[BUG] Ref to another spec file doesn't work

Description

My openapi spec is split into multiple files. In some cases, one of the subfiles will refer to a component from another.

openapi-generator version

3.3.4, not sure on regression

OpenAPI declaration file content or url

allOf:
  - $ref: 'common.yaml#/components/schemas/MyRemoteSchema'
  - $ref: '#/components/schemas/MyLocalSchema'

Command line used for generation

./openapi-generator-cli.sh generate -i openapi/openapi.yaml  -g kotlin-spring -c config.json

OR

/openapi-generator-cli.sh generate -i openapi/openapi.yaml -g spring -c config.json

config.json:

{
  "groupId": "com.myco.api",
  "artifactId": "my-thing",
  "artifactVersion": "0.0.0.1",
  "sourceFolder": "src/main/java",
  "title": "My Super Cool Thing",
  "interfaceOnly": false,
  "java8": true,
  "async": true,
  "reactive": false,
  "library": "spring-boot"
}

Steps to reproduce

Run the command given above. The output on the command line will be:

[main] WARN  o.o.codegen.utils.ModelUtils - Failed to get the schema name: common.yaml#/components/schemas/MyObject
[main] WARN  o.o.codegen.DefaultCodegen - Error obtaining the datatype from ref:common.yaml#/components/schemas/MyObject. Default to 'object'

Related issues/PRs

Nothing exact

Suggest a fix

It appears like the code in codegen.utils.ModelUtils for getSimpleRef is assuming that the string will always start with either #/components or #/definitions. It is valid yaml to have it be common.yaml#/components. I think that section of code should perhaps check if the reference contains #/components or #/definitions instead.

Start in codegen.utils.ModelUtils.getSimpleRef and trace how the generator parses refs such as common.yaml#/components/schemas/MyRemoteSchema. Reproduce with the provided openapi-generator-cli.sh generate command and verify that cross-file schemas resolve without the reported datatype warnings.