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
someminor 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
thatbe parsed? As an invalid decimal expression ("trailing junk after numeric literal”), or as a valid integer 2
followedby 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
decimalexpression. 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
thePostgres path parser. Curiously, this is only an issue for 0x/0o/0b numeric expressions; a decimal expression does
notbehave 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
