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c++modules: single import std target

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This commit is contained in:
Vito Gamberini
2026-06-18 15:20:54 -04:00
parent d9c35d02bb
commit 6d3e9d8220
27 changed files with 50 additions and 111 deletions
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Help/dev/experimental.rst
+1 -1
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@@ -66,7 +66,7 @@ In order to activate support for ``import std`` in C++23 and newer targets,
set
* variable ``CMAKE_EXPERIMENTAL_CXX_IMPORT_STD`` to
* value ``451f2fe2-a8a2-47c3-bc32-94786d8fc91b``.
* value ``f35a9ac6-8463-4d38-8eec-5d6008153e7d``.
This UUID may change in future versions of CMake. Be sure to use the value
documented here by the source tree of the version of CMake with which you are
Modules/CMakeDetermineCompilerSupport.cmake
+1 -1
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@@ -158,7 +158,7 @@ function(cmake_determine_compiler_support lang)
foreach(_cmake_import_std_version IN ITEMS 23 26)
if(CMAKE_CXX${_cmake_import_std_version}_COMPILE_FEATURES)
# Modules JSON covers all versions, otherwise rely on toolchain targets
if(CMAKE_CXX_STDLIB_MODULES_JSON OR (TARGET "__CMAKE:CXX${_cmake_import_std_version}"))
if(CMAKE_CXX_STDLIB_MODULES_JSON)
list(APPEND CMAKE_CXX_COMPILER_IMPORT_STD ${_cmake_import_std_version})
endif()
endif()
Source/cmExperimental.cxx
+1 -1
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@@ -31,7 +31,7 @@ cmExperimental::FeatureData const LookupTable[] = {
cmExperimental::TryCompileCondition::Always },
// CxxImportStd
{ "CxxImportStd",
"451f2fe2-a8a2-47c3-bc32-94786d8fc91b",
"f35a9ac6-8463-4d38-8eec-5d6008153e7d",
"CMAKE_EXPERIMENTAL_CXX_IMPORT_STD",
"CMake's support for `import std;` in C++23 and newer is experimental. It "
"is meant only for experimentation and feedback to CMake developers.",
Source/cmGeneratorTarget.cxx
+20 -43
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@@ -5330,8 +5330,6 @@ bool cmGeneratorTarget::IsNullImpliedByLinkLibraries(
namespace {
bool CreateCxxStdlibTarget(cmMakefile* makefile, cmLocalGenerator* lg,
std::string const& targetName,
std::string const& cxxTargetName,
std::string const& stdLevel,
std::vector<std::string> const& configs)
{
#ifndef CMAKE_BOOTSTRAP
@@ -5377,20 +5375,17 @@ bool CreateCxxStdlibTarget(cmMakefile* makefile, cmLocalGenerator* lg,
metadata = std::move(*parseResult.Meta);
}
auto const localTargetName = cmStrCat("__cmake_cxx_std_", stdLevel);
cmStandardLevelResolver standardResolver(makefile);
auto* stdlibTgt = makefile->AddLibrary(
localTargetName, cmStateEnums::STATIC_LIBRARY, {}, true);
"@cmake_cxx_std", cmStateEnums::STATIC_LIBRARY, {}, true);
cmCxxModuleMetadata::PopulateTarget(*stdlibTgt, *metadata, configs);
standardResolver.AddRequiredTargetFeature(stdlibTgt,
cmStrCat("cxx_std_", stdLevel));
cmStandardLevelResolver standardResolver(makefile);
standardResolver.AddRequiredTargetFeature(stdlibTgt, "cxx_std_20");
auto gt = cm::make_unique<cmGeneratorTarget>(stdlibTgt, lg);
for (auto const& config : configs) {
gt->ComputeCompileFeatures(config);
}
lg->AddGeneratorTarget(std::move(gt));
makefile->AddAlias(cxxTargetName, localTargetName);
#endif // CMAKE_BOOTSTRAP
@@ -5398,11 +5393,8 @@ bool CreateCxxStdlibTarget(cmMakefile* makefile, cmLocalGenerator* lg,
}
} // namespace
bool cmGeneratorTarget::ApplyCXXStdTargets()
bool cmGeneratorTarget::ApplyCXXStdTarget()
