FILE_SET: relax file uniqueness for HEADERS type

Enable to declare in multiple sets headers files.

This complements commit 167e903c15 (FILE_SET: enforce uniqueness of files, 2026-03-06)

Issue: #27035

Help/policy/CMP0211.rst

@@ -3,16 +3,19 @@ CMP0211
 
 .. versionadded:: 4.4
 
-A file may belong to at most one :ref:`file set <file sets>` in a target.
+A file may belong to at most one :ref:`file set <file sets>` in a target except
+for the ``HEADERS`` file set type.
 
 In CMake 4.3 and below, it was possible to specify the same file
 in multiple file sets in a target.  In CMake 4.4 and above, a file
-may belong to at most one file set in a target.  This policy provides
-compatibility for projects that have not been updated accordingly.
+may belong to at most one file set in a target except for the ``HEADERS`` file
+set type.  This policy provides compatibility for projects that have not been
+updated accordingly.
 
 The ``OLD`` behavior for this policy is to accept the same file in
 multiple file sets in a target.  The ``NEW`` behavior for this policy
-is to accept a given file in at most one file set in a target.
+is to accept a given file in at most one file set in a target except for the
+``HEADERS`` file set type.
 
 .. |INTRODUCED_IN_CMAKE_VERSION| replace:: 4.4
 .. |WARNS_OR_DOES_NOT_WARN| replace::

Source/cmFileSetMetadata.cxx

@@ -86,19 +86,19 @@ std::map<cm::string_view, FileSetDescriptor> const FileSetDescriptors{
       cm::FileSetMetadata::FileSetLookup::Target,
       { DependencyMode ::Includables },
       DependencyMode ::Includables,
-      FrameworkCompatible::No } },
+      { cm::FileSetMetadata::FileSetAttributes::FilesInMultipleFileSets } } },
   { cm::FileSetMetadata::SOURCES,
     { cm::FileSetMetadata::SOURCES,
       cm::FileSetMetadata::FileSetLookup::Dependencies,
       { DependencyMode ::IndependentFiles, DependencyMode ::Includables },
       DependencyMode ::Includables,
-      FrameworkCompatible::Yes } },
+      { cm::FileSetMetadata::FileSetAttributes::FrameworkCompatible } } },
   { cm::FileSetMetadata::CXX_MODULES,
     { cm::FileSetMetadata::CXX_MODULES,
       cm::FileSetMetadata::FileSetLookup::Target,
       { DependencyMode ::IndependentFiles },
       DependencyMode ::IndependentFiles,
-      FrameworkCompatible::No } },
+      {} } },
 };
 
 std::vector<cm::string_view> KnownTypes{ HEADERS, SOURCES, CXX_MODULES };
@@ -138,13 +138,17 @@ DependencyMode GetDependencyMode(cm::string_view type,
   return DependencyMode::Includables;
 }
 
-bool IsFrameworkSupported(cm::string_view type)
+AttributeSet GetAttributes(cm::string_view type)
 {
   auto descriptor = GetFileSetDescriptor(type);
   if (descriptor) {
-    return descriptor->FrameworkSupported == FrameworkCompatible::Yes;
+    return descriptor->Attributes;
   }
-  return false;
+  return {};
+}
+bool IsFrameworkSupported(cm::string_view type)
+{
+  return GetAttributes(type).contains(FileSetAttributes::FrameworkCompatible);
 }
 
 std::vector<cm::string_view> const& GetKnownTypes()

Source/cmFileSetMetadata.h

@@ -2,12 +2,14 @@
    file LICENSE.rst or https://cmake.org/licensing for details.  */
 #pragma once
 
+#include <cstdint>
 #include <set>
 #include <utility>
 #include <vector>
 
 #include <cm/optional>
 #include <cm/string_view>
+#include <cmext/enum_set>
 
 class cmMakefile;
 
@@ -48,27 +50,28 @@ enum class FileSetLookup
 enum class DependencyMode
 {
   IndependentFiles, // files in the file set are independent from each other
-  Includables,      // files can be used by another source during compilation
+  Includables       // files can be used by another source during compilation
 };
 using DependencySet = std::set<DependencyMode>;
 
