[clangd] Add -ffreestanding on VFS tests.

[ilya-biryukov]

Summary

They don't provide proper gcc installations and may fail on implicit
<stdc-predef.h> include.

[ilya-biryukov]

Implicit stdc-predef.h include is not yet there, but will appear after https://reviews.llvm.org/D34158 has landed.

[krasimir]

Looks good.

[mibintc]

Thanks so much!

[ilya-biryukov]

In D34936#799589, @mibintc wrote:

Thanks so much!

You're welcome.

clang-tools-extra/trunk/unittests/clangd/ClangdTests.cpp

 private:
   std::mutex Mutex;
   bool HadErrorInLastDiags = false;
   VFSTag LastVFSTag = VFSTag();
 };
 
 class MockCompilationDatabase : public GlobalCompilationDatabase {
 public:
+  MockCompilationDatabase(bool AddFreestandingFlag) {
+    // We have to add -ffreestanding to VFS-specific tests to avoid errors on
+    // implicit includes of stdc-predef.h.
+    if (AddFreestandingFlag)
+      ExtraClangFlags.push_back("-ffreestanding");
+  }
+
   std::vector<tooling::CompileCommand>
   getCompileCommands(PathRef File) override {
     if (ExtraClangFlags.empty())
       return {};
 
     std::vector<std::string> CommandLine;
     CommandLine.reserve(3 + ExtraClangFlags.size());
     CommandLine.insert(CommandLine.end(), {"clang", "-fsyntax-only"});
#endif
   }
 
   std::string parseSourceAndDumpAST(
       PathRef SourceFileRelPath, StringRef SourceContents,
       std::vector<std::pair<PathRef, StringRef>> ExtraFiles = {},
       bool ExpectErrors = false) {
     MockFSProvider FS;
     ErrorCheckingDiagConsumer DiagConsumer;
-    MockCompilationDatabase CDB;
+    MockCompilationDatabase CDB(/*AddFreestandingFlag=*/true);
     ClangdServer Server(CDB, DiagConsumer, FS,
                         /*RunSynchronously=*/false);
     for (const auto &FileWithContents : ExtraFiles)
       FS.Files[getVirtualTestFilePath(FileWithContents.first)] =
           FileWithContents.second;
 
     auto SourceFilename = getVirtualTestFilePath(SourceFileRelPath);
 
parseSourceAndDumpAST("foo.cpp", SourceContents, {{"foo.h", ""}},
                         /*ExpectErrors=*/true);
   parseSourceAndDumpAST("foo.cpp", SourceContents, {{"foo.h", "int a;"}},
                         /*ExpectErrors=*/false);
 }
 
 TEST_F(ClangdVFSTest, Reparse) {
   MockFSProvider FS;
   ErrorCheckingDiagConsumer DiagConsumer;
-  MockCompilationDatabase CDB;
+  MockCompilationDatabase CDB(/*AddFreestandingFlag=*/true);
   ClangdServer Server(CDB, DiagConsumer, FS,
                       /*RunSynchronously=*/false);
 
   const auto SourceContents = R"cpp(
 #include "foo.h"
 int b = a;
 )cpp";
 
)cpp";
 
   EXPECT_EQ(DumpParse1, DumpParse2);
   EXPECT_NE(DumpParse1, DumpParseEmpty);
 }
 
 TEST_F(ClangdVFSTest, ReparseOnHeaderChange) {
   MockFSProvider FS;
   ErrorCheckingDiagConsumer DiagConsumer;
-  MockCompilationDatabase CDB;
+  MockCompilationDatabase CDB(/*AddFreestandingFlag=*/true);
 
   ClangdServer Server(CDB, DiagConsumer, FS,
                       /*RunSynchronously=*/false);
 
   const auto SourceContents = R"cpp(
 #include "foo.h"
 int b = a;
 )cpp";
)cpp";
 
   EXPECT_EQ(DumpParse1, DumpParse2);
   EXPECT_NE(DumpParse1, DumpParseDifferent);
 }
 
 TEST_F(ClangdVFSTest, CheckVersions) {
   MockFSProvider FS;
   ErrorCheckingDiagConsumer DiagConsumer;
-  MockCompilationDatabase CDB;
+  MockCompilationDatabase CDB(/*AddFreestandingFlag=*/true);
   ClangdServer Server(CDB, DiagConsumer, FS,
                       /*RunSynchronously=*/true);
 
   auto FooCpp = getVirtualTestFilePath("foo.cpp");
   const auto SourceContents = "int a;";
   FS.Files[FooCpp] = SourceContents;
   FS.ExpectedFile = FooCpp;
 

 }
 
 // Only enable this test on Unix
 #ifdef LLVM_ON_UNIX
 TEST_F(ClangdVFSTest, SearchLibDir) {
   // Checks that searches for GCC installation is done through vfs.
   MockFSProvider FS;
   ErrorCheckingDiagConsumer DiagConsumer;
-  MockCompilationDatabase CDB;
-  CDB.ExtraClangFlags = {"-xc++", "-target", "x86_64-linux-unknown", "-m64"};
+  MockCompilationDatabase CDB(/*AddFreestandingFlag=*/true);
+  CDB.ExtraClangFlags.insert(
+      CDB.ExtraClangFlags.end(),
+      {"-xc++", "-target", "x86_64-linux-unknown", "-m64"});
   ClangdServer Server(CDB, DiagConsumer, FS,
                       /*RunSynchronously=*/true);
 
   // Just a random gcc version string
   SmallString<8> Version("4.9.3");
 
   // A lib dir for gcc installation
   SmallString<64> LibDir("/usr/lib/gcc/x86_64-linux-gnu");
bool ContainsItem(std::vector<CompletionItem> const &Items, StringRef Name) {
     }
     return false;
   }
 };
 
 TEST_F(ClangdCompletionTest, CheckContentsOverride) {
   MockFSProvider FS;
   ErrorCheckingDiagConsumer DiagConsumer;
-  MockCompilationDatabase CDB;
+  MockCompilationDatabase CDB(/*AddFreestandingFlag=*/true);
 
   ClangdServer Server(CDB, DiagConsumer, FS,
                       /*RunSynchronously=*/false);
 
   auto FooCpp = getVirtualTestFilePath("foo.cpp");
   const auto SourceContents = R"cpp(
 int aba;
 int b =   ;