Add options to run `ldd -u -r` as a "link-what-you-use" tool

Create a LINK_WHAT_YOU_USE target property and corresponding
CMAKE_LINK_WHAT_YOU_USE variable to enable this behavior.
Extend link commands by running `ldd -u -r` to detect shared
libraries that are linked but not needed.

1 files changed, 22 insertions, 2 deletions

diff --git a/Source/cmNinjaNormalTargetGenerator.cxx b/Source/cmNinjaNormalTargetGenerator.cxx
index 3e91545..7c18414 100644
--- a/Source/cmNinjaNormalTargetGenerator.cxx
+++ b/Source/cmNinjaNormalTargetGenerator.cxx
@@ -295,6 +295,22 @@ std::vector<std::string> cmNinjaNormalTargetGenerator::ComputeLinkCmd()
     const char* linkCmd = mf->GetDefinition(linkCmdVar);
     if (linkCmd) {
       cmSystemTools::ExpandListArgument(linkCmd, linkCmds);
+      if (this->GetGeneratorTarget()->GetProperty("LINK_WHAT_YOU_USE")) {
+        std::string cmakeCommand =
+          this->GetLocalGenerator()->ConvertToOutputFormat(
+            cmSystemTools::GetCMakeCommand(), cmLocalGenerator::SHELL);
+        cmakeCommand += " -E __run_iwyu --lwyu=";
+        cmGeneratorTarget& gt = *this->GetGeneratorTarget();
+        const std::string cfgName = this->GetConfigName();
+        std::string targetOutput = ConvertToNinjaPath(gt.GetFullPath(cfgName));
+        std::string targetOutputReal =
+          this->ConvertToNinjaPath(gt.GetFullPath(cfgName,
+                                                  /*implib=*/false,
+                                                  /*realpath=*/true));
+        cmakeCommand += targetOutputReal;
+        cmakeCommand += " || true";
+        linkCmds.push_back(cmakeCommand);
+      }
       return linkCmds;
     }
   }
@@ -467,6 +483,10 @@ void cmNinjaNormalTargetGenerator::WriteLinkStatement()
   vars["MANIFESTS"] = this->GetManifests();
 
   vars["LINK_PATH"] = frameworkPath + linkPath;
+  std::string lwyuFlags;
+  if (genTarget.GetProperty("LINK_WHAT_YOU_USE")) {
+    lwyuFlags = " -Wl,--no-as-needed";
+  }
 
   // Compute architecture specific link flags.  Yes, these go into a different
   // variable for executables, probably due to a mistake made when duplicating
@@ -474,16 +494,17 @@ void cmNinjaNormalTargetGenerator::WriteLinkStatement()
   if (targetType == cmState::EXECUTABLE) {
     std::string t = vars["FLAGS"];
     localGen.AddArchitectureFlags(t, &genTarget, TargetLinkLanguage, cfgName);
+    t += lwyuFlags;
     vars["FLAGS"] = t;
   } else {
     std::string t = vars["ARCH_FLAGS"];
     localGen.AddArchitectureFlags(t, &genTarget, TargetLinkLanguage, cfgName);
     vars["ARCH_FLAGS"] = t;
     t = "";
+    t += lwyuFlags;
     localGen.AddLanguageFlags(t, TargetLinkLanguage, cfgName);
     vars["LANGUAGE_COMPILE_FLAGS"] = t;
   }
-
   if (this->GetGeneratorTarget()->HasSOName(cfgName)) {
     vars["SONAME_FLAG"] = mf->GetSONameFlag(this->TargetLinkLanguage);
     vars["SONAME"] = this->TargetNameSO;
@@ -607,7 +628,6 @@ void cmNinjaNormalTargetGenerator::WriteLinkStatement()
     vars["POST_BUILD"] = ":";
     symlinkVars["POST_BUILD"] = postBuildCmdLine;
   }
-
   cmGlobalNinjaGenerator& globalGen = *this->GetGlobalGenerator();
 
   int commandLineLengthLimit = -1;