usm/spm/emerge/usm-spm-emerge

#!/usr/bin/env python3
"""USM system-package-manager helper for Portage (Gentoo) systems.

Implements the USM SPM contract (see usm/README.md, "System package manager
integration") for Gentoo systems:

    usm-spm-emerge query <usm-ref>...         -> contract JSON on STDOUT
    usm-spm-emerge install [--test] <atom>... -> contract JSONL events on STDOUT

API choice: a Gentoo stage3 ships Portage and python3, so this helper reads
the installed-package database through the portage Python API (with a raw
/var/db/pkg CONTENTS scan as fallback) and shells out to `emerge` for
dependency resolution (pretend) and installation. There is no binary
metadata to bind against beyond that: ebuild repositories carry no file
lists, so unlike the dnf/apt/apk helpers this one cannot search "which
package contains file X" for packages that are not installed yet.

File-backed refs are therefore resolved in two documented stages:

  1. INSTALLED files (exact): the ref is translated to candidate filesystem
     paths (gentoo layout: /usr/bin, /usr/sbin, /usr/lib64, /usr/share, ...)
     and matched against the portage vdb (/var/db/pkg/*/CONTENTS). A ref
     resolves to the installed package that owns the file.
  2. NOT-installed files (exception table only): Gentoo has no offline
     file-provides (PFL, the portage file list, is an online service), so a
     small curated table maps the USM stack's build/platform refs to Gentoo
     package atoms (valac -> dev-lang/vala, glib-2.0.pc -> dev-libs/glib,
     ...). Refs outside the table land in not-found; anything else would be
     guesswork.

dependency-count / installed-dependency-count are honest numbers parsed
from `emerge --pretend --quiet=y --ask=n <atom>`: dependency-count is the
number of packages in the merge list including the package itself,
installed-dependency-count is the subset of the merge list already
installed (action letters without N, e.g. [ebuild R]/[ebuild U] reinstalls
and upgrades; a fresh stage3 typically shows an all-N list). If the pretend
run fails (atom missing from the tree, masked, unresolvable) an
exception-table candidate falls back to not-found.

Install maps `emerge --ask=n --quiet=y <atoms>` onto the JSONL contract,
linking the unversioned tool names Gentoo ships versioned (UNVERSIONED_TOOL_LINKS):
`begin`/`total` come from a pretend run first, a `package` event is emitted
per ">>> Emerging (n of N)" status line, `package-complete` per
">>> Installing (n of N)" line (the moment a merge lands in the vdb),
`complete` carries the number of completed merges, and any failure emits a
terminal `error` event before a non-zero exit (resolution failures map to
exit 3, download failures to 4, build/merge failures to 5).

Documented Gentoo limitations:
  * No offline file-provides for not-yet-installed packages (see stage 2
    above); installed-file queries are exact.
  * USE flags are never touched: emerge runs with the system's configured
    defaults. The stack's platform libraries (glib, json-glib, libgee, ...)
    enable their introspection USE flag by default, but a system that
    disabled it (package.use/make.conf) will lack the matching .gir/
    .typelib/.vapi artifacts after install; re-enable the flag and re-emerge
    if a build needs them.
  * Packages are compiled from source; even small installs take minutes.
    Progress granularity is per package; emerge exposes no useful
    intra-package progress, so `package` events carry progress 0.0 and the
    completion signal is the ">>> Installing" line.
  * The query subcommand never modifies system state (at most Portage
    regenerates its dependency cache); install must run as root and never
    prompts (--ask=n answers Portage's own prompt for it).
"""

import argparse
import glob
import json
import os
import re
import subprocess
import sys
import threading

EMERGE = "/usr/bin/emerge"

EXIT_OK = 0
EXIT_FAILURE = 1
EXIT_RESOLVE = 3
EXIT_DOWNLOAD = 4
EXIT_TRANSACTION = 5

FILE_ROOTS = {
    "sbin": ["/usr/sbin", "/sbin"],
    "libexec": ["/usr/libexec"],
    "gir": ["/usr/share/gir-1.0"],
    "typelib": [
        "/usr/lib64/girepository-1.0",
        "/usr/lib/girepository-1.0",
        "/lib64/girepository-1.0",
        "/lib/girepository-1.0",
    ],
    "res": ["/usr/share"],
    "cfg": ["/etc"],
    "man": ["/usr/share/man"],
    "info": ["/usr/share/info"],
    "locale": ["/usr/share/locale"],
    "app": ["/usr/share/applications"],
    "opt": ["/opt"],
    "rootpath": [""],
    "tag": ["/usr/share/usm-tags"],
}

