imitate the approach in other branches more closely

Author: MichaelChirico

R/data.table.R

@@ -2989,9 +2989,9 @@ setDT = function(x, keep.rownames=FALSE, key=NULL, check.names=FALSE) {
     }
   } else if (name %iscall% "get") { # #6725
     name = match.call(get, name)
-    name[[1L]] = quote(assign)
-    name$value = quote(x)
-    eval(name, parent.frame())
+    e = eval(name$envir, parent.frame(), parent.frame())
+    k = eval(name$x, parent.frame(), parent.frame())
+    assign(k, x, envir=e)
   }
   .Call(CexpandAltRep, x)  # issue#2866 and PR#2882
   invisible(x)

inst/tests/tests.Rraw

@@ -20661,6 +20661,9 @@ foo = function(nm, env) {
 }
 foo('x', e)
 test(2295.4, is.data.table(x))
+e = new.env(parent=topenv())
+e$x = data.frame(a=1)
+foo('x', e)
 
 # #6588: .checkTypos used to give arbitrary strings to stopf as the first argument
 test(2296, d2[x %no such operator% 1], error = '%no such operator%')