ilya-biryukov created this revision.
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Clang 17 will land with unaddressed coroutine bugs, see
- https://github.com/llvm/llvm-project/issues/58459
- https://github.com/llvm/llvm-project/issues/56301
- https://github.com/llvm/llvm-project/issues/57638
- https://github.com/llvm/llvm-project/issues/63818
It would be useful to have a way to use other C++20, but guarantee
coroutines are not used. This patch achieves it with a warning that
fires on `co_await`, `co_return` and `co_yield`.
The new warning is `-Wpre-c++20-compat-coroutines`, which is also
enabled with `-Wpre-c++20-compat-pedantic`.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D156247
Files:
clang/include/clang/Basic/DiagnosticGroups.td
clang/include/clang/Basic/DiagnosticSemaKinds.td
clang/lib/Sema/SemaCoroutine.cpp
clang/test/SemaCXX/cxx20-coroutines-warning.cpp
Index: clang/test/SemaCXX/cxx20-coroutines-warning.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/cxx20-coroutines-warning.cpp
@@ -0,0 +1,105 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++20 -I%S/Inputs -Wpre-c++20-compat-pedantic %s
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++20 -I%S/Inputs -Wpre-c++20-compat-coroutines %s
+
+#include "std-coroutine.h"
+
+typedef __PTRDIFF_TYPE__ ptrdiff_t;
+
+using namespace std;
+
+template<class T>
+struct Task {
+ struct promise_type {
+ Task<T> get_return_object() noexcept;
+ suspend_always initial_suspend() noexcept;
+ suspend_always final_suspend() noexcept;
+ void return_value(T);
+ void unhandled_exception();
+ auto yield_value(Task<T>) noexcept { return final_suspend(); }
+ };
+ bool await_ready() noexcept { return false; }
+ void await_suspend(coroutine_handle<>) noexcept {}
+ T await_resume();
+};
+
+template<>
+struct Task<void> {
+ struct promise_type {
+ Task<void> get_return_object() noexcept;
+ suspend_always initial_suspend() noexcept;
+ suspend_always final_suspend() noexcept;
+ void return_void() noexcept;
+ void unhandled_exception() noexcept;
+ auto yield_value(Task<void>) noexcept { return final_suspend(); }
+ };
+ bool await_ready() noexcept { return false; }
+ void await_suspend(coroutine_handle<>) noexcept {}
+ void await_resume() noexcept {}
+};
+
+template <typename T>
+class generator
+{
+ struct Promise
+ {
+ auto get_return_object() { return generator{*this}; }
+ auto initial_suspend() { return suspend_never{}; }
+ auto final_suspend() noexcept { return suspend_always{}; }
+ void unhandled_exception() {}
+ void return_void() {}
+
+ auto yield_value(T value)
+ {
+ value_ = std::move(value);
+ return suspend_always{};
+ }
+
+ T value_;
+ };
+
+ using Handle = coroutine_handle<Promise>;
+
+ struct sentinel{};
+ struct iterator
+ {
+ using iterator_category = input_iterator_tag;
+ using value_type = T;
+ using difference_type = ptrdiff_t;
+ using reference = T &;
+ using const_reference = const T &;
+ using pointer = T *;
+
+ iterator &operator++()
+ {
+ h_.resume();
+ return *this;
+ }
+ const_reference &operator*() const { return h_.promise().value_; }
+ bool operator!=(sentinel) { return !h_.done(); }
+
+ Handle h_;
+ };
+
+ explicit generator(Promise &p) : h_(Handle::from_promise(p)) {}
+ Handle h_;
+public:
+ using promise_type = Promise;
+ auto begin() { return iterator{h_}; }
+ auto end() { return sentinel{}; }
+};
+
+Task<void> c(int i) { // expected-warning {{coroutines are incompatible with C++ standards before C++20}}
+ co_await (i = 0, std::suspend_always{});
+ co_await (i = 0, std::suspend_always{});
+}
+
+generator<int> range(int start, int end) // expected-warning {{coroutines are incompatible with C++ standards before C++20}}
+{
+ while (start < end)
+ co_yield start++;
+}
+
+Task<int> go(int const& val);
+Task<int> go1(int x) { // expected-warning {{coroutines are incompatible with C++ standards before C++20}}
+ co_return co_await go(++x);
+}
Index: clang/lib/Sema/SemaCoroutine.cpp
===================================================================
--- clang/lib/Sema/SemaCoroutine.cpp
+++ clang/lib/Sema/SemaCoroutine.cpp
@@ -701,6 +701,8 @@
auto *Fn = cast<FunctionDecl>(CurContext);
SourceLocation Loc = Fn->getLocation();
+ Diag(Loc, diag::warn_cxx17_compat_coroutines);
+
// Build the initial suspend point
auto buildSuspends = [&](StringRef Name) mutable -> StmtResult {
ExprResult Operand = buildPromiseCall(*this, ScopeInfo->CoroutinePromise,
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -230,6 +230,11 @@
"brace elision for designated initializer is a C99 extension">,
InGroup<C99Designator>, SFINAEFailure;
+// C++20 coroutines
+def warn_cxx17_compat_coroutines : Warning<
+ "coroutines are incompatible with C++ standards before C++20">,
+ InGroup<CXXPre20CompatCoroutines>, DefaultIgnore;
+
// Declarations.
def ext_plain_complex : ExtWarn<
"plain '_Complex' requires a type specifier; assuming '_Complex double'">;
Index: clang/include/clang/Basic/DiagnosticGroups.td
===================================================================
--- clang/include/clang/Basic/DiagnosticGroups.td
+++ clang/include/clang/Basic/DiagnosticGroups.td
@@ -305,8 +305,9 @@
[CXXPre17CompatPedantic]>;
def CXXPre20Compat : DiagGroup<"pre-c++20-compat">;
def : DiagGroup<"c++98-c++11-c++14-c++17-compat", [CXXPre20Compat]>;
+def CXXPre20CompatCoroutines : DiagGroup<"pre-c++20-compat-coroutines">;
def CXXPre20CompatPedantic : DiagGroup<"pre-c++20-compat-pedantic",
- [CXXPre20Compat]>;
+ [CXXPre20Compat, CXXPre20CompatCoroutines]>;
def : DiagGroup<"c++98-c++11-c++14-c++17-compat-pedantic",
[CXXPre20CompatPedantic]>;
def CXXPre23Compat : DiagGroup<"pre-c++23-compat">;
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