proposal: encoding/json/jsontext: add Kind.IsValid

[antoniszymanski]

Proposal Details

This is a sub-issue of the "encoding/json/v2" proposal (#71497).

I propose adding the following to the encoding/json/jsontext (Switch statement generates longer assembly).

func (k Kind) IsValid() bool {
	return k == 'n' || k == 'f' || k == 't' || k == '"' || k == '0' || k == '{' || k == '}' || k == '[' || k == ']'
}

Rationale

This provides a reliable way to determine whether Kind is valid, because as I learned, this is incorrect.

func (k Kind) IsValid() bool {
	return k != 0
}

[gabyhelp]

Related Issues

• proposal: encoding/json/jsontext: add constants for each Kind #71756

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[prattmic]

For reference, this is closely related to #71756, which in some variants proposes making the Kind completely opaque.

[dsnet]

We discussed this in the json/v2 proposal meeting and we're leaning towards:

1. Adding a KindInvalid constant (see #71756 ).
2. Making sure the API actually returns KindInvalid for invalid kinds.

The advantage of KindInvalid over an IsValid method is that it can be used within a switch statement (which are commonly used with the Kind type).

[gopherbot]

Change https://go.dev/cl/728380 mentions this issue: json/jsontext: normalize all invalid Kinds to 0