UseSWIG: Update option -interface usage

Option -interface must not be used if multiple SWIG files are part
of the same library.

Fixes: #21134

8 files changed, 62 insertions, 0 deletions

diff --git a/Tests/UseSWIG/CMakeLists.txt b/Tests/UseSWIG/CMakeLists.txt
index d10284674a..cd04a4a7cb 100644
--- a/Tests/UseSWIG/CMakeLists.txt
+++ b/Tests/UseSWIG/CMakeLists.txt
@@ -91,6 +91,15 @@ add_test(NAME UseSWIG.MultiplePython COMMAND
   --build-options ${build_options}
   --test-command ${CMAKE_CTEST_COMMAND} -V -C $<CONFIGURATION>
   )
+add_test(NAME UseSWIG.MultipleFiles COMMAND
+  ${CMAKE_CTEST_COMMAND} -C $<CONFIGURATION>
+  --build-and-test
+  "${CMake_SOURCE_DIR}/Tests/UseSWIG/MultipleFiles"
+  "${CMake_BINARY_DIR}/Tests/UseSWIG/MultipleFiles"
+  ${build_generator_args}
+  --build-project TestMultipleFiles
+  --build-options ${build_options}
+  )
 
 
 add_test(NAME UseSWIG.ModuleVersion2 COMMAND
diff --git a/Tests/UseSWIG/MultipleFiles/CMakeLists.txt b/Tests/UseSWIG/MultipleFiles/CMakeLists.txt
new file mode 100644
index 0000000000..bf3d9469e1
--- /dev/null
+++ b/Tests/UseSWIG/MultipleFiles/CMakeLists.txt
@@ -0,0 +1,30 @@
+cmake_minimum_required(VERSION 3.18)
+
+project(TestMultipleFiles CXX)
+
+find_package(SWIG REQUIRED)
+include(UseSWIG)
+
+unset(SWIG_LANG_TYPE)
+unset(SWIG_LANG_INCLUDE_DIRECTORIES)
+unset(SWIG_LANG_DEFINITIONS)
+unset(SWIG_LANG_OPTIONS)
+unset(SWIG_LANG_LIBRARIES)
+
+find_package(Python3 REQUIRED COMPONENTS Development)
+
+set_property(SOURCE "${CMAKE_CURRENT_SOURCE_DIR}/add.i" PROPERTY CPLUSPLUS ON)
+set_property(SOURCE "${CMAKE_CURRENT_SOURCE_DIR}/sub.i" PROPERTY CPLUSPLUS ON)
+set_property(SOURCE "${CMAKE_CURRENT_SOURCE_DIR}/add.i" PROPERTY SWIG_MODULE_NAME _add)
+set_property(SOURCE "${CMAKE_CURRENT_SOURCE_DIR}/sub.i" PROPERTY SWIG_MODULE_NAME _sub)
+
+
+swig_add_library(example
+                 LANGUAGE python
+                 TYPE MODULE
+                 SOURCES "${CMAKE_CURRENT_SOURCE_DIR}/add.i"
+                         "${CMAKE_CURRENT_SOURCE_DIR}/sub.i"
+                         "${CMAKE_CURRENT_SOURCE_DIR}/add.cxx"
+                         "${CMAKE_CURRENT_SOURCE_DIR}/sub.cxx")
+target_include_directories(example PUBLIC "${CMAKE_CURRENT_SOURCE_DIR}")
+target_link_libraries(example PRIVATE Python3::Module)
diff --git a/Tests/UseSWIG/MultipleFiles/add.cxx b/Tests/UseSWIG/MultipleFiles/add.cxx
new file mode 100644
index 0000000000..a4dcca391d
--- /dev/null
+++ b/Tests/UseSWIG/MultipleFiles/add.cxx
@@ -0,0 +1,6 @@
+#include "add.h"
+
+int add(int a, int b)
+{
+  return a + b;
+}
diff --git a/Tests/UseSWIG/MultipleFiles/add.h b/Tests/UseSWIG/MultipleFiles/add.h
new file mode 100644
index 0000000000..6295ab95cd
--- /dev/null
+++ b/Tests/UseSWIG/MultipleFiles/add.h
@@ -0,0 +1 @@
+int add(int a, int b);
diff --git a/Tests/UseSWIG/MultipleFiles/add.i b/Tests/UseSWIG/MultipleFiles/add.i
new file mode 100644
index 0000000000..204639701a
--- /dev/null
+++ b/Tests/UseSWIG/MultipleFiles/add.i
@@ -0,0 +1,4 @@
+%{
+#include "add.h"
+%}
+%include "add.h"
diff --git a/Tests/UseSWIG/MultipleFiles/sub.cxx b/Tests/UseSWIG/MultipleFiles/sub.cxx
new file mode 100644
index 0000000000..d6874ef137
--- /dev/null
+++ b/Tests/UseSWIG/MultipleFiles/sub.cxx
@@ -0,0 +1,6 @@
+#include "sub.h"
+
+int sub(int a, int b)
+{
+  return a - b;
+}
diff --git a/Tests/UseSWIG/MultipleFiles/sub.h b/Tests/UseSWIG/MultipleFiles/sub.h
new file mode 100644
index 0000000000..de77111745
--- /dev/null
+++ b/Tests/UseSWIG/MultipleFiles/sub.h
@@ -0,0 +1 @@
+int sub(int a, int b);
diff --git a/Tests/UseSWIG/MultipleFiles/sub.i b/Tests/UseSWIG/MultipleFiles/sub.i
new file mode 100644
index 0000000000..fc70f10676
--- /dev/null
+++ b/Tests/UseSWIG/MultipleFiles/sub.i
@@ -0,0 +1,5 @@
+%{
+#include "sub.h"
+%}
+
+%include "sub.h"