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RFC: [llvm] specialize cl::opt_storage for std::string#149172
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github-actionsbot commentedJul 16, 2025 • edited
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You can test this locally with the following command:git-clang-format --diff HEAD~1 HEAD --extensions h -- llvm/include/llvm/Support/CommandLine.h llvm/include/llvm/TargetParser/Triple.h View the diff from clang-format here.diff --git a/llvm/include/llvm/Support/CommandLine.h b/llvm/include/llvm/Support/CommandLine.hindex 823e31a80..7c041fbff 100644--- a/llvm/include/llvm/Support/CommandLine.h+++ b/llvm/include/llvm/Support/CommandLine.h@@ -1417,23 +1417,23 @@ public: const OptionValue<std::string> &getDefault() const { return Default; } // Support implicit conversions to std::string and LLVM string-like types.- //operator std::string() const { return Value; }- operator std::string&() { return Value; }- operator const std::string&() const { return Value; }+ // operator std::string() const { return Value; }+ operator std::string &() { return Value; }+ operator const std::string &() const { return Value; } operator llvm::StringRef() const { return llvm::StringRef(Value); } operator llvm::Twine() const { return llvm::Twine(llvm::StringRef(Value)); } // If the datatype is a pointer, support -> on it. std::string operator->() const { return Value; }- Self& operator=(const Self& rhs) = default;+ Self &operator=(const Self &rhs) = default;- Self& operator=(const std::string& rhs) {+ Self &operator=(const std::string &rhs) { Value = rhs; return *this; }- Self& operator=(const char* rhs) {+ Self &operator=(const char *rhs) { Value = rhs; return *this; }@@ -1491,43 +1491,39 @@ public: char operator[](size_t pos) const { return Value.at(pos); }- Self& assign(const std::string& rhs) {+ Self &assign(const std::string &rhs) { Value.assign(rhs); return *this; }- Self& assign(const char* rhs) {+ Self &assign(const char *rhs) { Value.assign(rhs); return *this; }- Self& operator+=(const std::string& rhs) {+ Self &operator+=(const std::string &rhs) { Value += rhs; return *this; }- Self& operator+=(const char* rhs) {+ Self &operator+=(const char *rhs) { Value += rhs; return *this; }- friend std::string- operator+(Self const& lhs, std::string const& rhs) {+ friend std::string operator+(Self const &lhs, std::string const &rhs) { return lhs.Value + rhs; }- friend std::string- operator+(std::string const& lhs, Self const& rhs) {+ friend std::string operator+(std::string const &lhs, Self const &rhs) { return lhs + rhs.Value; }- friend std::string- operator+(Self const& lhs, char const* rhs) {+ friend std::string operator+(Self const &lhs, char const *rhs) { return lhs.Value + rhs; }- friend std::string- operator+(char const* lhs, Self const& rhs) {+ friend std::string operator+(char const *lhs, Self const &rhs) { return lhs + rhs.Value; } |
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Purpose
Specialize
llvm::cl::opt_storagefor data typestd::stringso that it no longer inherits fromstd::string. With this patch in place, explicitly instantiatedcl::opt<std::string>can be safely exported from an LLVM Windows DLL.Overview
cl::opt_storagefor data typestd::string. It does NOT inherit fromstd::stringas it did previously when data typestd::stringmatched the partially specified templatecl::opt_storage<DataType, false, true>std::string,llvm::StringRef, andllvm::Twineso that instances can be used in many places wherestd::stringis used.std::stringmethods so that instances of the class are mostly interoperable withstd::string.Tripleso it properly constructs fromcl::opt_storage<std::string>. This change avoids having to modify clients that constructTriples fromcl::opt<std::string>instances.Background
This patch is in support of annotating LLVM's public symbols for Windows DLL export., tracked in#109483. Additional context is provided inthis discourse.
This change is needed because, without it, we cannot export
opt<std::string>from an LLVM Windows DLL. This is because MSVC exports all ancestor classes when exporting an instantiated template class. Since one ofopt's ancestor classes is its type argument (viaopt_storage), it is an ancestor ofstd::string. Therefore, if we exportopt<std::string>from the LLVM DLL, MSVC forcesstd::basic_stringto also be exported. This leads to duplicate symbol errors and generally seems like a bad idea. Compiling withclang-cldoes not exhibit this behavior.Validation
clandclang-cl.clangandgcc.