[BUG] Fix Swagger Parser doesn't handle in all cases well $refs in parameters

I have created the following issue in swagger-parser because in some cases it is resolving parameter references incorrectly.

• https://github.com/swagger-api/swagger-parser/issues/1948

If that issue is resolved quickly, I think it would be ideal to put the swagger-parser upload in the openapi-generator 7.0.0 upgrade.

Details

I have defined an api contract as follows:

├── openapi.yaml
├── product
    ├── product-api.yaml
    ├── product-components.yaml

openapi.yaml

openapi: 3.0.0
info:
  title: Demo
  description: Demo to crash parser
  version: 1.0.0
paths:
  /findById/{param1}:
    $ref: 'product/product-api.yaml#/paths/findById~1{param1}' 

product-api.yaml

paths:
  findById/{param1}:
    get:
      summary: Gets service health status
      parameters:
#        - $ref: '../product/product-components.yaml#/components/parameters/param1' #OK
        - $ref: 'product-components.yaml#/components/parameters/param1' #KO
      responses:
        '200':
          description: Success status
          content:
            application/json:
              schema:
                $ref: 'product-components.yaml#/components/schemas/responseBase' #OK

product-components.yaml

components:
  schemas:
    responseBase:
      type: object
      properties:
        status:
          type: string 
  parameters:
    param1:
      in: path
      name: param1
      schema:
        type: string
        maxLength: 2147483647
      description: Unique identifier

When parameters are referenced in this way, they fail (they take the current directory as root):

- $ref: 'product-components.yaml#/components/parameters/param1' 

Trace:

java.lang.RuntimeException: Unable to load RELATIVE ref: product-components.yaml path: swagger-parser/modules/swagger-parser-v3/src/test/resources/issue
	at io.swagger.v3.parser.util.RefUtils.readExternalRef(RefUtils.java:220)
	at io.swagger.v3.parser.ResolverCache.loadRef(ResolverCache.java:150)
	at io.swagger.v3.parser.processors.ExternalRefProcessor.processRefToExternalParameter(ExternalRefProcessor.java:755)
	at io.swagger.v3.parser.processors.ParameterProcessor.processParameter(ParameterProcessor.java:46)
	at io.swagger.v3.parser.processors.OperationProcessor.processOperation(OperationProcessor.java:43)
	at io.swagger.v3.parser.processors.PathsProcessor.processPaths(PathsProcessor.java:88)
	at io.swagger.v3.parser.OpenAPIResolver.resolve(OpenAPIResolver.java:72)
	at io.swagger.v3.parser.OpenAPIResolver.resolve(OpenAPIResolver.java:59)
	at io.swagger.v3.parser.OpenAPIV3Parser.resolve(OpenAPIV3Parser.java:238)
	at io.swagger.v3.parser.OpenAPIV3Parser.readContents(OpenAPIV3Parser.java:181)
	at io.swagger.v3.parser.OpenAPIV3Parser.readLocation(OpenAPIV3Parser.java:97)
	at io.swagger.v3.parser.test.OpenAPIV3ParserTest.testIssueJRM(OpenAPIV3ParserTest.java:452)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:59)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:56)
	at mockit.integration.junit4.JUnit4TestRunnerDecorator.executeTestMethod(JUnit4TestRunnerDecorator.java:157)
	at mockit.integration.junit4.JUnit4TestRunnerDecorator.invokeExplosively(JUnit4TestRunnerDecorator.java:71)
	at mockit.integration.junit4.FakeFrameworkMethod.invokeExplosively(FakeFrameworkMethod.java:29)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
	at org.junit.runners.BlockJUnit4ClassRunner$1.evaluate(BlockJUnit4ClassRunner.java:100)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:366)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:103)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:63)
	at org.junit.runners.ParentRunner$4.run(ParentRunner.java:331)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:79)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:329)
	at org.junit.runners.ParentRunner.access$100(ParentRunner.java:66)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:293)
	at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:413)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
	at com.intellij.rt.junit.IdeaTestRunner$Repeater$1.execute(IdeaTestRunner.java:38)
	at com.intellij.rt.execution.junit.TestsRepeater.repeat(TestsRepeater.java:11)
	at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:35)
	at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:232)
	at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:55)
Caused by: java.lang.RuntimeException: Could not find product-components.yaml on the classpath
	at io.swagger.v3.parser.util.ClasspathHelper.loadFileFromClasspath(ClasspathHelper.java:33)
	at io.swagger.v3.parser.util.RefUtils.readExternalRef(RefUtils.java:214)
	... 42 more

When they are referenced like this they go fine:

- $ref: '../product/product-components.yaml#/components/parameters/param1'

Prior to swagger-parser 2.0.31, the resolution of these references was correct (probably the bug is here:)

NOTE: Schemas from responses or request body work correctly in both cases.

my_openapi.zip

Reproduce the case described in OpenAPIV3ParserTest.testIssueJRM and inspect RefUtils, ResolverCache, ExternalRefProcessor, and ParameterProcessor in the stack trace. Compare parameter-reference resolution with the response-schema case, and review swagger-parser issue 1948 before changing openapi-generator. Done means the supplied nested YAML resolves both parameter-reference forms and the regression test passes.