build_mp.sh --icon: our executables can wear our own icon

The windows port hardcodes ports/windows/micropython.rc to
../../logo/vector-logo-2.ico, and the Makefile compiles it to
micropython.res and links that into $(PROG) whatever the program is
named - so every windows binary this script builds has been wearing
MicroPython's logo, including micropython-vst3's sidecar.

--icon PATH (env twin MP_ICON) rewrites that one line for the build.
Deliberately not a patch and deliberately no stored copy of the resource
script: the original is stashed and the EXIT trap already installed for the
mailbox overlays puts it back. Restored by copy, so the restored file is
newer than the .res built from ours and the next build without --icon
rebuilds back to the port's own logo. The icon is per-invocation, never
sticky - this checkout is shared.

Refuses rather than ignores: a non-windows port (an ELF binary has nowhere
to carry one), a path that is not there, and a file whose header is not
00 00 01 00 - a .png renamed .ico is the mistake everyone makes once, and
windres reports it as a parse error minutes into a build.

All three refusals were exercised, and the checkout was checked clean
afterwards; micropython-vst3 is the first consumer.

Author: bdbarnett

build_mp.sh

@@ -3,12 +3,14 @@
 #
 # Usage:
 #   ./build_mp.sh [--port PORT] [--board BOARD] [--variant VARIANT] [--debug]
+#                 [--icon PATH]
 #
 # Environment: WORKSPACE_DIR, MP_DIR, IDF_DIR, EMSDK_DIR, PORT, BOARD, VARIANT,
 #              OS_DUPTERM, OS_DUPTERM_SLOTS, MP_BUILD_DEBUG, MP_AUTOSIZE,
 #              MP_OVERLAY_SKIP (patch numbers excluded from the mailbox
 #              overlays, e.g. "0001 0003"), MP_MAKE_EXTRA (extra VAR=VALUE
-#              words appended to the make command line)
+#              words appended to the make command line), MP_ICON (same as
+#              --icon: the .ico the windows port's executable wears)
 #
 # USER_C_MODULES and FROZEN_MANIFEST are always cleared at startup so a prior
 # shell export cannot stick across port/board/variant builds. They then default
@@ -39,9 +41,24 @@
 set -euo pipefail
 
 APPLIED_MP_PATCHES=()
+# Set by apply_micropython_icon: where the port's own micropython.rc was put
+# while ours stood in its place.
+MP_ICON_RC_BACKUP=""
 
 restore_micropython_overlay() {
     local index
+    # The icon first: it is a plain file copy and cannot fail the way a patch
+    # reversal can, so doing it here means a patch that will not reverse still
+    # leaves the resource script as MicroPython wrote it.
+    if [[ -n "$MP_ICON_RC_BACKUP" && -f "$MP_ICON_RC_BACKUP" ]]; then
+        # Copied back rather than moved-with-timestamp on purpose: the restored
+        # file is NEWER than the .res built from ours, so the next build without
+        # --icon rebuilds the resource and the port's own logo returns. The icon
+        # is per-invocation, never sticky - this checkout is shared.
+        cp "$MP_ICON_RC_BACKUP" "$MP_DIR/ports/windows/micropython.rc"
+        rm -f "$MP_ICON_RC_BACKUP"
+        MP_ICON_RC_BACKUP=""
+    fi
     for ((index=${#APPLIED_MP_PATCHES[@]}-1; index>=0; index--)); do
         git -C "$MP_DIR" apply --reverse "${APPLIED_MP_PATCHES[index]}" || {
             echo "error: failed to remove MicroPython overlay ${APPLIED_MP_PATCHES[index]}" >&2
@@ -93,18 +110,22 @@ while [[ $# -gt 0 ]]; do
         --board)   BOARD="$2"; shift 2 ;;
         --variant) VARIANT="$2"; shift 2 ;;
         --debug)   MP_BUILD_DEBUG=1; shift ;;
+        --icon)    MP_ICON="$2"; shift 2 ;;
         --no-os-dupterm) OS_DUPTERM=0; OS_DUPTERM_EXPLICIT=1; shift ;;
         --os-dupterm) OS_DUPTERM=1; OS_DUPTERM_EXPLICIT=1; shift ;;
         -h|--help)
             cat <<EOF
 Usage: $0 [--port PORT] [--board BOARD] [--variant VARIANT] [--debug]
+          [--icon PATH]
 
 Build MicroPython with user C modules from the cmods workspace.
 
