Explicitly assign constructed C++ classes

C++ style guides I am aware of recommend specifically preferring = syntax
for any classes with fairly obvious constructors[^0] that do not perform
any complicated logic in their constructor. I contend that all constructors
that the `rustc_llvm` code uses qualify. This has only become more common
since C++ 17 guaranteed many cases of copy initialization elision.

The other detail is that I tried to ask another contributor with
infinitely more C++ experience than me (i.e. any) what this constructor
syntax was, and they thought it was a macro. I know of no other language
that has adopted this same syntax. As the rustc codebase features many
contributors experienced in many other languages, using a less...
unique... style has many other benefits in making this code more
lucid and maintainable, which is something it direly needs.

[^0]: e.g. https://abseil.io/tips/88

Author: workingjubilee

compiler/rustc_llvm/llvm-wrapper/CoverageMappingWrapper.cpp

@@ -120,7 +120,7 @@ extern "C" void LLVMRustCoverageWriteFilenamesSectionToBuffer(
   }
   auto FilenamesWriter =
       coverage::CoverageFilenamesSectionWriter(ArrayRef<std::string>(FilenameRefs));
-  RawRustStringOstream OS(BufferOut);
+  auto OS = RawRustStringOstream(BufferOut);
   FilenamesWriter.write(OS);
 }
 
@@ -160,7 +160,7 @@ extern "C" void LLVMRustCoverageWriteMappingToBuffer(
       ArrayRef<unsigned>(VirtualFileMappingIDs, NumVirtualFileMappingIDs),
       Expressions,
       MappingRegions);
-  RawRustStringOstream OS(BufferOut);
+  auto OS = RawRustStringOstream(BufferOut);
   CoverageMappingWriter.write(OS);
 }
 
@@ -184,7 +184,7 @@ static void WriteSectionNameToString(LLVMModuleRef M,
                                      RustStringRef Str) {
   Triple TargetTriple(unwrap(M)->getTargetTriple());
   auto name = getInstrProfSectionName(SK, TargetTriple.getObjectFormat());
-  RawRustStringOstream OS(Str);
+  auto OS = RawRustStringOstream(Str);
   OS << name;
 }
 
@@ -200,10 +200,11 @@ extern "C" void LLVMRustCoverageWriteFuncSectionNameToString(LLVMModuleRef M,
 
 extern "C" void LLVMRustCoverageWriteMappingVarNameToString(RustStringRef Str) {
   auto name = getCoverageMappingVarName();
-  RawRustStringOstream OS(Str);
+  auto OS = RawRustStringOstream(Str);
   OS << name;
 }
 
 extern "C" uint32_t LLVMRustCoverageMappingVersion() {
   return coverage::CovMapVersion::Version6;
 }
+

compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp

@@ -79,7 +79,7 @@ extern "C" void LLVMRustTimeTraceProfilerFinishThread() {
 extern "C" void LLVMRustTimeTraceProfilerFinish(const char* FileName) {
   StringRef FN(FileName);
   std::error_code EC;
-  raw_fd_ostream OS(FN, EC, sys::fs::CD_CreateAlways);
+  auto OS = raw_fd_ostream(FN, EC, sys::fs::CD_CreateAlways);
 
   timeTraceProfilerWrite(OS);
   timeTraceProfilerCleanup();
@@ -589,25 +589,25 @@ LLVMRustWriteOutputFile(LLVMTargetMachineRef Target, LLVMPassManagerRef PMR,
 
   std::string ErrorInfo;
   std::error_code EC;
-  raw_fd_ostream OS(Path, EC, sys::fs::OF_None);
+  auto OS = raw_fd_ostream(Path, EC, sys::fs::OF_None);
   if (EC)
     ErrorInfo = EC.message();
   if (ErrorInfo != "") {
     LLVMRustSetLastError(ErrorInfo.c_str());
     return LLVMRustResult::Failure;
   }
 
-  buffer_ostream BOS(OS);
+  auto BOS = buffer_ostream(OS);
   if (DwoPath) {
-    raw_fd_ostream DOS(DwoPath, EC, sys::fs::OF_None);
+    auto DOS = raw_fd_ostream(DwoPath, EC, sys::fs::OF_None);
     EC.clear();
     if (EC)
         ErrorInfo = EC.message();
     if (ErrorInfo != "") {
       LLVMRustSetLastError(ErrorInfo.c_str());
       return LLVMRustResult::Failure;
     }
-    buffer_ostream DBOS(DOS);
+    auto DBOS = buffer_ostream(DOS);
     unwrap(Target)->addPassesToEmitFile(*PM, BOS, &DBOS, FileType, false);
     PM->run(*unwrap(M));
   } else {
@@ -796,7 +796,7 @@ LLVMRustOptimize(
                         DebugInfoForProfiling);
   }
 
