[Support] Add a test for recursive response file expansion

[smeenai]

Summary

I'm going to be modifying the logic to avoid infinitely recursing on
self-referential response files, so add a unit test to verify the
expected behavior.

[hans]

Looks good to me.

llvm/unittests/Support/CommandLineTest.cpp

792

Not that it matters, but would using .str() instead of .c_str() work (relying on StringRef's conversion operator to std::sttring)?

794

ditto

[smeenai]

llvm/unittests/Support/CommandLineTest.cpp

792

That doesn't work, cos it tries to create a Twine. I could do .str().str(), but I don't think that's cleaner.

794

Sure.

[smeenai]

Review comments

llvm/unittests/Support/CommandLineTest.cpp

TEST(CommandLineTest, ResponseFiles) {
   EXPECT_STREQ(Argv[8], "-flag_2");
 
   llvm::sys::fs::remove(IncludedFileName2);
   llvm::sys::fs::remove(IncDir);
   llvm::sys::fs::remove(IncludedFileName);
   llvm::sys::fs::remove(TestDir);
 }
 
+TEST(CommandLineTest, RecursiveResponseFiles) {
+  SmallString<128> TestDir;
+  std::error_code EC = sys::fs::createUniqueDirectory("unittest", TestDir);
+  EXPECT_TRUE(!EC);
+
+  SmallString<128> ResponseFilePath;
+  sys::path::append(ResponseFilePath, TestDir, "recursive.rsp");
+  std::string ResponseFileRef = std::string("@") + ResponseFilePath.c_str();
+
+  std::ofstream ResponseFile(ResponseFilePath.str());
+  EXPECT_TRUE(ResponseFile.is_open());
+  ResponseFile << ResponseFileRef << "\n";
+  ResponseFile << ResponseFileRef << "\n";
+  ResponseFile.close();
+
+  // Ensure the recursive expansion terminates.
+  llvm::SmallVector<const char *, 4> Argv = {"test/test",
+                                             ResponseFileRef.c_str()};
+  llvm::BumpPtrAllocator A;
+  llvm::StringSaver Saver(A);
+  bool Res = llvm::cl::ExpandResponseFiles(
+      Saver, llvm::cl::TokenizeGNUCommandLine, Argv, false, false);
+  EXPECT_FALSE(Res);
+
+  // Ensure some expansion took place.
+  EXPECT_GT(Argv.size(), 2U);
+  EXPECT_STREQ(Argv[0], "test/test");
+  for (size_t i = 1; i < Argv.size(); ++i)
+    EXPECT_STREQ(Argv[i], ResponseFileRef.c_str());
+}
+
 TEST(CommandLineTest, SetDefautValue) {
   cl::ResetCommandLineParser();
 
   StackOption<std::string> Opt1("opt1", cl::init("true"));
   StackOption<bool> Opt2("opt2", cl::init(true));
   cl::alias Alias("alias", llvm::cl::aliasopt(Opt2));
   StackOption<int> Opt3("opt3", cl::init(3));