LINK_WHAT_YOU_USE feature: externalize configuration

Currently, this feature is only supported on ELF platforms. So, the property
LINK_WHAT_YOU_USE will be ignored for other plateforms.
Moreover, flags and commands are now controled by CMake variables.

Fixes: #20174

Help/manual/cmake-variables.7.rst

@@ -427,6 +427,7 @@ Variables that Control the Build
    /variable/CMAKE_LANG_LINKER_LAUNCHER
    /variable/CMAKE_LANG_LINK_LIBRARY_FILE_FLAG
    /variable/CMAKE_LANG_LINK_LIBRARY_FLAG
+   /variable/CMAKE_LANG_LINK_WHAT_YOU_USE_FLAG
    /variable/CMAKE_LANG_VISIBILITY_PRESET
    /variable/CMAKE_LIBRARY_OUTPUT_DIRECTORY
    /variable/CMAKE_LIBRARY_OUTPUT_DIRECTORY_CONFIG
@@ -437,6 +438,7 @@ Variables that Control the Build
    /variable/CMAKE_LINK_LIBRARY_FILE_FLAG
    /variable/CMAKE_LINK_LIBRARY_FLAG
    /variable/CMAKE_LINK_WHAT_YOU_USE
+   /variable/CMAKE_LINK_WHAT_YOU_USE_CHECK
    /variable/CMAKE_MACOSX_BUNDLE
    /variable/CMAKE_MACOSX_RPATH
    /variable/CMAKE_MAP_IMPORTED_CONFIG_CONFIG

Help/prop_tgt/LINK_WHAT_YOU_USE.rst

@@ -1,16 +1,22 @@
 LINK_WHAT_YOU_USE
----------------------------
+-----------------
 
 .. versionadded:: 3.7
 
-This is a boolean option that when set to ``TRUE`` will automatically run
-``ldd -r -u`` on the target after it is linked. In addition, the linker flag
-``-Wl,--no-as-needed`` will be passed to the target with the link command so
-that all libraries specified on the command line will be linked into the
-target. This will result in the link producing a list of libraries that
-provide no symbols used by this target but are being linked to it.
-This is only applicable to executable and shared library targets and
-will only work when ld and ldd accept the flags used.
+This is a boolean option that, when set to ``TRUE``, will automatically run
+contents of variable :variable:`CMAKE_LINK_WHAT_YOU_USE_CHECK` on the target
+after it is linked. In addition, the linker flag specified by variable
+:variable:`CMAKE_<LANG>_LINK_WHAT_YOU_USE_FLAG`  will be passed to the target
+with the link command so that all libraries specified on the command line will
+be linked into the target. This will result in the link producing a list of
+libraries that provide no symbols used by this target but are being linked to
+it.
+
+.. note::
+
+  For now, it is only supported for ``ELF`` platforms and is only applicable to
+  executable and shared or module library targets. This property will be
+  ignored for any other targets and configurations.
 
 This property is initialized by the value of
 the :variable:`CMAKE_LINK_WHAT_YOU_USE` variable if it is set

Help/release/dev/LINK_WHAT_USE_USE-configuration.rst

@@ -0,0 +1,5 @@
+LINK_WHAT_YOU_USE-configuration
+-------------------------------
+
+* Configuration for :prop_tgt:`LINK_WHAT_YOU_USE` feature is now controlled by
+  ``CMake`` variables and only active for ``ELF`` platforms.

Help/variable/CMAKE_LANG_LINK_WHAT_YOU_USE_FLAG.rst

@@ -0,0 +1,9 @@
+CMAKE_<LANG>_LINK_WHAT_YOU_USE_FLAG
+-----------------------------------
+
+.. versionadded:: 3.22
+
+Linker flag to be used to configure linker so that all specified libraries on
+the command line will be linked into the target.
+
+See also variable :variable:`CMAKE_LINK_WHAT_YOU_USE_CHECK`.

