Merge topic 'cxxmodules-no-longer-experimental'

437280b127 cxxmodules: scan C++ sources for imports by default
3cddd11649 Ninja: message about not compiled sources explicitly
068fde1c34 cmGeneratorTarget: use `this->` for method calls
197a6bf171 cxxmodules: rework control logic for scanning regular C++ sources
5eb7bd641a Tests/RunCMake/CXXModules: remove rules file requirement
ff18acc301 CXXModules: remove `EXPERIMENTAL` from C++ module variable names
0c07f39006 cmExperimental: remove the flag for C++ modules
68caec9137 Help: add a manpage for cxxmodule support

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: Pavel Solodovnikov <hellyeahdominate@gmail.com>
Merge-request: !8828

14 files changed, 184 insertions, 166 deletions

diff --git a/Source/cmCoreTryCompile.cxx b/Source/cmCoreTryCompile.cxx
index ee40bd5..67462f5 100644
--- a/Source/cmCoreTryCompile.cxx
+++ b/Source/cmCoreTryCompile.cxx
@@ -235,25 +235,16 @@ ArgumentParser::Continue cmCoreTryCompile::Arguments::SetSourceType(
     this->SourceTypeContext = SourceType::Normal;
     matched = true;
   } else if (sourceType == "CXX_MODULE"_s) {
-    bool const supportCxxModuleSources = cmExperimental::HasSupportEnabled(
-      *this->Makefile, cmExperimental::Feature::CxxModuleCMakeApi);
-    if (supportCxxModuleSources) {
-      this->SourceTypeContext = SourceType::CxxModule;
-      matched = true;
-    }
+    this->SourceTypeContext = SourceType::CxxModule;
+    matched = true;
   }
 
   if (!matched && this->SourceTypeError.empty()) {
-    bool const supportCxxModuleSources = cmExperimental::HasSupportEnabled(
-      *this->Makefile, cmExperimental::Feature::CxxModuleCMakeApi);
-    auto const* message = "'SOURCE'";
-    if (supportCxxModuleSources) {
-      message = "one of 'SOURCE' or 'CXX_MODULE'";
-    }
     // Only remember one error at a time; all other errors related to argument
     // parsing are "indicate one error and return" anyways.
     this->SourceTypeError =
-      cmStrCat("Invalid 'SOURCE_TYPE' '", sourceType, "'; must be ", message);
+      cmStrCat("Invalid 'SOURCE_TYPE' '", sourceType,
+               "'; must be one of 'SOURCE' or 'CXX_MODULE'");
   }
   return ArgumentParser::Continue::Yes;
 }
@@ -880,6 +871,13 @@ cm::optional<cmTryCompileResult> cmCoreTryCompile::TryCompileCode(
               ? "NEW"
               : "OLD");
 
+    /* Set the appropriate policy information for C++ module support */
+    fprintf(fout, "cmake_policy(SET CMP0155 %s)\n",
+            this->Makefile->GetPolicyStatus(cmPolicies::CMP0155) ==
+                cmPolicies::NEW
+              ? "NEW"
+              : "OLD");
+
     // Workaround for -Wl,-headerpad_max_install_names issue until we can avoid
     // adding that flag in the platform and compiler language files
     fprintf(fout,
diff --git a/Source/cmExperimental.cxx b/Source/cmExperimental.cxx
index 104ab81..d75879f 100644
--- a/Source/cmExperimental.cxx
+++ b/Source/cmExperimental.cxx
@@ -19,17 +19,6 @@ namespace {
  * up-to-date.
  */
 cmExperimental::FeatureData LookupTable[] = {
-  // CxxModuleCMakeApi
-  { "CxxModuleCMakeApi",
-    "ac01f462-0f5f-432a-86aa-acef252918a6",
-    "CMAKE_EXPERIMENTAL_CXX_MODULE_CMAKE_API",
-    "CMake's C++ module support is experimental. It is meant only for "
-    "experimentation and feedback to CMake developers.",
-    { "CMAKE_EXPERIMENTAL_CXX_SCANDEP_SOURCE",
-      "CMAKE_EXPERIMENTAL_CXX_MODULE_MAP_FORMAT",
-      "CMAKE_EXPERIMENTAL_CXX_MODULE_MAP_FLAG" },
-    cmExperimental::TryCompileCondition::SkipCompilerChecks,
-    false },
   // WindowsKernelModeDriver
   { "WindowsKernelModeDriver",
     "5c2d848d-4efa-4529-a768-efd57171bf68",
diff --git a/Source/cmExperimental.h b/Source/cmExperimental.h
index c958ab6..e4c1448 100644
--- a/Source/cmExperimental.h
+++ b/Source/cmExperimental.h
@@ -15,7 +15,6 @@ class cmExperimental
 public:
   enum class Feature
   {
-    CxxModuleCMakeApi,
     WindowsKernelModeDriver,
 
