FR: Error handling when variable is not found: specific error message and class

[DanChaltiel]

When using an unknown variable in glue(), the error message can be a little cryptic:

library(glue)
x=5
glue("x={x}")
#> x=5
glue("w={w}")
#> Error in eval(parse(text = text, keep.source = FALSE), envir): object 'w' not found

^{Created on 2021-10-24 by the reprex package (v2.0.1)}

This is most true when glue() is used within a package and even more if the pattern is provided by the package user.
A specific message, such as "Could not find variable 'w' when glueing '{pattern}'", would make it much clearer.

Moreover, as read in the book "Advanced R":

One of the challenges of error handling in R is that most functions generate one of the built-in conditions, which contain only a message and a call. That means that if you want to detect a specific type of error, you can only work with the text of the error message. This is error-prone, not only because the message might change over time, but also because messages can be translated into other languages.

Indeed, dealing with user-defined patterns in glue throwing this error would be a million times easier if this error had a specific error subclass that you would be able to check, as rlang::abort(.subclass=) would do.

Would this be an acceptable feature request?

[hadley]

We certainly now have the technology to wrap this to make it clear that it's coming from glue.

Similar example is glue::glue("w={w+}")