Better advertising of $ref sibling issues

[fredbi]

When writing yaml specs, indentation does matter.

It is vey easy to mismatch a $ref into a sibling object.

In that case, the parser overrides the schema by the $ref, which is correct behavior.

Often, valid vs invalid differ by only a few blanks.

Currently, the validator follows the parsed schema. Most likely, we get some difficult to understand errors such as 'xxx in body does not validate OneOf()' ... I found very frustrating to plow specs for hours to eventually figure out the problem.

Todo:

• A warning should be issued when $ref have sibling properties in schema.
• Similarly, $ref in inappropriate places according to swagger spec (not json schema) should be advertised as errors
• The previous line has been patched for the special case of headers by PR#44. This work around introduced a small bug, in the case the user spec's contains a "header" property with a "$ref" inside

[alexstojda]

@fredbi any progress on this?

[fredbi]

no I've very much busy patching up some other sides of go-openapi