[SPRING] Parameters defined on the `path` level are skipped during the generation when path definition is in separate file.

Description

Parameters defined on the path level (applicable for all methods for this path) are skipped during the generation when path definition is in separate file.
Language: Spring, generating controller interfaces

Swagger-codegen version

3.0.27

Swagger declaration file

openapi.yaml

openapi: 3.0.4
info:
  title: Test
  description: Test project
  version: 0.1.0
servers:
  - url: http://localhost:8080
    description: development server

components:

paths:
  /test/{testParam}:
    $ref: "path.yaml"

path.yaml

summary: Operation on configuration group
get:
  responses:
    '200':
      description: "OK"
    default:
      description: "ERROR"

parameters:
  - name: testParam
    in: path
    required: true
    schema:
      type: string

Output: (TestApi.java):

/**
 * NOTE: This class is auto generated by the swagger code generator program (3.0.27).
 * https://github.com/swagger-api/swagger-codegen
 * Do not edit the class manually.
 */
package com.example.controllers;

import com.fasterxml.jackson.databind.ObjectMapper;
import io.swagger.v3.oas.annotations.Operation;
import io.swagger.v3.oas.annotations.Parameter;
import io.swagger.v3.oas.annotations.enums.ParameterIn;
import io.swagger.v3.oas.annotations.responses.ApiResponses;
import io.swagger.v3.oas.annotations.responses.ApiResponse;
import io.swagger.v3.oas.annotations.media.ArraySchema;
import io.swagger.v3.oas.annotations.media.Content;
import io.swagger.v3.oas.annotations.media.Schema;
import io.swagger.v3.oas.annotations.security.SecurityRequirement;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.validation.annotation.Validated;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestHeader;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RequestPart;
import org.springframework.web.multipart.MultipartFile;
import org.springframework.web.bind.annotation.CookieValue;

import javax.servlet.http.HttpServletRequest;
import javax.validation.Valid;
import javax.validation.constraints.*;
import java.io.IOException;
import java.util.List;
import java.util.Map;
import java.util.Optional;

@javax.annotation.Generated(value = "io.swagger.codegen.v3.generators.java.SpringCodegen", date = "2021-07-08T11:54:07.880831+02:00[Europe/Warsaw]")
@Validated
public interface TestApi {

    Logger log = LoggerFactory.getLogger(TestApi.class);

    default Optional<ObjectMapper> getObjectMapper(){
        return Optional.empty();
    }

    default Optional<HttpServletRequest> getRequest(){
        return Optional.empty();
    }

    default Optional<String> getAcceptHeader() {
        return getRequest().map(r -> r.getHeader("Accept"));
    }

    @Operation(summary = "", description = "", tags={  })
    @ApiResponses(value = { 
        @ApiResponse(responseCode = "200", description = "OK"),
        
        @ApiResponse(responseCode = "200", description = "ERROR") })
    @RequestMapping(value = "/test/{testParam}",
        method = RequestMethod.GET)
    default ResponseEntity<Void> testTestParamGet() {
        if(getObjectMapper().isPresent() && getAcceptHeader().isPresent()) {
        } else {
            log.warn("ObjectMapper or HttpServletRequest not configured in default TestApi interface so no example is generated");
        }
        return new ResponseEntity<>(HttpStatus.NOT_IMPLEMENTED);
    }

}

Command line used for generation

java -jar swagger-codegen-cli-3.0.27.jar generate -i api/openapi.yaml -c swagger-codegen-spring-config.json -l spring -o result/

swagger-codegen-spring-config.json:

{
  "modelPackage": "com.example",
  "apiPackage": "com.example.controllers",
  "dateLibrary": "java8",
  "java8": true,
  "interfaceOnly": true,
  "useBeanValidation": true
}

Steps to reproduce

# Clone repository
git clone https://github.com/xsw2-2wsx/PossibleSwaggerCodegenBug
cd PossibleSwaggerCodegenBug

# Generate 
java -jar swagger-codegen-cli-3.0.27.jar generate -i api/openapi.yaml -c swagger-codegen-spring-config.json -l spring -o result/

# Display the result
cat result/src/main/java/com/example/controllers/TestApi.java

Related issues/PRs

#11088

Start by reproducing the command against openapi.yaml and path.yaml, then inspect the generated TestApi.java to trace where the path-level testParam is lost. Done means the generated Spring controller interface includes testParam for the referenced path while preserving the existing endpoint output.