CPack/WiX: Make InstallScope configurable

Add a new `CPACK_WIX_INSTALL_SCOPE` variable to set the `InstallScope`
when using the default WiX template.  Set the default to the bug-free
value `perMachine`.

Fixes: #20962

Help/cpack_gen/wix.rst

@@ -119,7 +119,8 @@ Windows using WiX.
 
  If this variable is set, the specified template will be used to generate
  the WiX wxs file.  This should be used if further customization of the
- output is required.
+ output is required. The template contents will override the effect of most
+ ``CPACK_WIX_`` variables.
 
  If this variable is not set, the default MSI template included with CMake
  will be used.
@@ -337,3 +338,31 @@ Windows using WiX.
  of the installer. May for example be set to ``x64`` or ``arm64``.
 
  When unspecified, CPack will default to ``x64`` or ``x86``.
+
+.. variable:: CPACK_WIX_INSTALL_SCOPE
+
+ .. versionadded:: 3.29
+
+ This variable can be optionally set to specify the ``InstallScope``
+ of the installer:
+
+ ``perMachine`` (default)
+   Create an installer that installs for all users and requires
+   administrative privileges.  Start menu entries created by the
+   installer are visible to all users.
+
+ ``perUser``
+   Not yet supported. This is reserved for future use.
+
+ ``NONE``
+   Create an installer without any ``InstallScope`` attribute.
+
+   .. deprecated:: 3.29
+
+     This value is only for compatibility with the inconsistent behavior used
+     by CPack 3.28 and older.  The resulting installer requires administrative
+     privileges and installs into the system-wide ``ProgramFiles`` directory,
+     but the start menu entry and uninstaller registration are created only
+     for the current user.
+
+ See https://wixtoolset.org/docs/v3/xsd/wix/package/

Help/release/dev/wix-installscope.rst

@@ -0,0 +1,13 @@
+wix-installscope
+----------------
+
+* The :cpack_gen:`CPack WIX Generator` gained a new variable,
+  :variable:`CPACK_WIX_INSTALL_SCOPE`, to control the
+  ``InstallScope`` property of WiX MSI installers.
+
+* The :cpack_gen:`CPack WIX Generator` now produces WiX MSI installers
+  that create start menu and uninstall entries for all users by default,
+  as documented by the :variable:`CPACK_WIX_INSTALL_SCOPE` variable
+  ``perMachine`` value.  Previously, without a custom WiX template,
+  it produced installers that would only create start menu and uninstall
+  entries for the current user, even though they install for all users.

Modules/Internal/CPack/CPackWIX.cmake

@@ -18,3 +18,7 @@ find_program(CPACK_WIX_LIGHT_EXECUTABLE light
 if(NOT CPACK_WIX_LIGHT_EXECUTABLE)
   message(FATAL_ERROR "Could not find the WiX light executable.")
 endif()
+
+if(NOT DEFINED CPACK_WIX_INSTALL_SCOPE)
+  set(CPACK_WIX_INSTALL_SCOPE "perMachine")
+endif()

Modules/Internal/CPack/WIX.template.in

@@ -12,7 +12,12 @@
         Manufacturer="$(var.CPACK_PACKAGE_VENDOR)"
         UpgradeCode="$(var.CPACK_WIX_UPGRADE_GUID)">
 
+
+        <?if $(var.CPACK_WIX_INSTALL_SCOPE) = "NONE" ?>
         <Package InstallerVersion="301" Compressed="yes"/>
+        <?else?>
+        <Package InstallerVersion="301" Compressed="yes" InstallScope="$(var.CPACK_WIX_INSTALL_SCOPE)"/>
+        <?endif?>
 
         <Media Id="1" Cabinet="media1.cab" EmbedCab="yes"/>
 

Source/CPack/WiX/cmCPackWIXGenerator.cxx

@@ -359,6 +359,7 @@ void cmCPackWIXGenerator::CreateWiXVariablesIncludeFile()
                     GetOption("CPACK_PACKAGE_NAME"));
   CopyDefinition(includeFile, "CPACK_WIX_PROGRAM_MENU_FOLDER");
   CopyDefinition(includeFile, "CPACK_WIX_UI_REF");
+  CopyDefinition(includeFile, "CPACK_WIX_INSTALL_SCOPE");
 }
 
 void cmCPackWIXGenerator::CreateWiXPropertiesIncludeFile()