Index: clang-tools-extra/trunk/clangd/GlobalCompilationDatabase.cpp
===================================================================
--- clang-tools-extra/trunk/clangd/GlobalCompilationDatabase.cpp
+++ clang-tools-extra/trunk/clangd/GlobalCompilationDatabase.cpp
@@ -21,11 +21,17 @@
 
 void adjustArguments(tooling::CompileCommand &Cmd,
                      llvm::StringRef ResourceDir) {
-  // Strip plugin related command line arguments. Clangd does
-  // not support plugins currently. Therefore it breaks if
-  // compiler tries to load plugins.
-  Cmd.CommandLine =
-      tooling::getStripPluginsAdjuster()(Cmd.CommandLine, Cmd.Filename);
+  tooling::ArgumentsAdjuster ArgsAdjuster = tooling::combineAdjusters(
+      // clangd should not write files to disk, including dependency files
+      // requested on the command line.
+      tooling::getClangStripDependencyFileAdjuster(),
+      // Strip plugin related command line arguments. Clangd does
+      // not support plugins currently. Therefore it breaks if
+      // compiler tries to load plugins.
+      tooling::combineAdjusters(tooling::getStripPluginsAdjuster(),
+                                tooling::getClangSyntaxOnlyAdjuster()));
+
+  Cmd.CommandLine = ArgsAdjuster(Cmd.CommandLine, Cmd.Filename);
   // Inject the resource dir.
   // FIXME: Don't overwrite it if it's already there.
   if (!ResourceDir.empty())
Index: clang-tools-extra/trunk/unittests/clangd/GlobalCompilationDatabaseTests.cpp
===================================================================
--- clang-tools-extra/trunk/unittests/clangd/GlobalCompilationDatabaseTests.cpp
+++ clang-tools-extra/trunk/unittests/clangd/GlobalCompilationDatabaseTests.cpp
@@ -16,15 +16,18 @@
 namespace clang {
 namespace clangd {
 namespace {
+using ::testing::AllOf;
+using ::testing::Contains;
 using ::testing::ElementsAre;
 using ::testing::EndsWith;
+using ::testing::Not;
 
 TEST(GlobalCompilationDatabaseTest, FallbackCommand) {
   DirectoryBasedGlobalCompilationDatabase DB(None);
   auto Cmd = DB.getFallbackCommand(testPath("foo/bar.cc"));
   EXPECT_EQ(Cmd.Directory, testPath("foo"));
-  EXPECT_THAT(Cmd.CommandLine, ElementsAre(
-    EndsWith("clang"), testPath("foo/bar.cc")));
+  EXPECT_THAT(Cmd.CommandLine,
+              ElementsAre(EndsWith("clang"), testPath("foo/bar.cc")));
   EXPECT_EQ(Cmd.Output, "");
 
   // .h files have unknown language, so they are parsed liberally as obj-c++.
@@ -65,16 +68,18 @@
 
 TEST_F(OverlayCDBTest, GetCompileCommand) {
   OverlayCDB CDB(Base.get(), {}, std::string(""));
-  EXPECT_EQ(CDB.getCompileCommand(testPath("foo.cc")),
-            Base->getCompileCommand(testPath("foo.cc")));
+  EXPECT_THAT(CDB.getCompileCommand(testPath("foo.cc"))->CommandLine,
+              AllOf(Contains(testPath("foo.cc")), Contains("-DA=1")));
   EXPECT_EQ(CDB.getCompileCommand(testPath("missing.cc")), llvm::None);
 
   auto Override = cmd(testPath("foo.cc"), "-DA=3");
   CDB.setCompileCommand(testPath("foo.cc"), Override);
-  EXPECT_EQ(CDB.getCompileCommand(testPath("foo.cc")), Override);
+  EXPECT_THAT(CDB.getCompileCommand(testPath("foo.cc"))->CommandLine,
+              Contains("-DA=3"));
   EXPECT_EQ(CDB.getCompileCommand(testPath("missing.cc")), llvm::None);
   CDB.setCompileCommand(testPath("missing.cc"), Override);
-  EXPECT_EQ(CDB.getCompileCommand(testPath("missing.cc")), Override);
+  EXPECT_THAT(CDB.getCompileCommand(testPath("missing.cc"))->CommandLine,
+              Contains("-DA=3"));
 }
 
 TEST_F(OverlayCDBTest, GetFallbackCommand) {
@@ -88,7 +93,8 @@
   EXPECT_EQ(CDB.getCompileCommand(testPath("bar.cc")), None);
   auto Override = cmd(testPath("bar.cc"), "-DA=5");
   CDB.setCompileCommand(testPath("bar.cc"), Override);
-  EXPECT_EQ(CDB.getCompileCommand(testPath("bar.cc")), Override);
+  EXPECT_THAT(CDB.getCompileCommand(testPath("bar.cc"))->CommandLine,
+              Contains("-DA=5"));
 
   EXPECT_THAT(CDB.getFallbackCommand(testPath("foo.cc")).CommandLine,
               ElementsAre(EndsWith("clang"), testPath("foo.cc"), "-DA=6"));
@@ -111,6 +117,35 @@
                                    ElementsAre("A.cpp"), ElementsAre("C.cpp")));
 }
 
+TEST_F(OverlayCDBTest, Adjustments) {
+  OverlayCDB CDB(Base.get(), {}, std::string(""));
+  auto Cmd = CDB.getCompileCommand(testPath("foo.cc")).getValue();
+  // Delete the file name.
+  Cmd.CommandLine.pop_back();
+
+  // Check dependency file commands are dropped.
+  Cmd.CommandLine.push_back("-MF");
+  Cmd.CommandLine.push_back("random-dependency");
+
+  // Check plugin-related commands are dropped.
+  Cmd.CommandLine.push_back("-Xclang");
+  Cmd.CommandLine.push_back("-load");
+  Cmd.CommandLine.push_back("-Xclang");
+  Cmd.CommandLine.push_back("random-plugin");
+
+  Cmd.CommandLine.push_back("-DA=5");
+  Cmd.CommandLine.push_back(Cmd.Filename);
+
+  CDB.setCompileCommand(testPath("foo.cc"), Cmd);
+
+  EXPECT_THAT(CDB.getCompileCommand(testPath("foo.cc"))->CommandLine,
+              AllOf(Contains("-fsyntax-only"), Contains("-DA=5"),
+                    Contains(testPath("foo.cc")), Not(Contains("-MF")),
+                    Not(Contains("random-dependency")),
+                    Not(Contains("-Xclang")), Not(Contains("-load")),
+                    Not(Contains("random-plugin"))));
+}
+
 } // namespace
 } // namespace clangd
 } // namespace clang