[BUG][Kotlin] Wrong default value is generated if the field type is BigDecimal

[alitams]

Bug Report Checklist

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

Description

If one of the type's mapping value is BigDecimal, and sets a default value, then a simple Int is given to the value.

Generated:

val bar: java.math.BigDecimal? = 0

Expected:

val bar: java.math.BigDecimal? = java.math.BigDecimal.ZERO

(or BigDecimal(0))

openapi-generator version

5.3.0

OpenAPI declaration file content or url

...
schemas:
  Foo:
      description: 'Xy'
      type: object
      properties:
        bar:
          type: number
          default: 0

Generation Details

java -jar -agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=5005 modules/openapi-generator-cli/target/openapi-generator-cli.jar generate \
   -i xy.yaml \
   -g kotlin-client \
   -o gen/generated \
   --additional-properties=library=jvm-retrofit2,useRxJava3=true,dateLibrary=threetenbp-localdatetime,enumPropertyNaming=UPPERCASE,serializationLibrary=jackson,enablePostProcessFile=true 

Steps to reproduce

Generate the code below, and check the result.

Related issues/PRs

Suggest a fix

The BigDecimal should handled to generate the schema well.

For example:

    override fun toDefaultValue(schema: Schema<*>?): String? {
        val referencedSchema = ModelUtils.getReferencedSchema(this.openAPI, schema)
        val defaultValue =
            if (referencedSchema.default is BigDecimal) {
                getBigDecimalDefaultValue(referencedSchema.default as BigDecimal)
            } else {
                super.toDefaultValue(schema)
            }

        return defaultValue ?: referencedSchema.default?.toString()
    }

[jaycarlton]

I see the same problem in Java. I was using

    ServiceUsage:
      description: Service Usage Consumer Quota Overrides
      properties:
        bigQueryDailyUsageQuotaOverrideValueBytes:
          description: |-
            Daily maximum query usage per project. Use 0 for no override (default limit is
            effectively unlimited).
          type: number
          format: long
          default: 0
      type: object

And the generated code tried to do

  @JsonProperty("bigQueryDailyUsageQuotaOverrideValueBytes")
 private BigDecimal bigQueryDailyUsageQuotaOverrideValueBytes = 0;

which fails at runtime with

error: incompatible types: int cannot be converted to BigDecimal
private BigDecimal bigQueryDailyUsageQuotaOverrideValueBytes = 0;

[sjoblomj]

@alitams: I have provided a PR to fix this bug in #12213.

@jaycarlton: I am unable to reproduce your results in the Java client. Could you please provide the generator settings that you use when the bug appears?

[jaycarlton]

@sjoblomj We actually use swagger-codegen, so unless the bug is before the fork (assuming I have the history right), it wouldn't necessarily show up here. Sorry for the confusion.