FASTBuild: fix iface targets with private sources

When `PRIVATE` sources are added to an `INTERFACE`
target A and A is a dependency of B - the target A
ends up in "direct dependencies" of the B targets
and it messes up the generated `fbuild.bff` file.

Fixes: #27644

Source/cmFastbuildUtilityTargetGenerator.cxx

@@ -15,6 +15,7 @@
 #include "cmGlobalFastbuildGenerator.h"
 #include "cmListFileCache.h"
 #include "cmMakefile.h"
+#include "cmSourceFile.h"
 #include "cmStateTypes.h"
 #include "cmStringAlgorithms.h"
 #include "cmTarget.h"
@@ -28,6 +29,9 @@ cmFastbuildUtilityTargetGenerator::cmFastbuildUtilityTargetGenerator(
 
 void cmFastbuildUtilityTargetGenerator::Generate()
 {
+  if (!this->GetGeneratorTarget()->IsInBuildSystem()) {
+    return;
+  }
   std::string targetName = GeneratorTarget->GetName();
 
   if (this->GeneratorTarget->GetType() == cmStateEnums::GLOBAL_TARGET) {
@@ -121,14 +125,27 @@ void cmFastbuildUtilityTargetGenerator::Generate()
     }
     this->GetGlobalGenerator()->AddTarget(std::move(exec));
   }
+  // The target has to be in the build system, but has no custom commands
+  // associated with it.
   if (fastbuildTarget.PreBuildDependencies.empty()) {
-    if (fastbuildTarget.ExcludeFromAll) {
-      return;
+    std::vector<cmSourceFile*> sources;
+    this->GetGeneratorTarget()->GetSourceFiles(sources, this->Config);
+    if (sources.empty()) {
+      FastbuildTargetDep dep{ FASTBUILD_NOOP_FILE_NAME };
+      dep.Type = FastbuildTargetDepType::ORDER_ONLY;
+      fastbuildTarget.PreBuildDependencies.emplace(std::move(dep));
+    } else {
+      for (cmSourceFile const* source : sources) {
+        FastbuildTargetDep dep{
+          this->GetGlobalGenerator()->ConvertToFastbuildPath(
+            source->GetFullPath())
+        };
+        dep.Type = FastbuildTargetDepType::ARTIFACT;
+        fastbuildTarget.PreBuildDependencies.emplace(std::move(dep));
+      }
     }
-    FastbuildTargetDep dep{ FASTBUILD_NOOP_FILE_NAME };
-    dep.Type = FastbuildTargetDepType::ORDER_ONLY;
-    fastbuildTarget.PreBuildDependencies.emplace(std::move(dep));
   }
+
   fastbuildTarget.Hidden = false;
   this->AdditionalCleanFiles();
 

Source/cmGlobalFastbuildGenerator.h

@@ -98,6 +98,8 @@ enum class FastbuildTargetDepType
   REGULAR,
   // Utility target dep.
   UTIL,
+  // A physical file on disk.
+  ARTIFACT,
 };
 struct FastbuildTargetDep
 {
@@ -137,6 +139,7 @@ struct FastbuildTargetBase
   std::set<FastbuildTargetDep> PreBuildDependencies;
   bool Hidden = true;
   FastbuildTargetType Type;
+  bool ExcludeFromAll = false;
   explicit FastbuildTargetBase(FastbuildTargetType TargetType)
     : Type(TargetType)
   {
@@ -146,7 +149,6 @@ using FastbuildTargetPtrT = std::unique_ptr<FastbuildTargetBase>;
 
 struct FastbuildAliasNode : public FastbuildTargetBase
 {
-  bool ExcludeFromAll = false;
   FastbuildAliasNode()
     : FastbuildTargetBase(FastbuildTargetType::ALIAS)
   {
@@ -169,7 +171,6 @@ struct FastbuildExecNode : public FastbuildTargetBase
   FastbuildAliasNode OutputsAlias;
   FastbuildAliasNode ByproductsAlias;
   std::string ConcurrencyGroupName;
-  bool ExcludeFromAll = false;
   FastbuildExecNode()
     : FastbuildTargetBase(FastbuildTargetType::EXEC)
   {
@@ -331,7 +332,6 @@ struct FastbuildTarget : public FastbuildTargetBase
   FastbuildExecNodes PreLinkExecNodes;
   FastbuildExecNodes PostBuildExecNodes;
   bool IsGlobal = false;
-  bool ExcludeFromAll = false;
   bool AllowDistribution = true;
   FastbuildTarget()
     : FastbuildTargetBase(FastbuildTargetType::LINK)

Tests/RunCMake/FASTBuild/InterfaceWithPrivateSource-check.cmake

@@ -0,0 +1,4 @@
+# We just check that generation succeeds,
+# so any regex is fine.
+set(REGEX_TO_MATCH ".*")
+include(${RunCMake_SOURCE_DIR}/check.cmake)

Tests/RunCMake/FASTBuild/InterfaceWithPrivateSource.cmake

@@ -0,0 +1,6 @@
+add_library(iface_lib INTERFACE EXCLUDE_FROM_ALL)
+target_sources(iface_lib PRIVATE header.hpp)
+
+add_library(static_lib STATIC main.cpp)
+
+target_link_libraries(static_lib PRIVATE iface_lib)

Tests/RunCMake/FASTBuild/RunCMakeTest.cmake

@@ -12,3 +12,4 @@ run_cmake(DisableCaching)
 run_cmake(DisableDistribution)
 run_cmake(SetCompilerProps)
 run_cmake(ImportedObjectLib)
+run_cmake(InterfaceWithPrivateSource)