-enum class FrameworkCompatible
+enum class FileSetAttributes : std::uint16_t
 {
-  No,
-  Yes
+  FrameworkCompatible,    // Can be part of an Apple framework
+  FilesInMultipleFileSets // Files of this file set type can be part of other
+                          // file sets
 };
+using AttributeSet = cm::enum_set<FileSetAttributes, 2>;
 
 struct FileSetDescriptor
 {
   FileSetDescriptor(cm::string_view type, FileSetLookup lookup,
                     DependencySet dependencies,
-                    DependencyMode defaultDependency,
-                    FrameworkCompatible frameworkSupported)
+                    DependencyMode defaultDependency, AttributeSet attributes)
     : Type(type)
     , Lookup(lookup)
     , SupportedDependencies(std::move(dependencies))
     , DefaultDependency(defaultDependency)
-    , FrameworkSupported(frameworkSupported)
+    , Attributes(attributes)
   {
   }
 
@@ -77,7 +80,6 @@ struct FileSetDescriptor
     , Lookup(lookup)
     , SupportedDependencies({ DependencyMode::Includables })
     , DefaultDependency(DependencyMode::Includables)
-    , FrameworkSupported(FrameworkCompatible::No)
   {
   }
 
@@ -85,13 +87,15 @@ struct FileSetDescriptor
   FileSetLookup const Lookup;
   DependencySet const SupportedDependencies;
   DependencyMode const DefaultDependency;
-  FrameworkCompatible const FrameworkSupported;
+  AttributeSet const Attributes;
 };
 
 cm::optional<FileSetDescriptor> GetFileSetDescriptor(cm::string_view type);
 DependencyMode GetDependencyMode(cm::string_view type);
 DependencyMode GetDependencyMode(cm::string_view type,
                                  DependencyMode requestedMode);
+
+AttributeSet GetAttributes(cm::string_view type);
 bool IsFrameworkSupported(cm::string_view type);
 
 std::vector<cm::string_view> const& GetKnownTypes();
@@ -101,3 +105,5 @@ bool IsKnownType(cm::string_view type);
 bool IsValidName(cm::string_view type);
 }
 }
+
+CM_ENUM_SET_TRAITS(cm::FileSetMetadata::AttributeSet)

Source/cmGeneratorFileSets.cxx

@@ -133,11 +133,10 @@ cmGeneratorFileSet const* cmGeneratorFileSets::GetFileSet(
   return nullptr;
 }
 
-cmGeneratorFileSet const* cmGeneratorFileSets::GetFileSetForSource(
-  std::string const& config, std::string const& path) const
+std::unordered_set<cmGeneratorFileSet const*> const&
+cmGeneratorFileSets::GetAllFileSetsForSource(std::string const& config,
+                                             std::string const& path) const
 {
-  using Lookup = cm::FileSetMetadata::FileSetLookup;
-
   this->BuildInfoCache(config);
 
   auto const& info = this->Configs[config];
@@ -149,14 +148,28 @@ cmGeneratorFileSet const* cmGeneratorFileSets::GetFileSetForSource(
 
   // search in all the dependents
   auto const it2 = info.InterfaceFileSetCache.find(path);
-  if (it2 != info.InterfaceFileSetCache.end() &&
-      cm::FileSetMetadata::GetFileSetDescriptor(it2->second->GetType())
-          .value_or(cm::FileSetMetadata::FileSetDescriptor{ Lookup::Target })
-          .Lookup == Lookup::Dependencies) {
+  if (it2 != info.InterfaceFileSetCache.end()) {
     return it2->second;
   }
 
-  return nullptr;
+  static std::unordered_set<cmGeneratorFileSet const*> emptySet;
+  return emptySet;
+}
+std::unordered_set<cmGeneratorFileSet const*> const&
+cmGeneratorFileSets::GetAllFileSetsForSource(std::string const& config,
+                                             cmSourceFile const* sf) const
+{
+  return this->GetAllFileSetsForSource(config, sf->GetFullPath());
+}
+
+cmGeneratorFileSet const* cmGeneratorFileSets::GetFileSetForSource(
+  std::string const& config, std::string const& file) const
+{
+  auto const& fileSets = this->GetAllFileSetsForSource(config, file);
+  if (fileSets.empty()) {
+    return nullptr;
+  }
+  return *fileSets.begin();
 }
 cmGeneratorFileSet const* cmGeneratorFileSets::GetFileSetForSource(
   std::string const& config, cmSourceFile const* sf) const
@@ -358,10 +371,10 @@ std::string cmGeneratorFileSets::EvaluateInterfaceProperty(
 }
 