     Sentinel,
diff --git a/Source/cmExportCommand.cxx b/Source/cmExportCommand.cxx
index 273296d..e78b869 100644
--- a/Source/cmExportCommand.cxx
+++ b/Source/cmExportCommand.cxx
@@ -16,7 +16,6 @@
 #include "cmArgumentParserTypes.h"
 #include "cmCryptoHash.h"
 #include "cmExecutionStatus.h"
-#include "cmExperimental.h"
 #include "cmExportBuildAndroidMKGenerator.h"
 #include "cmExportBuildFileGenerator.h"
 #include "cmExportSet.h"
@@ -69,15 +68,11 @@ bool cmExportCommand(std::vector<std::string> const& args,
     bool ExportOld = false;
   };
 
-  auto parser = cmArgumentParser<Arguments>{}
-                  .Bind("NAMESPACE"_s, &Arguments::Namespace)
-                  .Bind("FILE"_s, &Arguments::Filename);
-
-  bool const supportCxx20FileSetTypes = cmExperimental::HasSupportEnabled(
-    status.GetMakefile(), cmExperimental::Feature::CxxModuleCMakeApi);
-  if (supportCxx20FileSetTypes) {
-    parser.Bind("CXX_MODULES_DIRECTORY"_s, &Arguments::CxxModulesDirectory);
-  }
+  auto parser =
+    cmArgumentParser<Arguments>{}
+      .Bind("NAMESPACE"_s, &Arguments::Namespace)
+      .Bind("FILE"_s, &Arguments::Filename)
+      .Bind("CXX_MODULES_DIRECTORY"_s, &Arguments::CxxModulesDirectory);
 
   if (args[0] == "EXPORT") {
     parser.Bind("EXPORT"_s, &Arguments::ExportSetName);
diff --git a/Source/cmGeneratorTarget.cxx b/Source/cmGeneratorTarget.cxx
index 04d7bb1..96fcf7e 100644
--- a/Source/cmGeneratorTarget.cxx
+++ b/Source/cmGeneratorTarget.cxx
@@ -31,7 +31,6 @@
 #include "cmCustomCommandGenerator.h"
 #include "cmCxxModuleUsageEffects.h"
 #include "cmEvaluatedTargetProperty.h"
-#include "cmExperimental.h"
 #include "cmFileSet.h"
 #include "cmFileTimes.h"
 #include "cmGeneratedFileStream.h"
@@ -9047,7 +9046,7 @@ std::string cmGeneratorTarget::GetImportedXcFrameworkPath(
 
 bool cmGeneratorTarget::HaveFortranSources(std::string const& config) const
 {
-  auto sources = cmGeneratorTarget::GetSourceFiles(config);
+  auto sources = this->GetSourceFiles(config);
   return std::any_of(sources.begin(), sources.end(),
                      [](BT<cmSourceFile*> const& sf) -> bool {
                        return sf.Value->GetLanguage() == "Fortran"_s;
@@ -9106,54 +9105,93 @@ cmGeneratorTarget::Cxx20SupportLevel cmGeneratorTarget::HaveCxxModuleSupport(
   // Else, an empty CMAKE_CXX_STANDARD_DEFAULT means CMake does not detect and
   // set a default standard level for this compiler, so assume all standards
   // are available.
-  if (!cmExperimental::HasSupportEnabled(
-        *this->Makefile, cmExperimental::Feature::CxxModuleCMakeApi)) {
-    return Cxx20SupportLevel::MissingExperimentalFlag;
+  cmValue scandepRule =
+    this->Target->GetMakefile()->GetDefinition("CMAKE_CXX_SCANDEP_SOURCE");
+  if (!scandepRule) {
+    return Cxx20SupportLevel::MissingRule;
   }
   return Cxx20SupportLevel::Supported;
 }
 
