[VirtualFileSystem] Support directory entries in the YAMLVFSWriter

The current implementation of the JSONWriter does not support writing
out directory entries. Earlier today I added a unit test to illustrate
the problem. When an entry is added to the YAMLVFSWriter and the path is
a directory, it will incorrectly emit the directory as a file, and any
files inside that directory will not be found by the VFS.

It's possible to partially work around the issue by only adding "leaf
nodes" (files) to the YAMLVFSWriter. However, this doesn't work for
representing empty directories. This is a problem for clients of the VFS
that want to iterate over a directory. The directory not being there is
not the same as the directory being empty.

This is not just a hypothetical problem. The FileCollector for example
does not differentiate between file and directory paths. I temporarily
worked around the issue for LLDB by ignoring directories, but I suspect
this will prove problematic sooner rather than later.

This patch fixes the issue by extending the JSONWriter to support
writing out directory entries. We store whether an entry should be
emitted as a file or directory.

Differential revision: https://reviews.llvm.org/D76670

1 files changed, 26 insertions, 8 deletions

diff --git a/llvm/lib/Support/VirtualFileSystem.cpp b/llvm/lib/Support/VirtualFileSystem.cpp
index 737116c..22b4a08 100644
--- a/llvm/lib/Support/VirtualFileSystem.cpp
+++ b/llvm/lib/Support/VirtualFileSystem.cpp
@@ -1912,11 +1912,21 @@ UniqueID vfs::getNextVirtualUniqueID() {
   return UniqueID(std::numeric_limits<uint64_t>::max(), ID);
 }
 
-void YAMLVFSWriter::addFileMapping(StringRef VirtualPath, StringRef RealPath) {
+void YAMLVFSWriter::addEntry(StringRef VirtualPath, StringRef RealPath,
+                             bool IsDirectory) {
   assert(sys::path::is_absolute(VirtualPath) && "virtual path not absolute");
   assert(sys::path::is_absolute(RealPath) && "real path not absolute");
   assert(!pathHasTraversal(VirtualPath) && "path traversal is not supported");
-  Mappings.emplace_back(VirtualPath, RealPath);
+  Mappings.emplace_back(VirtualPath, RealPath, IsDirectory);
+}
+
+void YAMLVFSWriter::addFileMapping(StringRef VirtualPath, StringRef RealPath) {
+  addEntry(VirtualPath, RealPath, /*IsDirectory=*/false);
+}
+
+void YAMLVFSWriter::addDirectoryMapping(StringRef VirtualPath,
+                                        StringRef RealPath) {
+  addEntry(VirtualPath, RealPath, /*IsDirectory=*/true);
 }
 
 namespace {
@@ -2017,7 +2027,10 @@ void JSONWriter::write(ArrayRef<YAMLVFSEntry> Entries,
 
   if (!Entries.empty()) {
     const YAMLVFSEntry &Entry = Entries.front();
-    startDirectory(path::parent_path(Entry.VPath));
+    bool first_entry_is_directory = Entry.IsDirectory;
+    StringRef Dir =
+        first_entry_is_directory ? Entry.VPath : path::parent_path(Entry.VPath);
+    startDirectory(Dir);
 
     StringRef RPath = Entry.RPath;
     if (UseOverlayRelative) {
@@ -2027,13 +2040,18 @@ void JSONWriter::write(ArrayRef<YAMLVFSEntry> Entries,
       RPath = RPath.slice(OverlayDirLen, RPath.size());
     }
 
-    writeEntry(path::filename(Entry.VPath), RPath);
+    if (!first_entry_is_directory)
+      writeEntry(path::filename(Entry.VPath), RPath);
 
     for (const auto &Entry : Entries.slice(1)) {
-      StringRef Dir = path::parent_path(Entry.VPath);
-      if (Dir == DirStack.back())
-        OS << ",\n";
-      else {
+      StringRef Dir =
+          Entry.IsDirectory ? Entry.VPath : path::parent_path(Entry.VPath);
+      if (Dir == DirStack.back()) {
+        if (!first_entry_is_directory) {
+          OS << ",\n";
+          first_entry_is_directory = false;
+        }
+      } else {
         while (!DirStack.empty() && !containedIn(DirStack.back(), Dir)) {
           OS << "\n";
           endDirectory();