spec.ExpandSpec doesn't seem to terminate in some swagger spec with recursive references about spec HOT 8 CLOSED

The "isSeen" check is supposed to be the "parentRefs".
I found a first bug with unnormalized parent refs in isCircular, but this is not enough to resolve your test case.

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Looks like when the same $ref participates to several cycles, the simple path walking algorithm fails.
If I cache somewhere a memory of previous circular ref found, the hang is resolved.
Let's see how it goes with more extended tests...

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My solution works, but not as expected: depending on which cycle was first detected, the expanded result varies from run to run. Trying another way...

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Here is a more tractable test case demonstrating this issue.

swagger: "2.0"
info: 
  version: "0.0.1"
basePath: "/"
paths: 
  /cycles: 
    get: 
      responses: 
        200: 
          description: "ok"
          schema: 
            $ref: "#/definitions/node0"
definitions: 
  node0:
    type: object
    properties:
      p00:
        $ref: '#/definitions/node1'
      p01:
        $ref: '#/definitions/node3'
  node1:
    type: object
    properties:
      p1:
        $ref: '#/definitions/node2'
  node2:
    type: object
    properties:
      p2:
        $ref: '#/definitions/node0'
  node3:
    type: object
    properties:
      p3:
        $ref: '#/definitions/node1'

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@elakito I did some research on this today and produced a PR which is more like a work around.

Your comments are welcome.

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Fixed with PR#81.
However there are some limitations with this fix, that I am going to detail in more targeted issues.

@elakito feel free to reopen this if you think we missed an important point.

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@fredbi looks good. Thanks

from spec.

Hello @elakito

While fixing this with @pytlesk4, it occurred that we covered this use case, but some more devious
issues still remain. I did not find time to open a specific issue on those.

So for the record:

• expansion result with several cycles sharing a spec node remains non-deterministic, and the shortest cycle is not necessarily the one retained
• when cycles are formed in a remote, the resulting $ref is left as remote, so the expanded result
  is not entirely contained in a single root

Those are tricky cases...

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