 void cmGeneratorTarget::CheckCxxModuleStatus(std::string const& config) const
 {
+  bool haveScannableSources = false;
+
   // Check for `CXX_MODULE*` file sets and a lack of support.
   if (this->HaveCxx20ModuleSources()) {
-    switch (this->HaveCxxModuleSupport(config)) {
-      case cmGeneratorTarget::Cxx20SupportLevel::MissingCxx:
-        this->Makefile->IssueMessage(
-          MessageType::FATAL_ERROR,
-          cmStrCat("The target named \"", this->GetName(),
-                   "\" has C++ sources that export modules but the \"CXX\" "
-                   "language has not been enabled"));
-        break;
-      case cmGeneratorTarget::Cxx20SupportLevel::MissingExperimentalFlag:
-        this->Makefile->IssueMessage(
-          MessageType::FATAL_ERROR,
-          cmStrCat("The target named \"", this->GetName(),
-                   "\" has C++ sources that export modules but its "
-                   "experimental support has not been requested"));
-        break;
-      case cmGeneratorTarget::Cxx20SupportLevel::NoCxx20: {
-        cmStandardLevelResolver standardResolver(this->Makefile);
-        auto effStandard =
-          standardResolver.GetEffectiveStandard(this, "CXX", config);
-        if (effStandard.empty()) {
-          effStandard = "; no C++ standard found";
-        } else {
-          effStandard = cmStrCat("; found \"cxx_std_", effStandard, '"');
-        }
-        this->Makefile->IssueMessage(
-          MessageType::FATAL_ERROR,
-          cmStrCat(
-            "The target named \"", this->GetName(),
-            "\" has C++ sources that export modules but does not include "
-            "\"cxx_std_20\" (or newer) among its `target_compile_features`",
-            effStandard));
-      } break;
-      case cmGeneratorTarget::Cxx20SupportLevel::Supported:
-        // All is well.
-        break;
+    haveScannableSources = true;
+  }
+
+  if (!haveScannableSources) {
+    // Check to see if there are regular sources that have requested scanning.
+    auto sources = this->GetSourceFiles(config);
+    for (auto const& source : sources) {
+      auto const* sf = source.Value;
+      auto const& lang = sf->GetLanguage();
+      if (lang != "CXX"_s) {
+        continue;
+      }
+      // Ignore sources which do not need dyndep.
+      if (this->NeedDyndepForSource(lang, config, sf)) {
+        haveScannableSources = true;
+      }
     }
   }
+
+  // If there isn't anything scannable, ignore it.
+  if (!haveScannableSources) {
+    return;
+  }
+
+  // If the generator doesn't support modules at all, error that we have
+  // sources that require the support.
+  if (!this->GetGlobalGenerator()->CheckCxxModuleSupport()) {
+    this->Makefile->IssueMessage(
+      MessageType::FATAL_ERROR,
+      cmStrCat(
+        "The target named \"", this->GetName(),
+        "\" contains C++ "
+        "sources that use modules which is not supported by the generator"));
+    return;
+  }
+
+  switch (this->HaveCxxModuleSupport(config)) {
+    case cmGeneratorTarget::Cxx20SupportLevel::MissingCxx:
+      this->Makefile->IssueMessage(
+        MessageType::FATAL_ERROR,
+        cmStrCat("The target named \"", this->GetName(),
+                 "\" has C++ sources that use modules but the \"CXX\" "
+                 "language has not been enabled"));
+      break;
+    case cmGeneratorTarget::Cxx20SupportLevel::NoCxx20: {
+      cmStandardLevelResolver standardResolver(this->Makefile);
+      auto effStandard =
+        standardResolver.GetEffectiveStandard(this, "CXX", config);
+      if (effStandard.empty()) {
+        effStandard = "; no C++ standard found";
+      } else {
+        effStandard = cmStrCat("; found \"cxx_std_", effStandard, '"');
+      }
+      this->Makefile->IssueMessage(
+        MessageType::FATAL_ERROR,
+        cmStrCat(
+          "The target named \"", this->GetName(),
+          "\" has C++ sources that use modules but does not include "
+          "\"cxx_std_20\" (or newer) among its `target_compile_features`",
+          effStandard));
+    } break;
+    case cmGeneratorTarget::Cxx20SupportLevel::MissingRule: {
+      this->Makefile->IssueMessage(
+        MessageType::FATAL_ERROR,
+        cmStrCat("The target named \"", this->GetName(),
+                 "\" has C++ sources that use modules but the compiler does "
+                 "not provide a way to discover the import graph "
+                 "dependencies"));
+    } break;
+    case cmGeneratorTarget::Cxx20SupportLevel::Supported:
+      // All is well.
+      break;
+  }
 }
 
