Improve handling of invalid engine specifications

[caittrip]

Currently, the engine is validated in "R/properties.R" with this code:
engine_type <- new_property( class = class_character, validator = function(value) { if (!(value %in% c("TDA", "ripserr"))) { "must be TDAorripserr." } }, default = "TDA" )

If the user provides an invalid engine name, or specifies an engine that is incompatible with the requested filtration, the package currently stops with an error.

Possible Improvements
I'm interested in feedback on which method(s) would be best out of these:

• Keep the current behavior and improve the error message to be more descriptive
• Automatically correct obvious mistakes (e.g. fix "tda" to be "TDA")
• Automatically switch to the compatible engine if an incompatible engine is chosen, while issuing a warning

[caittrip]

@corybrunson

[corybrunson]

Thanks @caittrip for raising the issue!

I'm interested in others weighing in on bullets 1 and 3. On bullet 2, i believe phreng should be strict: Only exact matches to engine (package) names should be accepted. I have two main reasons: (1) This follows the convention of {parsnip}. (2) phreng is meant not only for interactive use but as a plug-in to {gggda} and {tdarec}, possibly among others later. I think lenience with these things only makes sense for purely interactive tools, i.e. when the user is calling the function directly, since it can require special handling or allow bugs to pop up unexpectedly when it is buried in source code.