❓ JSON Path Dot Precedence

Hello Hackers,

A question about the behavior of the JSON Path parser. The docs[1] have this to say about numbers:

> Numeric literals in SQL/JSON path expressions follow JavaScript rules, which are different from both SQL and JSON in some minor details. For example, SQL/JSON path allows .1 and 1., which are invalid in JSON.

In other words, this is valid:

david=# select '2.'::jsonpath;
jsonpath
----------
2

But this feature creates a bit of a conflict with the use of a dot for path expressions. Consider `0x2.p10`. How should that be parsed? As an invalid decimal expression ("trailing junk after numeric literal”), or as a valid integer 2 followed by the path segment “p10”? Here’s the parser’s answer:

david=# select '0x2.p10'::jsonpath;
jsonpath
-----------
(2)."p10"

So it would seem that, other things being equal, a path key expression (`.foo`) is slightly higher precedence than a decimal expression. Is that intentional/correct?

Discovered while writing my Go lexer and throwing all of Go’s floating point literal examples[2] at it and comparing to the Postgres path parser. Curiously, this is only an issue for 0x/0o/0b numeric expressions; a decimal expression does not behave in the same way:

david=# select '2.p10'::jsonpath;
ERROR: trailing junk after numeric literal at or near "2.p" of jsonpath input
LINE 1: select '2.p10'::jsonpath;

Which maybe seems a bit inconsistent.

Thoughts on what the “correct” behavior should be?

Best,

David

[1]: https://www.postgresql.org/docs/devel/datatype-json.html#DATATYPE-JSONPATH
[2]: https://tip.golang.org/ref/spec#Floating-point_literals