[Go] skip validator import if oneOf discriminator lookup is enabled

[ctreatma]

The Go generator produces invalid code for oneOf models that have discriminators when useOneOfDiscriminatorLookup is set to true. In this case, the model imports gopkg.in/validator.v2 but does not use it because validation is skipped when discriminator lookup is enabled.

This updates the Go generator so that the validator import is skipped if discriminator lookup is enabled. In order to make this change I had to move the validator import from AbstractGoCodegen to GoClientCodegen; this is a safe change because the oneOf validation code only exists in the Go client generator templates, not in the other Go generators.

This also updates the Go generator so that, when useOneOfDiscriminator is set to false and the gopkg.in/validator.v2 is used by a model, the validation library is included in the generated go.mod and go.sum files.

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@wing328

[wing328]

i did a test locally and the fix simply rearranged the import

--- a/model_object.go
+++ b/model_object.go
@@ -12,8 +12,8 @@ package openapi

 import (
        "encoding/json"
-       "gopkg.in/validator.v2"
        "fmt"
+       "gopkg.in/validator.v2"
 )

 // Object - struct for Object

and here is the error message I still got after applying the fix:

$ go test
model_object.go:16:2: no required module provides package gopkg.in/validator.v2; to add it:
        go get gopkg.in/validator.v2

[ctreatma]

This fix specifically covers the case where the validator.v2 import is specified in the model file but not used in the same file. The error you are running into is a different bug; when the validator.v2 library was added to the model files for validation, it was not added to the go.mod.mustache template. I haven't run into that bug in real use because we automatically run go mod tidy after generating the code, which automatically fixes our go.mod.

I'm happy to fix the missing dependency in go.mod.mustache while I'm in here, but I'm not entirely sure how to do that. The decision to import validator.v2 is made at the model level. Is there an existing pattern I can copy for setting a global flag that go.mod.mustache can reference if any model imported validator.v2?

[wing328]

When post processing the models, what about setting additional properties (e.g. importValidatorV2), which can be accessed by go.mod.mustache?

[wing328]

confirmed no longer seeing the error after your fix.