FileCheck: dump command line context with empty input

[davidxl]

Summary

FileCheck dumps minimal information when input is empty. We have many tests that include more than one FileCheck command lines. When such an error happens, figuring out which command actually is the problem can be hard sometimes (e.g, without running environment to reproduce).

This patch enables FileCheck to dump the full command line as a context line so that it is easier to identify the problem.

[silvas]

This sounds like a nice improvement.

[dblaikie]

Should we instead modify lit to indicate which command it stopped at? That
would seem more general/to cover other cases as well?

llvm/trunk/test/FileCheck/check-empty.txt

 // RUN: not FileCheck -check-prefix=FOO %s </dev/null 2>&1 | FileCheck -check-prefix=EMPTY-ERR %s
 // RUN: not FileCheck -check-prefix=NOFOO %s </dev/null 2>&1 | FileCheck -check-prefix=EMPTY-ERR %s
 // RUN: not FileCheck -check-prefix=FOO -allow-empty %s </dev/null 2>&1 | FileCheck -check-prefix=NO-EMPTY-ERR -check-prefix=NOT-FOUND %s
 // RUN: FileCheck -check-prefix=NOFOO -allow-empty %s </dev/null 2>&1 | FileCheck -allow-empty -check-prefix=NO-EMPTY-ERR %s
 
 ; FOO: foo
 ; NOFOO-NOT: foo
 
 ; EMPTY-ERR: FileCheck error: '-' is empty.
+; EMPTY-ERR-NEXT: FileCheck command line: {{.*}}FileCheck -check-prefix={{.*}}FOO {{.*}}check-empty.txt
 ; NO-EMPTY-ERR-NOT: FileCheck error: '-' is empty.
 ; NOT-FOUND: error: expected string not found in input

llvm/trunk/utils/FileCheck/FileCheck.cpp

 
 // I don't think there's a way to specify an initial value for cl::list,
 // so if nothing was specified, add the default
 static void AddCheckPrefixIfNeeded() {
   if (CheckPrefixes.empty())
     CheckPrefixes.push_back("CHECK");
 }
 
+static void DumpCommandLine(int argc, char **argv) {
+  errs() << "FileCheck command line: ";
+  for (int I = 0; I < argc; I++)
+    errs() << " " << argv[I];
+  errs() << "\n";
+}
+
 int main(int argc, char **argv) {
   sys::PrintStackTraceOnErrorSignal();
   PrettyStackTraceProgram X(argc, argv);
   cl::ParseCommandLineOptions(argc, argv);
 
   if (!ValidateCheckPrefixes()) {
     errs() << "Supplied check-prefix is invalid! Prefixes must be unique and "
               "start with a letter and contain only alphanumeric characters, "
if (std::error_code EC = FileOrErr.getError()) {
     errs() << "Could not open input file '" << InputFilename
            << "': " << EC.message() << '\n';
     return 2;
   }
   std::unique_ptr<MemoryBuffer> &File = FileOrErr.get();
 
   if (File->getBufferSize() == 0 && !AllowEmptyInput) {
     errs() << "FileCheck error: '" << InputFilename << "' is empty.\n";
+    DumpCommandLine(argc, argv);
     return 2;
   }
 
   // Remove duplicate spaces in the input file if requested.
   // Remove DOS style line endings.
   std::unique_ptr<MemoryBuffer> F =
       CanonicalizeInputFile(std::move(File), NoCanonicalizeWhiteSpace);