c++modules: discover synth targets for all configs

Fixes: #26312

Source/cmCommonTargetGenerator.cxx

@@ -193,7 +193,7 @@ cmCommonTargetGenerator::GetLinkedTargetDirectories(
       auto const& synthDeps = this->GeneratorTarget->GetSyntheticDeps(config);
       auto it = synthDeps.find(linkee);
       if (it != synthDeps.end() && !it->second.empty()) {
-        return it->second.front();
+        return *it->second.begin();
       }
 
       // Check linked targets to find synthetic targets for transitive deps
@@ -227,7 +227,7 @@ cmCommonTargetGenerator::GetLinkedTargetDirectories(
         auto itLinkeeSynth = transitiveSynthDeps.find(linkee);
         if (itLinkeeSynth != transitiveSynthDeps.end() &&
             !itLinkeeSynth->second.empty()) {
-          return itLinkeeSynth->second.front();
+          return *itLinkeeSynth->second.begin();
         }
         for (auto const& entry : transitiveSynthDeps) {
           for (auto const* synth : entry.second) {

Source/cmGeneratorTarget.cxx

@@ -5590,8 +5590,11 @@ cmGeneratorTarget const* cmGeneratorTarget::GetCxxSyntheticTarget(
 
   lg->AddGeneratorTarget(std::move(gtp));
   this->SynthCxxTargets[usageHash] = syntheticTarget;
-  if (!syntheticTarget->DiscoverSyntheticTargets(config, &bmiConsumer)) {
-    return nullptr;
+  for (auto const& innerConfig : allConfigs) {
+    if (!syntheticTarget->DiscoverSyntheticTargets(innerConfig,
+                                                   &bmiConsumer)) {
+      return nullptr;
+    }
   }
 
   return syntheticTarget;
@@ -5629,7 +5632,7 @@ bool cmGeneratorTarget::DiscoverSyntheticTargets(
       return false;
     }
     if (dep->IsSynthetic()) {
-      SyntheticDeps[gt].push_back(dep);
+      SyntheticDeps[gt].insert(dep);
     }
   }
 

Source/cmGeneratorTarget.h

@@ -1155,7 +1155,7 @@ public:
     std::string const& config, cmGeneratorTarget const* bmiConsumer = nullptr);
 
   using SyntheticDepsMap =
-    std::map<cmGeneratorTarget const*, std::vector<cmGeneratorTarget const*>>;
+    std::map<cmGeneratorTarget const*, std::set<cmGeneratorTarget const*>>;
   SyntheticDepsMap const& GetSyntheticDeps(std::string const& config) const;
 
   class CustomTransitiveProperty : public TransitiveProperty
@@ -1613,7 +1613,7 @@ public:
 private:
   struct InfoByConfig
   {
-    std::map<cmGeneratorTarget const*, std::vector<cmGeneratorTarget const*>>
+    std::map<cmGeneratorTarget const*, std::set<cmGeneratorTarget const*>>
       SyntheticDeps;
     std::map<cmSourceFile const*, ClassifiedFlags> SourceFlags;
   };

Tests/RunCMake/CXXModulesCompile/RunCMakeTest.cmake

@@ -219,11 +219,15 @@ if ("named" IN_LIST CMake_TEST_MODULE_COMPILATION)
   run_cxx_module_test(scan_props)
   run_cxx_module_test(target-objects)
 
