full_join(na_matches = "never") (#5367)

* closes #5359

* clarity

R/join-rows.R

@@ -37,6 +37,10 @@ join_rows <- function(x_key, y_key, type = c("inner", "left", "right", "full"),
   if (type == "right" || type == "full") {
     miss_x <- !vec_in(y_key, x_key, na_equal = na_equal)
 
+    if (!na_equal) {
+      miss_x[is.na(miss_x)] <- TRUE
+    }
+
     if (any(miss_x)) {
       y_extra <- seq_len(vec_size(y_key))[miss_x]
     }

tests/testthat/test-join.r

@@ -134,6 +134,19 @@ test_that("joins don't match NA when na_matches = 'never' (#2033)", {
 
   out <- anti_join(df1, df2, by = "a", na_matches = "never")
   expect_equal(out, tibble(a = NA_integer_))
+
+  dat1 <- tibble(
+    name = c("a", "c"),
+    var1 = c(1, 2)
+  )
+  dat3 <- tibble(
+    name = c("a", NA_character_),
+    var3 = c(5, 6)
+  )
+  expect_equal(
+    full_join(dat1, dat3, by = "name", na_matches = "never"),
+    tibble(name = c("a", "c", NA), var1 = c(1, 2, NA), var3 = c(5, NA, 6))
+  )
 })
 
 # nest_join ---------------------------------------------------------------