Help/variable/CMAKE_LINK_WHAT_YOU_USE.rst

@@ -1,5 +1,5 @@
 CMAKE_LINK_WHAT_YOU_USE
----------------------------------
+-----------------------
 
 .. versionadded:: 3.7
 

Help/variable/CMAKE_LINK_WHAT_YOU_USE_CHECK.rst

@@ -0,0 +1,10 @@
+CMAKE_LINK_WHAT_YOU_USE_CHECK
+-----------------------------
+
+.. versionadded:: 3.22
+
+Defines the command executed after the link step to check libraries usage.
+This check is currently only defined on ``ELF`` platforms with value
+``ldd -u -r``.
+
+See also :variable:`CMAKE_<LANG>_LINK_WHAT_YOU_USE_FLAG` variables.

Modules/CMakeCInformation.cmake

@@ -91,6 +91,14 @@ if(CMAKE_USER_MAKE_RULES_OVERRIDE_C)
   set(CMAKE_USER_MAKE_RULES_OVERRIDE_C "${_override}")
 endif()
 
+if(CMAKE_EXECUTABLE_FORMAT STREQUAL "ELF")
+  if(NOT DEFINED CMAKE_C_LINK_WHAT_YOU_USE_FLAG)
+    set(CMAKE_C_LINK_WHAT_YOU_USE_FLAG "LINKER:--no-as-needed")
+  endif()
+  if(NOT DEFINED CMAKE_LINK_WHAT_YOU_USE_CHECK)
+    set(CMAKE_LINK_WHAT_YOU_USE_CHECK ldd -u -r)
+  endif()
+endif()
 
 # for most systems a module is the same as a shared library
 # so unless the variable CMAKE_MODULE_EXISTS is set just
@@ -196,5 +204,3 @@ if(NOT CMAKE_EXECUTABLE_RPATH_LINK_C_FLAG)
 endif()
 
 set(CMAKE_C_INFORMATION_LOADED 1)
-
-

Modules/CMakeCUDAInformation.cmake

@@ -100,6 +100,15 @@ if(NOT CMAKE_MODULE_EXISTS)
   set(CMAKE_SHARED_MODULE_CREATE_CUDA_FLAGS ${CMAKE_SHARED_LIBRARY_CREATE_CUDA_FLAGS})
 endif()
 
+if(CMAKE_EXECUTABLE_FORMAT STREQUAL "ELF")
+  if(NOT DEFINED CMAKE_CUDA_LINK_WHAT_YOU_USE_FLAG)
+    set(CMAKE_CUDA_LINK_WHAT_YOU_USE_FLAG "LINKER:--no-as-needed")
+  endif()
+  if(NOT DEFINED CMAKE_LINK_WHAT_YOU_USE_CHECK)
+    set(CMAKE_LINK_WHAT_YOU_USE_CHECK ldd -u -r)
+  endif()
+endif()
+
 # add the flags to the cache based
 # on the initial values computed in the platform/*.cmake files
 # use _INIT variables so that this only happens the first time

Modules/CMakeCXXInformation.cmake

@@ -193,6 +193,15 @@ foreach(type SHARED_LIBRARY SHARED_MODULE EXE)
   endif()
 endforeach()
 
+if(CMAKE_EXECUTABLE_FORMAT STREQUAL "ELF")
+  if(NOT DEFINED CMAKE_CXX_LINK_WHAT_YOU_USE_FLAG)
+    set(CMAKE_CXX_LINK_WHAT_YOU_USE_FLAG "LINKER:--no-as-needed")
+  endif()
+  if(NOT DEFINED CMAKE_LINK_WHAT_YOU_USE_CHECK)
+    set(CMAKE_LINK_WHAT_YOU_USE_CHECK ldd -u -r)
+  endif()
+endif()
+
 # add the flags to the cache based
 # on the initial values computed in the platform/*.cmake files
 # use _INIT variables so that this only happens the first time

Modules/CMakeFortranInformation.cmake

@@ -157,6 +157,15 @@ if(NOT CMAKE_INCLUDE_FLAG_Fortran)
   set(CMAKE_INCLUDE_FLAG_Fortran ${CMAKE_INCLUDE_FLAG_C})
 endif()
 
