Added find-first and find-last formatters with corresponding tests

[lr-brown]

This PR adds two new formatters to the compiler, find-first and find-last that allow you to find the first/last element that returns a truthy given a path and lookup. See this ticket for the reason we need these new formatters.

Syntax

find-last/first
find-last/first|PATH
find-last/first|LOOKUP PATH

Arguments

• PATH (optional)
  • Dot-separated path within each element. Returns the last/first element where the value at this path is truthy.
• LOOKUP (optional, used with PATH)
  • Context path resolving to an object. The array is treated as a list of keys; each key is looked up in this object and the last/first key whose looked-up value has a truthy value at PATH is returned.

Examples

Return the last element unconditionally:

JSON

{
  "items": ["a", "b", "c"]
}

Json-t

{items|find-last}

Output

c

Return the last element where a nested field is truthy:

JSON

{
  "items": [
    { "id": "a", "enabled": true },
    { "id": "b", "enabled": true },
    { "id": "c", "enabled": false }
  ]
}

Json-t

{.var @last items|find-last enabled}{@last.id}

Output

b

Look up each key in a separate object and return the last key with a truthy value at a path:

JSON

{
  "keys": ["a", "b", "c"],
  "map": {
    "a": { "enabled": false },
    "b": { "enabled": true },
    "c": { "enabled": true }
  }
}

Json-t

#pragma example=lookup
{keys|find-first map enabled}

Output

b

[CLAassistant]

All committers have signed the CLA.

[lr-brown]

Wondering if having two explicit formatters is preferred over one that takes a first/last prop

[pscheffer]

Wondering if having two explicit formatters is preferred over one that takes a first/last prop

My 2cents is it makes sense to keep them split as it is analogous to :first-child :last-child filters we already use in the frontend.

[phensley]

I think my point still stands about the 95% overlap in the code.

You could generalize this and create a function that takes 3 args, then implement 3 formatters that wrap that function find-first, find-last, and find-nth with less overall code (the "bundle bloat" concern for frontend).

CSS supports first-child, last-child, and nth-child, if you are concerned about parity with CSS pseudo-classes.

[phensley]

This change is publishing to Maven Central (and should be there in a few minutes) in version 2.11.1.