{
cmStandardLevelResolver standardResolver(this->Makefile);
cmStandardLevel const cxxStd23 =
*standardResolver.LanguageStandardLevel("CXX", "23");
std::vector<std::string> const& configs =
this->Makefile->GetGeneratorConfigs(cmMakefile::IncludeEmptyConfig);
auto std_prop = this->GetProperty("CXX_MODULE_STD");
@@ -5466,35 +5458,18 @@ bool cmGeneratorTarget::ApplyCXXStdTargets()
return true;
}
for (auto const& config : configs) {
if (this->HaveCxxModuleSupport(config) != Cxx20SupportLevel::Supported) {
continue;
}
cm::optional<cmStandardLevel> explicitLevel =
this->GetExplicitStandardLevel("CXX", config);
if (!explicitLevel || *explicitLevel < cxxStd23) {
continue;
}
auto const stdLevel =
standardResolver.GetLevelString("CXX", *explicitLevel);
auto const cxxTargetName = cmStrCat("__CMAKE::CXX", stdLevel);
// Create the __CMAKE::CXX## target if it doesn't already exist
if (!this->Makefile->FindTargetToUse(cxxTargetName) &&
!CreateCxxStdlibTarget(this->Makefile, this->LocalGenerator,
this->GetName(), cxxTargetName, stdLevel,
configs)) {
return false;
}
this->Target->AppendProperty(
"LINK_LIBRARIES",
cmStrCat("$<BUILD_LOCAL_INTERFACE:$<$<CONFIG:", config,
">:", cxxTargetName, ">>"));
// Create the single, unreferenceable import std target if it doesn't
// already exist. BMI compatibility handles per-consumer standard level
// differences by creating synthetic targets as needed.
if (!this->Makefile->FindTargetToUse("@cmake_cxx_std") &&
!CreateCxxStdlibTarget(this->Makefile, this->LocalGenerator,
this->GetName(), configs)) {
return false;
}
this->Target->AppendProperty("LINK_LIBRARIES",
"$<BUILD_LOCAL_INTERFACE:@cmake_cxx_std>");
// Check the experimental feature here. A toolchain may have
// skipped the check in the toolchain preparation logic.
if (!cmExperimental::HasSupportEnabled(
@@ -5577,8 +5552,10 @@ cmGeneratorTarget const* cmGeneratorTarget::GetCxxSyntheticTarget(
}
}
// Copy properties which effect consumer compatibility
tgt->CopyUsageEffects(bmiConsumer.Target);
// Copy properties which effect consumer compatibility.
// CopyUsageEffects now uses the consumer's full (own + transitive)
// compile features and options.
tgt->CopyUsageEffects(&bmiConsumer, config);
// Copy properties which don't effect consumer compatibility
tgt->CopyCxxModulesEntries(model);
@@ -5599,9 +5576,9 @@ cmGeneratorTarget const* cmGeneratorTarget::GetCxxSyntheticTarget(
for (auto const& innerConfig : allConfigs) {
gtp->ComputeCompileFeatures(innerConfig);
}
// See `cmGlobalGenerator::ApplyCXXStdTargets` in
// See `cmGlobalGenerator::ApplyCXXStdTarget` in
// `cmGlobalGenerator::Compute` for non-synthetic target resolutions.
if (!gtp->ApplyCXXStdTargets()) {
if (!gtp->ApplyCXXStdTarget()) {
return nullptr;
}
Source/cmGeneratorTarget.h
+1 -1
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@@ -1146,7 +1146,7 @@ public:
std::string GetImportedXcFrameworkPath(std::string const& config) const;
bool ApplyCXXStdTargets();
bool ApplyCXXStdTarget();
cmCxxModuleUsageEffects const& GetCxxModuleUsageEffects() const;
cmGeneratorTarget const* GetTargetForCxxModules(
std::string const& config, cmGeneratorTarget const& bmiConsumer) const;
Source/cmGlobalGenerator.cxx
+7 -8
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@@ -1676,13 +1676,12 @@ bool cmGlobalGenerator::Compute()
}
}
// We now have all targets set up and std levels constructed. Add
// `__CMAKE::CXX*` targets as link dependencies to all targets which need
// them.
