[CSSimplify] Add omitted projection name label as valid argument label and consolidate all checks for argument and parameter label matches into new Param member function.

Author: amritpan

include/swift/AST/Types.h

@@ -2839,6 +2839,23 @@ class AnyFunctionType : public TypeBase {
 
     bool hasInternalLabel() const { return !InternalLabel.empty(); }
     Identifier getInternalLabel() const { return InternalLabel; }
+
+    /// Return true if argument name is valid and matches \c paramName.
+    ///
+    /// The three tests to check if argument name is valid are:
+    /// 1. allow argument if it matches \c paramName,
+    /// 2. allow argument if  $_  for omitted projected value label,
+    /// 3. allow argument if it matches \c paramName without its \c $ prefix.
+    bool matchParameterLabel(Identifier const &paramName) const {
+      auto argLabel = getLabel();
+      if (argLabel == paramName)
+        return true;
+      if ((argLabel.str() == "$_") && paramName.empty())
+        return true;
+      if (argLabel.hasDollarPrefix() && argLabel.str().drop_front() == paramName.str())
+        return true;
+      return false;
+    }
 
     ParameterTypeFlags getParameterFlags() const { return Flags; }
 

lib/Sema/CSSimplify.cpp

@@ -291,13 +291,10 @@ static bool matchCallArgumentsImpl(
     assert(argIdx != numArgs && "Must have a valid index to claim");
     assert(!claimedArgs[argIdx] && "Argument already claimed");
 
-    auto argLabel = args[argIdx].getLabel();
     if (!actualArgNames.empty()) {
       // We're recording argument names; record this one.
       actualArgNames[argIdx] = expectedName;
-    } else if (argLabel != expectedName && !ignoreNameClash &&
-               !(argLabel.str().startswith("$") &&
-                 argLabel.str().drop_front() == expectedName.str())) {
+    } else if (!ignoreNameClash && !args[argIdx].matchParameterLabel(expectedName)) {
       // We have an argument name mismatch. Start recording argument names.
       actualArgNames.resize(numArgs);