LINK_LIBRARIES: Evaluate separately for linking and usage requirements

We evaluate `LINK_LIBRARIES` and `INTERFACE_LINK_LIBRARIES` for two purposes:

* Constructing the link line.
* Collecting usage requirements.

We evaluate `INTERFACE_LINK_LIBRARIES` separately for each purpose in
order to support the `$<LINK_ONLY:...>` generator expression used to
express private link dependencies of a static library.  Previously we
only evaluated `LINK_LIBRARIES` for linking, and used that result for
collecting usage requirements too.  Therefore `$<LINK_ONLY:...>` does
not work in `LINK_LIBRARIES`.

With the introduction of `INTERFACE_LINK_LIBRARIES_DIRECT`, evaluation
of `LINK_LIBRARIES` now needs to distinguish these two cases in order to
honor link dependencies encountered through `$<LINK_ONLY:...>` without
also exposing other usage requirements through private dependencies of a
static library.  Revise internal infrastructure to distinguish the two
cases when evaluating `LINK_LIBRARIES`.  Make the information available
in code paths for `INTERFACE_LINK_LIBRARIES_DIRECT` and `LINK_ONLY`.
Defer actually using the information to later commits.

Issue: #22496

Source/cmComputeLinkDepends.cxx

@@ -677,8 +677,8 @@ void cmComputeLinkDepends::AddVarLinkEntries(int depender_index,
 void cmComputeLinkDepends::AddDirectLinkEntries()
 {
   // Add direct link dependencies in this configuration.
-  cmLinkImplementation const* impl =
-    this->Target->GetLinkImplementation(this->Config);
+  cmLinkImplementation const* impl = this->Target->GetLinkImplementation(
+    this->Config, cmGeneratorTarget::LinkInterfaceFor::Link);
   this->AddLinkEntries(-1, impl->Libraries);
   this->AddLinkObjects(impl->Objects);
 

Source/cmComputeTargetDepends.cxx

@@ -218,8 +218,8 @@ void cmComputeTargetDepends::CollectTargetDepends(int depender_index)
       emitted.insert(cmLinkItem(depender, false, cmListFileBacktrace()));
       emitted.insert(cmLinkItem(depender, true, cmListFileBacktrace()));
 
-      if (cmLinkImplementation const* impl =
-            depender->GetLinkImplementation(it)) {
+      if (cmLinkImplementation const* impl = depender->GetLinkImplementation(
+            it, cmGeneratorTarget::LinkInterfaceFor::Link)) {
         for (cmLinkImplItem const& lib : impl->Libraries) {
           // Don't emit the same library twice for this target.
           if (emitted.insert(lib).second) {

Source/cmExportBuildAndroidMKGenerator.cxx

@@ -168,7 +168,8 @@ void cmExportBuildAndroidMKGenerator::GenerateInterfaceProperties(
 
   // Tell the NDK build system if prebuilt static libraries use C++.
   if (target->GetType() == cmStateEnums::STATIC_LIBRARY) {
-    cmLinkImplementation const* li = target->GetLinkImplementation(config);
+    cmLinkImplementation const* li = target->GetLinkImplementation(
+      config, cmGeneratorTarget::LinkInterfaceFor::Link);
     if (cm::contains(li->Languages, "CXX")) {
       os << "LOCAL_HAS_CPP := true\n";
     }

Source/cmGeneratorExpressionNode.cxx

@@ -1415,7 +1415,8 @@ static std::string getLinkedTargetsContent(
 {
   std::string result;
   if (cmLinkImplementationLibraries const* impl =
-        target->GetLinkImplementationLibraries(context->Config)) {
+        target->GetLinkImplementationLibraries(
+          context->Config, cmGeneratorTarget::LinkInterfaceFor::Usage)) {
     for (cmLinkImplItem const& lib : impl->Libraries) {
       if (lib.Target) {
         // Pretend $<TARGET_PROPERTY:lib.Target,prop> appeared in our

Source/cmGeneratorTarget.cxx

@@ -752,6 +752,7 @@ void cmGeneratorTarget::ClearSourcesCache()
   this->Objects.clear();
   this->VisitedConfigsForObjects.clear();
   this->LinkImplMap.clear();
+  this->LinkImplUsageRequirementsOnlyMap.clear();
 }
 
 void cmGeneratorTarget::ClearLinkInterfaceCache()
@@ -1302,7 +1303,8 @@ bool cmGeneratorTarget::IsSystemIncludeDirectory(
                               &dagChecker, result, excludeImported, language);
     }
 
