[NFC] Use an Iterator Again in WMO Type Checking

Author: CodaFi

lib/Frontend/Frontend.cpp

@@ -1168,19 +1168,13 @@ bool CompilerInstance::loadPartialModulesAndImplicitImports(
 bool CompilerInstance::forEachFileToTypeCheck(
     llvm::function_ref<bool(SourceFile &)> fn) {
   if (isWholeModuleCompilation()) {
-    // FIXME: Do not refactor this to use an iterator as long as
-    // ModuleDecl::addFile is called during Sema. Synthesized files pushed
-    // during semantic analysis will cause iterator invalidation here.
-    // See notes in SourceFile::getOrCreateSynthesizedFile() for more.
-    unsigned i = 0;
-    while (i < getMainModule()->getFiles().size()) {
-      auto *SF = dyn_cast<SourceFile>(getMainModule()->getFiles()[i++]);
+    for (auto fileName : getMainModule()->getFiles()) {
+      auto *SF = dyn_cast<SourceFile>(fileName);
       if (!SF) {
         continue;
       }
       if (fn(*SF))
         return true;
-      ;
     }
   } else {
     for (auto *SF : getPrimarySourceFiles()) {