-  PassBuilder PB(TM, PTO, PGOOpt, &PIC);
+  auto PB = PassBuilder(TM, PTO, PGOOpt, &PIC);
   LoopAnalysisManager LAM;
   FunctionAnalysisManager FAM;
   CGSCCAnalysisManager CGAM;
@@ -1112,16 +1112,16 @@ extern "C" LLVMRustResult
 LLVMRustPrintModule(LLVMModuleRef M, const char *Path, DemangleFn Demangle) {
   std::string ErrorInfo;
   std::error_code EC;
-  raw_fd_ostream OS(Path, EC, sys::fs::OF_None);
+  auto OS = raw_fd_ostream(Path, EC, sys::fs::OF_None);
   if (EC)
     ErrorInfo = EC.message();
   if (ErrorInfo != "") {
     LLVMRustSetLastError(ErrorInfo.c_str());
     return LLVMRustResult::Failure;
   }
 
-  RustAssemblyAnnotationWriter AAW(Demangle);
-  formatted_raw_ostream FOS(OS);
+  auto AAW = RustAssemblyAnnotationWriter(Demangle);
+  auto FOS = formatted_raw_ostream(OS);
   unwrap(M)->print(FOS, &AAW);
 
   return LLVMRustResult::Success;
@@ -1281,8 +1281,8 @@ LLVMRustCreateThinLTOData(LLVMRustThinLTOModule *modules,
   // Load each module's summary and merge it into one combined index
   for (int i = 0; i < num_modules; i++) {
     auto module = &modules[i];
-    StringRef buffer(module->data, module->len);
-    MemoryBufferRef mem_buffer(buffer, module->identifier);
+    auto buffer = StringRef(module->data, module->len);
+    auto mem_buffer = MemoryBufferRef(buffer, module->identifier);
 
     Ret->ModuleMap[module->identifier] = mem_buffer;
 
@@ -1485,7 +1485,7 @@ LLVMRustPrepareThinLTOImport(const LLVMRustThinLTOData *Data, LLVMModuleRef M,
     return MOrErr;
   };
   bool ClearDSOLocal = clearDSOLocalOnDeclarations(Mod, Target);
-  FunctionImporter Importer(Data->Index, Loader, ClearDSOLocal);
+  auto Importer = FunctionImporter(Data->Index, Loader, ClearDSOLocal);
   Expected<bool> Result = Importer.importFunctions(Mod, ImportList);
   if (!Result) {
     LLVMRustSetLastError(toString(Result.takeError()).c_str());
@@ -1510,7 +1510,7 @@ extern "C" LLVMRustThinLTOBuffer*
 LLVMRustThinLTOBufferCreate(LLVMModuleRef M, bool is_thin) {
   auto Ret = std::make_unique<LLVMRustThinLTOBuffer>();
   {
-    raw_string_ostream OS(Ret->data);
+    auto OS = raw_string_ostream(Ret->data);
     {
       if (is_thin) {
         PassBuilder PB;
@@ -1557,8 +1557,8 @@ LLVMRustParseBitcodeForLTO(LLVMContextRef Context,
                            const char *data,
                            size_t len,
                            const char *identifier) {
-  StringRef Data(data, len);
-  MemoryBufferRef Buffer(Data, identifier);
+  auto Data = StringRef(data, len);
+  auto Buffer = MemoryBufferRef(Data, identifier);
   unwrap(Context)->enableDebugTypeODRUniquing();
   Expected<std::unique_ptr<Module>> SrcOrError =
       parseBitcodeFile(Buffer, *unwrap(Context));
@@ -1576,8 +1576,8 @@ extern "C" const char *LLVMRustGetSliceFromObjectDataByName(const char *data,
                                                             const char *name,
                                                             size_t *out_len) {
   *out_len = 0;
-  StringRef Data(data, len);
-  MemoryBufferRef Buffer(Data, ""); // The id is unused.
+  auto Data = StringRef(data, len);
+  auto Buffer = MemoryBufferRef(Data, ""); // The id is unused.
   file_magic Type = identify_magic(Buffer.getBuffer());
   Expected<std::unique_ptr<object::ObjectFile>> ObjFileOrError =
       object::ObjectFile::createObjectFile(Buffer, Type);
@@ -1633,3 +1633,4 @@ LLVMRustComputeLTOCacheKey(RustStringRef KeyOut, const char *ModId, LLVMRustThin
 
