[PDB][NativeSession] Use better error code for invalid format (#167885)

Replaces the default "Success" std::error_code with a more meaningful
one if `Magic != file_magic::pdb`.

Author: MuellerMP

llvm/lib/DebugInfo/PDB/Native/NativeSession.cpp

@@ -87,6 +87,19 @@ Error NativeSession::createFromPdb(std::unique_ptr<MemoryBuffer> Buffer,
   return Error::success();
 }
 
+static Error validatePdbMagic(StringRef PdbPath) {
+  file_magic Magic;
+  if (auto EC = identify_magic(PdbPath, Magic))
+    return make_error<RawError>(EC);
+
+  if (Magic != file_magic::pdb)
+    return make_error<RawError>(
+        raw_error_code::invalid_format,
+        "The input file did not contain the pdb file magic.");
+
+  return Error::success();
+}
+
 static Expected<std::unique_ptr<PDBFile>>
 loadPdbFile(StringRef PdbPath, std::unique_ptr<BumpPtrAllocator> &Allocator) {
   ErrorOr<std::unique_ptr<MemoryBuffer>> ErrorOrBuffer =
@@ -97,10 +110,8 @@ loadPdbFile(StringRef PdbPath, std::unique_ptr<BumpPtrAllocator> &Allocator) {
   std::unique_ptr<llvm::MemoryBuffer> Buffer = std::move(*ErrorOrBuffer);
 
   PdbPath = Buffer->getBufferIdentifier();
-  file_magic Magic;
-  auto EC = identify_magic(PdbPath, Magic);
-  if (EC || Magic != file_magic::pdb)
-    return make_error<RawError>(EC);
+  if (auto EC = validatePdbMagic(PdbPath))
+    return std::move(EC);
 
   auto Stream = std::make_unique<MemoryBufferByteStream>(
       std::move(Buffer), llvm::endianness::little);
@@ -152,10 +163,8 @@ Error NativeSession::createFromExe(StringRef ExePath,
   if (!PdbPath)
     return PdbPath.takeError();
 
-  file_magic Magic;
-  auto EC = identify_magic(PdbPath.get(), Magic);
-  if (EC || Magic != file_magic::pdb)
-    return make_error<RawError>(EC);
+  if (auto EC = validatePdbMagic(PdbPath.get()))
+    return EC;
 
   auto Allocator = std::make_unique<BumpPtrAllocator>();
   auto File = loadPdbFile(PdbPath.get(), Allocator);

llvm/unittests/DebugInfo/PDB/NativeSessionTest.cpp

@@ -40,6 +40,18 @@ TEST(NativeSessionTest, TestCreateFromExe) {
   ASSERT_THAT_ERROR(std::move(E), Succeeded());
 }
 
+TEST(NativeSessionTest, TestInvalidPdbMagicError) {
+  SmallString<128> InputsDir = unittest::getInputFileDirectory(TestMainArgv0);
+  llvm::sys::path::append(InputsDir, "SimpleTest.cpp");
+  std::string CppPath{InputsDir};
+  std::unique_ptr<IPDBSession> S;
+
+  Error E = NativeSession::createFromPdbPath(CppPath, S);
+  const char *FormatErr = "The record is in an unexpected format. "
+                          "The input file did not contain the pdb file magic.";
+  ASSERT_THAT_ERROR(std::move(E), FailedWithMessage(FormatErr));
+}
+
 TEST(NativeSessionTest, TestSetLoadAddress) {
   std::unique_ptr<IPDBSession> S;
   Error E = pdb::loadDataForEXE(PDB_ReaderType::Native, getExePath(), S);