add fix to set

Author: ben-schwen

R/data.table.R

@@ -2848,6 +2848,15 @@ setcolorder = function(x, neworder=key(x), before=NULL, after=NULL, skip_absent=
 
 set = function(x,i=NULL,j,value)  # low overhead, loopable
 {
+  # If removing columns from a table that's not selfrefok, need to call setalloccol first, #7488
+  if (is.null(value) || (is.list(value) && any(vapply_1b(value, is.null)))) {
+    # Removing at least one column
+    ok = selfrefok(x, verbose=FALSE)
+    if (ok < 1L) {
+      # Table is not safe to resize (either fresh from disk or shallow copy)
+      setalloccol(x, n=eval(getOption("datatable.alloccol")), verbose=FALSE)
+    }
+  }
   .Call(Cassign,x,i,j,NULL,value)
   invisible(x)
 }

inst/tests/tests.Rraw

@@ -21898,7 +21898,8 @@ rm(DT, strings)
 
 # do remove columns in freshly unserialized data.tables, #7488
 DT = unserialize(serialize(as.data.table(mtcars), NULL))
-test(2351, DT[,carb:=NULL], as.data.table(mtcars)[,carb:=NULL])
+test(2351.1, copy(DT)[,carb:=NULL], as.data.table(mtcars)[,carb:=NULL])
+test(2351.2, set(copy(DT), j="carb", value=NULL), as.data.table(mtcars)[,carb:=NULL])
 rm(DT)
 
 # rbindlist did not protect the temporary UTF-8 strings, #7452