FileCheck: Add a flag to allow checking empty input

Currently FileCheck errors out on empty input. This is usually the
right thing to do, but makes testing things like "this command does
not emit some error message" hard to test. This usually leads to
people using "command 2>&1 | count 0" instead, and then the bots that
use guard malloc fail a few hours later.

By adding a flag to FileCheck that allows empty inputs, we can make
tests that consist entirely of "CHECK-NOT" lines feasible.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215127 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 6 insertions, 1 deletions

diff --git a/utils/FileCheck/FileCheck.cpp b/utils/FileCheck/FileCheck.cpp
index 8c62ae7f5d1..e8365fc248a 100644
--- a/utils/FileCheck/FileCheck.cpp
+++ b/utils/FileCheck/FileCheck.cpp
@@ -57,6 +57,11 @@ static cl::list<std::string> ImplicitCheckNot(
              "this pattern occur which are not matched by a positive pattern"),
     cl::value_desc("pattern"));
 
+static cl::opt<bool> AllowEmptyInput(
+    "allow-empty", cl::init(false),
+    cl::desc("Allow the input file to be empty. This is useful when making\n"
+             "checks that some error message does not occur, for example."));
+
 typedef cl::list<std::string>::const_iterator prefix_iterator;
 
 //===----------------------------------------------------------------------===//
@@ -1260,7 +1265,7 @@ int main(int argc, char **argv) {
   }
   std::unique_ptr<MemoryBuffer> &File = FileOrErr.get();
 
-  if (File->getBufferSize() == 0) {
+  if (File->getBufferSize() == 0 && !AllowEmptyInput) {
     errs() << "FileCheck error: '" << InputFilename << "' is empty.\n";
     return 2;
   }