[llvm-pdbdump] in yaml2pdb, generate default output filename if none given

[inglorion]

Summary

llvm-pdbdump yaml2pdb used to fail with a misleading error
message ("An I/O error occurred on the file system") if no output file
was specified. This change adds an assert to PDBFileBuilder to check
that an output file name is specified, and makes llvm-pdbdump generate
an output file name based on the input file name if no output file
name is explicitly specified.

lib/DebugInfo/PDB/Native/PDBFileBuilder.cpp

 Expected<uint32_t> PDBFileBuilder::getNamedStreamIndex(StringRef Name) const {
   uint32_t SN = 0;
   if (!NamedStreams.get(Name, SN))
     return llvm::make_error<pdb::RawError>(raw_error_code::no_stream);
   return SN;
 }
 
 Error PDBFileBuilder::commit(StringRef Filename) {
+  assert(!Filename.empty());
   auto ExpectedLayout = finalizeMsfLayout();
   if (!ExpectedLayout)
     return ExpectedLayout.takeError();
   auto &Layout = *ExpectedLayout;
 
   uint64_t Filesize = Layout.SB->BlockSize * Layout.SB->NumBlocks;
   auto OutFileOrError = FileOutputBuffer::create(Filename, Filesize);
   if (OutFileOrError.getError())

tools/llvm-pdbdump/llvm-pdbdump.cpp

 #include "llvm/Support/COM.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/ConvertUTF.h"
 #include "llvm/Support/FileOutputBuffer.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Format.h"
 #include "llvm/Support/ManagedStatic.h"
 #include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/Path.h"
 #include "llvm/Support/PrettyStackTrace.h"
 #include "llvm/Support/Process.h"
 #include "llvm/Support/Regex.h"
 #include "llvm/Support/ScopedPrinter.h"
 #include "llvm/Support/Signals.h"
 #include "llvm/Support/raw_ostream.h"
 
 using namespace llvm;
cl::list<std::string> InputFilenames(cl::Positional,
                                      cl::OneOrMore, cl::sub(RawSubcommand));
 }
 
 namespace yaml2pdb {
 cl::opt<std::string>
     YamlPdbOutputFile("pdb", cl::desc("the name of the PDB file to write"),
                       cl::sub(YamlToPdbSubcommand));
 
-cl::list<std::string> InputFilename(cl::Positional,
-                                    cl::desc("<input YAML file>"), cl::Required,
-                                    cl::sub(YamlToPdbSubcommand));
+cl::opt<std::string> InputFilename(cl::Positional,
 }
 
 namespace pdb2yaml {
 cl::opt<bool>
     NoFileHeaders("no-file-headers",
                   cl::desc("Do not dump MSF file headers (you will not be able "
                            "to generate a fresh PDB from the resulting YAML)"),
                   cl::sub(PdbToYamlSubcommand), cl::init(false));
if (opts::RawSubcommand) {
     }
   }
 
   llvm::sys::InitializeCOMRAII COM(llvm::sys::COMThreadingMode::MultiThreaded);
 
   if (opts::PdbToYamlSubcommand) {
     pdb2Yaml(opts::pdb2yaml::InputFilename.front());
   } else if (opts::YamlToPdbSubcommand) {
-    yamlToPdb(opts::yaml2pdb::InputFilename.front());
+    if (opts::yaml2pdb::YamlPdbOutputFile.empty()) {
+      SmallString<16> OutputFilename(opts::yaml2pdb::InputFilename.getValue());
+      sys::path::replace_extension(OutputFilename, ".pdb");
+      opts::yaml2pdb::YamlPdbOutputFile = OutputFilename.str();
+    }
+    yamlToPdb(opts::yaml2pdb::InputFilename);
   } else if (opts::AnalyzeSubcommand) {
     dumpAnalysis(opts::analyze::InputFilename.front());
   } else if (opts::PrettySubcommand) {
     if (opts::pretty::Lines)
       opts::pretty::Compilands = true;
 
     if (opts::pretty::All) {
       opts::pretty::Compilands = true;