semi_join() / anti_join() do not correctly parse sql_on argument

[cole-johanson]

When using semi_join() and anti_join() in dbplyr, the sql_on= argument does not parse correctly. This is needed for more complicated joins than the by= argument can handle.

suppressMessages(library(dplyr))
suppressMessages(library(dbplyr))

x = memdb_frame(x=c(1,2))
x %>% left_join(x,sql_on='"LHS".x = "RHS".x') %>% show_query # works
#> <SQL>
#> SELECT `LHS`.`x` AS `x.x`, `RHS`.`x` AS `x.y`
#> FROM `dbplyr_001` AS `LHS`
#> LEFT JOIN `dbplyr_001` AS `RHS`
#> ON ("LHS".x = "RHS".x)

x %>% anti_join(x,by="x") %>% show_query # works
#> <SQL>
#> SELECT * FROM `dbplyr_001` AS `LHS`
#> WHERE NOT EXISTS (
#>   SELECT 1 FROM `dbplyr_001` AS `RHS`
#>   WHERE (`LHS`.`x` = `RHS`.`x`)
#> )

x %>% anti_join(x,sql_on='LHS".x = "RHS".x') %>% show_query # misses arguments
#> <SQL>
#> SELECT * FROM `dbplyr_001` AS `LHS`
#> WHERE NOT EXISTS (
#>   SELECT 1 FROM `dbplyr_001` AS `RHS`
#>   WHERE (`LHS`. = `RHS`.)
#> )

^{Created on 2020-05-06 by the reprex package (v0.3.0)}

[hadley]

@krlmlr can you please take a look at this?