Inconsistent warnings when combining eras with different labels/names

[joeroe]

Arithmetic with yrs with functionally equivalent, but differently named, eras throws a warning as expected:

library("era")
yr(1, "BP") + yr(1, "cal BP")
#> Warning: `era(x)` and `era(y)` have different label or name parameters.
#> # BP years <yr[1]>:
#> [1] 2
#> # Era: Before Present (BP): calendar years, counted backwards from 1950

But combining the same vectors doesn't:

c(yr(1, "BP"), yr(1, "cal BP"))
#> # BP years <yr[2]>:
#> [1] 1 1
#> # Era: Before Present (BP): calendar years, counted backwards from 1950

^{Created on 2020-12-08 by the reprex package (v0.3.0)}

The check currently in vec_arith.era_yr.era_yr() should be moved lower, to catch all instances of combination.

[joeroe]

Now checks for era compatibility only happen in vec_cast() and the warnings are consistent:

library("era")
yr(1, "BP") + yr(1, "cal BP")
#> Warning: eras have different label or name parameters.
#> # BP years <yr[1]>:
#> [1] 2
#> # Era: Before Present (BP): Gregorian years (365.2425 days), counted backwards from 1950
c(yr(1, "BP"), yr(1, "cal BP"))
#> Warning: eras have different label or name parameters.
#> # BP years <yr[2]>:
#> [1] 1 1
#> # Era: Before Present (BP): Gregorian years (365.2425 days), counted backwards from 1950

^{Created on 2022-03-09 by the reprex package (v2.0.1)}