Add and test extra assertion

Author: jansvoboda11

clang/lib/Tooling/DependencyScanning/DependencyScanningFilesystem.cpp

@@ -132,9 +132,13 @@ DependencyScanningFilesystemSharedCache::CacheShard::
   std::lock_guard<std::mutex> LockGuard(CacheLock);
   auto [It, Inserted] = CacheByFilename.insert({Filename, {nullptr, nullptr}});
   auto &[CachedEntry, CachedRealPath] = It->getValue();
-  if (!CachedEntry)
+  if (!CachedEntry) {
+    // The entry is not present in the shared cache. Either the cache doesn't
+    // know about the file at all, or it only knows about its real path.
+    assert((Inserted || CachedRealPath) && "existing file with empty pair");
     CachedEntry =
         new (EntryStorage.Allocate()) CachedFileSystemEntry(std::move(Stat));
+  }
   return *CachedEntry;
 }
 

clang/unittests/Tooling/DependencyScanning/DependencyScanningFilesystemTest.cpp

@@ -95,3 +95,58 @@ TEST(DependencyScanningFilesystem, CacheGetRealPath) {
     EXPECT_EQ(InstrumentingFS->NumGetRealPathCalls, 2u); // Shared cache.
   }
 }
+
+TEST(DependencyScanningFilesystem, RealPathAndStatusInvariants) {
+  auto InMemoryFS = llvm::makeIntrusiveRefCnt<llvm::vfs::InMemoryFileSystem>();
+  InMemoryFS->setCurrentWorkingDirectory("/");
+  InMemoryFS->addFile("/foo.c", 0, llvm::MemoryBuffer::getMemBuffer(""));
+  InMemoryFS->addFile("/bar.c", 0, llvm::MemoryBuffer::getMemBuffer(""));
+
+  auto InstrumentingFS =
+      llvm::makeIntrusiveRefCnt<InstrumentingFilesystem>(InMemoryFS);
+
+  DependencyScanningFilesystemSharedCache SharedCache;
+  DependencyScanningWorkerFilesystem DepFS(SharedCache, InstrumentingFS);
+
+  // Success.
+  {
+    DepFS.status("/foo.c");
+
+    llvm::SmallString<128> Result;
+    DepFS.getRealPath("/foo.c", Result);
+  }
+  {
+    llvm::SmallString<128> Result;
+    DepFS.getRealPath("/bar.c", Result);
+
+    DepFS.status("/bar.c");
+  }
+
+  // Failure.
+  {
+    DepFS.status("/foo.m");
+
+    llvm::SmallString<128> Result;
+    DepFS.getRealPath("/foo.m", Result);
+  }
+  {
+    llvm::SmallString<128> Result;
+    DepFS.getRealPath("/bar.m", Result);
+
+    DepFS.status("/bar.m");
+  }
+
+  // Failure without caching.
+  {
+    DepFS.status("/foo");
+
+    llvm::SmallString<128> Result;
+    DepFS.getRealPath("/foo", Result);
+  }
+  {
+    llvm::SmallString<128> Result;
+    DepFS.getRealPath("/bar", Result);
+
+    DepFS.status("/bar");
+  }
+}