Fix skipping of flags in getClangStripDependencyFileAdjuster

[kastiglione]

Summary

The ArgumentsAdjuster returned from getClangStripDependencyFileAdjuster will
skip dependency flags, and also their associated values for those flags that
take an argument. This change corrects the handling of the -MD and -MMD
flags, which do not take an argument.

[kastiglione]

Add a continue;

[alexander-shaposhnikov]

probably a test would be useful

[kastiglione]

Add tests

lib/Tooling/ArgumentsAdjusters.cpp

 
 ArgumentsAdjuster getClangStripDependencyFileAdjuster() {
   return [](const CommandLineArguments &Args, StringRef /*unused*/) {
     CommandLineArguments AdjustedArgs;
     for (size_t i = 0, e = Args.size(); i < e; ++i) {
       StringRef Arg = Args[i];
       // All dependency-file options begin with -M. These include -MM,
       // -MF, -MG, -MP, -MT, -MQ, -MD, and -MMD.
-      if (!Arg.startswith("-M"))
+      if (!Arg.startswith("-M")) {
         AdjustedArgs.push_back(Args[i]);
+        continue;
+      }
 
-      if ((Arg == "-MF") || (Arg == "-MT") || (Arg == "-MQ") ||
-          (Arg == "-MD") || (Arg == "-MMD")) {
-        // Output is specified as -MX foo. Skip the next argument also.
+      if (Arg == "-MF" || Arg == "-MT" || Arg == "-MQ")
+        // These flags take an argument: -MX foo. Skip the next argument also.
         ++i;
-      }
-    }
     return AdjustedArgs;
   };
 }
 
 ArgumentsAdjuster getInsertArgumentAdjuster(const CommandLineArguments &Extra,
                                             ArgumentInsertPosition Pos) {
   return [Extra, Pos](const CommandLineArguments &Args, StringRef /*unused*/) {
     CommandLineArguments Return(Args);

unittests/Tooling/ToolingTest.cpp

TEST(ClangToolTest, ArgumentAdjusters) {
   Tool.clearArgumentsAdjusters();
   Tool.appendArgumentsAdjuster(CheckSyntaxOnlyAdjuster);
   Tool.appendArgumentsAdjuster(getClangSyntaxOnlyAdjuster());
   Tool.run(Action.get());
   EXPECT_TRUE(Ran);
   EXPECT_FALSE(Found);
 }
 
+// Check getClangStripDependencyFileAdjuster doesn't strip args after -MD/-MMD.
+TEST(ClangToolTest, StripDependencyFileAdjuster) {
+  FixedCompilationDatabase Compilations("/", {"-MD", "-c", "-MMD", "-w"});
+
+  ClangTool Tool(Compilations, std::vector<std::string>(1, "/a.cc"));
+  Tool.mapVirtualFile("/a.cc", "void a() {}");
+
+  std::unique_ptr<FrontendActionFactory> Action(
+      newFrontendActionFactory<SyntaxOnlyAction>());
+
+  CommandLineArguments FinalArgs;
+  ArgumentsAdjuster CheckFlagsAdjuster =
+    [&FinalArgs](const CommandLineArguments &Args, StringRef /*unused*/) {
+      FinalArgs = Args;
+      return Args;
+    };
+  Tool.clearArgumentsAdjusters();
+  Tool.appendArgumentsAdjuster(getClangStripDependencyFileAdjuster());
+  Tool.appendArgumentsAdjuster(CheckFlagsAdjuster);
+  Tool.run(Action.get());
+
+  auto HasFlag = [&FinalArgs](const std::string &Flag) {
+    return std::find(FinalArgs.begin(), FinalArgs.end(), Flag) !=
+           FinalArgs.end();
+  };
+  EXPECT_FALSE(HasFlag("-MD"));
+  EXPECT_FALSE(HasFlag("-MMD"));
+  EXPECT_TRUE(HasFlag("-c"));
+  EXPECT_TRUE(HasFlag("-w"));
+}
+
 namespace {
 /// Find a target name such that looking for it in TargetRegistry by that name
 /// returns the same target. We expect that there is at least one target
 /// configured with this property.
 std::string getAnyTarget() {
   llvm::InitializeAllTargets();
   for (const auto &Target : llvm::TargetRegistry::targets()) {
     std::string Error;