+if(CMAKE_EXECUTABLE_FORMAT STREQUAL "ELF")
+  if(NOT DEFINED CMAKE_Fortran_LINK_WHAT_YOU_USE_FLAG)
+    set(CMAKE_Fortran_LINK_WHAT_YOU_USE_FLAG "LINKER:--no-as-needed")
+  endif()
+  if(NOT DEFINED CMAKE_LINK_WHAT_YOU_USE_CHECK)
+    set(CMAKE_LINK_WHAT_YOU_USE_CHECK ldd -u -r)
+  endif()
+endif()
+
 set(CMAKE_VERBOSE_MAKEFILE FALSE CACHE BOOL "If this value is on, makefiles will be generated without the .SILENT directive, and all commands will be echoed to the console during the make.  This is useful for debugging only. With Visual Studio IDE projects all commands are done without /nologo.")
 
 set(CMAKE_Fortran_FLAGS_INIT "$ENV{FFLAGS} ${CMAKE_Fortran_FLAGS_INIT}")

Modules/CMakeHIPInformation.cmake

@@ -68,6 +68,15 @@ if(NOT CMAKE_MODULE_EXISTS)
   set(CMAKE_SHARED_MODULE_CREATE_HIP_FLAGS ${CMAKE_SHARED_LIBRARY_CREATE_HIP_FLAGS})
 endif()
 
+if(CMAKE_EXECUTABLE_FORMAT STREQUAL "ELF")
+  if(NOT DEFINED CMAKE_HIP_LINK_WHAT_YOU_USE_FLAG)
+    set(CMAKE_HIP_LINK_WHAT_YOU_USE_FLAG "LINKER:--no-as-needed")
+  endif()
+  if(NOT DEFINED CMAKE_LINK_WHAT_YOU_USE_CHECK)
+    set(CMAKE_LINK_WHAT_YOU_USE_CHECK ldd -u -r)
+  endif()
+endif()
+
 # add the flags to the cache based
 # on the initial values computed in the platform/*.cmake files
 # use _INIT variables so that this only happens the first time

Modules/CMakeOBJCInformation.cmake

@@ -91,6 +91,15 @@ if(CMAKE_USER_MAKE_RULES_OVERRIDE_OBJC)
   set(CMAKE_USER_MAKE_RULES_OVERRIDE_OBJC "${_override}")
 endif()
 
+if(CMAKE_EXECUTABLE_FORMAT STREQUAL "ELF")
+  if(NOT DEFINED CMAKE_OBJC_LINK_WHAT_YOU_USE_FLAG)
+    set(CMAKE_OBJC_LINK_WHAT_YOU_USE_FLAG "LINKER:--no-as-needed")
+  endif()
+  if(NOT DEFINED CMAKE_LINK_WHAT_YOU_USE_CHECK)
+    set(CMAKE_LINK_WHAT_YOU_USE_CHECK ldd -u -r)
+  endif()
+endif()
+
 
 # for most systems a module is the same as a shared library
 # so unless the variable CMAKE_MODULE_EXISTS is set just

Modules/CMakeOBJCXXInformation.cmake

@@ -189,6 +189,15 @@ foreach(type SHARED_LIBRARY SHARED_MODULE EXE)
   endif()
 endforeach()
 
+if(CMAKE_EXECUTABLE_FORMAT STREQUAL "ELF")
+  if(NOT DEFINED CMAKE_OBJCXX_LINK_WHAT_YOU_USE_FLAG)
+    set(CMAKE_OBJCXX_LINK_WHAT_YOU_USE_FLAG "LINKER:--no-as-needed")
+  endif()
+  if(NOT DEFINED CMAKE_LINK_WHAT_YOU_USE_CHECK)
+    set(CMAKE_LINK_WHAT_YOU_USE_CHECK ldd -u -r)
+  endif()
+endif()
+
 # add the flags to the cache based
 # on the initial values computed in the platform/*.cmake files
 # use _INIT variables so that this only happens the first time