 bool cmGeneratorTarget::NeedCxxModuleSupport(std::string const& lang,
@@ -9191,14 +9229,30 @@ bool cmGeneratorTarget::NeedDyndepForSource(std::string const& lang,
                                             std::string const& config,
                                             cmSourceFile const* sf) const
 {
-  bool const needDyndep = this->NeedDyndep(lang, config);
-  if (!needDyndep) {
+  // Fortran always needs to be scanned.
+  if (lang == "Fortran"_s) {
+    return true;
+  }
+  // Only C++ code needs scanned otherwise.
+  if (lang != "CXX"_s) {
     return false;
   }
+
+  // Any file in `CXX_MODULES` file sets need scanned (it being `CXX` is
+  // enforced elsewhere).
   auto const* fs = this->GetFileSetForSource(config, sf);
   if (fs && fs->GetType() == "CXX_MODULES"_s) {
     return true;
   }
+
+  switch (this->HaveCxxModuleSupport(config)) {
+    case Cxx20SupportLevel::MissingCxx:
+    case Cxx20SupportLevel::NoCxx20:
+      return false;
+    case Cxx20SupportLevel::MissingRule:
+    case Cxx20SupportLevel::Supported:
+      break;
+  }
   auto const sfProp = sf->GetProperty("CXX_SCAN_FOR_MODULES");
   if (sfProp.IsSet()) {
     return sfProp.IsOn();
@@ -9207,7 +9261,22 @@ bool cmGeneratorTarget::NeedDyndepForSource(std::string const& lang,
   if (tgtProp.IsSet()) {
     return tgtProp.IsOn();
   }
-  return true;
+
+  bool policyAnswer = false;
+  switch (this->GetPolicyStatusCMP0155()) {
+    case cmPolicies::WARN:
+    case cmPolicies::OLD:
+      // The OLD behavior is to not scan the source.
+      policyAnswer = false;
+      break;
+    case cmPolicies::REQUIRED_ALWAYS:
+    case cmPolicies::REQUIRED_IF_USED:
+    case cmPolicies::NEW:
+      // The NEW behavior is to scan the source.
+      policyAnswer = true;
+      break;
+  }
+  return policyAnswer;
 }
 
 void cmGeneratorTarget::BuildFileSetInfoCache(std::string const& config) const
diff --git a/Source/cmGeneratorTarget.h b/Source/cmGeneratorTarget.h
index 751f907..72920d6 100644
--- a/Source/cmGeneratorTarget.h
+++ b/Source/cmGeneratorTarget.h
@@ -1288,10 +1288,10 @@ public:
   {
     // C++ is not available.
     MissingCxx,
-    // The experimental feature is not available.
-    MissingExperimentalFlag,
     // The target does not require at least C++20.
     NoCxx20,
+    // C++20 module scanning rules are not present.
+    MissingRule,
     // C++20 modules are available and working.
     Supported,
   };
diff --git a/Source/cmGlobalVisualStudio7Generator.cxx b/Source/cmGlobalVisualStudio7Generator.cxx
index 6953ec6..1abdd0b 100644
--- a/Source/cmGlobalVisualStudio7Generator.cxx
+++ b/Source/cmGlobalVisualStudio7Generator.cxx
@@ -435,14 +435,6 @@ void cmGlobalVisualStudio7Generator::WriteTargetsToSolution(
       target->CheckCxxModuleStatus(c);
     }
 
-    if (target->HaveCxx20ModuleSources() && !this->SupportsCxxModuleDyndep()) {
-      root->GetMakefile()->IssueMessage(
-        MessageType::FATAL_ERROR,
-        cmStrCat("The target named \"", target->GetName(),
-                 "\" contains C++ sources that export modules which is not "
-                 "supported by the generator"));
-    }
-
     // handle external vc project files
     cmValue expath = target->GetProperty("EXTERNAL_MSPROJECT");
     if (expath) {
diff --git a/Source/cmGlobalXCodeGenerator.cxx b/Source/cmGlobalXCodeGenerator.cxx
index 90b8839..5076e6c 100644
--- a/Source/cmGlobalXCodeGenerator.cxx
+++ b/Source/cmGlobalXCodeGenerator.cxx
@@ -1384,14 +1384,6 @@ bool cmGlobalXCodeGenerator::CreateXCodeTarget(
     gtgt->CheckCxxModuleStatus(configName);
   }
 
