remove use of rbindlist(..., use.names=FALSE, fill=TRUE) in merge

NEWS.md

@@ -204,7 +204,7 @@
     #  v1.14.4  0.4826  0.5586  0.6586  0.6329  0.7348  1.318   100
     ```
 
-30. `rbind()` and `rbindlist()` now support `fill=TRUE` with `use.names=FALSE` instead of issuing the warning `use.names= cannot be FALSE when fill is TRUE. Setting use.names=TRUE.`, [#5444](https://github.com/Rdatatable/data.table/issues/5444). Thanks to @sindribaldur for testing dev and filing a bug report which was fixed before release.
+30. `rbind()` and `rbindlist()` now support `fill=TRUE` with `use.names=FALSE` instead of issuing the warning `use.names= cannot be FALSE when fill is TRUE. Setting use.names=TRUE.`, [#5444](https://github.com/Rdatatable/data.table/issues/5444). Thanks to @sindribaldur, @dcaseykc, @fox34, @adrian-quintario and @berg-michael for testing dev and filing a bug report which was fixed before release.
 
     ```R
     DT1

R/merge.R

@@ -96,8 +96,19 @@ merge.data.table = function(x, y, by = NULL, by.x = NULL, by.y = NULL, all = FAL
   if (all.y && nrow(y)) {  # If y does not have any rows, no need to proceed
     # Perhaps not very commonly used, so not a huge deal that the join is redone here.
     missingyidx = y[!x, which=TRUE, on=by, allow.cartesian=allow.cartesian]
+    # TO DO: replace by following once #5446 is merged
+    # if (length(missingyidx)) dt = rbind(dt, y[missingyidx], use.names=FALSE, fill=TRUE, ignore.attr=TRUE)
     if (length(missingyidx)) {
-      dt = rbind(dt, y[missingyidx], use.names=FALSE, fill=TRUE)
+      yy = y[missingyidx]
+      othercolsx = setdiff(nm_x, by)
+      if (length(othercolsx)) {
+        tmp = rep.int(NA_integer_, length(missingyidx))
+        # TO DO: use set() here instead..
+        yy = cbind(yy, x[tmp, othercolsx, with = FALSE])
+      }
+      # empty data.tables (nrow =0, ncol>0) doesn't skip names anymore in new rbindlist
+      # takes care of #24 without having to save names. This is how it should be, IMHO.
+      dt = rbind(dt, yy, use.names=FALSE)
     }
   }
   # X[Y] syntax puts JIS i columns at the end, merge likes them alongside i.

inst/tests/tests.Rraw

@@ -1921,6 +1921,11 @@ test(631.5, DT3, data.table(a=c(2), total=c(5), key="a"))
 # .. nrow(y)=1, i subset y with 1 and match with x
 test(631.6, merge(DT1,DT4,all.y=TRUE), data.table(a=c(3),total.x=c(1),total.y=c(1),key="a"))
 test(631.7, DT4, data.table(a=c(3), total=c(1), key="a"))
+# merge columns with different attributes #5309
+x = data.table(a=1L, b=as.IDate(16801))
+y = data.table(a=2L, b=NA)
+test(631.8, merge(x,y,by="a",all=TRUE), data.table(a=c(1L,2L), b.x=as.IDate(c(16801,NA)), b.y=NA, key="a"))
+test(631.9, merge(y,x,by="a",all=TRUE), data.table(a=c(1L,2L), b.x=NA, b.y=as.IDate(c(16801,NA)), key="a"))
 
 test(632, merge(DT1,DT2,all=TRUE), data.table(a=c(1,2,3,4,5),total.x=c(2,NA,1,3,1),total.y=c(NA,5,1,NA,2),key="a"))
 test(632.1, merge(DT1,DT2,all=TRUE), setkey(adt(merge(adf(DT1),adf(DT2),by="a",all=TRUE)),a))