Adding modding folder with a hacked build.

modding/hacked-build-image/docker-entrypoint.sh

@@ -0,0 +1,35 @@
+#!/usr/bin/env bash
+# Drops from root (needed to read the Go toolchain and module cache under
+# /usr/local/go and /opt/go) to a user matching the host's UID/GID, so
+# anything written into the bind-mounted repo (hacked/_build/, ...) is owned
+# by the host user instead of root.
+set -euo pipefail
+
+USER_UID="${HOST_UID:-1000}"
+USER_GID="${HOST_GID:-1000}"
+
+groupadd -g "$USER_GID" builder 2>/dev/null || true
+useradd -u "$USER_UID" -g "$USER_GID" -m -s /bin/bash builder 2>/dev/null || true
+
+# /workspace (the bind-mounted repo) may actually be owned by a group the
+# host user only has via *supplementary* membership rather than their
+# primary GID above - e.g. a VirtualBox vboxsf shared folder, which shows
+# up as root:vboxsf on the host and would otherwise be inaccessible to
+# `builder` here (falls through to "other", which vboxsf's default mode
+# leaves with no permissions at all). Join whatever group actually owns
+# /workspace too, if it differs.
+WORKSPACE_GID="$(stat -c %g /workspace 2>/dev/null || true)"
+if [ -n "$WORKSPACE_GID" ] && [ "$WORKSPACE_GID" != "$USER_GID" ]; then
+    groupadd -g "$WORKSPACE_GID" workspace 2>/dev/null || true
+    usermod -aG "$WORKSPACE_GID" builder 2>/dev/null || true
+fi
+
+# The Go module cache under /opt/go was populated as root at image-build
+# time (see Dockerfile) - readable by anyone, but go build also wants to
+# write GOCACHE (build cache) under there by default. Point it at a
+# per-run tmpfs-friendly location inside the builder's own home instead of
+# fighting permissions on the image's baked-in GOPATH.
+export GOCACHE=/home/builder/.cache/go-build
+export GOMODCACHE=/opt/go/pkg/mod
+
+exec gosu builder "$@"