[BUG][GO] use value receiver for JSON marshal

[perhallgren]

In the case of a required anyOf property, JSON marshalling would has been incorrect.

Required properties are not nullable, and thus always use value receivers. For the single case of anyOf models, a pointer receiver was used for MarshalJSON. All other instances of json marshalling use value receivers.

This change is simply to use a value receiver instead of a pointer receiver in the template for MarshalJSON on anyOf models.

Testing

On master, we can check that this is the only occurance of pointer receiver for json marshalling with

$ grep -ie "func (\w\+ \*.*) MarshalJSON" ./modules/openapi-generator/src/main/resources/go/*
./modules/openapi-generator/src/main/resources/go/model_anyof.mustache:func (src *{{classname}}) MarshalJSON() ([]byte, error) {

The above command gives an empty output with the proposed change.

Also verified with the test in this gist. In the created tmp folder:

$ java -jar ~/code/OpenAPITools/openapi-generator/modules/openapi-generator-cli/target/openapi-generator-cli.jar generate \
        --input-spec go-json-marshal.yaml \
        --generator-name go \
        --additional-properties "withGoMod=false" \
        --package-name gen \
        --output gen
[main] INFO  o.o.codegen.DefaultGenerator - Generating with dryRun=false
[...]
$ go test .
ok  	github.com/OpenAPITools/bugs	0.004s

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[perhallgren]

Pings for technical committee: @antihax @grokify @kemokemo @jirikuncar @ph4r5h4d @lwj5

[daisukixci]

Fixed worked on my spec, thank you for it!

[wing328]

thanks for the PR

do we need to apply the same fix model_oneof.mustache (oneOf template) as well?

[perhallgren]

No, it already uses a value receiver. I searched for other occurances using this:

$ grep -ie "func (\w\+ \*.*) MarshalJSON" ./modules/openapi-generator/src/main/resources/go/*

Which only gives a hit in model_anyof.mustache.

[wing328]

thanks for the confirmation.

can you please add a test or 2 in samples/openapi3/client/petstore/go/model_test.go?

you may want to update modules/openapi-generator/src/test/resources/3_0/go/petstore-with-fake-endpoints-models-for-testing-with-http-signature.yaml with new test schemas (e.g. anyOf)

[perhallgren]

Added a test, looks OK!

Failing here with:

    model_test.go:82: 
                Error Trace:    /home/circleci/OpenAPITools/openapi-generator/samples/openapi3/client/petstore/go/model_test.go:82
                Error:          Not equal: 
                                expected: "{\"fruit\":{\"Apple\":null,\"Banana\":{\"lengthCm\":23.4}}}"
                                actual  : "{\"fruit\":{\"lengthCm\":23.4}}"

And green with the fix.