Simplify TypeChecker::fixAbstractFunctionNames and eliminate a silly crash.

Don't crash here when we need to add '_' to a parameter list. However,
while we're here, stop trying to emit Fix-Its for implicit
declarations and stop worrying about introducing a ':' after the name
for functions such as

  func foo(Int) { ... }

because they're no longer permitted. Fixes rdar://problem/21333445.

Swift SVN r30195

Author: DougGregor

lib/Sema/TypeCheckDecl.cpp

@@ -7160,6 +7160,10 @@ static void validateAttributes(TypeChecker &TC, Decl *D) {
 void TypeChecker::fixAbstractFunctionNames(InFlightDiagnostic &diag,
                                            AbstractFunctionDecl *func,
                                            DeclName targetName) {
+  // There is no reasonable way to fix an implicitly-generated function.
+  if (func->isImplicit())
+    return;
+
   auto name = func->getFullName();
 
   // Fix the name of the function itself.
@@ -7183,7 +7187,6 @@ void TypeChecker::fixAbstractFunctionNames(InFlightDiagnostic &diag,
 
     // Find the location to update or insert.
     SourceLoc loc;
-    bool needColon = false;
     if (tuplePattern) {
       auto origPattern = tuplePattern->getElement(i).getPattern();
       if (auto param = cast_or_null<ParamDecl>(origPattern->getSingleVar())) {
@@ -7215,7 +7218,6 @@ void TypeChecker::fixAbstractFunctionNames(InFlightDiagnostic &diag,
         }
 
         if (param->isImplicit()) {
-          needColon = true;
           loc = origPattern->getLoc();
         } else {
           continue;
@@ -7225,35 +7227,25 @@ void TypeChecker::fixAbstractFunctionNames(InFlightDiagnostic &diag,
       if (auto any = dyn_cast<AnyPattern>(
                        origPattern->getSemanticsProvidingPattern())) {
         if (any->isImplicit()) {
-          needColon = true;
           loc = origPattern->getLoc();
         } else {
-          needColon = false;
           loc = any->getLoc();
         }
       } else {
         loc = origPattern->getLoc();
-        needColon = true;
       }
     } else if (auto paren = dyn_cast<ParenPattern>(pattern)) {
       loc = paren->getSubPattern()->getLoc();
-      needColon = true;
-
-      // FIXME: Representation doesn't let us fix this easily.
-      if (targetArg.empty())
-        continue;
-
     } else {
       loc = pattern->getLoc();
-      needColon = true;
     }
 
-    assert(!targetArg.empty() && "Must have a name here");
-    llvm::SmallString<8> replacement;
-    replacement += targetArg.str();
-    if (needColon)
-      replacement += ": ";
-    
+    StringRef replacement;
+    if (targetArg.empty())
+      replacement = "_";
+    else
+      replacement = targetArg.str();
+
     diag.fixItInsert(loc, replacement);
   }
 

test/decl/protocol/req/name_mismatch.swift

@@ -33,3 +33,12 @@ protocol LabeledRequirement {
 struct UnlabeledWitness : LabeledRequirement {
   func method(x _: Loadable) {}
 }
+
+// rdar://problem/21333445
+protocol P2 {
+	init(_ : Int) // expected-note{{requirement 'init' declared here}}
+}
+
+struct XP2 : P2 { // expected-error{{initializer 'init(foo:)' has different argument names from those required by protocol 'P2' ('init')}}
+  let foo: Int 
+}