From 5210a3ae01dbbbb308de866516b2788680c371f0 Mon Sep 17 00:00:00 2001
From: Dan Smith <dan.smith@maxar.com>
Date: Wed, 28 Dec 2022 08:51:06 -0500
Subject: [PATCH] use a macro to determine whether except::Throwable derives
 from std::exception

---
 modules/c++/except/include/except/Exception.h | 10 ++++----
 modules/c++/except/include/except/Throwable.h | 24 +++++++++++++++++++
 modules/c++/sys/tests/MemoryTest1.cpp         | 10 ++++----
 3 files changed, 33 insertions(+), 11 deletions(-)

diff --git a/modules/c++/except/include/except/Exception.h b/modules/c++/except/include/except/Exception.h
index f7d95c924..782494a0f 100644
--- a/modules/c++/except/include/except/Exception.h
+++ b/modules/c++/except/include/except/Exception.h
@@ -51,7 +51,7 @@
     #endif
 #endif
 
-#define DECLARE_EXTENDED_EXCEPTION_(_Name, Exception_, _Base, getType_specifiers) \
+#define DECLARE_EXTENDED_EXCEPTION_(_Name, Exception_, _Base) \
   struct _Name##Exception_ : public _Base \
   { \
       _Name##Exception_() = default; virtual ~_Name##Exception_() = default; \
@@ -62,12 +62,10 @@
       _Name##Exception_(const except::Throwable& t, const except::Context& c) : _Base(t, c){} \
       _Name##Exception_(const except::Throwable11& t, const except::Context& c) : _Base(t, c){} \
       CODA_OSS_except_Exception_suppress_26447_BEGIN_ \
-      std::string getType() getType_specifiers { return #_Name #Exception_; } \
+      std::string getType() const noexcept override { return #_Name #Exception_; } \
      CODA_OSS_except_Exception_suppress_26447_END_ };
-#define DECLARE_EXTENDED_EXCEPTION(_Name, _Base) \
-    DECLARE_EXTENDED_EXCEPTION_(_Name, Exception, _Base, const override)
-#define DECLARE_EXTENDED_EXCEPTION11(_Name, _Base) \
-    DECLARE_EXTENDED_EXCEPTION_(_Name, Exception11, _Base, const noexcept override)
+#define DECLARE_EXTENDED_EXCEPTION(_Name, _Base) DECLARE_EXTENDED_EXCEPTION_(_Name, Exception, _Base)
+#define DECLARE_EXTENDED_EXCEPTION11(_Name, _Base) DECLARE_EXTENDED_EXCEPTION_(_Name, Exception11, _Base)
 
 #define DECLARE_EXCEPTION(_Name) \
     DECLARE_EXTENDED_EXCEPTION(_Name, except::Exception) \
diff --git a/modules/c++/except/include/except/Throwable.h b/modules/c++/except/include/except/Throwable.h
index ac322a974..88b9a7158 100644
--- a/modules/c++/except/include/except/Throwable.h
+++ b/modules/c++/except/include/except/Throwable.h
@@ -36,6 +36,23 @@
 #include "config/compiler_extensions.h"
 #include "except/Trace.h"
 
+/* Determine whether except::Throwable derives from std::exception.
+ *
+ * It can be quite convenient to derive from std::exception as often one less
+ * "catch" will be needed and we'll have standard what().  But doing so could
+ * break existing code as "catch (const std::exception&)" will catch
+ * except::Throwable when it didn't before.
+ */
+#ifdef CODA_OSS_THROWABLE_IS_NOT_AN_EXCEPTION // -DCODA_OSS_THROWABLE_IS_NOT_AN_EXCEPTION
+#ifdef CODA_OSS_except_Throwable_ISA_std_exception
+#error "CODA_OSS_except_Throwable_ISA_std_exception already #define'd."
+#endif
+#define CODA_OSS_except_Throwable_ISA_std_exception 0
+#endif
+#ifndef CODA_OSS_except_Throwable_ISA_std_exception // or, -DCODA_OSS_except_Throwable_ISA_std_exception=0
+#define CODA_OSS_except_Throwable_ISA_std_exception 0
+#endif
+
 /*!
  * \file Throwable.h
  * \brief Contains the classes to do with error handling
@@ -55,6 +72,9 @@ namespace except
 
 class Throwable11;
 class CODA_OSS_API Throwable
+#if CODA_OSS_except_Throwable_ISA_std_exception    
+    : public std::exception
+#endif
 {
     void doGetBacktrace();
     template<typename TThrowable>
@@ -169,6 +189,10 @@ class CODA_OSS_API Throwable
     }
 
     const char* what() const noexcept
+    #if CODA_OSS_except_Throwable_ISA_std_exception    
+    // can't use "final" unless what() is virtual
+    final  // derived classes override toString()
+    #endif
     {
         // adding this to toString() output could (significantly) alter existing display
         mWhat = toString(true /*includeBacktrace*/); // call any derived toString()
diff --git a/modules/c++/sys/tests/MemoryTest1.cpp b/modules/c++/sys/tests/MemoryTest1.cpp
index 76d9500c3..534c0586b 100644
--- a/modules/c++/sys/tests/MemoryTest1.cpp
+++ b/modules/c++/sys/tests/MemoryTest1.cpp
@@ -35,17 +35,17 @@ int main(int, char**)
         std::cout << "Total system memory: " << totalPhysMem << " MB" << std::endl;
         std::cout << "Free system memory: " << freePhysMem << " MB" << std::endl;
     }
-    catch (const std::exception& ex)
-    {
-        std::cerr << "Caught std::exception: " << ex.what() << std::endl;
-        return 1;
-    }
     catch (const except::Exception& ex)
     {
         std::cerr << "Caught except::exception: " << ex.getMessage()
                   << std::endl;
         return 1;
     }
+    catch (const std::exception& ex)
+    {
+        std::cerr << "Caught std::exception: " << ex.what() << std::endl;
+        return 1;
+    }
     catch(...)
     {
         std::cerr << "Caught unknown exception\n";