`get_ext` is mispecified

[chainsawriot]

https://github.com/gesistsa/rio/blob/f0198a386db58335adee1a435cc39c5eba6d9103/R/utils.R#L11-L30

The function actually is not actually doing what #169 and the documentation ("A characters string containing a file type recognized by rio.") said and what @billdenney requested. Actually, "file type" is confusing. Let's call this format (as in the argument of import). The main issue is that get_type() is just running inside get_ext() without assigning it to anything.

To give an example:

rio::get_ext("hello.arff")
#> [1] "arff"
rio::get_ext("hello.matlab")
#> [1] "matlab"

rio::get_ext("hello.yaml")
#> [1] "yaml"
rio::get_ext("hello.yml")
#> [1] "yml"

^{Created on 2023-09-07 with reprex v2.0.2}

It is almost the same as tools::file_ext, just with an additional care of URL.

Also a consequence to this, get_ext("twotables.htm") actually return "htm". And therefore, this bunch of check for html wont work

https://github.com/gesistsa/rio/blob/f0198a386db58335adee1a435cc39c5eba6d9103/R/import_list.R#L115-L130

temp_htm <- tempfile(fileext = ".htm")
download.file("https://github.com/gesistsa/rio/blob/main/tests/testdata/twotables.html", temp_htm, quiet = TRUE)

dat <- rio::import_list(temp_htm) ## only one table is imported

## failed
testthat::expect_true(identical(dim(dat[[2]]), dim(iris)))
#> Error in dat[[2]]: subscript out of bounds

^{Created on 2023-09-08 with reprex v2.0.2}

May I ask you @billdenney : What did you really want in the first place? You want it to be like tools::file_ext() (I get confused by the function name get_ext()) or to return format.

[billdenney]

@chainsawriot, That's a good question, and I understand the complexity you're asking about.

My main goal was the slight extension of what is done in tools::file_ext(). But, if we had something that could detect the real file format, from your example, returning html for an htm file extension, I see a benefit of that, too. I think that your idea to normalize file extension with expected file format ("htm" becomes "html", "yml" becomes "yaml") would be more beneficial.

[chainsawriot]

TODO

• [x] Create a user-facing function get_info() that queries the internal data to get complete information (ext, format, format_name, input_function, export_function) of file input
• [x] Keep get_ext() by wrapping get_info(), something like get_info(file)$ext.

Need to coordinate with #313 #351