[FileSystem] Fix regression in FileSystem::Resolve

[JDevlieghere]

Summary

When I moved the resolve code from FileSpec to the FileSystem class, I introduced a regression. If you compare the two implementations, you'll notice that if the path doesn't exist, we should only reverse the effects of makeAbsolute, not the effects of tilde expansion. As a result, the logic to create the ~/.lldb directory broke, because we would resolve the path before creating it. Because the directory didn't exist yet, we'd call create_directories on the unresolved path, which failed.

[davide]

LGTM, also discussed in person.

source/Host/common/FileSystem.cpp

std::error_code FileSystem::GetRealPath(const Twine &path,
                                         SmallVectorImpl<char> &output) const {
   return m_fs->getRealPath(path, output);
 }
 
 void FileSystem::Resolve(SmallVectorImpl<char> &path) {
   if (path.empty())
     return;
 
-  // Resolve tilde.
-  SmallString<128> original_path(path.begin(), path.end());
+  // Resolve tilde in path.
+  SmallString<128> resolved(path.begin(), path.end());
   StandardTildeExpressionResolver Resolver;
-  Resolver.ResolveFullPath(original_path, path);
+  Resolver.ResolveFullPath(llvm::StringRef(path.begin(), path.size()),
+                           resolved);
 
   // Try making the path absolute if it exists.
-  SmallString<128> absolute_path(path.begin(), path.end());
-  MakeAbsolute(path);
-  if (!Exists(path)) {
-    path.clear();
-    path.append(original_path.begin(), original_path.end());
+  SmallString<128> absolute(resolved.begin(), resolved.end());
+  MakeAbsolute(absolute);
+
+  if (Exists(absolute)) {
+    path.append(absolute.begin(), absolute.end());
+  } else {
+    path.append(resolved.begin(), resolved.end());
   }
 }
 
 void FileSystem::Resolve(FileSpec &file_spec) {
   // Extract path from the FileSpec.
   SmallString<128> path;
   file_spec.GetPath(path);