Add an option to disable errorVerbose

[makotonakai]

This PR adds disableErrorVerbose option to Logger type.
This option allows users to disable the output of error verbose when they use pkg/errors.

Closes #650 #1168

[prashantv]

We avoid adding new struct fields to the Field type for performance reasons, as the struct is passed as a value.

We could add a new FieldType to indicate an error that should only have the message included, though that could have backwards compatibility concerns with some encoders.

[makotonakai]

@prashantv

I appreciate your feedback. I will create a new type with error field and DisableErrorVerbose field.

[makotonakai]

@prashantv

Sorry for bothering you. Could you review my PR, please?

[Amphaal]

Also eager to see this merged ! Many thanks in advance for your consideration :)

[prashantv]

Here's a simple test that shows that this approach does not work in common cases:

func TestDisableErrorVerbose(t *testing.T) {
	err := errTooManyUsers(4) // custom error with %+v formatting.

	logger := zap.NewExample(zap.DisableErrorVerbose())
	logger.Error("test error log", zap.Error(err))
	logger.Info("test info log", zap.Error(err))
	if ce := logger.Check(zap.InfoLevel, "test check"); ce != nil {
		ce.Write(zap.Error(err))
	}
}

This outputs:

{"level":"error","msg":"test error log","test error log":"4 too many users"}
{"level":"info","msg":"test info log","error":"4 too many users","errorVerbose":"4 too many users verbose"}
{"level":"info","msg":"test check","error":"4 too many users","errorVerbose":"4 too many users verbose"}

Though the Error method is handled, other methods are not, and the path for logger.Check can't be handled with this approach.

This approach also has some performance implications as it iterates over every field and checks the type, though it only impacts the DisableErrorVerbose case.

Before a code review, I'd recommend discussing the design on the issue to make sure it will solve the problem fully (and ideally in a performant way).