build: manual update scripts (#786)

people asked for this often enough

src/spice2x/build_updaters.sh

@@ -0,0 +1,57 @@
+#!/usr/bin/env bash
+
+# builds the standalone updater scripts from the shared PowerShell logic in
+# update_spice.ps1. each output is a self-contained polyglot .bat: a small batch
+# header (with the release channel baked in) followed by the shared PowerShell
+# body after the marker line.
+#
+# usage: build_updaters.sh OUT_DIR
+#   OUT_DIR  directory to write the generated .bat files into
+
+set -eu
+
+if [ $# -lt 1 ]; then
+	echo "usage: build_updaters.sh OUT_DIR" >&2
+	exit 1
+fi
+
+SRC_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+PS_BODY="${SRC_DIR}/update_spice.ps1"
+OUT_DIR="$1"
+
+[ -f "$PS_BODY" ] || { echo "error: $PS_BODY not found" >&2; exit 1; }
+
+MARKER='#___PS___'
+
+gen() {
+	channel="$1"; label="$2"; out="$3"
+	{
+		cat <<HEADER
+@echo off
+setlocal
+REM ============================================================================
+REM  spice2x updater  -  updates spice.exe, spice64.exe and spicecfg.exe in
+REM  this folder to the latest spice2x release from GitHub.
+REM
+REM  release channel: ${label}
+REM  make sure spice/spicecfg are NOT running before updating.
+REM ============================================================================
+
+REM expose the script folder + channel to the embedded PowerShell, then run the
+REM PowerShell part: re-read this file and execute everything after the marker.
+set "SPICE_DIR=%~dp0"
+set "SPICE_CHANNEL=${channel}"
+powershell -NoProfile -ExecutionPolicy Bypass -Command "\$m='#___'+'PS'+'___'; \$code=((Get-Content -LiteralPath '%~f0' -Raw) -split \$m)[-1]; Invoke-Expression \$code"
+set "RC=%ERRORLEVEL%"
+endlocal & exit /b %RC%
+
+${MARKER}
+HEADER
+		cat "$PS_BODY"
+	} | sed -e 's/\r$//' -e 's/$/\r/' > "${OUT_DIR}/${out}"
+	echo "  generated ${OUT_DIR}/${out}"
+}
+
+echo "Generating updater scripts from $(basename "$PS_BODY")..."
+gen "" "stable (pre-releases excluded)" "update_spice.bat"
+gen "beta" "beta (newest, pre-releases included)" "update_spice_beta.bat"