[Omit needless words] Only move "lonely of" arguments back to the base name.

If the first argument label would end up as "of" following splitting
and pruning, move that "of" onto the base name.

lib/Basic/StringExtras.cpp

@@ -873,10 +873,6 @@ static bool shouldPlacePrepositionOnArgLabel(StringRef beforePreposition,
       afterPreposition == "Z")
     return false;
 
-  // The preposition "of" binds tightly to the left word.
-  if (camel_case::sameWordIgnoreFirstCase(preposition, "of"))
-    return false;
-
   return true;
 }
 
@@ -1147,9 +1143,12 @@ bool swift::omitNeedlessWords(StringRef &baseName,
   }
 
   // If needed, split the base name.
+  bool didSplitBaseName = false;
   if (!argNames.empty() &&
-      splitBaseName(baseName, argNames[0], paramTypes[0], firstParamName))
+      splitBaseName(baseName, argNames[0], paramTypes[0], firstParamName)) {
+    didSplitBaseName = true;
     anyChanges = true;
+  }
 
   // Omit needless words based on parameter types.
   for (unsigned i = 0, n = argNames.size(); i != n; ++i) {
@@ -1182,5 +1181,16 @@ bool swift::omitNeedlessWords(StringRef &baseName,
     }
   }
 
+  // Place a "lonely of" on the base name, rather than having it as
+  // the first argument label.
+  if (didSplitBaseName &&
+      camel_case::sameWordIgnoreFirstCase(argNames[0], "of")) {
+    SmallString<16> newBaseName;
+    newBaseName += baseName;
+    newBaseName += "Of";
+    baseName = scratch.copyString(newBaseName);
+    argNames[0] = StringRef();
+  }
+
   return lowercaseAcronymsForReturn();
 }