cmSourceGroup: Constify clients The generators do not need to modify the groups.

diff --git a/Source/cmFileAPICodemodel.cxx b/Source/cmFileAPICodemodel.cxx
index 2950c67..0d916b0 100644
--- a/Source/cmFileAPICodemodel.cxx
+++ b/Source/cmFileAPICodemodel.cxx

@@ -487,7 +487,7 @@
   void ProcessLanguages();
   void ProcessLanguage(std::string const& lang);
 
-  Json::ArrayIndex AddSourceGroup(cmSourceGroup* sg);
+  Json::ArrayIndex AddSourceGroup(cmSourceGroup const* sg);
   CompileData BuildCompileData(cmSourceFile* sf);
   CompileData MergeCompileData(CompileData const& fd);
   Json::ArrayIndex AddSourceCompileGroup(cmSourceFile* sf,
@@ -1477,7 +1477,7 @@
   }
 }
 
-Json::ArrayIndex Target::AddSourceGroup(cmSourceGroup* sg)
+Json::ArrayIndex Target::AddSourceGroup(cmSourceGroup const* sg)
 {
   auto i = this->SourceGroupsMap.find(sg);
   if (i == this->SourceGroupsMap.end()) {
@@ -1829,7 +1829,8 @@
     source["fileSetIndex"] = fsit->second;
   }
 
-  if (cmSourceGroup* sg = this->GT->LocalGenerator->FindSourceGroup(path)) {
+  if (cmSourceGroup const* sg =
+        this->GT->LocalGenerator->FindSourceGroup(path)) {
     Json::ArrayIndex const groupIndex = this->AddSourceGroup(sg);
     source["sourceGroupIndex"] = groupIndex;
     this->SourceGroups[groupIndex].SourceIndexes.append(si);
@@ -1913,7 +1914,8 @@
     source["fileSetIndex"] = fsit->second;
   }
 
-  if (cmSourceGroup* sg = this->GT->LocalGenerator->FindSourceGroup(path)) {
+  if (cmSourceGroup const* sg =
+        this->GT->LocalGenerator->FindSourceGroup(path)) {
     Json::ArrayIndex const groupIndex = this->AddSourceGroup(sg);
     source["sourceGroupIndex"] = groupIndex;
     this->SourceGroups[groupIndex].InterfaceSourceIndexes.append(si);

diff --git a/Source/cmGhsMultiTargetGenerator.cxx b/Source/cmGhsMultiTargetGenerator.cxx
index 16e68fd..8c9c658 100644
--- a/Source/cmGhsMultiTargetGenerator.cxx
+++ b/Source/cmGhsMultiTargetGenerator.cxx

@@ -513,7 +513,7 @@
   std::map<std::string, std::vector<cmSourceFile*>> groupFiles;
   std::set<std::string> groupNames;
   for (cmSourceFile* sf : sources) {
-    cmSourceGroup* sourceGroup =
+    cmSourceGroup const* sourceGroup =
       this->LocalGenerator->FindSourceGroup(sf->ResolveFullPath());
     std::string gn = sourceGroup->GetFullName();
     groupFiles[gn].push_back(sf);

diff --git a/Source/cmGlobalVisualStudioGenerator.cxx b/Source/cmGlobalVisualStudioGenerator.cxx
index 074caea..f0cca84 100644
--- a/Source/cmGlobalVisualStudioGenerator.cxx
+++ b/Source/cmGlobalVisualStudioGenerator.cxx

@@ -1062,7 +1062,7 @@
       item =
         cmSystemTools::CollapseFullPath(item, mf->GetCurrentSourceDirectory());
     }
-    cmSourceGroup* sg =
+    cmSourceGroup const* sg =
       cmSourceGroup::FindSourceGroup(item, mf->GetSourceGroups());
     std::string folderName = sg->GetFullName();
     if (folderName.empty()) {

diff --git a/Source/cmGlobalXCodeGenerator.cxx b/Source/cmGlobalXCodeGenerator.cxx
index 68614bb..5ac06eb 100644
--- a/Source/cmGlobalXCodeGenerator.cxx
+++ b/Source/cmGlobalXCodeGenerator.cxx