 namespace {
-void GetInterfaceFiles(cmGeneratorTarget const* target,
-                       cm::GenEx::Context const& context,
-                       std::unordered_set<cmGeneratorTarget const*>& targets,
-                       std::map<std::string, cmGeneratorFileSet const*>& cache)
+void GetInterfaceFiles(
+  cmGeneratorTarget const* target, cm::GenEx::Context const& context,
+  std::unordered_set<cmGeneratorTarget const*>& targets,
+  std::map<std::string, std::unordered_set<cmGeneratorFileSet const*>>& cache)
 {
   namespace Metadata = cm::FileSetMetadata;
 
@@ -375,7 +388,7 @@ void GetInterfaceFiles(cmGeneratorTarget const* target,
         for (auto const& it : files.first) {
           for (auto const& filename : it.second) {
             auto collapsedFile = cmSystemTools::CollapseFullPath(filename);
-            cache[collapsedFile] = fileSet;
+            cache[collapsedFile].insert(fileSet);
           }
         }
       }
@@ -413,7 +426,7 @@ void cmGeneratorFileSets::BuildInfoCache(std::string const& config) const
     for (auto const& it : files.first) {
       for (auto const& filename : it.second) {
         auto collapsedFile = cmSystemTools::CollapseFullPath(filename);
-        info.FileSetCache[collapsedFile] = fileSet;
+        info.FileSetCache[collapsedFile].insert(fileSet);
       }
     }
   }

Source/cmGeneratorFileSets.h

@@ -9,6 +9,7 @@
 #include <memory>
 #include <string>
 #include <unordered_map>
+#include <unordered_set>
 #include <vector>
 
 #include <cm/string_view>
@@ -53,6 +54,12 @@ public:
 
   cmGeneratorFileSet const* GetFileSet(std::string const& name) const;
 
+  std::unordered_set<cmGeneratorFileSet const*> const& GetAllFileSetsForSource(
+    std::string const& config, std::string const& file) const;
+  std::unordered_set<cmGeneratorFileSet const*> const& GetAllFileSetsForSource(
+    std::string const& config, cmSourceFile const* sf) const;
+
+  // returns the first FileSet of the set
   cmGeneratorFileSet const* GetFileSetForSource(std::string const& config,
                                                 std::string const& file) const;
   cmGeneratorFileSet const* GetFileSetForSource(std::string const& config,
@@ -102,8 +109,10 @@ private:
   struct InfoByConfig
   {
     bool BuiltCache = false;
-    std::map<std::string, cmGeneratorFileSet const*> FileSetCache;
-    std::map<std::string, cmGeneratorFileSet const*> InterfaceFileSetCache;
+    std::map<std::string, std::unordered_set<cmGeneratorFileSet const*>>
+      FileSetCache;
+    std::map<std::string, std::unordered_set<cmGeneratorFileSet const*>>
+      InterfaceFileSetCache;
   };
   mutable std::map<std::string, InfoByConfig> Configs;
 

Source/cmGeneratorTarget_Sources.cxx

@@ -6,6 +6,7 @@
 
 #include "cmConfigure.h"
 
+#include <algorithm>
 #include <cstddef>
 #include <functional>
 #include <map>
@@ -160,8 +161,22 @@ bool processSources(cmGeneratorTarget const* tgt, std::string const& config,
           usedSources += cmStrCat(" * ", src, '\n');
         }
       } else {
-        if (auto const* fileSet =
-              tgt->GetGeneratorFileSets()->GetFileSetForSource(config, src)) {
+        auto const& fileSets =
+          tgt->GetGeneratorFileSets()->GetAllFileSetsForSource(config, src);
+        if (fileSets.empty()) {
+          continue;
+        }
+        auto fileMustBeUnique = [&fileSets]() -> bool {
+          return std::none_of(
+            fileSets.begin(), fileSets.end(),
+            [](cmGeneratorFileSet const* fileSet) {
+              return cm::FileSetMetadata::GetAttributes(fileSet->GetType())
+                .contains(cm::FileSetMetadata::FileSetAttributes::
+                            FilesInMultipleFileSets);
+            });
+        };
+        if (fileMustBeUnique()) {
+          auto const* fileSet = *fileSets.begin();
           switch (tgt->GetPolicyStatusCMP0211()) {
             case cmPolicies::WARN:
               tgt->GetLocalGenerator()->IssueDiagnostic(

