[PATCH] D144352: Do not emit exception diagnostics from coroutines and coroutine lambdas

[Deniz Evrenci via Phabricator via cfe-commits]

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Fixes #48797

All exceptions thrown in coroutine bodies are caught and
`unhandled_exception` member of the coroutine promise type is called.
In accordance with the existing rules of diagnostics related to
exceptions thrown in functions marked `noexcept`, even if the promise
type's constructor, `get_return_object`, or `unhandled_exception`
throws, diagnostics should not be emitted.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D144352

Files:
  clang/lib/Sema/AnalysisBasedWarnings.cpp
  clang/test/SemaCXX/warn-throw-out-noexcept-coro.cpp


Index: clang/test/SemaCXX/warn-throw-out-noexcept-coro.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/warn-throw-out-noexcept-coro.cpp
@@ -0,0 +1,63 @@
+// RUN: %clang_cc1 -std=c++20 %s -fcxx-exceptions -fsyntax-only -Wexceptions -verify -fdeclspec
+
+#include "Inputs/std-coroutine.h"
+
+// expected-no-diagnostics
+
+template <typename T>
+struct promise;
+ 
+template <typename T>
+struct task {
+    using promise_type = promise<T>;
+
+    explicit task(promise_type& p) noexcept { p.return_val = this; }
+
+    task(const task&) = delete;
+
+    T value;
+};
+ 
+template <typename T>
+struct promise {
+    task<T> get_return_object() noexcept { return task{*this}; }
+
+    std::suspend_never initial_suspend() const noexcept { return {}; }
+
+    std::suspend_never final_suspend() const noexcept { return {}; }
+
+    template <typename U>
+    void return_value(U&& val) { return_val->value = static_cast<U&&>(val); }
+
+    void unhandled_exception() {}
+
+    task<T>* return_val;
+};
+
+task<int> a_ShouldNotDiag(const int a, const int b) {
+  if (b == 0)
+    throw b;
+
+  co_return a / b;
+}
+
+task<int> b_ShouldNotDiag(const int a, const int b) noexcept {
+  if (b == 0)
+    throw b;
+
+  co_return a / b;
+}
+
+const auto c_ShouldNotDiag = [](const int a, const int b) -> task<int> {
+  if (b == 0)
+    throw b;
+
+  co_return a / b;
+};
+
+const auto d_ShouldNotDiag = [](const int a, const int b) noexcept -> task<int> {
+  if (b == 0)
+    throw b;
+
+  co_return a / b;
+};
Index: clang/lib/Sema/AnalysisBasedWarnings.cpp
===================================================================
--- clang/lib/Sema/AnalysisBasedWarnings.cpp
+++ clang/lib/Sema/AnalysisBasedWarnings.cpp
@@ -2509,7 +2509,7 @@
   // Check for throw out of non-throwing function.
   if (!Diags.isIgnored(diag::warn_throw_in_noexcept_func, D->getBeginLoc()))
     if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D))
-      if (S.getLangOpts().CPlusPlus && isNoexcept(FD))
+      if (S.getLangOpts().CPlusPlus && !fscope->isCoroutine() && isNoexcept(FD))
         checkThrowInNonThrowingFunc(S, FD, AC);
 
   // Emit unsafe buffer usage warnings and fixits.


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