-  if (gtgt->HaveCxx20ModuleSources()) {
-    gtgt->Makefile->IssueMessage(
-      MessageType::FATAL_ERROR,
-      cmStrCat("The target named \"", gtgt->GetName(),
-               "\" contains C++ sources that export modules which is not "
-               "supported by the generator"));
-  }
-
   auto& gtgt_visited = this->CommandsVisited[gtgt];
   auto const& deps = this->GetTargetDirectDepends(gtgt);
   for (auto const& d : deps) {
diff --git a/Source/cmInstallCommand.cxx b/Source/cmInstallCommand.cxx
index 1b47ec4..0fc4011 100644
--- a/Source/cmInstallCommand.cxx
+++ b/Source/cmInstallCommand.cxx
@@ -21,7 +21,6 @@
 #include "cmArgumentParser.h"
 #include "cmArgumentParserTypes.h"
 #include "cmExecutionStatus.h"
-#include "cmExperimental.h"
 #include "cmExportSet.h"
 #include "cmFileSet.h"
 #include "cmGeneratorExpression.h"
@@ -491,6 +490,7 @@ bool HandleTargetsMode(std::vector<std::string> const& args,
   publicHeaderArgs.Parse(argVectors.PublicHeader, &unknownArgs);
   resourceArgs.Parse(argVectors.Resource, &unknownArgs);
   includesArgs.Parse(&argVectors.Includes, &unknownArgs);
+  cxxModuleBmiArgs.Parse(argVectors.CxxModulesBmi, &unknownArgs);
   for (std::size_t i = 0; i < argVectors.FileSets.size(); i++) {
     // We have to create a separate object for the parsing because
     // cmArgumentParser<void>::Bind() binds to a specific address, but the
@@ -501,15 +501,6 @@ bool HandleTargetsMode(std::vector<std::string> const& args,
     fileSetArgs[i] = std::move(fileSetArg);
   }
 
-  bool const supportCxx20FileSetTypes = cmExperimental::HasSupportEnabled(
-    *helper.Makefile, cmExperimental::Feature::CxxModuleCMakeApi);
-  if (!supportCxx20FileSetTypes) {
-    std::copy(argVectors.CxxModulesBmi.begin(), argVectors.CxxModulesBmi.end(),
-              std::back_inserter(unknownArgs));
-  } else {
-    cxxModuleBmiArgs.Parse(argVectors.CxxModulesBmi, &unknownArgs);
-  }
-
   if (!unknownArgs.empty()) {
     // Unknown argument.
     status.SetError(
@@ -541,12 +532,10 @@ bool HandleTargetsMode(std::vector<std::string> const& args,
   success = success && privateHeaderArgs.Finalize();
   success = success && publicHeaderArgs.Finalize();
   success = success && resourceArgs.Finalize();
+  success = success && cxxModuleBmiArgs.Finalize();
   for (auto& fileSetArg : fileSetArgs) {
     success = success && fileSetArg.Finalize();
   }
-  if (supportCxx20FileSetTypes) {
-    success = success && cxxModuleBmiArgs.Finalize();
-  }
 
   if (!success) {
     return false;
@@ -1173,8 +1162,7 @@ bool HandleTargetsMode(std::vector<std::string> const& args,
       }
     }
 
-    if (supportCxx20FileSetTypes &&
-        !cxxModuleBmiArgs.GetDestination().empty()) {
+    if (!cxxModuleBmiArgs.GetDestination().empty()) {
       cxxModuleBmiGenerator = cm::make_unique<cmInstallCxxModuleBmiGenerator>(
         target.GetName(),
         helper.GetCxxModulesBmiDestination(&cxxModuleBmiArgs),
@@ -2071,12 +2059,7 @@ bool HandleExportMode(std::vector<std::string> const& args,
   ica.Bind("NAMESPACE"_s, name_space);
   ica.Bind("EXPORT_LINK_INTERFACE_LIBRARIES"_s, exportOld);
   ica.Bind("FILE"_s, filename);
-
-  bool const supportCxx20FileSetTypes = cmExperimental::HasSupportEnabled(
-    *helper.Makefile, cmExperimental::Feature::CxxModuleCMakeApi);
-  if (supportCxx20FileSetTypes) {
-    ica.Bind("CXX_MODULES_DIRECTORY"_s, cxx_modules_directory);
-  }
+  ica.Bind("CXX_MODULES_DIRECTORY"_s, cxx_modules_directory);
 
