[BC break] Custom validation with context + smaller fixes

[annismckenzie]

Smaller fixes

• fixed various code smells and coding style that the static analyzers found (vet, vetshadow, golint)
• updated test suite errors reported in Tests for IsRequestURI and IsRequestURL fail #118

Feature enhancement

I enhanced the custom type validators so their validation functions get the object being validated passed as a second argument. It is a BC break but the changes necessary are mechanical in nature (see the updated unit test for an example on how this can be used).

This is not finished yet (working on fixing #116) but I wanted to put this out there in order to ask you about the BC break: is that even an option? I thought about doing it in a backwards-compatible way but that would involve reflection. Variadic parameters aren't an option either. The only other way would be to wrap the value to validate and the object being validated in a custom object. That would make it more future-proof and the custom type validation function signature could be changed so as to not require passing an empty interface. Still, that also breaks BC or worse, breaks all current usages (because the custom validation wrapper object is also an interface{}).

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This change is

[annismckenzie]

Alright, this is now done. I took care of #118 and fixed #116. Unfortunately, the BC break was unavoidable – the only good thing is that projects updating the library after this is merged will get broken builds (bear with me here…) and the fix is mechanical in nature: just update the function signature from

  // old signature
  func(i interface{}) bool

to

  // new signature
  func(i interface{}, o interface{}) bool

and you're done.

I added a few tests that were missing but otherwise didn't change anything so as to not introduce regressions.

I have no clue why the Wercker build is failing, executing all tests locally takes about 0.5s but the Wercker build takes a minute before it fails. Maybe it's running into a timeout?

[annismckenzie]

Fixing the data race introduced another BC break:

  // before
  CustomTypeTagMap["customByteArrayValidator"] = CustomTypeValidator(func(i interface{}, o interface{}) bool {
    // ...
  })

to

  // after
  CustomTypeTagMap.Set("customByteArrayValidator", CustomTypeValidator(func(i interface{}, o interface{}) bool {
    // ...
  }))

Again, deeply sorry for the inconvenience. :-/

[ayeshapatel]

can u give example

[annismckenzie]

You can find an example in the readme: https://github.com/asaskevich/govalidator#custom-validation-functions. :)