Issues when joining by named vector

[mgirlich]

I wanted to fix #198 and discovered some more issues when joining by a named vector:

• wrong tbl_vars for left/full/inner_join()
• wrong column order in left/full/inner_join()
• right_join() complains about missing variable
• semi/anti_join() complain about missing variable

library(dtplyr)
library(dplyr, warn.conflicts = FALSE)

df1 <- data.frame(x = 1, y = 1, z = 2)
df2 <- data.frame(x = 1, y = 2)
dt1 <- lazy_dt(df1, "dt1")
dt2 <- lazy_dt(df2, "dt2")

# left/full/inner
left_join(dt1, dt2, by = c("x", z = "y"))
#> Source: local data table [1 x 3]
#> Call:   merge(dt1, dt2, all.x = TRUE, all.y = FALSE, by.x = c("x", "z"
#> ), by.y = c("x", "y"), allow.cartesian = TRUE)
#> 
#>       x     z     y
#>   <dbl> <dbl> <dbl>
#> 1     1     2     1
#> 
#> # Use as.data.table()/as.data.frame()/as_tibble() to access results
left_join(df1, df2, by = c("x", z = "y"))
#>   x y z
#> 1 1 1 2

# note the wrong order here
left_join(dt1, dt2, by = c("x", z = "y")) %>% tbl_vars()
#> <dplyr:::vars>
#> [1] "x"   "z"   "y.x" "y.y"

# right
right_join(dt1, dt2, by = c("x", z = "y"))
#> Error: `by` can't contain join column `z` which is missing from LHS.
right_join(df1, df2, by = c("x", z = "y"))
#>   x y z
#> 1 1 1 2

# semi/anti
semi_join(dt1, dt2, by = c("x", z = "y"))
#> Error: argument specifying columns specify non existing column(s): cols[2]='z'
semi_join(df1, df2, by = c("x", z = "y"))
#>   x y z
#> 1 1 1 2

anti_join(dt1, dt2, by = c("x", z = "y"))
#> Error in colnamesInt(i, unname(on), check_dups = FALSE): argument specifying columns specify non existing column(s): cols[2]='z'
anti_join(df1, df2, by = c("x", z = "y"))
#> [1] x y z
#> <0 rows> (or 0-length row.names)

^{Created on 2021-03-09 by the reprex package (v1.0.0)}

[hadley]

I have great difficulty correctly reasoning about joins so this doesn't surprise me 😞