Closes #1341. Unlock .SD correctly for DT[i, .SD].

R/data.table.R

@@ -1222,6 +1222,11 @@ chmatch2 <- function(x, table, nomatch=NA_integer_) {
             } else if ( length(jcpy <- which(sapply(jval, address) %in% sapply(SDenv, address))) ) {
                 for (jidx in jcpy) jval[[jidx]] = copy(jval[[jidx]])
             }
+        } else {
+            if (is.data.table(jval)) {
+                setattr(jval, '.data.table.locked', NULL) # fix for #1341
+                if (!truelength(jval)) alloc.col(jval)
+            }
         }
 
         if (!is.null(lhs)) {   # *** TO DO ***: use set() here now that it can add new column(s) and remove newnames and alloc logic above

README.md

@@ -31,6 +31,8 @@
 
   6. Fixed a rare case in `melt.data.table` not setting `variable` factor column properly when `na.rm=TRUE`, [#1359](https://github.com/Rdatatable/data.table/issues/1359). Thanks @mplatzer.
 
+  7. `dt[i, .SD]` unlocks `.SD` and overallocates correctly now, [#1341](https://github.com/Rdatatable/data.table/issues/1341). Thanks @marc-outins.
+
 #### NOTES
 
 

inst/tests/tests.Rraw

@@ -6987,6 +6987,12 @@ test(1562, melt(DT, measure=patterns("^g[12]"), variable.factor=FALSE), data.tab
 
 # tet 1563 added for melt above, fix for #1359.
 
+# fix for #1341
+dt <- data.table(a = 1:10)
+test(1564.1, truelength(dt[, .SD]), 100L)
+test(1564.2, truelength(dt[a==5, .SD]), 100L)
+test(1564.3, dt[a==5, .SD][, b := 1L], data.table(a=5L, b=1L))
+
 ##########################