// We now have all targets set up. Add the `@cmake_cxx_std` target as a link
// dependency to all targets which need it.
//
// Synthetic targets performed this inside of
// `cmLocalGenerator::DiscoverSyntheticTargets`
if (!this->ApplyCXXStdTargets()) {
if (!this->ApplyCXXStdTarget()) {
return false;
}
@@ -1997,12 +1996,12 @@ void cmGlobalGenerator::ComputeTargetOrder(cmGeneratorTarget const* gt,
entry->second = index++;
}
bool cmGlobalGenerator::ApplyCXXStdTargets()
bool cmGlobalGenerator::ApplyCXXStdTarget()
{
for (auto const& gen : this->LocalGenerators) {
// tgt->ApplyCXXStd can create targets itself, so we need iterators which
// won't be invalidated by that target creation
// tgt->ApplyCXXStdTarget can create a target itself, so we need iterators
// which won't be invalidated by that target creation
auto const& genTgts = gen->GetGeneratorTargets();
std::vector<cmGeneratorTarget*> existingTgts;
existingTgts.reserve(genTgts.size());
@@ -2011,7 +2010,7 @@ bool cmGlobalGenerator::ApplyCXXStdTargets()
}
for (auto const& tgt : existingTgts) {
if (!tgt->ApplyCXXStdTargets()) {
if (!tgt->ApplyCXXStdTarget()) {
return false;
}
}
Source/cmGlobalGenerator.h
+1 -1
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@@ -800,7 +800,7 @@ protected:
virtual bool CheckALLOW_DUPLICATE_CUSTOM_TARGETS() const;
bool ApplyCXXStdTargets();
bool ApplyCXXStdTarget();
bool DiscoverSyntheticTargets();
bool AddHeaderSetVerification();
Tests/RunCMake/CXXModules/CMP0155-NEW.cmake
-3
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@@ -1,6 +1,3 @@
# Block making C++ `import std` targets.
add_library(__CMAKE::CXX23 IMPORTED INTERFACE)
enable_language(CXX)
unset(CMAKE_CXX_SCANDEP_SOURCE)
Tests/RunCMake/CXXModules/CMP0155-OLD.cmake
-3
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@@ -1,6 +1,3 @@
# Block making C++ `import std` targets.
add_library(__CMAKE::CXX23 IMPORTED INTERFACE)
enable_language(CXX)
unset(CMAKE_CXX_SCANDEP_SOURCE)
Tests/RunCMake/CXXModules/ImplicitCXX20.cmake
-3
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@@ -1,9 +1,6 @@
# Enable scanning by default for targets that explicitly use C++ 20.
cmake_policy(SET CMP0155 NEW)
# Block making C++ `import std` targets.
add_library(__CMAKE::CXX23 IMPORTED INTERFACE)
# Force CMAKE_CXX_STANDARD_DEFAULT to be C++ 20.
set(ENV{CXXFLAGS} "$ENV{CXXFLAGS} ${CMAKE_CXX20_STANDARD_COMPILE_OPTION}")
enable_language(CXX)
Tests/RunCMake/CXXModules/Inspect.cmake
-16
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@@ -15,22 +15,6 @@ if (CMAKE_CXX_FLAGS MATCHES "-std=")
set(forced_cxx_standard 1)
endif ()
macro (cxx_check_import_std version)
set(have_cxx${version}_import_std 0)
if ("${version}" IN_LIST CMAKE_CXX_COMPILER_IMPORT_STD)
set(have_cxx${version}_import_std 1)
endif ()
if (TARGET "__CMAKE:CXX${version}" AND NOT have_cxx${version}_import_std)
message(FATAL_ERROR
"The toolchain's C++${version} target exists, but the user variable does "
"not indicate it.")