-    cmLinkImplementation const* impl = this->GetLinkImplementation(config);
+    cmLinkImplementation const* impl =
+      this->GetLinkImplementation(config, LinkInterfaceFor::Usage);
     if (impl != nullptr) {
       auto runtimeEntries = impl->LanguageRuntimeLibraries.find(language);
       if (runtimeEntries != impl->LanguageRuntimeLibraries.end()) {
@@ -1519,7 +1521,8 @@ void AddLangSpecificImplicitIncludeDirectories(
   const std::string& config, const std::string& propertyName,
   IncludeDirectoryFallBack mode, EvaluatedTargetPropertyEntries& entries)
 {
-  if (const auto* libraries = target->GetLinkImplementationLibraries(config)) {
+  if (const auto* libraries = target->GetLinkImplementationLibraries(
+        config, LinkInterfaceFor::Usage)) {
     cmGeneratorExpressionDAGChecker dag{ target->GetBacktrace(), target,
                                          propertyName, nullptr, nullptr };
 
@@ -1609,7 +1612,7 @@ void AddInterfaceEntries(
 {
   if (searchRuntime == IncludeRuntimeInterface::Yes) {
     if (cmLinkImplementation const* impl =
-          headTarget->GetLinkImplementation(config)) {
+          headTarget->GetLinkImplementation(config, interfaceFor)) {
       entries.HadContextSensitiveCondition =
         impl->HadContextSensitiveCondition;
 
@@ -1623,7 +1626,7 @@ void AddInterfaceEntries(
     }
   } else {
     if (cmLinkImplementationLibraries const* impl =
-          headTarget->GetLinkImplementationLibraries(config)) {
+          headTarget->GetLinkImplementationLibraries(config, interfaceFor)) {
       entries.HadContextSensitiveCondition =
         impl->HadContextSensitiveCondition;
       addInterfaceEntry(headTarget, config, prop, lang, dagChecker, entries,
@@ -1638,7 +1641,8 @@ void AddObjectEntries(cmGeneratorTarget const* headTarget,
                       EvaluatedTargetPropertyEntries& entries)
 {
   if (cmLinkImplementationLibraries const* impl =
-        headTarget->GetLinkImplementationLibraries(config)) {
+        headTarget->GetLinkImplementationLibraries(config,
+                                                   LinkInterfaceFor::Usage)) {
     entries.HadContextSensitiveCondition = impl->HadContextSensitiveCondition;
     for (cmLinkImplItem const& lib : impl->Libraries) {
       if (lib.Target &&
@@ -2821,7 +2825,7 @@ bool cmGeneratorTarget::ComputeLinkClosure(const std::string& config,
   // Get languages built in this target.
   std::unordered_set<std::string> languages;
   cmLinkImplementation const* impl =
-    this->GetLinkImplementation(config, secondPass);
+    this->GetLinkImplementation(config, LinkInterfaceFor::Link, secondPass);
   assert(impl);
   languages.insert(impl->Languages.cbegin(), impl->Languages.cend());
 
@@ -3089,7 +3093,7 @@ cmGeneratorTarget::GetLinkImplementationClosure(
     std::set<cmGeneratorTarget const*> emitted;
 
     cmLinkImplementationLibraries const* impl =
-      this->GetLinkImplementationLibraries(config);
+      this->GetLinkImplementationLibraries(config, LinkInterfaceFor::Usage);
     assert(impl);
 
     for (cmLinkImplItem const& lib : impl->Libraries) {
@@ -3831,7 +3835,8 @@ std::vector<BT<std::string>> cmGeneratorTarget::GetIncludeDirectories(
 
