[Type checker] Fix assertion diagnosting a rename with a different # of arguments.

Author: DougGregor

lib/Sema/TypeCheckAvailability.cpp

@@ -1775,12 +1775,15 @@ static void fixItAvailableAttrRename(InFlightDiagnostic &diag,
   //   argumentLabelIDs = {"w", "x", "", "", "z"}
   auto I = argumentLabelIDs.begin();
 
-  auto updateLabelsForArg = [&](Expr *expr) {
+  auto updateLabelsForArg = [&](Expr *expr) -> bool {
     if (isa<DefaultArgumentExpr>(expr) ||
         isa<CallerDefaultArgumentExpr>(expr)) {
       // Defaulted: remove param label of it.
+      if (I == argumentLabelIDs.end())
+        return true;
+
       I = argumentLabelIDs.erase(I);
-      return;
+      return false;
     }
 
     if (auto *varargExpr = dyn_cast<VarargExpansionExpr>(expr)) {
@@ -1800,19 +1803,26 @@ static void fixItAvailableAttrRename(InFlightDiagnostic &diag,
           I = argumentLabelIDs.insert(I, variadicArgsNum, Identifier());
           I += variadicArgsNum;
         }
-        return;
+        return false;
       }
     }
 
     // Normal: Just advance.
+    if (I == argumentLabelIDs.end())
+      return true;
+
     ++I;
+    return false;
   };
 
   if (auto *parenExpr = dyn_cast<ParenExpr>(argExpr)) {
-    updateLabelsForArg(parenExpr->getSubExpr());
+    if (updateLabelsForArg(parenExpr->getSubExpr()))
+      return;
   } else {
-    for (auto *arg : cast<TupleExpr>(argExpr)->getElements())
-      updateLabelsForArg(arg);
+    for (auto *arg : cast<TupleExpr>(argExpr)->getElements()) {
+      if (updateLabelsForArg(arg))
+        return;
+    }
   }
 
   if (argumentLabelIDs.size() != argList.args.size()) {

test/attr/attr_availability.swift

@@ -1100,3 +1100,16 @@ func unavailableFunc(_ arg: UnavailableProto) -> UnavailableProto {}
 struct S {
   var a: UnavailableProto
 }
+
+// Bad rename.
+struct BadRename {
+  @available(*, deprecated, renamed: "init(range:step:)")
+  init(from: Int, to: Int, step: Int = 1) { }
+
+  init(range: Range<Int>, step: Int) { }
+}
+
+func testBadRename() {
+  _ = BadRename(from: 5, to: 17) // expected-warning{{'init(from:to:step:)' is deprecated: replaced by 'init(range:step:)'}}
+  // expected-note@-1{{use 'init(range:step:)' instead}}
+}