build: aarch64 Linux build script (foundation for the Slint ARM workflow)

Native (on an ARM runner: apt deps + cargo build -p qbz) and cross (from
x86-64 via cross + Cross.toml arm64 sysroot) paths, auto-selected by host
arch. Documents the ~30 GB qbz_ui RAM wall (8 GB Macs / 4 GB Pis cannot build
natively). Cross path is best-effort/untested pending a first run.

cc

scripts/build-aarch64-linux.sh

@@ -0,0 +1,86 @@
+#!/usr/bin/env bash
+#
+# build-aarch64-linux.sh — build the Linux aarch64 (ARM64) `qbz` binary, e.g.
+# for a Raspberry Pi 4 / other ARM single-board boxes.
+#
+# ── READ FIRST: where can this run? ──────────────────────────────────────────
+# The generated Slint crate `qbz_ui` compiles as ONE ~1.6M-line module whose
+# single `rustc` needs ~30 GB RAM (RSS+swap). Consequences:
+#   • An 8 GB Mac or a 4 GB Pi CANNOT build it natively — it OOMs. Don't try.
+#   • Build on a box with >= ~16 GB RAM + swap (the wall is survivable at
+#     ~14 GB RAM + swap, proven on the dev box).
+#
+# This script has two modes, auto-selected by the host arch:
+#
+#   1. NATIVE  (running ON aarch64 Linux: an ARM runner, an ARM VM, etc.)
+#        -> apt-installs the build deps and runs `cargo build --release -p qbz`.
+#        This is exactly what a future Slint aarch64 CI job runs — treat the
+#        dep list + build line below as the workflow's source of truth.
+#
+#   2. CROSS   (running on x86-64 Linux with Docker, e.g. the dev box, 30 GB)
+#        -> uses `cross` (https://github.com/cross-rs/cross): a container with
+#        the aarch64 sysroot + the arm64 dev libs (see crates/Cross.toml) does
+#        the compile. Needs Docker running and ~30 GB RAM available to it.
+#
+# macOS is intentionally NOT a build host here: cross from macOS to
+# linux-gnu means re-creating a full Linux sysroot for every native dep
+# (ALSA, dbus, fontconfig, …). Run the CROSS mode on a Linux box instead.
+#
+# Output: dist/qbz-aarch64-linux (an aarch64 ELF — verify with `file`).
+# ─────────────────────────────────────────────────────────────────────────────
+set -euo pipefail
+
+cd "$(dirname "$0")/.."          # repo root (qbz-nix)
+REPO="$(pwd)"
+TARGET="aarch64-unknown-linux-gnu"
+OUT="$REPO/dist/qbz-aarch64-linux"
+
+# The Linux build deps for the Slint `qbz` binary (kept in sync with the CI
+# workflows). PipeWire is reached through its ALSA/JACK compat shims, so only
+# libasound2-dev + libjack-jackd2-dev are needed.
+DEPS=(
+  build-essential pkg-config cmake clang libclang-dev mold nasm
+  libasound2-dev libjack-jackd2-dev
+  libfontconfig1-dev libfreetype-dev
+  libxkbcommon-dev libwayland-dev libxcb1-dev
+  libgl1-mesa-dev libegl1-mesa-dev
+  libdbus-1-dev libssl-dev
+)
+
+arch="$(uname -m)"
+case "$arch" in
+  aarch64 | arm64)
+    echo "[aarch64-build] NATIVE build on $arch"
+    if command -v apt-get >/dev/null; then
+      sudo apt-get update
+      sudo apt-get install -y --no-install-recommends "${DEPS[@]}"
+    else
+      echo "[aarch64-build] non-apt distro: install the equivalents of: ${DEPS[*]}" >&2
+    fi
+    ( cd crates && cargo build --release -p qbz )
+    install -Dm755 "crates/target/release/qbz" "$OUT"
+    ;;
+  x86_64 | amd64)
+    echo "[aarch64-build] CROSS-compile from $arch via cross (Docker)"
+    if ! docker info >/dev/null 2>&1; then
+      echo "[aarch64-build] ERROR: Docker is not running. cross needs it." >&2
+      exit 1
+    fi
+    command -v cross >/dev/null || cargo install cross --locked
+    # Cap the container's RAM so a runaway qbz_ui rustc gets OOM-killed
+    # (losing the build) instead of swap-thrashing the host into a hard freeze
+    # — the dev box has no hibernation and dies under memory pressure. Override
+    # via CROSS_CONTAINER_OPTS if your box has more headroom.
+    export CROSS_CONTAINER_OPTS="${CROSS_CONTAINER_OPTS:---memory=18g --memory-swap=26g}"
+    # Cross.toml (workspace root) injects the arm64 dev libs into the image.
+    ( cd crates && cross build --release --target "$TARGET" -p qbz )
+    install -Dm755 "crates/target/$TARGET/release/qbz" "$OUT"
+    ;;
+  *)
+    echo "[aarch64-build] ERROR: unsupported build host arch: $arch" >&2
+    exit 1
+    ;;
+esac
+
+echo "[aarch64-build] done -> $OUT"
+file "$OUT" || true