Modules/CMakeSwiftInformation.cmake

@@ -70,6 +70,15 @@ set(CMAKE_Swift_FLAGS_RELEASE_INIT "-O")
 set(CMAKE_Swift_FLAGS_RELWITHDEBINFO_INIT "-O -g")
 set(CMAKE_Swift_FLAGS_MINSIZEREL_INIT "-Osize")
 
+if(CMAKE_EXECUTABLE_FORMAT STREQUAL "ELF")
+  if(NOT DEFINED CMAKE_Swift_LINK_WHAT_YOU_USE_FLAG)
+    set(CMAKE_Swift_LINK_WHAT_YOU_USE_FLAG "LINKER:--no-as-needed")
+  endif()
+  if(NOT DEFINED CMAKE_LINK_WHAT_YOU_USE_CHECK)
+    set(CMAKE_LINK_WHAT_YOU_USE_CHECK ldd -u -r)
+  endif()
+endif()
+
 cmake_initialize_per_config_variable(CMAKE_Swift_FLAGS "Swift Compiler Flags")
 
 # NOTE(compnerd) we do not have an object compile rule since we build the objects as part of the link step

Source/cmCommonTargetGenerator.h

@@ -40,6 +40,7 @@ protected:
   cmLocalCommonGenerator* LocalCommonGenerator;
   cmGlobalCommonGenerator* GlobalCommonGenerator;
   std::vector<std::string> ConfigNames;
+  bool UseLWYU = false;
 
   void AppendFortranFormatFlags(std::string& flags,
                                 cmSourceFile const& source);

Source/cmLocalGenerator.cxx

@@ -3047,6 +3047,30 @@ void cmLocalGenerator::AppendPositionIndependentLinkerFlags(
   }
 }
 
+bool cmLocalGenerator::AppendLWYUFlags(std::string& flags,
+                                       const cmGeneratorTarget* target,
+                                       const std::string& lang)
+{
+  auto useLWYU = target->GetPropertyAsBool("LINK_WHAT_YOU_USE") &&
+    (target->GetType() == cmStateEnums::TargetType::EXECUTABLE ||
+     target->GetType() == cmStateEnums::TargetType::SHARED_LIBRARY ||
+     target->GetType() == cmStateEnums::TargetType::MODULE_LIBRARY);
+
+  if (useLWYU) {
+    const auto& lwyuFlag = this->GetMakefile()->GetSafeDefinition(
+      cmStrCat("CMAKE_", lang, "_LINK_WHAT_YOU_USE_FLAG"));
+    useLWYU = !lwyuFlag.empty();
+
+    if (useLWYU) {
+      std::vector<BT<std::string>> lwyuOpts;
+      lwyuOpts.emplace_back(lwyuFlag);
+      this->AppendFlags(flags, target->ResolveLinkerWrapper(lwyuOpts, lang));
+    }
+  }
+
+  return useLWYU;
+}
+
 void cmLocalGenerator::AppendCompileOptions(std::string& options,
                                             std::string const& options_list,
                                             const char* regex) const

Source/cmLocalGenerator.h

@@ -171,6 +171,8 @@ public:
                                             cmGeneratorTarget* target,
                                             const std::string& config,
                                             const std::string& lang);
+  bool AppendLWYUFlags(std::string& flags, const cmGeneratorTarget* target,
+                       const std::string& lang);
 
   enum class IncludePathStyle
   {

Source/cmMakefileExecutableTargetGenerator.cxx

@@ -397,9 +397,8 @@ void cmMakefileExecutableTargetGenerator::WriteExecutableRule(bool relink)
                                     this->LocalGenerator->GetLinkLibsCMP0065(
                                       linkLanguage, *this->GeneratorTarget));
 
-  if (this->GeneratorTarget->GetPropertyAsBool("LINK_WHAT_YOU_USE")) {
-    this->LocalGenerator->AppendFlags(linkFlags, " -Wl,--no-as-needed");
-  }
+  this->UseLWYU = this->LocalGenerator->AppendLWYUFlags(
+    linkFlags, this->GeneratorTarget, linkLanguage);
 
