(reflector.JSONSchemaReflector().DefaultOptions, jsonschema.InterceptSchema(func(params jsonschema.InterceptSchemaParams) (bool, error) {
+		if !params.Processed || !params.Value.IsValid() {
+			return false, nil
+		}
+
+		typ := params.Value.Type()
+		if typ.Kind() == reflect.Pointer {
+			typ = typ.Elem()
+		}
+		if typ != reflect.TypeOf(variable.DefaultValue{}) {
+			return false, nil
+		}
+
+		stringItem := jsonschema.String.ToSchemaOrBool()
+		params.Schema.Type = nil
+		params.Schema.Properties = nil
+		params.Schema.WithOneOf(
+			jsonschema.String.ToSchemaOrBool(),
+			(&jsonschema.Schema{}).
+				WithType(jsonschema.Array.Type()).
+				WithItems(jsonschema.Items{SchemaOrBool: &stringItem}).
+				ToSchemaOrBool(),
+		)
+
+		return false, nil
+	}))
+
 	reflector.Spec.WithInfo(*(&openapi3.Info{}).
 		WithTitle("SigNoz").
 		WithDescription("OpenTelemetry-Native Logs, Metrics and Traces in a single pane").

pkg/types/dashboardtypes/perses_replicas.go

@@ -156,23 +156,6 @@ type ListVariableSpec struct {
 	Name            string                 `json:"name" required:"true" minLength:"1"`
 }
 
-// PrepareJSONSchema types defaultValue as the string | []string union.
-func (ListVariableSpec) PrepareJSONSchema(s *jsonschema.Schema) error {
-	if _, ok := s.Properties["defaultValue"]; !ok {
-		return nil
-	}
-	stringItem := jsonschema.String.ToSchemaOrBool()
-	defaultValue := (&jsonschema.Schema{}).WithOneOf(
-		jsonschema.String.ToSchemaOrBool(),
-		(&jsonschema.Schema{}).
-			WithType(jsonschema.Array.Type()).
-			WithItems(jsonschema.Items{SchemaOrBool: &stringItem}).
-			ToSchemaOrBool(),
-	)
-	s.Properties["defaultValue"] = defaultValue.ToSchemaOrBool()
-	return nil
-}
-
 // validate mirrors perses ListVariableSpec validation (plus the digits-only name
 // check perses only applies to text variables); run by decodeSpec on unmarshal.
 func (s *ListVariableSpec) validate() error {