   if (this->Makefile->IsOn("APPLE")) {
     if (cmLinkImplementationLibraries const* impl =
-          this->GetLinkImplementationLibraries(config)) {
+          this->GetLinkImplementationLibraries(config,
+                                               LinkInterfaceFor::Usage)) {
       for (cmLinkImplItem const& lib : impl->Libraries) {
         std::string libDir = cmSystemTools::CollapseFullPath(
           lib.AsStr(), this->Makefile->GetHomeOutputDirectory());
@@ -6845,8 +6850,8 @@ void cmGeneratorTarget::ComputeLinkInterface(
         emitted.insert(lib);
       }
       if (this->GetType() != cmStateEnums::INTERFACE_LIBRARY) {
-        cmLinkImplementation const* impl =
-          this->GetLinkImplementation(config, secondPass);
+        cmLinkImplementation const* impl = this->GetLinkImplementation(
+          config, LinkInterfaceFor::Link, secondPass);
         for (cmLinkImplItem const& lib : impl->Libraries) {
           if (emitted.insert(lib).second) {
             if (lib.Target) {
@@ -6868,15 +6873,16 @@ void cmGeneratorTarget::ComputeLinkInterface(
              this->GetPolicyStatusCMP0022() == cmPolicies::OLD) {
     // The link implementation is the default link interface.
     cmLinkImplementationLibraries const* impl =
-      this->GetLinkImplementationLibrariesInternal(config, headTarget);
+      this->GetLinkImplementationLibrariesInternal(config, headTarget,
+                                                   LinkInterfaceFor::Link);
     iface.ImplementationIsInterface = true;
     iface.WrongConfigLibraries = impl->WrongConfigLibraries;
   }
 
   if (this->LinkLanguagePropagatesToDependents()) {
     // Targets using this archive need its language runtime libraries.
-    if (cmLinkImplementation const* impl =
-          this->GetLinkImplementation(config, secondPass)) {
+    if (cmLinkImplementation const* impl = this->GetLinkImplementation(
+          config, LinkInterfaceFor::Link, secondPass)) {
       iface.Languages = impl->Languages;
     }
   }
@@ -7307,7 +7313,8 @@ void cmGeneratorTarget::ComputeLinkInterfaceLibraries(
 
   // The link implementation is the default link interface.
   if (cmLinkImplementationLibraries const* impl =
-        this->GetLinkImplementationLibrariesInternal(config, headTarget)) {
+        this->GetLinkImplementationLibrariesInternal(config, headTarget,
+                                                     interfaceFor)) {
     iface.Libraries.insert(iface.Libraries.end(), impl->Libraries.begin(),
                            impl->Libraries.end());
     if (this->GetPolicyStatusCMP0022() == cmPolicies::WARN &&
@@ -7686,27 +7693,30 @@ cmGeneratorTarget::GetHeadToLinkInterfaceUsageRequirementsMap(
 }
 
 const cmLinkImplementation* cmGeneratorTarget::GetLinkImplementation(
-  const std::string& config) const
+  const std::string& config, LinkInterfaceFor implFor) const
 {
-  return this->GetLinkImplementation(config, false);
+  return this->GetLinkImplementation(config, implFor, false);
 }
 
 const cmLinkImplementation* cmGeneratorTarget::GetLinkImplementation(
-  const std::string& config, bool secondPass) const
+  const std::string& config, LinkInterfaceFor implFor, bool secondPass) const
 {
   // There is no link implementation for targets that cannot compile sources.
   if (!this->CanCompileSources()) {
     return nullptr;
   }
 
-  cmOptionalLinkImplementation& impl =
-    this->LinkImplMap[cmSystemTools::UpperCase(config)][this];
+  HeadToLinkImplementationMap& hm =
+    (implFor == LinkInterfaceFor::Usage
+       ? this->GetHeadToLinkImplementationUsageRequirementsMap(config)
+       : this->GetHeadToLinkImplementationMap(config));
+  cmOptionalLinkImplementation& impl = hm[this];
   if (secondPass) {
     impl = cmOptionalLinkImplementation();
   }
   if (!impl.LibrariesDone) {
     impl.LibrariesDone = true;
-    this->ComputeLinkImplementationLibraries(config, impl, this);
+    this->ComputeLinkImplementationLibraries(config, impl, this, implFor);
   }
   if (!impl.LanguagesDone) {
     impl.LanguagesDone = true;
@@ -7716,6 +7726,21 @@ const cmLinkImplementation* cmGeneratorTarget::GetLinkImplementation(
   return &impl;
 }
 