   // Add language feature flags.
   this->LocalGenerator->AddLanguageFlagsForLinking(
@@ -577,12 +576,18 @@ void cmMakefileExecutableTargetGenerator::WriteExecutableRule(bool relink)
       vars.Launcher = linkerLauncher.c_str();
     }
 
-    if (this->GeneratorTarget->GetPropertyAsBool("LINK_WHAT_YOU_USE")) {
-      std::string cmakeCommand =
-        cmStrCat(this->LocalGenerator->ConvertToOutputFormat(
-                   cmSystemTools::GetCMakeCommand(), cmLocalGenerator::SHELL),
-                 " -E __run_co_compile --lwyu=", targetOutPathReal);
-      real_link_commands.push_back(std::move(cmakeCommand));
+    if (this->UseLWYU) {
+      cmProp lwyuCheck =
+        this->Makefile->GetDefinition("CMAKE_LINK_WHAT_YOU_USE_CHECK");
+      if (lwyuCheck) {
+        std::string cmakeCommand = cmStrCat(
+          this->LocalGenerator->ConvertToOutputFormat(
+            cmSystemTools::GetCMakeCommand(), cmLocalGenerator::SHELL),
+          " -E __run_co_compile --lwyu=");
+        cmakeCommand += this->LocalGenerator->EscapeForShell(*lwyuCheck);
+        cmakeCommand += cmStrCat(" --source=", targetOutPathReal);
+        real_link_commands.push_back(std::move(cmakeCommand));
+      }
     }
 
     std::string launcher;

Source/cmMakefileLibraryTargetGenerator.cxx

@@ -178,9 +178,9 @@ void cmMakefileLibraryTargetGenerator::WriteSharedLibraryRules(bool relink)
   this->AddModuleDefinitionFlag(linkLineComputer.get(), extraFlags,
                                 this->GetConfigName());
 
-  if (this->GeneratorTarget->GetPropertyAsBool("LINK_WHAT_YOU_USE")) {
-    this->LocalGenerator->AppendFlags(extraFlags, " -Wl,--no-as-needed");
-  }
+  this->UseLWYU = this->LocalGenerator->AppendLWYUFlags(
+    extraFlags, this->GeneratorTarget, linkLanguage);
+
   this->WriteLibraryRules(linkRuleVar, extraFlags, relink);
 }
 
@@ -871,13 +871,18 @@ void cmMakefileLibraryTargetGenerator::WriteLibraryRules(
       // Get the set of commands.
       std::string linkRule = this->GetLinkRule(linkRuleVar);
       cmExpandList(linkRule, real_link_commands);
-      if (this->GeneratorTarget->GetPropertyAsBool("LINK_WHAT_YOU_USE") &&
-          (this->GeneratorTarget->GetType() == cmStateEnums::SHARED_LIBRARY)) {
-        std::string cmakeCommand = cmStrCat(
-          this->LocalGenerator->ConvertToOutputFormat(
-            cmSystemTools::GetCMakeCommand(), cmLocalGenerator::SHELL),
-          " -E __run_co_compile --lwyu=", targetOutPathReal);
-        real_link_commands.push_back(std::move(cmakeCommand));
+      if (this->UseLWYU) {
+        cmProp lwyuCheck =
+          this->Makefile->GetDefinition("CMAKE_LINK_WHAT_YOU_USE_CHECK");
+        if (lwyuCheck) {
+          std::string cmakeCommand = cmStrCat(
+            this->LocalGenerator->ConvertToOutputFormat(
+              cmSystemTools::GetCMakeCommand(), cmLocalGenerator::SHELL),
+            " -E __run_co_compile --lwyu=");
+          cmakeCommand += this->LocalGenerator->EscapeForShell(*lwyuCheck);
+          cmakeCommand += cmStrCat(" --source=", targetOutPathReal);
+          real_link_commands.push_back(std::move(cmakeCommand));
+        }
       }
 
       // Expand placeholders.

