Rework kubecfg diff code.

[mplzik]

The old code relied on gojsondiff library, which provides more semantic
JSON diffs. This library, however, had some long-standing issues which
have not been yet fixed, namely:

• Confusing Array Diff Output yudai/gojsondiff#24
• Incorrect diff when first item of array changed yudai/gojsondiff#30

These sometimes resulted in diffs that were too noisy and/or showed
false information; this has been reported as

#229

This patch reworks kubecfg's diff code to first marshal JSON using
golang's encoding/json and then calculates the diff using
diffmatchpatch library, formatting the output as close to the
original as possible. Although this results in a more
syntactic-level diff, it might just do the job until gojsondiff
gets the above-mentioned bugs fixed.

Signed-off-by: Milan Plzik milan.plzik@ceai.io

[mkmik]

I tried it with --diff-strategy subset and it shows "ERROR Differences found" although no differences are shown in the output. Example:

---
- live services zerozone.zerozone
+ config services zerozone.zerozone
  {
    "apiVersion": "v1",
    "kind": "Service",
    "metadata": {
      "labels": {
        "name": "foo"
      },
      "name": "foo",
      "namespace": "foo"
    },
    "spec": {
      "ports": [
        {
          "port": 8080
        }
      ],
      "selector": {
        "name": "foo"
      },
      "type": "LoadBalancer"
    }
  }
ERROR Differences found.

Master, for the same config shows:

...
-         "port": 8080
+         "port": 8080
...

[mplzik]

PTAL.

[mkmik]

LGTM.

but sadly EMENOMAINTAINER of this repo; pinging my colleague @anguslees.

[jjo]

LGTM also, thanks @emempi -- verified it fixes false diff positives
on numeric values, and much better handles e.g. configmap diffs
with multiline valued fields.

[anguslees]

@mkmik / @jjo: Thanks for doing the leg-work to verify the results.

Edit: @emempi .. and of course, thanks for the actual patch!