endif ()
endmacro ()
cxx_check_import_std(23)
cxx_check_import_std(26)
# Forward information about the C++ compile features.
string(APPEND info "\
set(CMAKE_CXX_COMPILE_FEATURES \"${CMAKE_CXX_COMPILE_FEATURES}\")
Tests/RunCMake/CXXModules/NoCXX20.cmake
-3
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@@ -1,6 +1,3 @@
# Block making C++ `import std` targets.
add_library(__CMAKE::CXX23 IMPORTED INTERFACE)
enable_language(CXX)
add_library(nocxx20)
Tests/RunCMake/CXXModules/NoScanningVariable.cmake
-3
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@@ -1,9 +1,6 @@
# Enable scanning by default for targets that explicitly use C++ 20.
cmake_policy(SET CMP0155 NEW)
# Block making C++ `import std` targets.
add_library(__CMAKE::CXX23 IMPORTED INTERFACE)
enable_language(CXX)
# Hide any real scanning rule that may be available.
Tests/RunCMake/CXXModulesCompile/imp-dummy-std/CMakeLists.txt
+1 -1
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@@ -1,5 +1,5 @@
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
"451f2fe2-a8a2-47c3-bc32-94786d8fc91b")
"f35a9ac6-8463-4d38-8eec-5d6008153e7d")
set(CMAKE_CXX_STDLIB_MODULES_JSON
"${CMAKE_CURRENT_LIST_DIR}/../dummy-std/manifest/dummy-std.modules.json"
)
Tests/RunCMake/CXXModulesCompile/imp-std-exp-no-std-build/CMakeLists.txt
+1 -1
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@@ -1,5 +1,5 @@
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
"451f2fe2-a8a2-47c3-bc32-94786d8fc91b")
"f35a9ac6-8463-4d38-8eec-5d6008153e7d")
cmake_minimum_required(VERSION 3.29)
project(cxx_modules_import_std_export_no_std CXX)
Tests/RunCMake/CXXModulesCompile/imp-std-exp-no-std-build/test/CMakeLists.txt
+2 -2
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@@ -39,7 +39,7 @@ list(FILTER usage_dependent_targets EXCLUDE REGEX "CXXModules::")
# Strip quotes.
string(REPLACE "\"" "" usage_dependent_targets "${usage_dependent_targets}")
if ("__CMAKE::CXX23" IN_LIST usage_dependent_targets)
if ("@cmake_cxx_std" IN_LIST usage_dependent_targets)
message(SEND_ERROR
"The main export requires the '__CMAKE::CXX23' target")
"The main export requires the '@cmake_cxx_std' target")
endif ()
Tests/RunCMake/CXXModulesCompile/imp-std-exp-no-std-install/CMakeLists.txt
+1 -1
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@@ -1,5 +1,5 @@
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
"451f2fe2-a8a2-47c3-bc32-94786d8fc91b")
"f35a9ac6-8463-4d38-8eec-5d6008153e7d")
cmake_minimum_required(VERSION 3.29)
project(cxx_modules_import_std_export_no_std CXX)
Tests/RunCMake/CXXModulesCompile/imp-std-exp-no-std-install/test/CMakeLists.txt
+2 -2
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@@ -39,7 +39,7 @@ list(FILTER usage_dependent_targets EXCLUDE REGEX "CXXModules::")
# Strip quotes.
string(REPLACE "\"" "" usage_dependent_targets "${usage_dependent_targets}")
if ("__CMAKE::CXX23" IN_LIST usage_dependent_targets)
if ("@cmake_cxx_std" IN_LIST usage_dependent_targets)
message(SEND_ERROR
"The main export requires the '__CMAKE::CXX23' target")
"The main export requires the '@cmake_cxx_std' target")
endif ()
Tests/RunCMake/CXXModulesCompile/imp-std-no-std-prop/CMakeLists.txt
+1 -1
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@@ -1,5 +1,5 @@
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
"451f2fe2-a8a2-47c3-bc32-94786d8fc91b")
"f35a9ac6-8463-4d38-8eec-5d6008153e7d")
cmake_minimum_required(VERSION 3.29)
project(cxx_modules_import_std_no_std_property CXX)
Tests/RunCMake/CXXModulesCompile/imp-std-not-in-exp-build/CMakeLists.txt
+1 -1
View File
@@ -1,5 +1,5 @@
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
"451f2fe2-a8a2-47c3-bc32-94786d8fc91b")
"f35a9ac6-8463-4d38-8eec-5d6008153e7d")
cmake_minimum_required(VERSION 3.29)
project(cxx_modules_import_std_not_in_export CXX)
Tests/RunCMake/CXXModulesCompile/imp-std-not-in-exp-build/test/CMakeLists.txt
+2 -2
View File
@@ -39,7 +39,7 @@ list(FILTER usage_dependent_targets EXCLUDE REGEX "CXXModules::")