   std::vector<std::string> unknownArgs;
   ica.Parse(args, &unknownArgs);
diff --git a/Source/cmMakefileTargetGenerator.cxx b/Source/cmMakefileTargetGenerator.cxx
index caa5e67..0c2a719 100644
--- a/Source/cmMakefileTargetGenerator.cxx
+++ b/Source/cmMakefileTargetGenerator.cxx
@@ -204,14 +204,6 @@ void cmMakefileTargetGenerator::WriteTargetBuildRules()
 {
   this->GeneratorTarget->CheckCxxModuleStatus(this->GetConfigName());
 
-  if (this->GeneratorTarget->HaveCxx20ModuleSources()) {
-    this->Makefile->IssueMessage(
-      MessageType::FATAL_ERROR,
-      cmStrCat("The target named \"", this->GeneratorTarget->GetName(),
-               "\" contains C++ sources that export modules which is not "
-               "supported by the generator"));
-  }
-
   // -- Write the custom commands for this target
 
   // Evaluates generator expressions and expands prop_value
diff --git a/Source/cmNinjaTargetGenerator.cxx b/Source/cmNinjaTargetGenerator.cxx
index 193cc0f..0bda945 100644
--- a/Source/cmNinjaTargetGenerator.cxx
+++ b/Source/cmNinjaTargetGenerator.cxx
@@ -266,7 +266,7 @@ std::string cmNinjaTargetGenerator::ComputeFlagsForObject(
 
     if (!this->GeneratorTarget->Target->IsNormal()) {
       auto flag = this->GetMakefile()->GetSafeDefinition(
-        "CMAKE_EXPERIMENTAL_CXX_MODULE_BMI_ONLY_FLAG");
+        "CMAKE_CXX_MODULE_BMI_ONLY_FLAG");
       cmRulePlaceholderExpander::RuleVariables compileObjectVars;
       compileObjectVars.Object = objectFileName.c_str();
       auto rulePlaceholderExpander =
@@ -710,7 +710,7 @@ void cmNinjaTargetGenerator::WriteCompileRule(const std::string& lang,
     }
   }
   std::string const modmapFormatVar =
-    cmStrCat("CMAKE_EXPERIMENTAL_", lang, "_MODULE_MAP_FORMAT");
+    cmStrCat("CMAKE_", lang, "_MODULE_MAP_FORMAT");
   std::string const modmapFormat =
     this->Makefile->GetSafeDefinition(modmapFormatVar);
 
@@ -734,7 +734,7 @@ void cmNinjaTargetGenerator::WriteCompileRule(const std::string& lang,
 
   if (withScanning == WithScanning::Yes) {
     const auto& scanDepType = this->GetMakefile()->GetSafeDefinition(
-      cmStrCat("CMAKE_EXPERIMENTAL_", lang, "_SCANDEP_DEPFILE_FORMAT"));
+      cmStrCat("CMAKE_", lang, "_SCANDEP_DEPFILE_FORMAT"));
 
     // Rule to scan dependencies of sources that need preprocessing.
     {
@@ -745,7 +745,7 @@ void cmNinjaTargetGenerator::WriteCompileRule(const std::string& lang,
         scanRuleName = this->LanguageScanRule(lang, config);
         ppFileName = "$PREPROCESSED_OUTPUT_FILE";
         std::string const& scanCommand = mf->GetRequiredDefinition(
-          cmStrCat("CMAKE_EXPERIMENTAL_", lang, "_SCANDEP_SOURCE"));
+          cmStrCat("CMAKE_", lang, "_SCANDEP_SOURCE"));
         scanCommands.assign(scanCommand);
         for (auto& i : scanCommands) {
           i = cmStrCat(launcher, i);
@@ -893,8 +893,8 @@ void cmNinjaTargetGenerator::WriteCompileRule(const std::string& lang,
   }
 