LIB_ROOTS = ["/usr/lib64", "/lib64", "/usr/lib", "/lib"]
PC_ROOTS = ["/usr/lib64/pkgconfig", "/usr/share/pkgconfig", "/usr/lib/pkgconfig"]

TRANSLATED_PREFIXES = set(FILE_ROOTS) | {
    "bin", "lib", "libres", "pc", "vapi", "inc"}

USR_MERGE_ALIASES = [
    ("/lib64/", "/usr/lib64/"),
    ("/lib/", "/usr/lib/"),
    ("/bin/", "/usr/bin/"),
    ("/sbin/", "/usr/sbin/"),
]

EXCEPTIONS = {
    "bin:valac": "dev-lang/vala",
    "bin:vapigen": "dev-lang/vala",
    "bin:meson": "dev-build/meson",
    "bin:ninja": "dev-build/ninja",
    "bin:pkg-config": "dev-util/pkgconf",
    "bin:pkgconf": "dev-util/pkgconf",
    "bin:g-ir-scanner": "dev-libs/gobject-introspection",
    "bin:g-ir-compiler": "dev-libs/gobject-introspection",
    "bin:gcc": "sys-devel/gcc",
    "bin:g++": "sys-devel/gcc",
    "bin:cc": "sys-devel/gcc",
    "bin:c++": "sys-devel/gcc",
    "bin:ld": "sys-devel/binutils",
    "bin:make": "dev-build/make",
    "bin:python3": "dev-lang/python",
    "bin:bash": "app-shells/bash",
    "bin:git": "dev-vcs/git",
    "bin:curl": "net-misc/curl",
    "bin:tar": "app-arch/tar",
    "bin:xz": "app-arch/xz-utils",
    "bin:gzip": "app-arch/gzip",
    "bin:sed": "sys-apps/sed",
    "bin:awk": "sys-apps/gawk",
    "bin:grep": "sys-apps/grep",
    "bin:ldconfig": "sys-libs/glibc",
    "pc:glib-2.0.pc": "dev-libs/glib",
    "pc:gobject-2.0.pc": "dev-libs/glib",
    "pc:gio-2.0.pc": "dev-libs/glib",
    "pc:gio-unix-2.0.pc": "dev-libs/glib",
    "pc:gmodule-2.0.pc": "dev-libs/glib",
    "pc:gmodule-no-export-2.0.pc": "dev-libs/glib",
    "pc:gthread-2.0.pc": "dev-libs/glib",
    "pc:json-glib-1.0.pc": "dev-libs/json-glib",
    "pc:gee-0.8.pc": "dev-libs/libgee",
    "pc:libsodium.pc": "dev-libs/libsodium",
    "pc:libarchive.pc": "app-arch/libarchive",
    "pc:sqlite3.pc": "dev-db/sqlite",
    "pc:libxml-2.0.pc": "dev-libs/libxml2",
    "pc:libsoup-3.0.pc": "net-libs/libsoup",
    "pc:libmicrohttpd.pc": "net-libs/libmicrohttpd",
    "pc:gobject-introspection-1.0.pc": "dev-libs/gobject-introspection",
    "pc:zlib.pc": "sys-libs/zlib",
    "pc:libzstd.pc": "app-arch/zstd",
    "pc:libbrotlienc.pc": "app-arch/brotli",
    "pc:libbrotlidec.pc": "app-arch/brotli",
    "pc:libbrotlicommon.pc": "app-arch/brotli",
    "pc:libffi.pc": "dev-libs/libffi",
    "pc:pcre2.pc": "dev-libs/libpcre2",
    "vapi:glib-2.0.vapi": "dev-lang/vala",
    "vapi:gobject-2.0.vapi": "dev-lang/vala",
    "vapi:gio-2.0.vapi": "dev-lang/vala",
    "vapi:gio-unix-2.0.vapi": "dev-lang/vala",
    "vapi:posix.vapi": "dev-lang/vala",
    "vapi:json-glib-1.0.vapi": "dev-lang/vala",
    "vapi:libxml-2.0.vapi": "dev-lang/vala",
    "vapi:sqlite3.vapi": "dev-lang/vala",
    "vapi:gee-0.8.vapi": "dev-libs/libgee",
    "gir:GLib-2.0.gir": "dev-libs/gobject-introspection",
    "gir:GObject-2.0.gir": "dev-libs/gobject-introspection",
    "gir:Gio-2.0.gir": "dev-libs/gobject-introspection",
    "gir:GioUnix-2.0.gir": "dev-libs/gobject-introspection",
    "typelib:GLib-2.0.typelib": "dev-libs/gobject-introspection",
    "typelib:GObject-2.0.typelib": "dev-libs/gobject-introspection",
    "typelib:Gio-2.0.typelib": "dev-libs/gobject-introspection",
    "typelib:GioUnix-2.0.typelib": "dev-libs/gobject-introspection",
    "lib:libglib-2.0.so.0": "dev-libs/glib",
    "lib:libgobject-2.0.so.0": "dev-libs/glib",
    "lib:libgio-2.0.so.0": "dev-libs/glib",
    "lib:libgmodule-2.0.so.0": "dev-libs/glib",
    "lib:libgthread-2.0.so.0": "dev-libs/glib",
    "lib:libjson-glib-1.0.so.0": "dev-libs/json-glib",
    "lib:libgee-0.8.so.2": "dev-libs/libgee",
    "lib:libsodium.so.26": "dev-libs/libsodium",
    "lib:libarchive.so.13": "app-arch/libarchive",
    "lib:libsqlite3.so.0": "dev-db/sqlite",
    "lib:libxml2.so.2": "dev-libs/libxml2",
    "lib:libsoup-3.0.so.0": "net-libs/libsoup",
    "lib:libmicrohttpd.so.12": "net-libs/libmicrohttpd",
    "lib:libz.so.1": "sys-libs/zlib",
    "lib:libzstd.so.1": "app-arch/zstd",
    "lib:libbrotlienc.so.1": "app-arch/brotli",
    "lib:libbrotlidec.so.1": "app-arch/brotli",
    "lib:libbrotlicommon.so.1": "app-arch/brotli",
    "lib:libffi.so.8": "dev-libs/libffi",
    "lib:libpcre2-8.so.0": "dev-libs/libpcre2",
    "lib:libc.so.6": "sys-libs/glibc",
    "lib:libm.so.6": "sys-libs/glibc",
    "lib:libblkid.so.1": "sys-apps/util-linux",
    "lib:libmount.so.1": "sys-apps/util-linux",
    "lib:libuuid.so.1": "sys-apps/util-linux",
    "inc:glib-2.0": "dev-libs/glib",
    "inc:json-glib-1.0": "dev-libs/json-glib",
    "inc:gee-0.8": "dev-libs/libgee",
    "inc:libsodium.h": "dev-libs/libsodium",
    "inc:archive.h": "app-arch/libarchive",
    "inc:sqlite3.h": "dev-db/sqlite",
}