# Strip quotes.
string(REPLACE "\"" "" usage_dependent_targets "${usage_dependent_targets}")
if ("__CMAKE::CXX23" IN_LIST usage_dependent_targets)
if ("@cmake_cxx_std" IN_LIST usage_dependent_targets)
message(SEND_ERROR
"The main export requires the '__CMAKE::CXX23' target")
"The main export requires the '@cmake_cxx_std' target")
endif ()
Tests/RunCMake/CXXModulesCompile/imp-std-not-in-exp-install/CMakeLists.txt
+1 -1
View File
@@ -1,5 +1,5 @@
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
"451f2fe2-a8a2-47c3-bc32-94786d8fc91b")
"f35a9ac6-8463-4d38-8eec-5d6008153e7d")
cmake_minimum_required(VERSION 3.29)
project(cxx_modules_import_std_not_in_export CXX)
Tests/RunCMake/CXXModulesCompile/imp-std-not-in-exp-install/test/CMakeLists.txt
+2 -2
View File
@@ -39,7 +39,7 @@ list(FILTER usage_dependent_targets EXCLUDE REGEX "CXXModules::")
# Strip quotes.
string(REPLACE "\"" "" usage_dependent_targets "${usage_dependent_targets}")
if ("__CMAKE::CXX23" IN_LIST usage_dependent_targets)
if ("@cmake_cxx_std" IN_LIST usage_dependent_targets)
message(SEND_ERROR
"The main export requires the '__CMAKE::CXX23' target")
"The main export requires the '@cmake_cxx_std' target")
endif ()
Tests/RunCMake/CXXModulesCompile/imp-std-trans/CMakeLists.txt
+1 -7
View File
@@ -1,14 +1,8 @@
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
"451f2fe2-a8a2-47c3-bc32-94786d8fc91b")
"f35a9ac6-8463-4d38-8eec-5d6008153e7d")
cmake_minimum_required(VERSION 3.29)
if (EXPORT_NO_STD)
# Block making C++ `import std` targets.
add_library(__CMAKE::CXX23 IMPORTED INTERFACE)
add_library(__CMAKE::CXX26 IMPORTED INTERFACE)
endif ()
project(cxx_modules_import_std_transitive CXX)
include("${CMAKE_SOURCE_DIR}/../cxx-modules-rules.cmake")
Tests/RunCMake/CXXModulesCompile/imp-std/CMakeLists.txt
+1 -1
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@@ -1,5 +1,5 @@
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
"451f2fe2-a8a2-47c3-bc32-94786d8fc91b")
"f35a9ac6-8463-4d38-8eec-5d6008153e7d")
cmake_minimum_required(VERSION 3.29)
project(cxx_modules_import_std CXX)
Tests/RunCMake/cmake_language/Experimental/CxxImportStd-quiet.cmake
+1 -1
View File
@@ -13,7 +13,7 @@ if (NOT feature_present STREQUAL "FALSE")
endif ()
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
"451f2fe2-a8a2-47c3-bc32-94786d8fc91b")
"f35a9ac6-8463-4d38-8eec-5d6008153e7d")
cmake_language(GET_EXPERIMENTAL_FEATURE_ENABLED
"CxxImportStd"
Tests/RunCMake/cmake_language/Experimental/CxxImportStd-set.cmake
+1 -1
View File
@@ -1,5 +1,5 @@
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
"451f2fe2-a8a2-47c3-bc32-94786d8fc91b")
"f35a9ac6-8463-4d38-8eec-5d6008153e7d")
cmake_language(GET_EXPERIMENTAL_FEATURE_ENABLED
"CxxImportStd"