rsonpath-specific behavior

We try to implement the JSONPath spec as closely as possible. There are currently two major differences between rsonpath’s JSONPath and the standard.

Nested descendant segments

The standard semantics of the descendant segment lead to duplicated results, and a potentially exponential blowup in execution time and output size. In rsonpath we diverge from the spec to guarantee unduplicated results:

$ rq '$..a..a' --json '{ "a": { "a": { "a": 42 } } }'
{ "a": 42 }
42

In standard semantics the value 42 would be matched twice1.

Unicode

Currently rsonpath compares JSON keys bytewise, meaning that labels using Unicode escape sequences will be handled incorrectly.

For example, the key "a" can be equivalently represented by "\u0041".

$ rq '$["a"]' --json '{ "a": 42 }'
42

The above results should be the same if either or both of the "a" characters were replaced with the "\u0041" unicode escape sequence, but rsonpath does not support it at this time. This limitation is known and tracked at #117.

1

The reason behind this is a bit subtle. The standard defines the result as a concatenation of lists of results of executing the rest of the query after a descendant segment, and a recursive execution of the entire query. So the inner "a" key in the example is matched first when evaluating the outermost one, and then again when evaluating the middle "a". We consider this to be counter-intuitive and undesirable.