[BUG][Go] UnmarshalJSON() does not allow unknown fields even when they are not forbidden in schema about openapi-generator

[ctreatma]

The model template only generates the decoder.DisallowUnknownFields() code if the generator thinks that additional properties are not allowed: https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/go/model_simple.mustache#L493-L511

What config are you passing in when running the generator? There is a disallowAdditionalPropertiesIfNotPresent config option that controls the behavior of generated code for all languages: https://openapi-generator.tech/docs/generators/go/#config-options

For legacy reasons, the disallowAdditionalPropertiesIfNotPresent defaults to true. This means that by default, the generator will produce models that assume additional properties are not allowed if the additionalProperties key is not explicitly specified.

To configure the generator to produce code that complies with the additionalProperties behavior documented in OAS, you have to set disallowAdditionalPropertiesIfNotPresent to false.

[dyurovskykh-tivo]

@wing328 @ctreatma
Please, check this bug.

[dyurovskykh-tivo]

@ctreatma
Thank you! I did not know about disallowAdditionalPropertiesIfNotPresent config.
When I run the generator like docker run --rm -u 1001:1001 -v "${PWD}:/local" openapitools/openapi-generator-cli generate --additional-properties=disallowAdditionalPropertiesIfNotPresent=false -i /local/test.yaml -g go -o /local/out/go, decoder.DisallowUnknownFields() is not generated