jsondocck: replace JSONPath with jq as json query language.

[aDotInTheVoid]

Impetus: #142327 (comment)

Currently, jsondocck uses JSONPath to query the output in assertions. Unfortunately, it's not a particularly flexible query language. In particular, it can't feed the result of one query to index an object. We'd really like this, so we can run a query to get an ID, then look up the item with that ID.

Using jq, we can do this. It has an implementation in rust: https://docs.rs/jaq-core/2.2.0/jaq_core/index.html

How

In jsondoc, this place would need to be changed to call into jaq instead.

rust/src/tools/jsondocck/src/cache.rs

Lines 31 to 34 in 8da6239

	// FIXME: Make this failible, so jsonpath syntax error has line number.
	pub fn select(&self, path: &str) -> Vec<&Value> {
	jsonpath_rust::query::js_path_vals(path, &self.value).unwrap()
	}

When doing so, the contents of Cache::variables should be provided, so they can be used in selectors.

Test Migration

I think the longest part of this will be migrating the tests from jsonpath to jq. It might be possible to hack up jsondocck to call jsonpath_rust::parser::parse_json_path on all the JSONPath queries, and then convert the JSONPath ast to a equivalent jq query.

I'm not sure if this would be more or less effort than "just" doing it manually. But it'd be easier to review the resulting change this way, and it'd probably be more interesting.

[aDotInTheVoid]

@fluiderson, you expressed interest in working on this (#142327 (comment)).

Do you still want to? If so, please @ rustbot claim (without the space) to assign it to you. I can't, due to github permissions reasons.

[fluiderson]

@rustbot claim

[aDotInTheVoid]

and then convert the JSONPath ast to a equivalent jq query.

https://github.com/jqlang/jq/wiki/For-JSONPath-users is probably a useful start here

[aDotInTheVoid]

Why not something like jq?

See #t-rustdoc > jsondocck @ 💬. The disussion then was entirely about the availibility of rust impls, and not at all about the expressiveness of the query language.