A helper to write the JSON OpenAPI spec from tapir (https://github.com/softwaremill/tapir)

GenerateSwaggerJson.scala

package io.policarp

import java.io.{BufferedWriter, FileWriter}
import java.nio.file.Paths

import cats.implicits._
import cats.kernel.Semigroup
import io.circe.Printer
import io.circe.syntax._
import tapir.docs.openapi._
import tapir.openapi.circe._
import tapir.openapi.{Components, OpenAPI, PathItem}

import scala.annotation.tailrec
import scala.collection.immutable.ListMap

/**
 * A helper to generate an OpenAPI JSON spec from tapir endpoints
 */
object GenerateSwaggerJson {

  implicit val openAPISemigroup: Semigroup[OpenAPI] = Semigroup.instance((a, b) => {

    @tailrec
    def mergePaths(a: OpenAPI, paths: ListMap[String, PathItem]): OpenAPI = {
      paths.toList match {
        case Nil => a
        case (path, pathItem) :: Nil => a.addPathItem(path, pathItem)
        case (path, pathItem) :: tail => mergePaths(a.addPathItem(path, pathItem), tail.toListMap)
      }
    }

    def mergeComponents(a: OpenAPI, optComponents: Option[Components]): OpenAPI = {
      val optionalMerge =
        for {
          bComponents <- optComponents
          aComponents <- a.components
        } yield {
          val schemas = (bComponents.schemas.toSet union aComponents.schemas.toSet).toListMap
          val securitySchemas = (bComponents.securitySchemes.toSet union aComponents.securitySchemes.toSet).toListMap
          Components(schemas, securitySchemas)
        }

      a.copy(components = optionalMerge.orElse(a.components))
    }

    mergeComponents(mergePaths(a, b.paths), b.components)
  })

  def main(args: Array[String]): Unit = {
    
    val endpointA = ???
    val endpointB = ???

    // endpoints to include
    val openAPI = endpointA |+| endpointB

    val swaggerFile = Paths.get("src/main/resources/static/doc/swagger.json").toFile // or wherever you want to write it

    val writer = new BufferedWriter(new FileWriter(swaggerFile))
    writer.write(Printer.spaces2.copy(dropNullValues = true).print(openAPI.asJson))
    writer.close()

  }

}