as.data.table.array: copy shared dimnames before reversing them (#7509)

* regression test

* copy shared values before overwriting

Author: aitap

R/as.data.table.R

@@ -102,8 +102,9 @@ as.data.table.array = function(x, keep.rownames=FALSE, key=NULL, sorted=TRUE, va
     lapply(dx, seq_len)
   } else if (any(nulldnx <- vapply_1b(dnx, is.null))) {
     dnx[nulldnx] = lapply(dx[nulldnx], seq_len) #3636
+    setattr(dnx, 'names', copy(names(dnx)))
     dnx
-  } else dnx
+  } else copy(dnx)
   setfrev(val)
   if (is.null(names(val)) || !any(nzchar(names(val))))
     setattr(val, 'names', paste0("V", frev(seq_along(val))))

inst/tests/tests.Rraw

@@ -21927,3 +21927,14 @@ rm(DTn, DTl, DT)
 DT = unserialize(serialize(as.data.table(mtcars), NULL))
 test(2353, DT[,foo:=mean(mpg),by=cyl], as.data.table(mtcars)[,foo:=mean(mpg),by=cyl])
 rm(DT)
+
+# as.data.table.array(x) shouldn't overwrite dimnames(x), #7506
+Xdn = list(foo = letters[1:2], bar = LETTERS[1:3], baz = as.character(1:4))
+X = array(1:24, 2:4, copy(Xdn))
+DT = as.data.table(X)
+test(2354.1, dimnames(X), Xdn)
+Xdn['baz'] = list(NULL)
+dimnames(X) = copy(Xdn)
+DT = as.data.table(X)
+test(2354.2, dimnames(X), Xdn)
+rm(X, Xdn, DT)