Source/cmNinjaNormalTargetGenerator.cxx

@@ -581,17 +581,23 @@ std::vector<std::string> cmNinjaNormalTargetGenerator::ComputeLinkCmd(
         }
       }
       cmExpandList(linkCmdStr, linkCmds);
-      if (this->GetGeneratorTarget()->GetPropertyAsBool("LINK_WHAT_YOU_USE")) {
-        std::string cmakeCommand = cmStrCat(
-          this->GetLocalGenerator()->ConvertToOutputFormat(
-            cmSystemTools::GetCMakeCommand(), cmLocalGenerator::SHELL),
-          " -E __run_co_compile --lwyu=");
-        cmGeneratorTarget& gt = *this->GetGeneratorTarget();
-        std::string targetOutputReal = this->ConvertToNinjaPath(
-          gt.GetFullPath(config, cmStateEnums::RuntimeBinaryArtifact,
-                         /*realname=*/true));
-        cmakeCommand += targetOutputReal;
-        linkCmds.push_back(std::move(cmakeCommand));
+      if (this->UseLWYU) {
+        cmProp lwyuCheck = mf->GetDefinition("CMAKE_LINK_WHAT_YOU_USE_CHECK");
+        if (lwyuCheck) {
+          std::string cmakeCommand = cmStrCat(
+            this->GetLocalGenerator()->ConvertToOutputFormat(
+              cmSystemTools::GetCMakeCommand(), cmLocalGenerator::SHELL),
+            " -E __run_co_compile --lwyu=");
+          cmakeCommand +=
+            this->GetLocalGenerator()->EscapeForShell(*lwyuCheck);
+
+          std::string targetOutputReal =
+            this->ConvertToNinjaPath(this->GetGeneratorTarget()->GetFullPath(
+              config, cmStateEnums::RuntimeBinaryArtifact,
+              /*realname=*/true));
+          cmakeCommand += cmStrCat(" --source=", targetOutputReal);
+          linkCmds.push_back(std::move(cmakeCommand));
+        }
       }
       return linkCmds;
     }
@@ -1156,9 +1162,11 @@ void cmNinjaNormalTargetGenerator::WriteLinkStatement(
 
   this->AddModuleDefinitionFlag(linkLineComputer.get(), vars["LINK_FLAGS"],
                                 config);
-  if (gt->GetPropertyAsBool("LINK_WHAT_YOU_USE")) {
-    vars["LINK_FLAGS"] += " -Wl,--no-as-needed";
-  }
+
+  this->UseLWYU = this->GetLocalGenerator()->AppendLWYUFlags(
+    vars["LINK_FLAGS"], this->GetGeneratorTarget(),
+    this->TargetLinkLanguage(config));
+
   vars["LINK_FLAGS"] = globalGen->EncodeLiteral(vars["LINK_FLAGS"]);
 
   vars["MANIFESTS"] = this->GetManifests(config);

Source/cmcmd.cxx

@@ -385,18 +385,15 @@ int HandleTidy(const std::string& runCmd, const std::string& sourceFile,
   return ret;
 }
 
-int HandleLWYU(const std::string& runCmd, const std::string& /* sourceFile */,
+int HandleLWYU(const std::string& runCmd, const std::string& sourceFile,
                const std::vector<std::string>&)
 {
   // Construct the ldd -r -u (link what you use lwyu) command line
   // ldd -u -r lwuy target
-  std::vector<std::string> lwyu_cmd;
-  lwyu_cmd.emplace_back("ldd");
-  lwyu_cmd.emplace_back("-u");
-  lwyu_cmd.emplace_back("-r");
-  lwyu_cmd.push_back(runCmd);
+  std::vector<std::string> lwyu_cmd = cmExpandedList(runCmd, true);
+  lwyu_cmd.push_back(sourceFile);
 
-  // Run the ldd -u -r command line.
+  // Run the lwyu check command line,  currently ldd is expected.
   // Capture its stdout and hide its stderr.
   // Ignore its return code because the tool always returns non-zero
   // if there are any warnings, but we just want to warn.