From 0dc88adc788674ab20af02fc128f33f7f429ccf1 Mon Sep 17 00:00:00 2001
From: Edward Nolan <eddiejnolan@gmail.com>
Date: Fri, 1 May 2026 22:33:42 -0400
Subject: [PATCH] Update flag forking approach to use split config.hpp and
 config_generated.hpp files

This commit reflects the new flag forking approach discussed in the
most recent Beman weekly sync:

- For any configuration option where a compiler flag could cause
  differences in behavior that lead to ODR issues when linking two
  artifacts generated with different flags, maintainers generate a
  compiler definition like BEMAN_EXEMPLAR_FOOBAR into a
  config_generated.hpp header from a config_generated.hpp.in template.
- Separately, a config.hpp file contains defaults for each
  definition. These defaults are only enabled if __has_include shows
  that the config_generated.hpp file is not present.
---
 CMakeLists.txt                                    |  6 +++---
 include/beman/iterator_interface/CMakeLists.txt   |  3 ++-
 include/beman/iterator_interface/config.hpp       | 15 +++++++++++++++
 .../{config.hpp.in => config_generated.hpp.in}    |  4 ++--
 4 files changed, 22 insertions(+), 6 deletions(-)
 create mode 100644 include/beman/iterator_interface/config.hpp
 rename include/beman/iterator_interface/{config.hpp.in => config_generated.hpp.in} (63%)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 31c4964..98f5b0a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -49,8 +49,8 @@ if(
 endif()
 
 configure_file(
-    "${PROJECT_SOURCE_DIR}/include/beman/iterator_interface/config.hpp.in"
-    "${PROJECT_BINARY_DIR}/include/beman/iterator_interface/config.hpp"
+    "${PROJECT_SOURCE_DIR}/include/beman/iterator_interface/config_generated.hpp.in"
+    "${PROJECT_BINARY_DIR}/include/beman/iterator_interface/config_generated.hpp"
     @ONLY
 )
 
@@ -67,7 +67,7 @@ target_sources(
         FILE_SET HEADERS
             BASE_DIRS
                 "${CMAKE_CURRENT_SOURCE_DIR}/include"
-                "${PROJECT_BINARY_DIR}/include"
+                "${CMAKE_CURRENT_BINARY_DIR}/include"
 )
 
 set_target_properties(
diff --git a/include/beman/iterator_interface/CMakeLists.txt b/include/beman/iterator_interface/CMakeLists.txt
index fd546b1..1affc32 100644
--- a/include/beman/iterator_interface/CMakeLists.txt
+++ b/include/beman/iterator_interface/CMakeLists.txt
@@ -5,10 +5,11 @@ target_sources(
     PUBLIC
         FILE_SET HEADERS
             FILES
+                config.hpp
                 iterator_interface.hpp
                 iterator_interface_access.hpp
                 detail/stl_interfaces/config.hpp
                 detail/stl_interfaces/fwd.hpp
                 detail/stl_interfaces/iterator_interface.hpp
-                "${PROJECT_BINARY_DIR}/include/beman/iterator_interface/config.hpp"
+                "${PROJECT_BINARY_DIR}/include/beman/iterator_interface/config_generated.hpp"
 )
diff --git a/include/beman/iterator_interface/config.hpp b/include/beman/iterator_interface/config.hpp
new file mode 100644
index 0000000..f823ff9
--- /dev/null
+++ b/include/beman/iterator_interface/config.hpp
@@ -0,0 +1,15 @@
+#ifndef BEMAN_ITERATOR_INTERFACE_CONFIG_HPP
+#define BEMAN_ITERATOR_INTERFACE_CONFIG_HPP
+
+#if !defined(__has_include) || __has_include(<beman/iterator_interface/config_generated.hpp>)
+    #include <beman/iterator_interface/config_generated.hpp>
+#else
+    #include <version>
+    #if defined(__cpp_explicit_this_parameter) && __cpp_explicit_this_parameter >= 202110L
+        #define BEMAN_ITERATOR_INTERFACE_USE_DEDUCING_THIS() 1
+    #else
+        #define BEMAN_ITERATOR_INTERFACE_USE_DEDUCING_THIS() 0
+    #endif
+#endif
+
+#endif
diff --git a/include/beman/iterator_interface/config.hpp.in b/include/beman/iterator_interface/config_generated.hpp.in
similarity index 63%
rename from include/beman/iterator_interface/config.hpp.in
rename to include/beman/iterator_interface/config_generated.hpp.in
index 30455a2..3aebf28 100644
--- a/include/beman/iterator_interface/config.hpp.in
+++ b/include/beman/iterator_interface/config_generated.hpp.in
@@ -1,8 +1,8 @@
 // include/beman/iterator_interface/config.hpp.in -*-C++-*-
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#ifndef BEMAN_ITERATOR_INTERFACE_CONFIG_HPP
-#define BEMAN_ITERATOR_INTERFACE_CONFIG_HPP
+#ifndef BEMAN_ITERATOR_INTERFACE_CONFIG_GENERATED_HPP
+#define BEMAN_ITERATOR_INTERFACE_CONFIG_GENERATED_HPP
 
 #cmakedefine01 BEMAN_ITERATOR_INTERFACE_USE_DEDUCING_THIS()