Unity Builds: Support explicit specification of sources to groups

Instead of having CMake determine which files should go into each
unity file, the user can now use explicitly state the mapping.

2 files changed, 65 insertions, 3 deletions

diff --git a/Source/cmLocalGenerator.cxx b/Source/cmLocalGenerator.cxx
index dee5cb4..63b7578 100644
--- a/Source/cmLocalGenerator.cxx
+++ b/Source/cmLocalGenerator.cxx
@@ -2821,6 +2821,53 @@ std::vector<std::string> AddUnityFilesModeAuto(
   }
   return unity_files;
 }
+
+std::vector<std::string> AddUnityFilesModeGroup(
+  cmGeneratorTarget* target, std::string const& lang,
+  std::vector<cmSourceFile*> const& filtered_sources, cmProp beforeInclude,
+  cmProp afterInclude, std::string const& filename_base)
+{
+  std::vector<std::string> unity_files;
+
+  // sources organized by group name. Drop any source
+  // without a group
+  std::unordered_map<std::string, std::vector<cmSourceFile*>> explicit_mapping;
+  for (cmSourceFile* sf : filtered_sources) {
+    if (cmProp value = sf->GetProperty("UNITY_GROUP")) {
+      auto i = explicit_mapping.find(*value);
+      if (i == explicit_mapping.end()) {
+        std::vector<cmSourceFile*> sources{ sf };
+        explicit_mapping.emplace(*value, sources);
+      } else {
+        i->second.emplace_back(sf);
+      }
+    }
+  }
+
+  for (auto const& item : explicit_mapping) {
+    auto const& name = item.first;
+    std::string filename = cmStrCat(filename_base, "unity_", name,
+                                    (lang == "C") ? "_c.c" : "_cxx.cxx");
+
+    const std::string filename_tmp = cmStrCat(filename, ".tmp");
+    {
+      cmGeneratedFileStream file(
+        filename_tmp, false,
+        target->GetGlobalGenerator()->GetMakefileEncoding());
+      file << "/* generated by CMake */\n\n";
+
+      for (cmSourceFile* sf : item.second) {
+        RegisterUnitySources(target, sf, filename);
+        IncludeFileInUnitySources(file, sf->ResolveFullPath(), beforeInclude,
+                                  afterInclude);
+      }
+    }
+    cmSystemTools::MoveFileIfDifferent(filename_tmp, filename);
+    unity_files.emplace_back(std::move(filename));
+  }
+
+  return unity_files;
+}
 }
 
 void cmLocalGenerator::AddUnityBuild(cmGeneratorTarget* target)
@@ -2851,6 +2898,7 @@ void cmLocalGenerator::AddUnityBuild(cmGeneratorTarget* target)
   cmProp beforeInclude =
     target->GetProperty("UNITY_BUILD_CODE_BEFORE_INCLUDE");
   cmProp afterInclude = target->GetProperty("UNITY_BUILD_CODE_AFTER_INCLUDE");
+  cmProp unityMode = target->GetProperty("UNITY_BUILD_MODE");
 
   for (std::string lang : { "C", "CXX" }) {
     std::vector<cmSourceFile*> filtered_sources;
@@ -2865,9 +2913,22 @@ void cmLocalGenerator::AddUnityBuild(cmGeneratorTarget* target)
                      !sf->GetProperty("INCLUDE_DIRECTORIES");
                  });
 
-    std::vector<std::string> unity_files =
-      AddUnityFilesModeAuto(target, lang, filtered_sources, beforeInclude,
-                            afterInclude, filename_base, unityBatchSize);
+    std::vector<std::string> unity_files;
+    if (!unityMode || *unityMode == "BATCH") {
+      unity_files =
+        AddUnityFilesModeAuto(target, lang, filtered_sources, beforeInclude,
+                              afterInclude, filename_base, unityBatchSize);
+    } else if (unityMode && *unityMode == "GROUP") {
+      unity_files =
+        AddUnityFilesModeGroup(target, lang, filtered_sources, beforeInclude,
+                               afterInclude, filename_base);
+    } else {
+      // unity mode is set to an unsupported value
+      std::string e("Invalid UNITY_BUILD_MODE value of " + *unityMode +
+                    " assigned to target " + target->GetName() +
+                    ". Acceptable values are BATCH and GROUP.");
+      this->IssueMessage(MessageType::FATAL_ERROR, e);
+    }
 
     for (auto const& file : unity_files) {
       auto unity = this->GetMakefile()->GetOrCreateSource(file);
diff --git a/Source/cmTarget.cxx b/Source/cmTarget.cxx
index a776398..d43fbe5 100644
--- a/Source/cmTarget.cxx
+++ b/Source/cmTarget.cxx
@@ -372,6 +372,7 @@ cmTarget::cmTarget(std::string const& name, cmStateEnums::TargetType type,
     initProp("DISABLE_PRECOMPILE_HEADERS");
     initProp("UNITY_BUILD");
     initPropValue("UNITY_BUILD_BATCH_SIZE", "8");
+    initPropValue("UNITY_BUILD_MODE", "BATCH");
     initPropValue("PCH_WARN_INVALID", "ON");
 #ifdef __APPLE__
     if (this->GetGlobalGenerator()->IsXcode()) {