fix(packaging/windows): Allow WiX installer downgrades (#5435)

cmake/packaging/windows_wix.cmake

@@ -64,6 +64,10 @@ set(CPACK_WIX_HELP_LINK "https://docs.lizardbyte.dev/projects/sunshine/latest/md
 set(CPACK_WIX_PRODUCT_ICON "${SUNSHINE_ICON_PATH}")
 set(CPACK_WIX_PRODUCT_URL "${CMAKE_PROJECT_HOMEPAGE_URL}")
 set(CPACK_WIX_PROGRAM_MENU_FOLDER "LizardByte")
+# Force package files to replace existing files when switching between release
+# and PR builds, regardless of their embedded file versions.
+# https://learn.microsoft.com/en-us/windows/win32/msi/reinstallmode
+set(CPACK_WIX_PROPERTY_REINSTALLMODE "amus")
 
 set(CPACK_WIX_EXTENSIONS
         "WixToolset.UI.wixext"
@@ -82,6 +86,12 @@ set(CPACK_WIX_EXTRA_SOURCES
 set(CPACK_WIX_PATCH_FILE
         "${WIX_BUILD_PARENT_DIRECTORY}/patch.xml"
 )
+# CPack's default WiX template blocks downgrades. Sunshine users commonly switch
+# between release and PR builds, so allow any build to replace the installed one.
+# https://docs.firegiant.com/wix/schema/wxs/majorupgrade/#allowdowngrades
+set(CPACK_WIX_TEMPLATE
+        "${WIX_BUILD_PARENT_DIRECTORY}/wix.template.in"
+)
 
 # Copy root LICENSE and rename to have .txt extension
 file(COPY "${CMAKE_SOURCE_DIR}/LICENSE"

cmake/packaging/wix_resources/wix.template.in

@@ -0,0 +1,51 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<?include "cpack_variables.wxi"?>
+
+<Wix
+    xmlns="http://wixtoolset.org/schemas/v4/wxs"@CPACK_WIX_CUSTOM_XMLNS_EXPANDED@
+    RequiredVersion="4.0"
+    >
+    <Package
+        Name="$(var.CPACK_PACKAGE_NAME)"
+        Version="$(var.CPACK_PACKAGE_VERSION)"
+        Manufacturer="$(var.CPACK_PACKAGE_VENDOR)"
+        UpgradeCode="$(var.CPACK_WIX_UPGRADE_GUID)"
+        ProductCode="$(var.CPACK_WIX_PRODUCT_GUID)"
+        Scope="$(var.CPACK_WIX_INSTALL_SCOPE)"
+        InstallerVersion="500"
+        Language="1033"
+        Compressed="yes"
+        >
+        <?ifndef CPACK_WIX_CAB_PER_COMPONENT?>
+        <Media Id="1" Cabinet="media1.cab" EmbedCab="yes"/>
+        <?endif?>
+
+        <MajorUpgrade
+            Schedule="afterInstallInitialize"
+            AllowDowngrades="yes"/>
+
+        <WixVariable Id="WixUILicenseRtf" Value="$(var.CPACK_WIX_LICENSE_RTF)"/>
+        <Property Id="WIXUI_INSTALLDIR" Value="INSTALL_ROOT"/>
+
+        <?ifdef CPACK_WIX_PRODUCT_ICON?>
+        <Property Id="ARPPRODUCTICON" Value="ProductIcon.ico" />
+        <Icon Id="ProductIcon.ico" SourceFile="$(var.CPACK_WIX_PRODUCT_ICON)"/>
+        <?endif?>
+
+        <?ifdef CPACK_WIX_UI_BANNER?>
+        <WixVariable Id="WixUIBannerBmp" Value="$(var.CPACK_WIX_UI_BANNER)"/>
+        <?endif?>
+
+        <?ifdef CPACK_WIX_UI_DIALOG?>
+        <WixVariable Id="WixUIDialogBmp" Value="$(var.CPACK_WIX_UI_DIALOG)"/>
+        <?endif?>
+
+        <FeatureRef Id="ProductFeature"/>
+        <ui:WixUI Id="$(var.CPACK_WIX_UI_REF)" />
+        <UIRef Id="WixUI_ErrorProgressText" />
+
+        <?include "properties.wxi"?>
+        <?include "product_fragment.wxi"?>
+    </Package>
+</Wix>