Bug 538952: [R-Editor] Fix argument name completion

Follow-up-to: b89427948ad7a35b28506bffb66b729ba6be14c8
Change-Id: I9aef30a61eb118f946cd77ab58cbd5bad6984861
diff --git a/r/org.eclipse.statet.r.ui/src/org/eclipse/statet/r/ui/sourceediting/RElementCompletionComputer.java b/r/org.eclipse.statet.r.ui/src/org/eclipse/statet/r/ui/sourceediting/RElementCompletionComputer.java
index 31a0402..5b9e53f 100644
--- a/r/org.eclipse.statet.r.ui/src/org/eclipse/statet/r/ui/sourceediting/RElementCompletionComputer.java
+++ b/r/org.eclipse.statet.r.ui/src/org/eclipse/statet/r/ui/sourceediting/RElementCompletionComputer.java
@@ -782,7 +782,7 @@
 					for (int i= 0; i < argsDef.size(); i++) {
 						final ArgsDefinition.Arg arg= argsDef.get(i);
 						if (arg.name != null && arg.name.length() > 0 && !arg.name.equals("...")) {
-							if (parameters.matchesNamePattern(prefixSegmentName)
+							if (parameters.matchesNamePattern(arg.name)
 									&& this.argNames.add(arg.name)) {
 								final RElementName name= RElementName.create(RElementName.MAIN_DEFAULT, arg.name);
 								parameters.baseRelevance= contextRelevance + ARG_NAME_PRIO;