   if (withScanning == WithScanning::Yes && !modmapFormat.empty()) {
-    std::string modmapFlags = mf->GetRequiredDefinition(
-      cmStrCat("CMAKE_EXPERIMENTAL_", lang, "_MODULE_MAP_FLAG"));
+    std::string modmapFlags =
+      mf->GetRequiredDefinition(cmStrCat("CMAKE_", lang, "_MODULE_MAP_FLAG"));
     cmSystemTools::ReplaceString(modmapFlags, "<MODULE_MAP_FILE>",
                                  "$DYNDEP_MODULE_MAP_FILE");
     flags += cmStrCat(' ', modmapFlags);
@@ -1143,6 +1143,30 @@ void cmNinjaTargetGenerator::WriteObjectBuildStatements(
     }
   }
 
+  // Detect sources in `CXX_MODULES` which are not compiled.
+  {
+    std::vector<cmSourceFile*> sources;
+    this->GeneratorTarget->GetSourceFiles(sources, config);
+    for (cmSourceFile const* sf : sources) {
+      cmFileSet const* fs =
+        this->GeneratorTarget->GetFileSetForSource(config, sf);
+      if (!fs) {
+        continue;
+      }
+      if (fs->GetType() != "CXX_MODULES"_s) {
+        continue;
+      }
+      if (sf->GetLanguage().empty()) {
+        this->GeneratorTarget->Makefile->IssueMessage(
+          MessageType::FATAL_ERROR,
+          cmStrCat("Target \"", this->GeneratorTarget->GetName(),
+                   "\" has source file\n  ", sf->GetFullPath(),
+                   "\nin a \"FILE_SET TYPE CXX_MODULES\" but it is not "
+                   "scheduled for compilation."));
+      }
+    }
+  }
+
   for (auto const& langScanningFiles : this->Configs[config].ScanningInfo) {
     std::string const& language = langScanningFiles.first;
     std::vector<ScanningFiles> const& scanningFiles = langScanningFiles.second;
@@ -1477,7 +1501,7 @@ void cmNinjaTargetGenerator::WriteObjectBuildStatement(
   std::string modmapFormat;
   if (needDyndep) {
     std::string const modmapFormatVar =
-      cmStrCat("CMAKE_EXPERIMENTAL_", language, "_MODULE_MAP_FORMAT");
+      cmStrCat("CMAKE_", language, "_MODULE_MAP_FORMAT");
     modmapFormat = this->Makefile->GetSafeDefinition(modmapFormatVar);
   }
 
@@ -1758,7 +1782,7 @@ void cmNinjaTargetGenerator::WriteCxxModuleBmiBuildStatement(
   std::string modmapFormat;
   if (true) {
     std::string const modmapFormatVar =
-      cmStrCat("CMAKE_EXPERIMENTAL_", language, "_MODULE_MAP_FORMAT");
+      cmStrCat("CMAKE_", language, "_MODULE_MAP_FORMAT");
     modmapFormat = this->Makefile->GetSafeDefinition(modmapFormatVar);
   }
 
@@ -1969,12 +1993,12 @@ void cmNinjaTargetGenerator::ExportObjectCompileCommand(
     bool const needDyndep =
       this->GetGeneratorTarget()->NeedDyndep(language, outputConfig);
     std::string const modmapFormatVar =
-      cmStrCat("CMAKE_EXPERIMENTAL_", language, "_MODULE_MAP_FORMAT");
+      cmStrCat("CMAKE_", language, "_MODULE_MAP_FORMAT");
     std::string const modmapFormat =
       this->Makefile->GetSafeDefinition(modmapFormatVar);
     if (needDyndep && !modmapFormat.empty()) {
       std::string modmapFlags = this->GetMakefile()->GetRequiredDefinition(
-        cmStrCat("CMAKE_EXPERIMENTAL_", language, "_MODULE_MAP_FLAG"));
+        cmStrCat("CMAKE_", language, "_MODULE_MAP_FLAG"));
       // XXX(modmap): If changing this path construction, change
       // `cmGlobalNinjaGenerator::WriteDyndep` and
       // `cmNinjaTargetGenerator::WriteObjectBuildStatement` to expect the
diff --git a/Source/cmPolicies.h b/Source/cmPolicies.h
index e894073..1ea2ce2 100644
--- a/Source/cmPolicies.h
+++ b/Source/cmPolicies.h
@@ -469,6 +469,10 @@ class cmMakefile;
   SELECT(                                                                     \
     POLICY, CMP0154,                                                          \
     "Generated files are private by default in targets using file sets.", 3,  \
+    28, 0, cmPolicies::WARN)                                                  \
+  SELECT(                                                                     \
+    POLICY, CMP0155,                                                          \
+    "C++ sources in targets with at least C++20 are scanned for imports", 3,  \
     28, 0, cmPolicies::WARN)
 
