Allow .SD; allow original is.sorted portion to escape if irows is.null

R/data.table.R

@@ -1337,21 +1337,21 @@ replace_dot_alias = function(e) {
     if (is.data.table(jval)) {
       setattr(jval, 'class', class(x)) # fix for #64
       # can jval be sorted by the same key as x? improved for #4498
-      get_shared_keys = function(jsub, jvnames, key) {
+      get_shared_keys = function(jsub, jvnames, sdvars, key) {
         if (is.null(key)) return(NULL)
-        if (!jsub %iscall% "list") return(NULL)
-        jnames = as.character(Filter(is.name, jsub)[-1L])
+        if (!((SD_only <- jsub == quote(.SD))|| jsub %iscall% "list")) return(NULL)
+        jnames = if (SD_only) sdvars else as.character(Filter(is.name, jsub)[-1L])
         key_idx = chmatch(key, jnames)
         missing_keys = which(is.na(key_idx))
         if (length(missing_keys) && missing_keys[1L] == 1L) return(NULL)
         if (!length(missing_keys)) return(jvnames[key_idx])
         return(jvnames[head(key_idx, missing_keys[1L] - 1L)])
       }
-      shared_keys = get_shared_keys(jsub, jvnames, key(x))
+      shared_keys = get_shared_keys(jsub, jvnames, sdvars = sdvars, key(x))
       if (is.null(irows) && !is.null(shared_keys)) {
         setattr(jval, 'sorted', shared_keys)
         # potentially inefficient backup -- check if jval is sorted by key(x)
-      } else if (haskey(x) && all(key(x) %chin% names(jval)) && suppressWarnings(is.sorted(jval, by=key(x)))) { # TO DO: perhaps this usage of is.sorted should be allowed internally then (tidy up and make efficient)
+      } else if (haskey(x) && all(key(x) %chin% names(jval)) && (is.null(irows) || (!roll && .Call(CisOrderedSubset, irows, nrow(x))) || suppressWarnings(is.sorted(jval, by=key(x))))) { # TO DO: perhaps this usage of is.sorted should be allowed internally then (tidy up and make efficient)
         setattr(jval, 'sorted', key(x))
       }
       if (any(vapply_1b(jval, is.null))) stop("Internal error: j has created a data.table result containing a NULL column") # nocov