[clangd] Reuse compile commands during reparse

Summary:
Previously we always queried the compilation database and discarded the results
if the file was already opened.

Reviewers: ilya-biryukov

Reviewed By: ilya-biryukov

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D35825

llvm-svn: 308970

clang-tools-extra/clangd/ClangdUnit.cpp

@@ -245,6 +245,8 @@ void ClangdUnit::reparse(StringRef Contents,
   for (const auto &S : Command.CommandLine)
     ArgStrs.push_back(S.c_str());
 
+  VFS->setCurrentWorkingDirectory(Command.Directory);
+
   std::unique_ptr<CompilerInvocation> CI;
   {
     // FIXME(ibiryukov): store diagnostics from CommandLine when we start
@@ -398,6 +400,8 @@ ClangdUnit::codeComplete(StringRef Contents, Position Pos,
   for (const auto &S : Command.CommandLine)
     ArgStrs.push_back(S.c_str());
 
+  VFS->setCurrentWorkingDirectory(Command.Directory);
+
   std::unique_ptr<CompilerInvocation> CI;
   EmptyDiagsConsumer DummyDiagsConsumer;
   {

clang-tools-extra/clangd/ClangdUnitStore.h

@@ -79,13 +79,12 @@ private:
                      IntrusiveRefCntPtr<vfs::FileSystem> VFS, Func Action) {
     std::lock_guard<std::mutex> Lock(Mutex);
 
-    auto Commands = getCompileCommands(CDB, File);
-    assert(!Commands.empty() &&
-           "getCompileCommands should add default command");
-    VFS->setCurrentWorkingDirectory(Commands.front().Directory);
-
     auto It = OpenedFiles.find(File);
     if (It == OpenedFiles.end()) {
+      auto Commands = getCompileCommands(CDB, File);
+      assert(!Commands.empty() &&
+             "getCompileCommands should add default command");
+
       It = OpenedFiles
                .insert(std::make_pair(File, ClangdUnit(File, FileContents,
                                                        ResourceDir, PCHs,