Dockerfile.linux-build

# Reproducible Linux x86_64 build environment for Ultimate64 Manager.
#
# Ubuntu 20.04 base → glibc 2.31 → the resulting AppImage runs on
# Ubuntu 20.04+, Debian 11+, Fedora 33+, and most distros from 2020
# onward. Building on a newer host links against newer glibc symbols
# (e.g. GLIBC_2.38) which would break compatibility.
#
# We deliberately AVOID running `linuxdeploy`/`appimagetool` inside the
# build (both are themselves AppImages, whose runtimes can't bootstrap
# inside Docker without FUSE/binfmt support — fatal under QEMU
# emulation on ARM hosts). Instead, the `linux_docker` make target
# assembles the AppImage from raw parts using `mksquashfs` + the
# pre-downloaded AppImage runtime ELF baked into this image.
#
# Build the image once:
#   make linux_docker_image
#
# Build the AppImage:
#   make linux_docker

# Platform is pinned to linux/amd64 by the caller (see Makefile:
# `docker build --platform=linux/amd64`), not here — BuildKit lints
# against hard-coded `--platform` in FROM.
FROM ubuntu:20.04

ENV DEBIAN_FRONTEND=noninteractive \
    PATH="/root/.cargo/bin:${PATH}"

RUN apt-get update \
    && apt-get install -y --no-install-recommends \
        ca-certificates \
        curl \
        file \
        build-essential \
        pkg-config \
        libudev-dev \
        libasound2-dev \
        libgtk-3-dev \
        libssl-dev \
        libxkbcommon-dev \
        libfontconfig1-dev \
        libfreetype6-dev \
        libwayland-dev \
        libxcb1-dev \
        libxcb-render0-dev \
        libxcb-shape0-dev \
        libxcb-xfixes0-dev \
        squashfs-tools \
        desktop-file-utils \
    && rm -rf /var/lib/apt/lists/*

RUN curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs \
    | sh -s -- -y --default-toolchain stable --profile minimal

# Pre-download the standalone AppImage runtime. This is a tiny ELF (~190 KB)
# from the AppImage project that knows how to mount its own squashfs payload
# at run time on the user's machine — exactly what `appimagetool` produces.
# Baking it here means `make linux_docker` is fully offline and doesn't need
# any AppImage tooling at build time.
RUN set -eux \
    && curl -fSL -o /opt/appimage-runtime \
        https://github.com/AppImage/type2-runtime/releases/download/continuous/runtime-x86_64 \
    && file /opt/appimage-runtime | grep -q 'ELF 64-bit' \
    && chmod +x /opt/appimage-runtime

WORKDIR /src