+cmGeneratorTarget::HeadToLinkImplementationMap&
+cmGeneratorTarget::GetHeadToLinkImplementationMap(
+  std::string const& config) const
+{
+  return this->LinkImplMap[cmSystemTools::UpperCase(config)];
+}
+
+cmGeneratorTarget::HeadToLinkImplementationMap&
+cmGeneratorTarget::GetHeadToLinkImplementationUsageRequirementsMap(
+  std::string const& config) const
+{
+  return this
+    ->LinkImplUsageRequirementsOnlyMap[cmSystemTools::UpperCase(config)];
+}
+
 bool cmGeneratorTarget::GetConfigCommonSourceFilesForXcode(
   std::vector<cmSourceFile*>& files) const
 {
@@ -7956,7 +7981,7 @@ bool cmGeneratorTarget::HaveBuildTreeRPATH(const std::string& config) const
     return true;
   }
   if (cmLinkImplementationLibraries const* impl =
-        this->GetLinkImplementationLibraries(config)) {
+        this->GetLinkImplementationLibraries(config, LinkInterfaceFor::Link)) {
     return !impl->Libraries.empty();
   }
   return false;
@@ -7964,14 +7989,15 @@ bool cmGeneratorTarget::HaveBuildTreeRPATH(const std::string& config) const
 
 cmLinkImplementationLibraries const*
 cmGeneratorTarget::GetLinkImplementationLibraries(
-  const std::string& config) const
+  const std::string& config, LinkInterfaceFor implFor) const
 {
-  return this->GetLinkImplementationLibrariesInternal(config, this);
+  return this->GetLinkImplementationLibrariesInternal(config, this, implFor);
 }
 
 cmLinkImplementationLibraries const*
 cmGeneratorTarget::GetLinkImplementationLibrariesInternal(
-  const std::string& config, cmGeneratorTarget const* head) const
+  const std::string& config, cmGeneratorTarget const* head,
+  LinkInterfaceFor implFor) const
 {
   // There is no link implementation for targets that cannot compile sources.
   if (!this->CanCompileSources()) {
@@ -7980,7 +8006,9 @@ cmGeneratorTarget::GetLinkImplementationLibrariesInternal(
 
   // Populate the link implementation libraries for this configuration.
   HeadToLinkImplementationMap& hm =
-    this->LinkImplMap[cmSystemTools::UpperCase(config)];
+    (implFor == LinkInterfaceFor::Usage
+       ? this->GetHeadToLinkImplementationUsageRequirementsMap(config)
+       : this->GetHeadToLinkImplementationMap(config));
 
   // If the link implementation does not depend on the head target
   // then re-use the one from the head we computed first.
@@ -7991,7 +8019,7 @@ cmGeneratorTarget::GetLinkImplementationLibrariesInternal(
   cmOptionalLinkImplementation& impl = hm[head];
   if (!impl.LibrariesDone) {
     impl.LibrariesDone = true;
-    this->ComputeLinkImplementationLibraries(config, impl, head);
+    this->ComputeLinkImplementationLibraries(config, impl, head, implFor);
   }
   return &impl;
 }
@@ -8110,8 +8138,9 @@ void ComputeLinkImplTransitive(cmGeneratorTarget const* self,
 
 void cmGeneratorTarget::ComputeLinkImplementationLibraries(
   const std::string& config, cmOptionalLinkImplementation& impl,
-  cmGeneratorTarget const* head) const
+  cmGeneratorTarget const* head, LinkInterfaceFor implFor) const
 {
+  static_cast<void>(implFor);
   cmLocalGenerator const* lg = this->LocalGenerator;
   cmMakefile const* mf = lg->GetMakefile();
   cmBTStringRange entryRange = this->Target->GetLinkImplementationEntries();

Source/cmGeneratorTarget.h

@@ -399,17 +399,18 @@ public:
   LinkClosure const* GetLinkClosure(const std::string& config) const;
 
   cmLinkImplementation const* GetLinkImplementation(
-    const std::string& config) const;
+    const std::string& config, LinkInterfaceFor implFor) const;
 
   void ComputeLinkImplementationLanguages(
     const std::string& config, cmOptionalLinkImplementation& impl) const;
 
   cmLinkImplementationLibraries const* GetLinkImplementationLibraries(
-    const std::string& config) const;
+    const std::string& config, LinkInterfaceFor implFor) const;
 
   void ComputeLinkImplementationLibraries(const std::string& config,
                                           cmOptionalLinkImplementation& impl,
-                                          const cmGeneratorTarget* head) const;
+                                          const cmGeneratorTarget* head,
+                                          LinkInterfaceFor implFor) const;
 
