From 6de274277753f03ef6e59167e397438ccd04e930 Mon Sep 17 00:00:00 2001
From: jangorecki <j.gorecki@wit.edu.pl>
Date: Wed, 4 Oct 2023 09:05:52 +0200
Subject: [PATCH] custom data.frame classes redirected to as.data.frame before
 as.data.table, #5699

---
 R/as.data.table.R     |  1 +
 inst/tests/tests.Rraw | 12 ++++++++++++
 2 files changed, 13 insertions(+)

diff --git a/R/as.data.table.R b/R/as.data.table.R
index feae0f5ac..e8e5939c9 100644
--- a/R/as.data.table.R
+++ b/R/as.data.table.R
@@ -214,6 +214,7 @@ as.data.table.list = function(x,
 }
 
 as.data.table.data.frame = function(x, keep.rownames=FALSE, key=NULL, ...) {
+  if (!identical(class(x), "data.frame")) return(as.data.frame(x))
   if (!isFALSE(keep.rownames)) {
     # can specify col name to keep.rownames, #575; if it's the same as key,
     #   kludge it to 'rn' since we only apply the new name afterwards, #4468
diff --git a/inst/tests/tests.Rraw b/inst/tests/tests.Rraw
index 9117c0fcb..4e87bacd4 100644
--- a/inst/tests/tests.Rraw
+++ b/inst/tests/tests.Rraw
@@ -18094,3 +18094,15 @@ test(2238.6, "a" %notin% integer(), TRUE)
 test(2238.7, "a" %notin% NULL, TRUE)
 test(2238.8, NA %notin% 1:5, TRUE)
 test(2238.9, NA %notin% c(1:5, NA), FALSE)
+
+# as.data.table should remove extra attributes from extended data.frames #5699
+x = data.frame(a=c(1,5,3), b=c(2,4,6))
+class(x) = c("tbl","data.frame")
+attr(x, "t1") = "a"
+as.data.frame.tbl = function(x) {
+  attr(x, "t1") = NULL
+  class(x) = "data.frame"
+  x
+}
+y = as.data.table(x)
+test(2239.1, attr(y, "t1", TRUE), NULL)