class HelperError(Exception):
    """Fatal helper failure; message is emitted as a contract error event."""

    def __init__(self, message, exit_code=EXIT_FAILURE):
        super(HelperError, self).__init__(message)
        self.exit_code = exit_code


def emit_event(event):
    """Write one contract JSONL event to STDOUT and flush it."""
    sys.stdout.write(json.dumps(event) + "\n")
    sys.stdout.flush()


def fail(message, exit_code=EXIT_FAILURE):
    """Emit the terminal error event and exit non-zero."""
    emit_event({"type": "error", "message": message})
    sys.exit(exit_code)


def fail_plain(message, exit_code=EXIT_FAILURE):
    """Report a query failure on STDERR only, keeping STDOUT contract-clean."""
    sys.stderr.write("usm-spm-emerge: %s\n" % message)
    sys.exit(exit_code)


def category_package(cpv):
    """Strip version and ::repository suffix from a cpv -> category/package."""
    atom = cpv.split("::", 1)[0]
    try:
        import portage

        key = portage.cpv_getkey(atom)
        if key:
            return key
    except Exception:
        pass
    category, sep, package_version = atom.partition("/")
    if not sep:
        return atom
    return re.sub(r"-\d.*$", "", package_version) or package_version


def parse_contents_line(line):
    """Path recorded on one CONTENTS line, or None for junk lines."""
    fields = line.split()
    if len(fields) >= 2 and fields[0] in ("obj", "dir", "sym", "dev", "fif"):
        return fields[1]
    return None


def build_vdb_index():
    """Map every installed file path -> cpv via the portage vdb.