   LLVMRustStringWriteImpl(KeyOut, Key.c_str(), Key.size());
 }
+

compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp

@@ -109,7 +109,7 @@ extern "C" void LLVMRustSetNormalizedTarget(LLVMModuleRef M,
 
 extern "C" const char *LLVMRustPrintPassTimings(size_t *Len) {
   std::string buf;
-  raw_string_ostream SS(buf);
+  auto SS = raw_string_ostream(buf);
   TimerGroup::printAll(SS);
   SS.flush();
   *Len = buf.length();
@@ -120,7 +120,7 @@ extern "C" const char *LLVMRustPrintPassTimings(size_t *Len) {
 
 extern "C" const char *LLVMRustPrintStatistics(size_t *Len) {
   std::string buf;
-  raw_string_ostream SS(buf);
+  auto SS = raw_string_ostream(buf);
   llvm::PrintStatistics(SS);
   SS.flush();
   *Len = buf.length();
@@ -174,7 +174,7 @@ extern "C" LLVMValueRef LLVMRustGetOrInsertFunction(LLVMModuleRef M,
 extern "C" LLVMValueRef
 LLVMRustGetOrInsertGlobal(LLVMModuleRef M, const char *Name, size_t NameLen, LLVMTypeRef Ty) {
   Module *Mod = unwrap(M);
-  StringRef NameRef(Name, NameLen);
+  auto NameRef = StringRef(Name, NameLen);
 
   // We don't use Module::getOrInsertGlobal because that returns a Constant*,
   // which may either be the real GlobalVariable*, or a constant bitcast of it
@@ -285,7 +285,7 @@ static Attribute::AttrKind fromRust(LLVMRustAttribute Kind) {
 template<typename T> static inline void AddAttributes(T *t, unsigned Index,
                                                       LLVMAttributeRef *Attrs, size_t AttrsLen) {
   AttributeList PAL = t->getAttributes();
-  AttrBuilder B(t->getContext());
+  auto B = AttrBuilder(t->getContext());
   for (LLVMAttributeRef Attr : ArrayRef<LLVMAttributeRef>(Attrs, AttrsLen))
     B.addAttribute(unwrap(Attr));
   AttributeList PALNew = PAL.addAttributesAtIndex(t->getContext(), Index, B);
@@ -1195,13 +1195,13 @@ extern "C" int64_t LLVMRustDIBuilderCreateOpLLVMFragment() {
 }
 
 extern "C" void LLVMRustWriteTypeToString(LLVMTypeRef Ty, RustStringRef Str) {
-  RawRustStringOstream OS(Str);
+  auto OS = RawRustStringOstream(Str);
   unwrap<llvm::Type>(Ty)->print(OS);
 }
 
 extern "C" void LLVMRustWriteValueToString(LLVMValueRef V,
                                            RustStringRef Str) {
-  RawRustStringOstream OS(Str);
+  auto OS = RawRustStringOstream(Str);
   if (!V) {
     OS << "(null)";
   } else {
@@ -1224,7 +1224,7 @@ extern "C" LLVMTypeRef LLVMRustArrayType(LLVMTypeRef ElementTy,
 DEFINE_SIMPLE_CONVERSION_FUNCTIONS(Twine, LLVMTwineRef)
 
 extern "C" void LLVMRustWriteTwineToString(LLVMTwineRef T, RustStringRef Str) {
-  RawRustStringOstream OS(Str);
+  auto OS = RawRustStringOstream(Str);
   unwrap(T)->print(OS);
 }
 
@@ -1236,19 +1236,19 @@ extern "C" void LLVMRustUnpackOptimizationDiagnostic(
   llvm::DiagnosticInfoOptimizationBase *Opt =
       static_cast<llvm::DiagnosticInfoOptimizationBase *>(unwrap(DI));
 
-  RawRustStringOstream PassNameOS(PassNameOut);
+  auto PassNameOS = RawRustStringOstream(PassNameOut);
   PassNameOS << Opt->getPassName();
   *FunctionOut = wrap(&Opt->getFunction());
 
-  RawRustStringOstream FilenameOS(FilenameOut);
+  auto FilenameOS = RawRustStringOstream(FilenameOut);
   DiagnosticLocation loc = Opt->getLocation();
   if (loc.isValid()) {
     *Line = loc.getLine();
     *Column = loc.getColumn();
     FilenameOS << loc.getAbsolutePath();
   }
 