 Options:
   --port PORT        MicroPython port (e.g. unix, esp32, rp2)
   --board BOARD      Board name for board-based ports
   --variant VARIANT  Board variant (board ports) or build variant (unix, etc.)
+  --icon PATH        windows: .ico the built executable wears, in place of
+                     the port's own logo. Restored after the build.
   --debug            esp32: UART REPL + USB Serial/JTAG debug console
                      (ESP32_GENERIC_S3/SPIRAM_OCT → SPIRAM_OCT_DEBUG).
                      USB jack = IDF secondary console / ESP_LOG; UART jack = REPL.
@@ -120,6 +141,7 @@ Environment:
                      file for the selected port/board/variant (read by manifest-micropython.py)
   PORT, BOARD, VARIANT  Same as the corresponding options
   MP_BUILD_DEBUG     Same as --debug when set to 1/true/yes/on
+  MP_ICON            Same as --icon (windows only)
   OS_DUPTERM         Enable os.dupterm on unix/webassembly (default: 1); windows default: 0
   OS_DUPTERM_SLOTS   dupterm slot count for desktop ports (default: 1)
   SDL2_DEV           Unpacked SDL2 MinGW development ZIP root (windows; required when displayif usdl2 links)
@@ -542,6 +564,50 @@ ensure_host_mpy_cross() {
     make -C "$MP_DIR/mpy-cross" USER_C_MODULES= FROZEN_MANIFEST=
 }
 
+# --icon / MP_ICON: give the built executable our own icon instead of the
+# port's. ports/windows/micropython.rc is a single line naming an .ico, and the
+# windows Makefile compiles it to micropython.res and links that into $(PROG)
+# whatever the program is named - so rewriting that one line is the entire
+# mechanism. Deliberately not a patch and deliberately no stored copy of the
+# resource script: the original is stashed and the EXIT trap puts it back, the
+# same transactional shape the mailbox overlays use.
+apply_micropython_icon() {
+    [[ -n "${MP_ICON:-}" ]] || return 0
+
+    if [[ "$PORT" != windows ]]; then
+        echo "error: --icon is only meaningful for --port windows - an ELF binary" >&2
+        echo "  has nowhere to carry one. Port requested: $PORT" >&2
+        return 1
+    fi
+
+    local icon
+    icon=$(realpath -e -- "$MP_ICON" 2>/dev/null) || {
+        echo "error: --icon: no such file: $MP_ICON" >&2
+        return 1
+    }
+    # Checked here because windres reports a bad file as a parse error minutes
+    # into the build, and a .png renamed .ico is the mistake everyone makes
+    # once. An ICONDIR opens 00 00 01 00: reserved, then resource type 1.
+    local magic
+    magic=$(od -An -tx1 -N4 -- "$icon" | tr -d ' \n')
+    if [[ "$magic" != "00000100" ]]; then
+        echo "error: --icon: not a Windows .ico (header reads $magic): $icon" >&2
+        return 1
+    fi
+
+    local rc="$MP_DIR/ports/windows/micropython.rc"
+    [[ -f "$rc" ]] || {
+        echo "error: --icon: the windows port has no micropython.rc at $rc" >&2
+        return 1
+    }
+
+    MP_ICON_RC_BACKUP=$(mktemp)
+    cp "$rc" "$MP_ICON_RC_BACKUP"
+    printf 'app     ICON    "%s"\n' "$icon" > "$rc"
+    echo "Icon: $icon"
+    echo "  ports/windows/micropython.rc rewritten for this build; restored on exit"
+}
+
 apply_micropython_cmods_patches() {
     # Apply mailbox patches whose names contain micropython-<PORT> as temporary
     # working-tree overlays. No matches means there is nothing to do.
@@ -1013,6 +1079,7 @@ echo "  FROZEN_MANIFEST_UPSTREAM=$FROZEN_MANIFEST_UPSTREAM"
 ensure_windows_cross_compile
 ensure_windows_sdl2_env
 apply_micropython_cmods_patches
+apply_micropython_icon
 
 print_rerun_hint
 print_make_commands