walk back update for check.names default

Author: MichaelChirico

NEWS.md

@@ -46,7 +46,7 @@
 
 13. In rare cases, `data.table` failed to expand ALTREP columns when assigning a full column by reference. This could result in the target column getting modified unintentionally if the next call to the data.table was a modification by reference of the source column. E.g. in `DT[, b := as.character(a)]` the string conversion gets deferred and subsequent modification of column `a` would also modify column `b`, [#5400](https://github.com/Rdatatable/data.table/issues/5400). Thanks to @aquasync for the report and Václav Tlapák for the PR.
 
-14. `data.table()` function is now more aligned with `data.frame()` with respect to the names of the output when one of its inputs is a single-column matrix object, [#4124](https://github.com/Rdatatable/data.table/issues/4124). We also prevent returning duplicate names for matrix column inputs, [#3193](https://github.com/Rdatatable/data.table/issues/3193). Thanks @PavoDive and @MichaelChirico for the reports and @jangorecki for the PR.
+14. `data.table()` function is now more aligned with `data.frame()` with respect to the names of the output when one of its inputs is a single-column matrix object, [#4124](https://github.com/Rdatatable/data.table/issues/4124). Thanks @PavoDive for the report and @jangorecki for the PR.
 
 ### NOTES
 

R/data.table.R

@@ -50,7 +50,6 @@ data.table = function(..., keep.rownames=FALSE, check.names=FALSE, key=NULL, str
   names(x) = nd$vnames
   if (length(x)==0L) return( null.data.table() )
   if (length(x)==1L && (is.null(x[[1L]]) || (is.list(x[[1L]]) && length(x[[1L]])==0L))) return( null.data.table() ) #48
-  if (missing(check.names)) check.names = NULL ## inherit missingness #3193
   ans = as.data.table.list(x, keep.rownames=keep.rownames, check.names=check.names, .named=nd$.named)  # see comments inside as.data.table.list re copies
   if (!is.null(key)) {
     if (!is.character(key)) stopf("key argument of data.table() must be character")

inst/tests/tests.Rraw

@@ -21234,6 +21234,3 @@ test(2321.1, DT <- data.table(a=1:2, b=matrix(1:2)), data.table(a=1:2, b=1:2))
 test(2321.2, names(DT), names(data.frame(a=1:2, b=matrix(1:2))))
 test(2321.3, DT <- data.table(a=integer(), b=matrix(1L, nrow=0L, ncol=1L)), data.table(a=integer(), b=integer()))
 test(2321.4, names(DT), names(data.frame(a=integer(), b=matrix(1L, nrow=0L, ncol=1L))))
-# data.table(vector, matrix) can return duplicate column names #3193
-test(2321.5, anyDuplicated(names(data.table(1:5, matrix(6:15, nrow = 5L)))), 0L)
-test(2321.6, anyDuplicated(names(data.table(integer(), matrix(1L, nrow=0L, ncol=2L)))), 0L)