-  RawRustStringOstream MessageOS(MessageOut);
+  auto MessageOS = RawRustStringOstream(MessageOut);
   MessageOS << Opt->getMsg();
 }
 
@@ -1291,8 +1291,8 @@ LLVMRustUnpackInlineAsmDiagnostic(LLVMDiagnosticInfoRef DI,
 
 extern "C" void LLVMRustWriteDiagnosticInfoToString(LLVMDiagnosticInfoRef DI,
                                                     RustStringRef Str) {
-  RawRustStringOstream OS(Str);
-  DiagnosticPrinterRawOStream DP(OS);
+  auto OS = RawRustStringOstream(Str);
+  auto DP = DiagnosticPrinterRawOStream(OS);
   unwrap(DI)->print(DP);
 }
 
@@ -1406,7 +1406,7 @@ extern "C" LLVMTypeKind LLVMRustGetTypeKind(LLVMTypeRef Ty) {
   default:
     {
       std::string error;
-      llvm::raw_string_ostream stream(error);
+      auto stream = llvm::raw_string_ostream(error);
       stream << "Rust does not support the TypeID: " << unwrap(Ty)->getTypeID()
              << " for the type: " << *unwrap(Ty);
       stream.flush();
@@ -1432,7 +1432,7 @@ extern "C" bool LLVMRustUnpackSMDiagnostic(LLVMSMDiagnosticRef DRef,
                                            unsigned* RangesOut,
                                            size_t* NumRanges) {
   SMDiagnostic& D = *unwrap(DRef);
-  RawRustStringOstream MessageOS(MessageOut);
+  auto MessageOS = RawRustStringOstream(MessageOut);
   MessageOS << D.getMessage();
 
   switch (D.getKind()) {
@@ -1547,7 +1547,7 @@ extern "C" void LLVMRustPositionBuilderAtStart(LLVMBuilderRef B,
 
 extern "C" void LLVMRustSetComdat(LLVMModuleRef M, LLVMValueRef V,
                                   const char *Name, size_t NameLen) {
-  Triple TargetTriple(unwrap(M)->getTargetTriple());
+  Triple TargetTriple = Triple(unwrap(M)->getTargetTriple());
   GlobalObject *GV = unwrap<GlobalObject>(V);
   if (TargetTriple.supportsCOMDAT()) {
     StringRef NameRef(Name, NameLen);
@@ -1711,7 +1711,7 @@ extern "C" LLVMRustModuleBuffer*
 LLVMRustModuleBufferCreate(LLVMModuleRef M) {
   auto Ret = std::make_unique<LLVMRustModuleBuffer>();
   {
-    raw_string_ostream OS(Ret->data);
+    auto OS = raw_string_ostream(Ret->data);
     WriteBitcodeToFile(*unwrap(M), OS);
   }
   return Ret.release();
@@ -1741,8 +1741,8 @@ LLVMRustModuleCost(LLVMModuleRef M) {
 extern "C" void
 LLVMRustModuleInstructionStats(LLVMModuleRef M, RustStringRef Str)
 {
-  RawRustStringOstream OS(Str);
-  llvm::json::OStream JOS(OS);
+  auto OS = RawRustStringOstream(Str);
+  auto JOS = llvm::json::OStream(OS);
   auto Module = unwrap(M);
 
   JOS.object([&] {
@@ -1857,7 +1857,7 @@ extern "C" LLVMRustResult LLVMRustWriteImportLibrary(
     MinGW);
   if (Error) {
     std::string errorString;
-    llvm::raw_string_ostream stream(errorString);
+    auto stream = llvm::raw_string_ostream(errorString);
     stream << Error;
     stream.flush();
     LLVMRustSetLastError(errorString.c_str());
@@ -2041,7 +2041,7 @@ extern "C" void LLVMRustContextConfigureDiagnosticHandler(
 }
 
 extern "C" void LLVMRustGetMangledName(LLVMValueRef V, RustStringRef Str) {
-  RawRustStringOstream OS(Str);
+  auto OS = RawRustStringOstream(Str);
   GlobalValue *GV = unwrap<GlobalValue>(V);
   Mangler().getNameWithPrefix(OS, GV, true);
 }
@@ -2079,3 +2079,4 @@ extern "C" bool LLVMRustLLVMHasZlibCompressionForDebugSymbols() {
 extern "C" bool LLVMRustLLVMHasZstdCompressionForDebugSymbols() {
   return llvm::compression::zstd::isAvailable();
 }
+