CPackWIX: Introduce new CPACK_WIX_ROOT_FOLDER_ID variable

The new variable allows specification of a custom root folder ID.
The implicit default is "ProgramFiles<64>Folder".

The "<64>" token is replaced by "" for 32-bit and "64" for 64-bit builds.

Inspired-By: Eric Backus
Fixes: #16573

Help/release/dev/wix-custom-root-id.rst

+wix-custom-root-id
+------------------
+
+* The CPack WIX generator implemented a new
+  :variable:`CPACK_WIX_ROOT_FOLDER_ID` variable which allows
+  using a custom root folder ID instead of the default
+  ``ProgramFilesFolder`` / ``ProgramFiles64Folder``.

Modules/CPackWIX.cmake

@@ -268,6 +268,17 @@
 #     follow the localization or convention of the system on which the
 #     installation is performed.
 #
+# .. variable:: CPACK_WIX_ROOT_FOLDER_ID
+#
+# This variable allows specification of a custom root folder ID.
+# The generator specific ``<64>`` token can be used for
+# folder IDs that come in 32-bit and 64-bit variants.
+# In 32-bit builds the token will expand empty while in 64-bit builds
+# it will expand to ``64``.
+#
+# When unset generated installers will default installing to
+# ``ProgramFiles<64>Folder``.
+#
 
 if(NOT CPACK_WIX_ROOT)
   file(TO_CMAKE_PATH "$ENV{WIX}" CPACK_WIX_ROOT)

Source/CPack/WiX/cmCPackWIXGenerator.cxx

@@ -437,8 +437,8 @@ bool cmCPackWIXGenerator::CreateWiXSourceFiles()
   directoryDefinitions.AddAttribute("Name", "SourceDir");
 
   size_t installRootSize =
-    directoryDefinitions.BeginInstallationPrefixDirectory(
-      GetProgramFilesFolderId(), installRoot);
+    directoryDefinitions.BeginInstallationPrefixDirectory(GetRootFolderId(),
+                                                          installRoot);
 
   std::string fileDefinitionsFilename = this->CPackTopLevel + "/files.wxs";
 
@@ -570,16 +570,26 @@ bool cmCPackWIXGenerator::CreateWiXSourceFiles()
   return this->Patch->CheckForUnappliedFragments();
 }
 
-std::string cmCPackWIXGenerator::GetProgramFilesFolderId() const
+std::string cmCPackWIXGenerator::GetRootFolderId() const
 {
   if (cmSystemTools::IsOn(GetOption("CPACK_WIX_SKIP_PROGRAM_FOLDER"))) {
     return "";
   }
+
+  std::string result = "ProgramFiles<64>Folder";
+
+  const char* rootFolderId = GetOption("CPACK_WIX_ROOT_FOLDER_ID");
+  if (rootFolderId) {
+    result = rootFolderId;
+  }
+
   if (GetArchitecture() == "x86") {
-    return "ProgramFilesFolder";
+    cmSystemTools::ReplaceString(result, "<64>", "");
   } else {
-    return "ProgramFiles64Folder";
+    cmSystemTools::ReplaceString(result, "<64>", "64");
   }
+
+  return result;
 }
 
 bool cmCPackWIXGenerator::GenerateMainSourceFileFromTemplate()

Source/CPack/WiX/cmCPackWIXGenerator.h

@@ -65,7 +65,7 @@ private:
 
   bool CreateWiXSourceFiles();
 
-  std::string GetProgramFilesFolderId() const;
+  std::string GetRootFolderId() const;
 
   bool GenerateMainSourceFileFromTemplate();