Access (Untagged) Port Config check crashes on FEX attachment fault DN #481

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Describe the bug

The Access (Untagged) Port Config (F0467 native-or-untagged-encap-failure) check returns an unexpected error when the fault is associated with an FEX attachment.

The current DN parser recognizes the standard fvStPathAtt form:

.../stpathatt-[{pathName}]/nwissues/fault-F0467

APIC model documentation also defines the fvExtStPathAtt form used for FEX attachments:

.../extstpathatt-[{pathName}]-extchid-{extChId}/nwissues/fault-F0467

When the FEX form does not match the current regex, the fallback path calls:

unformatted_data.append(fc, fault_description, recommended_action)

Because list.append() accepts one argument, the check raises:

TypeError: append() takes exactly one argument (3 given)

This changes an actionable FAIL - OUTAGE WARNING!! finding into ERROR !! and prevents the fault details from being displayed.

Script output

The following output uses synthetic, non-customer-identifying values:

[Check 25/102] Access (Untagged) Port Config
(F0467 native-or-untagged-encap-failure)...
Unexpected Error: append() takes exactly one argument (3 given) ERROR !!

Traceback (most recent call last):
  File "aci-preupgrade-validation-script.py", line <wrapper-line>, in wrapper
    r = check_func(*args, **kwargs)
  File "aci-preupgrade-validation-script.py", line <check-line>, in access_untagged_check
    unformatted_data.append(fc, faultInst["faultInst"]["attributes"]["descr"], recommended_action)
TypeError: append() takes exactly one argument (3 given)

Representative scrubbed fault DN:

topology/pod-1/node-101/local/svc-policyelem-id-0/uni/epp/fv-[uni/tn-TENANT-A/ap-APP-A/epg-EPG-A]/node-101/extstpathatt-[eth1/10]-extchid-110/nwissues/fault-F0467

Representative scrubbed description:

Configuration failed for uni/tn-TENANT-A/ap-APP-A/epg-EPG-A node 101 eth1/10 on FEX 110 due to Only One Native or Untagged Encap Allowed on Interface

To Reproduce

1. Return an active faultInst whose changeSet contains native-or-untagged-encap-failure.

2. Use the documented FEX DN form:

   .../node-101/extstpathatt-[eth1/10]-extchid-110/nwissues/fault-F0467
   

3. Run access_untagged_check.

4. Observe that the DN does not match the stpathatt-only regex.

5. Observe the fallback raising TypeError from list.append().

The current positive unit-test fixtures use only stpathatt-[...] DNs and assert only the final result, so they do not exercise this path.

Expected behavior

The check should support both APIC-documented direct attachment forms:

stpathatt-[{pathName}]
extstpathatt-[{pathName}]-extchid-{extChId}

For the FEX example, the check should return FAIL - OUTAGE WARNING!! and preserve the port and FEX ID in the failure details.

If a future or otherwise unrecognized DN is returned, the fallback should append one complete row:

unformatted_data.append([fc, fault_description, recommended_action])

An unrecognized DN must produce an unformatted failure entry rather than an unexpected check error.

Additional context

APIC model documentation identifies:

• fvStPathAtt RN: stpathatt-[{pathName}]
• fvExtStPathAtt RN: extstpathatt-[{pathName}]-extchid-{extChId}
• fvNwIssues beneath both attachment types
• faultInst RN: fault-{code}

Suggested regression coverage:

1. Existing non-FEX stpathatt fault.
2. FEX extstpathatt ... extchid fault.
3. Unknown or malformed DN exercising unformatted_data.
4. Assertions for data and unformatted_data, not only the overall result.