push logic into helper to tidy up merge body

Author: MichaelChirico

R/merge.R

@@ -63,26 +63,8 @@ merge.data.table = function(x, y, by = NULL, by.x = NULL, by.y = NULL, all = FAL
   }
 
   # warn about unused arguments #2587
-  # TODO(R >= 3.5.0): use ...length()
-  if (n_dots <- length(dots <- list(...))) {
-    if (is.null(nm <- names(dots))) {
-      warningf(ngettext(n_dots, "merge.data.table() received %d unnamed argument in '...' which will be ignored.",
-                                "merge.data.table() received %d unnamed arguments in '...' which will be ignored."),
-               n_dots)
-    } else {
-      named_idx = nzchar(nm)
-      if (all(named_idx)) {
-        warningf(ngettext(n_dots, "merge.data.table() received %d unknown keyword argument which will be ignored: %s",
-                                  "merge.data.table() received %d unknown keyword arguments which will be ignored: %s"),
-                 n_dots, brackify(nm))
-      } else {
-        n_named <- sum(named_idx)
-        unnamed_clause <- sprintf(ngettext(n_dots - n_named, "%d unnamed argument in '...'", "%d unnamed arguments in '...'"), n_dots - n_named)
-        named_clause <- sprintf(ngettext(n_named, "%d unknown keyword argument", "%d unknown keyword arguments"), n_named)
-        warningf("merge.data.table() received %s and %s, all of which will be ignored: %s", unnamed_clause, named_clause, brackify(nm[named_idx]))
-      }
-    }
-  }
+  .maybe_warn_merge_dots(...)
+
   # with i. prefix in v1.9.3, this goes away. Left here for now ...
   ## sidestep the auto-increment column number feature-leading-to-bug by
   ## ensuring no names end in ".1", see unit test
@@ -138,3 +120,28 @@ merge.data.table = function(x, y, by = NULL, by.x = NULL, by.y = NULL, all = FAL
   setattr(dt, "class", class_x)
   dt
 }
+
+.maybe_warn_merge_dots <- function(...) {
+  # TODO(R >= 3.5.0): use ...length()
+  n_dots <- length(dots <- list(...))
+  if (!n_dots) return(invisible())
+
+  nm <- names(dots)
+  if (is.null(nm)) {
+    warningf(ngettext(n_dots, "merge.data.table() received %d unnamed argument in '...' which will be ignored.",
+                              "merge.data.table() received %d unnamed arguments in '...' which will be ignored."),
+              n_dots)
+  } else {
+    named_idx = nzchar(nm)
+    if (all(named_idx)) {
+      warningf(ngettext(n_dots, "merge.data.table() received %d unknown keyword argument which will be ignored: %s",
+                                "merge.data.table() received %d unknown keyword arguments which will be ignored: %s"),
+                n_dots, brackify(nm))
+    } else {
+      n_named <- sum(named_idx)
+      unnamed_clause <- sprintf(ngettext(n_dots - n_named, "%d unnamed argument in '...'", "%d unnamed arguments in '...'"), n_dots - n_named)
+      named_clause <- sprintf(ngettext(n_named, "%d unknown keyword argument", "%d unknown keyword arguments"), n_named)
+      warningf("merge.data.table() received %s and %s, all of which will be ignored: %s", unnamed_clause, named_clause, brackify(nm[named_idx]))
+    }
+  }
+}