ZipkinTracingAutoConfiguration does not guard for the absence of an Encoding bean

[snicoll]

I suppose this was due to the codebase modularization so I am going to flag that as a task.

A sample app with spring-boot-zipkin fails as follows:

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APPLICATION FAILED TO START
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Description:

Parameter 0 of method mutableSpanBytesEncoder in org.springframework.boot.tracing.autoconfigure.zipkin.ZipkinTracingAutoConfiguration$BraveConfiguration required a bean of type 'zipkin2.reporter.Encoding' that could not be found.


Action:

Consider defining a bean of type 'zipkin2.reporter.Encoding' in your configuration.

Looking at the auto-configuration, it doesn't have a condition for this bean. Also, this bean seems to be contributed by ZipkinAutoConfiguration but those two auto-configurations don't declare an explict order.