`write_xpt(version=5)` silently truncates variable names

[gowerc]

V5 of the xport format only supports variable names up to length 8. Currently write_xpt() allows you to specify names greater than 8 but then silently truncates them. This behaviour seems to be in contradiction to the V8 format implementation which has a length limit of 32 and will throw an error if you exceed it

dat <- data.frame(
    "X1234567_ABC" = c(1,2,3,4,5),
    "X1234567_XYZ" = c(6,7,8,9, 10)
)
haven::write_xpt(dat, "data/longvar.xpt", version = 5)

haven::read_xpt("data/longvar.xpt")

New names:
• `X1234567` -> `X1234567...1`
• `X1234567` -> `X1234567...2`
# A tibble: 5 × 2
  X1234567...1 X1234567...2
         <dbl>        <dbl>
1            1            6
2            2            7
3            3            8
4            4            9
5            5           10

Example of V8 throwing an error if variable name exceeds 32 bytes

dat <- data.frame(
    "X1111222223333344444555556666677777" = c(1,2,3,4,5)
)
haven::write_xpt(dat, "data/longvar.xpt", version = 8)

Error: Failed to create column `X1111222223333344444555556666677777`: A provided name is too long for the file format.

Ideally v5 should also throw an error if variable names exceed the length limit.

[gowerc]

@gorcha - Awesome thank you for fixing !