Tests/RunCMake/target_sources/CMP0211-Common.cmake

@@ -2,8 +2,8 @@
 enable_language(C)
 
 add_library(foo1 STATIC lib1.c)
-target_sources(foo1 PRIVATE FILE_SET h1 TYPE HEADERS FILES h1.h)
-target_sources(foo1 PRIVATE FILE_SET h2 TYPE HEADERS FILES h1.h)
+target_sources(foo1 PRIVATE FILE_SET s1 TYPE SOURCES FILES lib2.c)
+target_sources(foo1 PRIVATE FILE_SET s2 TYPE SOURCES FILES lib2.c)
 
-add_library(foo2 STATIC lib1.c h1.h)
-target_sources(foo2 PRIVATE FILE_SET h1 TYPE HEADERS FILES h1.h)
+add_library(foo2 STATIC lib1.c lib2.c)
+target_sources(foo2 PRIVATE FILE_SET s1 TYPE SOURCES FILES lib2.c)

Tests/RunCMake/target_sources/CMP0211-NEW-HEADERS.cmake

@@ -0,0 +1,13 @@
+
+cmake_policy(SET CMP0211 NEW)
+
+enable_language(C)
+
+# files in HEADERS file sets can also be specified in other file sets
+
+add_library(foo1 STATIC lib1.c)
+target_sources(foo1 PRIVATE FILE_SET s1 TYPE SOURCES FILES lib2.c h1.h)
+target_sources(foo1 PRIVATE FILE_SET h1 TYPE HEADERS FILES h1.h)
+
+add_library(foo2 STATIC lib1.c h1.h)
+target_sources(foo2 PRIVATE FILE_SET h1 TYPE HEADERS FILES h1.h)

Tests/RunCMake/target_sources/CMP0211-NEW-stderr.txt

@@ -1,14 +1,14 @@
 CMake Error in CMakeLists\.txt:
   In target "foo1" the file
 
-    .+/Tests/RunCMake/target_sources/h1\.h
+    .+/Tests/RunCMake/target_sources/lib2\.c
 
-  already belongs to file set "h2"\.
+  already belongs to file set "s[12]"\.
 
 
 CMake Error in CMakeLists\.txt:
   In target "foo2" the file
 
-    .+/Tests/RunCMake/target_sources/h1\.h
+    .+/Tests/RunCMake/target_sources/lib2\.c
 
-  already belongs to file set "h1"\.
+  already belongs to file set "s1"\.

Tests/RunCMake/target_sources/CMP0211-WARN-stderr.txt

@@ -5,9 +5,9 @@ CMake Warning \(author\) in CMakeLists\.txt:
 
   In target "foo1" the file
 
-    .+/Tests/RunCMake/target_sources/h1\.h
+    .+/Tests/RunCMake/target_sources/lib2\.c
 
-  already belongs to file set "h2"\.
+  already belongs to file set "s[12]"\.
 This warning is for project developers\.  Use -Wno-author to suppress it\.
 
 CMake Warning \(author\) in CMakeLists\.txt:
@@ -17,7 +17,7 @@ CMake Warning \(author\) in CMakeLists\.txt:
 
   In target "foo2" the file
 
-    .+/Tests/RunCMake/target_sources/h1\.h
+    .+/Tests/RunCMake/target_sources/lib2\.c
 
-  already belongs to file set "h1"\.
+  already belongs to file set "s1"\.
 This warning is for project developers\.  Use -Wno-author to suppress it\.

Tests/RunCMake/target_sources/RunCMakeTest.cmake

@@ -52,6 +52,7 @@ endif()
 run_cmake(CMP0211-OLD)
 run_cmake(CMP0211-NEW)
 run_cmake(CMP0211-WARN)
+run_cmake(CMP0211-NEW-HEADERS)
 
 set(RunCMake_TEST_NO_CLEAN 1)
 set(RunCMake_TEST_BINARY_DIR "${RunCMake_BINARY_DIR}/FileSetGeneratedDependency-build")