 #define CM_SELECT_ID(F, A1, A2, A3, A4, A5, A6) F(A1)
@@ -508,7 +512,8 @@ class cmMakefile;
   F(CMP0119)                                                                  \
   F(CMP0131)                                                                  \
   F(CMP0142)                                                                  \
-  F(CMP0154)
+  F(CMP0154)                                                                  \
+  F(CMP0155)
 
 #define CM_FOR_EACH_CUSTOM_COMMAND_POLICY(F)                                  \
   F(CMP0116)                                                                  \
diff --git a/Source/cmTargetSourcesCommand.cxx b/Source/cmTargetSourcesCommand.cxx
index 3d484f5..babbaa5 100644
--- a/Source/cmTargetSourcesCommand.cxx
+++ b/Source/cmTargetSourcesCommand.cxx
@@ -10,7 +10,6 @@
 
 #include "cmArgumentParser.h"
 #include "cmArgumentParserTypes.h"
-#include "cmExperimental.h"
 #include "cmFileSet.h"
 #include "cmGeneratorExpression.h"
 #include "cmList.h"
@@ -260,28 +259,18 @@ bool TargetSourcesImpl::HandleOneFileSet(
       this->SetError("Must specify a TYPE when creating file set");
       return false;
     }
-    bool const supportCxx20FileSetTypes = cmExperimental::HasSupportEnabled(
-      *this->Makefile, cmExperimental::Feature::CxxModuleCMakeApi);
+    if (type != "HEADERS"_s && type != "CXX_MODULES"_s) {
+      this->SetError(
+        R"(File set TYPE may only be "HEADERS" or "CXX_MODULES")");
+      return false;
+    }
 
-    if (supportCxx20FileSetTypes) {
-      if (type != "HEADERS"_s && type != "CXX_MODULES"_s) {
+    if (cmFileSetVisibilityIsForInterface(visibility) &&
+        !cmFileSetVisibilityIsForSelf(visibility) &&
+        !this->Target->IsImported()) {
+      if (type == "CXX_MODULES"_s) {
         this->SetError(
-          R"(File set TYPE may only be "HEADERS" or "CXX_MODULES")");
-        return false;
-      }
-
-      if (cmFileSetVisibilityIsForInterface(visibility) &&
-          !cmFileSetVisibilityIsForSelf(visibility) &&
-          !this->Target->IsImported()) {
-        if (type == "CXX_MODULES"_s) {
-          this->SetError(
-            R"(File set TYPE "CXX_MODULES" may not have "INTERFACE" visibility)");
-          return false;
-        }
-      }
-    } else {
-      if (type != "HEADERS"_s) {
-        this->SetError("File set TYPE may only be \"HEADERS\"");
+          R"(File set TYPE "CXX_MODULES" may not have "INTERFACE" visibility)");
         return false;
       }
     }
diff --git a/Source/cmVisualStudio10TargetGenerator.cxx b/Source/cmVisualStudio10TargetGenerator.cxx
index 2a54a55..ce94fe1 100644
--- a/Source/cmVisualStudio10TargetGenerator.cxx
+++ b/Source/cmVisualStudio10TargetGenerator.cxx
@@ -362,15 +362,6 @@ void cmVisualStudio10TargetGenerator::Generate()
     this->GeneratorTarget->CheckCxxModuleStatus(config);
   }
 
-  if (this->GeneratorTarget->HaveCxx20ModuleSources() &&
-      !this->GlobalGenerator->SupportsCxxModuleDyndep()) {
-    this->Makefile->IssueMessage(
-      MessageType::FATAL_ERROR,
-      cmStrCat("The target named \"", this->GeneratorTarget->GetName(),
-               "\" contains C++ sources that export modules which is not "
-               "supported by the generator"));
-  }
-
   this->ProjectType = computeProjectType(this->GeneratorTarget);
   this->Managed = this->ProjectType == VsProjectType::csproj;
   const std::string ProjectFileExtension =