From f4a3ae1ef5ec951f007c4bd530f30e44945c5f0d Mon Sep 17 00:00:00 2001
From: Nathaniel Shead <nathanieloshead@gmail.com>
Date: Fri, 4 Apr 2025 19:08:40 +1100
Subject: [PATCH] c++/modules: Propagate bits to DECL_MAYBE_DELETED dups
 [PR119462]

In the linked PR, we're importing over a DECL_MAYBE_DELETED decl with a
decl that has already been instantiated.  This patch ensures that the
needed bits are propagated across and that DECL_MAYBE_DELETED is cleared
from the existing decl, so that later synthesize_method doesn't crash
due to a definition unexpectedly already existing.

	PR c++/119462

gcc/cp/ChangeLog:

	* module.cc (trees_in::is_matching_decl): Propagate exception
	spec and constexpr to DECL_MAYBE_DELETED; clear if appropriate.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/noexcept-3_a.C: New test.
	* g++.dg/modules/noexcept-3_b.C: New test.
	* g++.dg/modules/noexcept-3_c.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
Reviewed-by: Jason Merrill <jason@redhat.com>
---
 gcc/cp/module.cc                            | 16 +++++++++++++++-
 gcc/testsuite/g++.dg/modules/noexcept-3_a.C | 14 ++++++++++++++
 gcc/testsuite/g++.dg/modules/noexcept-3_b.C | 12 ++++++++++++
 gcc/testsuite/g++.dg/modules/noexcept-3_c.C | 11 +++++++++++
 4 files changed, 52 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/modules/noexcept-3_a.C
 create mode 100644 gcc/testsuite/g++.dg/modules/noexcept-3_b.C
 create mode 100644 gcc/testsuite/g++.dg/modules/noexcept-3_c.C

diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index 89deabbfee3..ff8cd86c427 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -12122,7 +12122,7 @@ trees_in::is_matching_decl (tree existing, tree decl, bool is_typedef)
 	 instantiate it in the middle of loading.   */
       tree e_spec = TYPE_RAISES_EXCEPTIONS (e_type);
       tree d_spec = TYPE_RAISES_EXCEPTIONS (d_type);
-      if (DEFERRED_NOEXCEPT_SPEC_P (e_spec))
+      if (DECL_MAYBE_DELETED (e_inner) || DEFERRED_NOEXCEPT_SPEC_P (e_spec))
 	{
 	  if (!DEFERRED_NOEXCEPT_SPEC_P (d_spec)
 	      || (UNEVALUATED_NOEXCEPT_SPEC_P (e_spec)
@@ -12161,6 +12161,20 @@ trees_in::is_matching_decl (tree existing, tree decl, bool is_typedef)
       else if (type_uses_auto (d_ret)
 	       && !same_type_p (TREE_TYPE (d_type), TREE_TYPE (e_type)))
 	goto mismatch;
+
+      /* Similarly if EXISTING has undeduced constexpr, but DECL's
+	 is already deduced.  */
+      if (DECL_MAYBE_DELETED (e_inner) && !DECL_MAYBE_DELETED (d_inner)
+	  && DECL_DECLARED_CONSTEXPR_P (d_inner))
+	DECL_DECLARED_CONSTEXPR_P (e_inner) = true;
+      else if (DECL_DECLARED_CONSTEXPR_P (e_inner)
+	       != DECL_DECLARED_CONSTEXPR_P (d_inner))
+	goto mismatch;
+
+      /* Don't synthesize a defaulted function if we're importing one
+	 we've already determined.  */
+      if (!DECL_MAYBE_DELETED (d_inner))
+	DECL_MAYBE_DELETED (e_inner) = false;
     }
   else if (is_typedef)
     {
diff --git a/gcc/testsuite/g++.dg/modules/noexcept-3_a.C b/gcc/testsuite/g++.dg/modules/noexcept-3_a.C
new file mode 100644
index 00000000000..00494d33d7c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/noexcept-3_a.C
@@ -0,0 +1,14 @@
+// PR c++/119462
+// { dg-additional-options "-fmodules -std=c++20 -Wno-global-module" }
+// { dg-module-cmi M:part }
+
+module;
+struct exception_ptr {
+  // implicitly noexcept and constexpr
+  friend bool operator==(const exception_ptr&, const exception_ptr&) = default;
+};
+export module M:part;
+export template <typename = int> void enqueue() {
+  exception_ptr e;
+  e == e;
+}
diff --git a/gcc/testsuite/g++.dg/modules/noexcept-3_b.C b/gcc/testsuite/g++.dg/modules/noexcept-3_b.C
new file mode 100644
index 00000000000..f26f8f0f5d3
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/noexcept-3_b.C
@@ -0,0 +1,12 @@
+// PR c++/119462
+// { dg-additional-options "-fmodules -std=c++20 -Wno-global-module" }
+// { dg-module-cmi M }
+
+module;
+struct exception_ptr {
+  // implicitly noexcept and constexpr, but this isn't known yet
+  friend bool operator==(const exception_ptr&, const exception_ptr&) = default;
+};
+export module M;
+export import :part;
+export using ::exception_ptr;
diff --git a/gcc/testsuite/g++.dg/modules/noexcept-3_c.C b/gcc/testsuite/g++.dg/modules/noexcept-3_c.C
new file mode 100644
index 00000000000..a1e98a5461a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/noexcept-3_c.C
@@ -0,0 +1,11 @@
+// PR c++/119462
+// { dg-additional-options "-fmodules -std=c++20" }
+
+import M;
+int main() {
+  enqueue();
+
+  constexpr exception_ptr e;
+  static_assert(e == e);
+  static_assert(noexcept(e == e));
+}