@@ -4516,7 +4516,7 @@
 
       auto addSourceToGroup = [this, &gtgt,
                                &generator](std::string const& source) {
-        cmSourceGroup* sourceGroup = generator->FindSourceGroup(source);
+        cmSourceGroup const* sourceGroup = generator->FindSourceGroup(source);
         cmXCodeObject* pbxgroup =
           this->CreateOrGetPBXGroup(gtgt.get(), sourceGroup);
         std::string key = GetGroupMapKeyFromPath(gtgt.get(), source);
@@ -4592,7 +4592,7 @@
 }
 
 cmXCodeObject* cmGlobalXCodeGenerator::CreateOrGetPBXGroup(
-  cmGeneratorTarget* gtgt, cmSourceGroup* sg)
+  cmGeneratorTarget* gtgt, cmSourceGroup const* sg)
 {
   std::string s;
   std::string target;

diff --git a/Source/cmGlobalXCodeGenerator.h b/Source/cmGlobalXCodeGenerator.h
index 82bb9d5..114caec 100644
--- a/Source/cmGlobalXCodeGenerator.h
+++ b/Source/cmGlobalXCodeGenerator.h

@@ -161,7 +161,7 @@
                             cm::string_view attributeValue);
 
   cmXCodeObject* CreateOrGetPBXGroup(cmGeneratorTarget* gtgt,
-                                     cmSourceGroup* sg);
+                                     cmSourceGroup const* sg);
   cmXCodeObject* CreatePBXGroup(cmXCodeObject* parent,
                                 std::string const& name);
   bool CreateGroups(std::vector<cmLocalGenerator*>& generators);

diff --git a/Source/cmVisualStudio10TargetGenerator.cxx b/Source/cmVisualStudio10TargetGenerator.cxx
index 364fd56..d617dc69 100644
--- a/Source/cmVisualStudio10TargetGenerator.cxx
+++ b/Source/cmVisualStudio10TargetGenerator.cxx

@@ -2004,14 +2004,16 @@
   std::set<cmSourceGroup const*> groupsUsed;
   for (cmGeneratorTarget::AllConfigSource const& si : sources) {
     std::string const& source = si.Source->GetFullPath();
-    cmSourceGroup* sourceGroup = this->LocalGenerator->FindSourceGroup(source);
+    cmSourceGroup const* sourceGroup =
+      this->LocalGenerator->FindSourceGroup(source);
     groupsUsed.insert(sourceGroup);
   }
 
   if (cmSourceFile const* srcCMakeLists =
         this->LocalGenerator->CreateVCProjBuildRule()) {
     std::string const& source = srcCMakeLists->GetFullPath();
-    cmSourceGroup* sourceGroup = this->LocalGenerator->FindSourceGroup(source);
+    cmSourceGroup const* sourceGroup =
+      this->LocalGenerator->FindSourceGroup(source);
     groupsUsed.insert(sourceGroup);
   }
 
@@ -2170,7 +2172,8 @@
   for (ToolSource const& s : sources) {
     cmSourceFile const* sf = s.SourceFile;
     std::string const& source = sf->GetFullPath();
-    cmSourceGroup* sourceGroup = this->LocalGenerator->FindSourceGroup(source);
+    cmSourceGroup const* sourceGroup =
+      this->LocalGenerator->FindSourceGroup(source);
     std::string const& filter = sourceGroup->GetFullName();
     std::string path = this->ConvertPath(source, s.RelativePath);
     ConvertToWindowsSlash(path);
@@ -6031,7 +6034,7 @@
   std::string const& fullFileName = source->GetFullPath();
   std::string const& srcDir = this->Makefile->GetCurrentSourceDirectory();
   std::string const& binDir = this->Makefile->GetCurrentBinaryDirectory();
-  cmSourceGroup* sourceGroup =
+  cmSourceGroup const* sourceGroup =
     this->LocalGenerator->FindSourceGroup(fullFileName);
   if (sourceGroup && !sourceGroup->GetFullName().empty()) {
     sourceGroupedFile =