   struct TargetOrString
   {
@@ -984,6 +985,7 @@ private:
                             const cmGeneratorTarget* head,
                             bool secondPass) const;
   cmLinkImplementation const* GetLinkImplementation(const std::string& config,
+                                                    LinkInterfaceFor implFor,
                                                     bool secondPass) const;
 
   enum class LinkItemRole
@@ -1108,9 +1110,16 @@ private:
   };
   using LinkImplMapType = std::map<std::string, HeadToLinkImplementationMap>;
   mutable LinkImplMapType LinkImplMap;
+  mutable LinkImplMapType LinkImplUsageRequirementsOnlyMap;
+
+  HeadToLinkImplementationMap& GetHeadToLinkImplementationMap(
+    std::string const& config) const;
+  HeadToLinkImplementationMap& GetHeadToLinkImplementationUsageRequirementsMap(
+    std::string const& config) const;
 
   cmLinkImplementationLibraries const* GetLinkImplementationLibrariesInternal(
-    const std::string& config, const cmGeneratorTarget* head) const;
+    const std::string& config, const cmGeneratorTarget* head,
+    LinkInterfaceFor implFor) const;
   bool ComputeOutputDir(const std::string& config,
                         cmStateEnums::ArtifactType artifact,
                         std::string& out) const;

Source/cmGlobalXCodeGenerator.cxx

@@ -1627,7 +1627,10 @@ void cmGlobalXCodeGenerator::ForceLinkerLanguage(cmGeneratorTarget* gtgt)
 
   // If the language is compiled as a source trust Xcode to link with it.
   for (auto const& Language :
-       gtgt->GetLinkImplementation("NOCONFIG")->Languages) {
+       gtgt
+         ->GetLinkImplementation("NOCONFIG",
+                                 cmGeneratorTarget::LinkInterfaceFor::Link)
+         ->Languages) {
     if (Language == llang) {
       return;
     }

Source/cmLinkItemGraphVisitor.cxx

@@ -98,8 +98,8 @@ void cmLinkItemGraphVisitor::GetDependencies(cmGeneratorTarget const& target,
                                              std::string const& config,
                                              DependencyMap& dependencies)
 {
-  const auto* implementationLibraries =
-    target.GetLinkImplementationLibraries(config);
+  const auto* implementationLibraries = target.GetLinkImplementationLibraries(
+    config, cmGeneratorTarget::LinkInterfaceFor::Link);
   if (implementationLibraries != nullptr) {
     for (auto const& lib : implementationLibraries->Libraries) {
       auto const& name = lib.AsStr();

Source/cmLinkLineDeviceComputer.cxx

@@ -136,7 +136,8 @@ void cmLinkLineDeviceComputer::ComputeLinkLibraries(
       linkLib.Value += " ";
 
       const cmLinkImplementation* linkImpl =
-        cli.GetTarget()->GetLinkImplementation(cli.GetConfig());
+        cli.GetTarget()->GetLinkImplementation(
+          cli.GetConfig(), cmGeneratorTarget::LinkInterfaceFor::Link);
 
       for (const cmLinkImplItem& iter : linkImpl->Libraries) {
         if (iter.Target != nullptr &&

Source/cmQtAutoGenInitializer.cxx

@@ -114,7 +114,8 @@ bool StaticLibraryCycle(cmGeneratorTarget const* targetOrigin,
       }
       // Collect all static_library dependencies from the test target
       cmLinkImplementationLibraries const* libs =
-        testTarget->GetLinkImplementationLibraries(config);
+        testTarget->GetLinkImplementationLibraries(
+          config, cmGeneratorTarget::LinkInterfaceFor::Link);
       if (libs) {
         for (cmLinkItem const& item : libs->Libraries) {
           cmGeneratorTarget const* depTarget = item.Target;
@@ -1266,7 +1267,8 @@ bool cmQtAutoGenInitializer::InitAutogenTarget()
       std::map<cmGeneratorTarget const*, std::size_t> commonTargets;
       for (std::string const& config : this->ConfigsList) {
         cmLinkImplementationLibraries const* libs =
-          this->GenTarget->GetLinkImplementationLibraries(config);
+          this->GenTarget->GetLinkImplementationLibraries(
+            config, cmGeneratorTarget::LinkInterfaceFor::Link);
         if (libs) {
           for (cmLinkItem const& item : libs->Libraries) {
             cmGeneratorTarget const* libTarget = item.Target;