[VFS] Unify iteration code for VFSFromYamlDirIterImpl, NFC intended.

[vsapsai]

Summary

First and subsequent iteration steps are similar, capture this similarity.

[bruno]

Thanks for the clean up! LGTM

lib/Basic/VirtualFileSystem.cpp

 
 class RedirectingFileSystem;
 
 class VFSFromYamlDirIterImpl : public clang::vfs::detail::DirIterImpl {
   std::string Dir;
   RedirectingFileSystem &FS;
   RedirectingDirectoryEntry::iterator Current, End;
 
+  std::error_code incrementImpl();
+
 public:
   VFSFromYamlDirIterImpl(const Twine &Path, RedirectingFileSystem &FS,
                          RedirectingDirectoryEntry::iterator Begin,
                          RedirectingDirectoryEntry::iterator End,
                          std::error_code &EC);
 
   std::error_code increment() override;
 };
JSONWriter(OS).write(Mappings, UseExternalNames, IsCaseSensitive,
                        OverlayDir);
 }
 
 VFSFromYamlDirIterImpl::VFSFromYamlDirIterImpl(
     const Twine &_Path, RedirectingFileSystem &FS,
     RedirectingDirectoryEntry::iterator Begin,
     RedirectingDirectoryEntry::iterator End, std::error_code &EC)
     : Dir(_Path.str()), FS(FS), Current(Begin), End(End) {
-  while (Current != End) {
-    SmallString<128> PathStr(Dir);
-    llvm::sys::path::append(PathStr, (*Current)->getName());
-    llvm::ErrorOr<vfs::Status> S = FS.status(PathStr);
-    if (S) {
-      CurrentEntry = *S;
-      return;
-    }
-    // Skip entries which do not map to a reliable external content.
-    if (FS.ignoreNonExistentContents() &&
-        S.getError() == llvm::errc::no_such_file_or_directory) {
-      ++Current;
-      continue;
-    } else {
-      EC = S.getError();
-      break;
-    }
-  }
+  EC = incrementImpl();
 }
 
 std::error_code VFSFromYamlDirIterImpl::increment() {
   assert(Current != End && "cannot iterate past end");
-  while (++Current != End) {
+  ++Current;
+  return incrementImpl();
+}
+
+std::error_code VFSFromYamlDirIterImpl::incrementImpl() {
+  while (Current != End) {
     SmallString<128> PathStr(Dir);
     llvm::sys::path::append(PathStr, (*Current)->getName());
     llvm::ErrorOr<vfs::Status> S = FS.status(PathStr);
     if (!S) {
       // Skip entries which do not map to a reliable external content.
       if (FS.ignoreNonExistentContents() &&
           S.getError() == llvm::errc::no_such_file_or_directory) {
+        ++Current;
         continue;
       } else {
         return S.getError();
       }
     }
     CurrentEntry = *S;
     break;
   }