added nocov for R 3.4/5 fix and TODO

Author: skitsy24

R/print.data.table.R

@@ -32,19 +32,25 @@ print.data.table = function(x, topn=getOption("datatable.print.topn"),
     # Other options investigated (could revisit): Cstack_info(), .Last.value gets set first before autoprint, history(), sys.status(),
     #   topenv(), inspecting next statement in caller, using clock() at C level to timeout suppression after some number of cycles
     SYS = sys.calls()
+
+    # TODO(R>=3.6): Remove this branch once the minimal supported R version is raised. No need for is_print_call. Just
+    # identical(SYS[[1L]][[1L]], print)
+
     # is_print_call detects whether print() was called either explicitly or through autoprint,
     # is wrapped in a promise or not to account for R 3.4/3.5.
     is_print_call = FALSE
     if (identical(SYS[[1L]][[1L]], print)) {
       is_print_call = TRUE
-    } else if (typeof(SYS[[1L]][[1L]]) == "promise") {
+    } 
+      # nocov start 
+      else if (typeof(SYS[[1L]][[1L]]) == "promise") {
        # in R 3.4 and R 3.5, auto-print uses a promise to reference base::print due to lazy loading
        # safely evaluate promise to get the actual function
       evaluated = tryCatch(eval(SYS[[1L]][[1L]]), error = function(e) NULL)
       if (identical(evaluated, print)) {
         is_print_call = TRUE
       }
-    }
+    } # nocov end
     if (is_print_call || # this is what auto-print looks like, i.e. '> DT' and '> DT[, a:=b]' in the terminal; see #3029.
         ( length(SYS) >= 3L && is.symbol(thisSYS <- SYS[[length(SYS)-2L]][[1L]]) &&
           as.character(thisSYS) == 'source') ) { # suppress printing from source(echo = TRUE) calls, #2369