From 031dc2268627919ff512fa5cbf81d39900790159 Mon Sep 17 00:00:00 2001
From: William S Fulton <wsf@fultondesigns.co.uk>
Date: Sun, 16 Jun 2024 19:11:11 +0100
Subject: [PATCH] Don't ignore overloaded friend functions that are also
 declared constexpr

Closes #2927
---
 CHANGES.current                               |  4 +++
 Examples/test-suite/common.mk                 |  1 +
 Examples/test-suite/cpp11_constexpr_friend.i  | 35 +++++++++++++++++++
 .../csharp/cpp11_constexpr_friend_runme.cs    | 20 +++++++++++
 Source/CParse/parser.y                        |  2 +-
 5 files changed, 61 insertions(+), 1 deletion(-)
 create mode 100644 Examples/test-suite/cpp11_constexpr_friend.i
 create mode 100644 Examples/test-suite/csharp/cpp11_constexpr_friend_runme.cs

diff --git a/CHANGES.current b/CHANGES.current
index f5f7fa155..2eda2d853 100644
--- a/CHANGES.current
+++ b/CHANGES.current
@@ -7,6 +7,10 @@ the issue number to the end of the URL: https://github.com/swig/swig/issues/
 Version 4.3.0 (in progress)
 ===========================
 
+2024-06-16: wsfulton
+            #2927 Don't ignore overloaded friend functions that are also declared
+            constexpr.
+
 2024-06-15: wsfulton
             [Python] Removed deprecated pytuplehlp.swg file and t_output_helper.
             Use SWIG_Python_AppendOutput instead of t_output_helper.
diff --git a/Examples/test-suite/common.mk b/Examples/test-suite/common.mk
index 79f154b25..c380e47de 100644
--- a/Examples/test-suite/common.mk
+++ b/Examples/test-suite/common.mk
@@ -615,6 +615,7 @@ CPP11_TEST_CASES += \
 	cpp11_auto_variable \
 	cpp11_brackets_expression \
 	cpp11_constexpr \
+	cpp11_constexpr_friend \
 	cpp11_copyctor_delete \
 	cpp11_decltype \
 	cpp11_default_delete \
diff --git a/Examples/test-suite/cpp11_constexpr_friend.i b/Examples/test-suite/cpp11_constexpr_friend.i
new file mode 100644
index 000000000..c1d3872e9
--- /dev/null
+++ b/Examples/test-suite/cpp11_constexpr_friend.i
@@ -0,0 +1,35 @@
+%module cpp11_constexpr_friend
+
+%rename("isEqual") operator==(FriendA const& lhs, FriendA const& rhs) noexcept;
+%rename("isEqual") operator==(FriendB const& lhs, FriendB const& rhs) noexcept;
+
+%inline %{
+  class FriendA final
+  {
+    public:
+      FriendA(int const v) noexcept : _v(v)
+      {
+      }
+
+      constexpr friend bool operator==(FriendA const& lhs, FriendA const& rhs) noexcept
+      {
+        return lhs._v == rhs._v;
+      }
+    private:
+      int _v{};
+  };
+  class FriendB final
+  {
+    public:
+      FriendB(int const v) noexcept : _v(v)
+      {
+      }
+
+      constexpr friend bool operator==(FriendB const& lhs, FriendB const& rhs) noexcept
+      {
+        return lhs._v == rhs._v;
+      }
+    private:
+      int _v{};
+  };
+%}
diff --git a/Examples/test-suite/csharp/cpp11_constexpr_friend_runme.cs b/Examples/test-suite/csharp/cpp11_constexpr_friend_runme.cs
new file mode 100644
index 000000000..adc6c6dba
--- /dev/null
+++ b/Examples/test-suite/csharp/cpp11_constexpr_friend_runme.cs
@@ -0,0 +1,20 @@
+using System;
+using cpp11_constexpr_friendNamespace;
+
+public class cpp11_constexpr_friend_runme {
+  public static void Main() {
+    FriendA fa10 = new FriendA(10);
+    FriendA fa20 = new FriendA(20);
+    if (!cpp11_constexpr_friend.isEqual(fa10, fa10))
+      throw new Exception("Friend fa10 fa10 fail");
+    if (cpp11_constexpr_friend.isEqual(fa10, fa20))
+      throw new Exception("Friend fa10 fa20 fail");
+
+    FriendB fb10 = new FriendB(10);
+    FriendB fb20 = new FriendB(20);
+    if (!cpp11_constexpr_friend.isEqual(fb10, fb10))
+      throw new Exception("Friend fb10 fb10 fail");
+    if (cpp11_constexpr_friend.isEqual(fb10, fb20))
+      throw new Exception("Friend fb10 fb20 fail");
+  }
+}
diff --git a/Source/CParse/parser.y b/Source/CParse/parser.y
index 1593df2ff..c1e3faa36 100644
--- a/Source/CParse/parser.y
+++ b/Source/CParse/parser.y
@@ -420,7 +420,7 @@ static void add_symbols(Node *n) {
     String *symname = 0;
     String *old_prefix = 0;
     Symtab *old_scope = 0;
-    int isfriend = inclass && Checkattr(n, "storage", "friend");
+    int isfriend = inclass && Strstr(Getattr(n, "storage"), "friend") != NULL;
     int iscdecl = Cmp(nodeType(n),"cdecl") == 0;
     int only_csymbol = 0;