-  # mixed-bmi-compatibility requires a generator that implements per-importer
-  # BMI generation
+  # Requires a generator that implements per-importer BMI generation
   if ("cxx_std_23" IN_LIST CMAKE_CXX_COMPILE_FEATURES AND
       RunCMake_GENERATOR MATCHES "Ninja")
     run_cxx_module_test(mixed-bmi-compatibility)
+    if (RunCMake_GENERATOR_IS_MULTI_CONFIG AND
+        "collation" IN_LIST CMake_TEST_MODULE_COMPILATION AND
+        "bmionly" IN_LIST CMake_TEST_MODULE_COMPILATION)
+      run_cxx_module_test(multi-config-synth)
+    endif()
   endif()
 
   if ("cxx_std_23" IN_LIST CMAKE_CXX_COMPILE_FEATURES AND

Tests/RunCMake/CXXModulesCompile/multi-config-synth/CMakeLists.txt

@@ -0,0 +1,54 @@
+cmake_minimum_required(VERSION 3.24...3.28)
+project(cxx_modules_multi_config_synth CXX)
+
+include("${CMAKE_SOURCE_DIR}/../cxx-modules-rules.cmake")
+
+add_library(importable)
+target_sources(importable
+  PUBLIC FILE_SET CXX_MODULES FILES importable.cxx)
+target_compile_features(importable PUBLIC cxx_std_20)
+
+export(TARGETS importable
+  NAMESPACE CXXModules::
+  FILE "${CMAKE_CURRENT_BINARY_DIR}/importable-targets.cmake"
+  CXX_MODULES_DIRECTORY "importable-cxx-modules"
+  )
+
+file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/importable-config.cmake"
+  "include(\"\${CMAKE_CURRENT_LIST_DIR}/importable-targets.cmake\")\n"
+  )
+
+set(generator
+  -G "${CMAKE_GENERATOR}")
+if (CMAKE_GENERATOR_TOOLSET)
+  list(APPEND generator -T "${CMAKE_GENERATOR_TOOLSET}")
+endif ()
+if (CMAKE_GENERATOR_PLATFORM)
+  list(APPEND generator -A "${CMAKE_GENERATOR_PLATFORM}")
+endif ()
+
+add_test(NAME multi_config_synth_consumer
+  COMMAND
+    "${CMAKE_COMMAND}"
+    "-DCMAKE_PREFIX_PATH=${CMAKE_CURRENT_BINARY_DIR}"
+    ${generator}
+    -S "${CMAKE_CURRENT_SOURCE_DIR}/consumer"
+    -B "${CMAKE_CURRENT_BINARY_DIR}/consumer"
+  )
+add_test(NAME multi_config_synth_build_debug
+  COMMAND
+    "${CMAKE_COMMAND}" --build "${CMAKE_CURRENT_BINARY_DIR}/consumer" --config Debug
+  )
+add_test(NAME multi_config_synth_build_release
+  COMMAND
+    "${CMAKE_COMMAND}" --build "${CMAKE_CURRENT_BINARY_DIR}/consumer" --config Release
+  )
+set_tests_properties(
+  multi_config_synth_build_debug
+  multi_config_synth_build_release
+  PROPERTIES DEPENDS multi_config_synth_consumer)
+add_test(NAME multi_config_synth_run
+  COMMAND "${CMAKE_CTEST_COMMAND}" -C Debug --test-dir "${CMAKE_CURRENT_BINARY_DIR}/consumer"
+  )
+set_tests_properties(multi_config_synth_run
+  PROPERTIES DEPENDS multi_config_synth_build_debug)

Tests/RunCMake/CXXModulesCompile/multi-config-synth/consumer/CMakeLists.txt

@@ -0,0 +1,10 @@
+cmake_minimum_required(VERSION 3.24...3.28)
+project(cxx_modules_multi_config_consumer CXX)
+
+find_package(importable REQUIRED)
+
+add_executable(consumer main.cxx)
+target_link_libraries(consumer PRIVATE CXXModules::importable)
+target_compile_features(consumer PRIVATE cxx_std_20)
+
+add_test(NAME consumer COMMAND consumer)

Tests/RunCMake/CXXModulesCompile/multi-config-synth/consumer/main.cxx

@@ -0,0 +1,5 @@
+import importable;
+int main()
+{
+  return from_import();
+}

Tests/RunCMake/CXXModulesCompile/multi-config-synth/importable.cxx

@@ -0,0 +1,5 @@
+export module importable;
+export int from_import()
+{
+  return 0;
+}