Fix: "isAlias" of CodegenModel

[ackintosh]

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
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Description of the PR

components:
  schemas:
    MyParameterTextField:
      $ref: '#/components/schemas/AliasToString'
    AliasToString:
      type: string
      minLength: 1
      maxLength: 50

A CodegenModel instance built from the MyParameterTextField definition should be alias. (the instance should have a property isAlias = true.)

[ackintosh]

In some of generators (e.g. Kotlin which supports Type Alias), it may expected that the dataType property has a specific model type for better type alias support.

ref #2574

[ackintosh]

cc @OpenAPITools/generator-core-team

[wing328]

Looks like the fix breaks the haskell client generator:

➜  graphql-generator git:(ackintosh-is-alias) ./bin/haskell-http-client-petstore.sh
# START SCRIPT: ./bin/haskell-http-client-petstore.sh
java  -Xmx1024M -DloggerPath=conf/log4j.properties -jar ./modules/openapi-generator-cli/target/openapi-generator-cli.jar generate -t modules/openapi-generator/src/main/resources/haskell-http-client -i modules/openapi-generator/src/test/resources/2_0/petstore-with-fake-endpoints-models-for-testing.yaml -g haskell-http-client -o samples/client/petstore/haskell-http-client
[main] INFO  o.o.codegen.DefaultGenerator - OpenAPI Generator: haskell-http-client (client)
[main] INFO  o.o.codegen.DefaultGenerator - Generator 'haskell-http-client' is considered stable.
[main] WARN  o.o.codegen.utils.ModelUtils - Multiple schemas found in content, returning only the first one
[main] WARN  o.o.codegen.utils.ModelUtils - Multiple schemas found in content, returning only the first one
[main] WARN  o.o.codegen.utils.ModelUtils - Multiple schemas found in content, returning only the first one
[main] WARN  o.o.codegen.utils.ModelUtils - Multiple schemas found in content, returning only the first one
[main] WARN  o.o.codegen.utils.ModelUtils - Multiple schemas found in content, returning only the first one
[main] WARN  o.o.codegen.utils.ModelUtils - Multiple schemas found in content, returning only the first one
[main] WARN  o.o.codegen.utils.ModelUtils - Multiple schemas found in content, returning only the first one
[main] WARN  o.o.codegen.utils.ModelUtils - Multiple schemas found in content, returning only the first one
[main] WARN  o.o.codegen.utils.ModelUtils - Multiple schemas found in content, returning only the first one
[main] WARN  o.o.codegen.utils.ModelUtils - Multiple schemas found in content, returning only the first one
[main] WARN  o.o.codegen.utils.ModelUtils - Multiple schemas found in content, returning only the first one
[main] WARN  o.o.codegen.utils.ModelUtils - Multiple schemas found in content, returning only the first one
[main] WARN  o.o.codegen.utils.ModelUtils - Multiple schemas found in content, returning only the first one
[main] WARN  o.o.codegen.utils.ModelUtils - Multiple schemas found in content, returning only the first one
[main] WARN  o.o.codegen.utils.ModelUtils - Multiple schemas found in content, returning only the first one
[main] WARN  o.o.codegen.utils.ModelUtils - Multiple schemas found in content, returning only the first one
[main] WARN  o.o.codegen.utils.ModelUtils - Multiple schemas found in content, returning only the first one
[main] INFO  o.o.c.l.HaskellHttpClientCodegen - Hint: Environment variable HASKELL_POST_PROCESS_FILE not defined so the Haskell code may not be properly formatted. To define it, try 'export HASKELL_POST_PROCESS_FILE="$HOME/.local/bin/hfmt -w"' (Linux/Mac)
Exception in thread "main" java.lang.RuntimeException: Could not process model 'Dog'.Please make sure that your schema is correct!
	at org.openapitools.codegen.DefaultGenerator.generateModels(DefaultGenerator.java:470)
	at org.openapitools.codegen.DefaultGenerator.generate(DefaultGenerator.java:919)
	at org.openapitools.codegen.cmd.Generate.run(Generate.java:396)
	at org.openapitools.codegen.OpenAPIGenerator.main(OpenAPIGenerator.java:60)
Caused by: java.lang.NullPointerException
	at org.openapitools.codegen.languages.HaskellHttpClientCodegen.postProcessModels(HaskellHttpClientCodegen.java:1234)
	at org.openapitools.codegen.DefaultGenerator.processModels(DefaultGenerator.java:1195)
	at org.openapitools.codegen.DefaultGenerator.generateModels(DefaultGenerator.java:465)
	... 3 more

[hosswald]

@ackintosh @wing328 I realized that #2574 is still open... I would appreciate if this would find its way into a release soon. Thanks.

[ackintosh]

Thanks for pinging me. I'll restart working on this issue later this week. 😃

[ackintosh]

I've fixed the error in haskel client generator. @wing328 Please have a look when you have time.

[wing328]

cc @OpenAPITools/generator-core-team as well.

[wing328]

Looks good to me but I didn't test it locally.