Allow dot notation without root in Proposal A

[glyn]

Many of the implementations allow eliding the dot where a dot child appears at the start of the path. See https://cburgmer.github.io/json-path-comparison/results/dot_notation_without_root.html.

This seems like reasonable syntactic sugar and I'd like it to be considered for Proposal A. If this proposal is rejected, it would be great to document the rational.

[cburgmer]

I must admit with Proposal A so far I've been conservative and restrictive. While this might make it easier for implementers, it does not favour the user. So, I'm happy to open up a little.

Dot child without the root so far is the only case I could come up with as a short form. As such I feel introducing a single exception might provide more headache than help. If we see other short forms, that concern would be void though. Do we have others?

[glyn]

Perhaps ..name should be regarded as a contracted form of ...name? I know we probably want to avoid the long form, but the short form could be expressed as a combination of .. and a dot child with elided dot.

[remorhaz]

Here is k8s dialect of JsonPath, and it oficially allows to omit root (k8s uses exponent-io/jsonpath - seems we don't have it in the table yet).

[remorhaz]

As for me, root can be easily omitted in outer expressions ($.foo -> .foo), but that may become confusing in filters ($.foo[?(@.bar==$.baz)] -> .foo[?(@.bar==.baz)]? Or should we omit most commonly used @: .foo[?(.bar==$.baz)]?). Too many defaults may cause more problems than solve.

[glyn]

The OP was about eliding the dot from a dot child at the start of a JSONPath and assumed, perhaps incorrectly, that the root ($) could already be elided at the start of a JSONPath. I think it should certainly be ok to omit both at the start of a JSONPath, but I think it's too confusing and error prone to allow either (or indeed @s) to be omitted within filter expressions.

[cleidiano]

I think that make $ optional could cause more problem then solve, it could make expression more confuse, my personal preference is to maintain $ required.

[glyn]

Here is k8s dialect of JsonPath, and it oficially allows to omit root (k8s uses exponent-io/jsonpath - seems we don't have it in the table yet).

Where is exponent-io/jsonpath used by Kubernetes? I was under the impression that kubectl uses k8s client jsonpath, but I may be wrong.

(I spent half an hour a while back trying to add the k8s client jsonpath to the table, but I lost the will to live trying to suss out the usages of interface {}.)

[remorhaz]

Where is exponent-io/jsonpath used by Kubernetes?

I've just looked into it's go.mod without further investigations, so I may be wrong, too.

[glyn]

As far as kubectl is concerned,exponent-io/jsonpath seems to be used only during schema validation. A recent PR modifies the JSONPath behaviour of kubectl by changing k8s client jsonpath. Confusing, eh?