feat: allow comparing OAS 3.0 to 3.1 (#31)

Author: b41ex

src/api.ts

@@ -14,9 +14,23 @@ import {
   SPEC_TYPE_OPEN_API_30,
   SPEC_TYPE_OPEN_API_31,
   SpecType,
+  OpenApiSpecVersion,
 } from '@netcracker/qubership-apihub-api-unifier'
 import { DEFAULT_NORMALIZED_RESULT, DEFAULT_OPTION_DEFAULTS_META_KEY, DEFAULT_OPTION_ORIGINS_META_KEY, DIFF_META_KEY } from './core'
 
+function isOpenApiSpecVersion(specType: SpecType): specType is OpenApiSpecVersion {
+  return specType === SPEC_TYPE_OPEN_API_30 || specType === SPEC_TYPE_OPEN_API_31
+}
+
+function areSpecTypesCompatible(beforeType: SpecType, afterType: SpecType): boolean {
+  if (beforeType === afterType) {
+    return true
+  }
+  
+  // Allow comparison between different OpenAPI versions
+  return isOpenApiSpecVersion(beforeType) && isOpenApiSpecVersion(afterType)
+}
+
 export const COMPARE_ENGINES_MAP: Record<SpecType, CompareEngine> = {
   [SPEC_TYPE_JSON_SCHEMA_04]: compareJsonSchema(SPEC_TYPE_JSON_SCHEMA_04),
   [SPEC_TYPE_JSON_SCHEMA_06]: compareJsonSchema(SPEC_TYPE_JSON_SCHEMA_06),
@@ -31,7 +45,7 @@ export const COMPARE_ENGINES_MAP: Record<SpecType, CompareEngine> = {
 export function apiDiff(before: unknown, after: unknown, options: CompareOptions = {}): CompareResult {
   const beforeSpec = resolveSpec(before)
   const afterSpec = resolveSpec(after)
-  if (beforeSpec.type !== afterSpec.type) {
+  if (!areSpecTypesCompatible(beforeSpec.type, afterSpec.type)) {
     throw new Error(`Specification cannot be different. Got ${beforeSpec.type} and ${afterSpec.type}`)
   }
   const engine = COMPARE_ENGINES_MAP[beforeSpec.type]