[BUG][JAVA] import mapping of alias types in API interface

[PhilippParis]

Bug Report Checklist

• [x] Have you provided a full/minimal spec to reproduce the issue?
• [x] Have you validated the input using an OpenAPI validator (example)?
• [ ] Have you tested with the latest master to confirm the issue still exists?
• [x] Have you searched for related issues/PRs?
• [x] What's the actual output vs expected output?
• [x] [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

when using importMapping for alias types, the generated code does not use the importmapping in the api interface

Expected

    @POST
    @Path("/{id}")
    Response typeAliasIdPost(@PathParam("id") foo.bar.TypeAlias id);

Actual

    @POST
    @Path("/{id}")
    Response typeAliasIdPost(@PathParam("id") String id);

openapi-generator version

5.0.0

OpenAPI declaration file content or url

https://gist.github.com/PhilippParis/28c40d590b4a9019cb8040b143e09884

Generation Details

<generatorName>jaxrs-spec</generatorName>
<interfaceOnly>true</interfaceOnly>
 <java8>true</java8>
<importMappings>
    <importMapping>TypeAlias=foo.bar.TypeAlias</importMapping>
</importMappings>

Steps to reproduce

run openapi-generator 5.0.0 with specified generation details

Related issues/PRs

https://github.com/OpenAPITools/openapi-generator/issues/3589

[borsch]

The problem here is that you describe this object by your own here https://gist.github.com/PhilippParis/28c40d590b4a9019cb8040b143e09884#file-openapi-yaml-L36

to work with alias do the following

1. don't create you own definition for alias in yaml file
2. in place where you need to use that alias don't $ref them, but just use type: TypeAlias

At least this is how I configured alias for my project. Version of openapi-maven-plugin-generator is 4.3.1 Example:

/type-alias/{id}:
    post:
      parameters:
        - name: id
          in: path
          required: true
          schema:
            type: TypeAlias     <--
      responses:
        200:
          description: OK

[PhilippParis]

I've just tested this, and it also works in version 5.0.0 But without the definition of the alias type the yaml is an incomplete api specification and cannot be used by a third party..

[borsch]

I'll fix this

[Zomzog]

I think the issue is that "TypeAlias" is a String, It's impossible to generate in java such object that extends String. How looks the custom implementation provided?

[creckord]

The problem here is that in DefaultCodegen#fromParameter, the schema gets prematurely dereferenced - losing the schema name that is later used to handle the importMapping/typeMapping/languageSpecificPrimitives stuff through a call to DefaultCodegen#fromProperty.

In my projects, everything looks good when I either avoid the dereferencing in DefaultCodegen#fromParameter:

    parameterSchema = unaliasSchema(parameterSchema, importMapping); // <-- this was Collections.emptySet()

or hand the original schema of the parameter into DefaultCodegen#fromProperty:

   CodegenProperty codegenProperty = fromProperty(parameter.getName(), 
            parameter.getSchema() != null ? parameter.getSchema() : parameterSchema);

However, I have no clue why the unaliasSchema was done without importMappings in the first place, so I'm not sure what breakage this might cause (at least all tests stay green).