    Prefers the portage API (aux_get CONTENTS, present on any portage
    system); falls back to a raw /var/db/pkg/<cat>/<pkg>/CONTENTS scan.
    """
    index = {}
    try:
        import portage

        root = portage.settings.get("ROOT", "/")
        vdb = portage.db[root]["vartree"].dbapi
        for cpv in vdb.cpv_all():
            raw = vdb.aux_get(cpv, ["CONTENTS"])[0] or ""
            for line in raw.splitlines():
                path = parse_contents_line(line)
                if path is not None:
                    index.setdefault(path, cpv)
        if index:
            return index
    except Exception as e:
        sys.stderr.write("usm-spm-emerge: portage API vdb read failed (%s), "
                         "falling back to /var/db/pkg scan\n" % e)
    for contents_path in glob.glob("/var/db/pkg/*/*/CONTENTS"):
        category = os.path.basename(os.path.dirname(os.path.dirname(contents_path)))
        package_version = os.path.basename(os.path.dirname(contents_path))
        cpv = category + "/" + package_version
        try:
            with open(contents_path, "r", errors="replace") as handle:
                for line in handle:
                    path = parse_contents_line(line)
                    if path is not None:
                        index.setdefault(path, cpv)
        except OSError:
            continue
    return index


def path_aliases(path):
    """path plus its /usr-merge variant(s) (/lib64/x -> /usr/lib64/x...)."""
    aliases = [path]
    for merged, unmerged in USR_MERGE_ALIASES:
        if path.startswith(merged):
            variant = unmerged + path[len(merged):]
        elif path.startswith(unmerged):
            variant = merged + path[len(unmerged):]
        else:
            continue
        if variant not in aliases:
            aliases.append(variant)
    return aliases


def bin_candidates(resource):
    """PATH directories in order (plus /usr/bin) as candidate directories."""
    directories = [d for d in os.environ.get("PATH", "").split(os.pathsep) if d]
    if "/usr/bin" not in directories:
        directories.append("/usr/bin")
    return [os.path.join(d, resource) for d in directories]


def translate_paths(prefix, resource):
    """Candidate filesystem paths for a file-backed ref prefix."""
    if prefix == "bin":
        return bin_candidates(resource)
    if prefix == "tag":
        return ["/usr/share/usm-tags/" + resource.replace(".", "/") + ".tag"]
    if prefix in FILE_ROOTS:
        return ["/".join(FILE_ROOTS[prefix] + [resource])]
    if prefix in ("lib", "libres"):
        return [os.path.join(d, resource) for d in LIB_ROOTS]
    if prefix == "pc":
        return [os.path.join(d, resource) for d in PC_ROOTS]
    return None


def resolve_installed(ref, index):
    """cpv of the installed package owning the ref's file, or None.

    Candidate paths (PATH order for bin:, gentoo root table otherwise) are
    matched exactly against the vdb index, with /usr-merge aliases tried on
    both sides; files present on disk but owned by no package do not count
    as provided by the system package manager.
    """
    prefix, sep, resource = ref.partition(":")
    if not sep or not resource:
        return None
    resource = resource.strip("/")
    if prefix == "vapi":
        pattern = re.compile(
            r"^/usr/share/vala[^/]*/vapi/" + re.escape(resource) + "$")
        for path, cpv in index.items():
            if pattern.match(path):
                return cpv
        return None
    if prefix == "inc":
        directory = "/usr/include/" + resource.strip("/")
        for path, cpv in index.items():
            if path == directory or path.startswith(directory + "/"):
                return cpv
        return None
    candidates = translate_paths(prefix, resource)
    if candidates is None:
        return None
    for path in candidates:
        for alias in path_aliases(path):
            if alias in index:
                return index[alias]
    return None


def emerge_pretend(atoms):
    """Run emerge --pretend; returns (returncode, stdout, stderr)."""
    command = [EMERGE, "--pretend", "--quiet=y", "--ask=n"] + list(atoms)
    try:
        proc = subprocess.run(
            command, stdout=subprocess.PIPE, stderr=subprocess.PIPE,
            text=True, errors="replace")
    except OSError as e:
        return EXIT_FAILURE, "", str(e)
    return proc.returncode, proc.stdout, proc.stderr


MERGE_LINE = re.compile(r"^\[(ebuild|binary)\s+([A-Za-z*]+)\s*\]\s+(\S+)")


def parse_merge_list(output):
    """(total, already_installed, atoms) from pretend output merge lines."""
    total = 0
    installed = 0
    atoms = []
    for line in output.splitlines():
        match = MERGE_LINE.match(line)
        if not match:
            continue
        total += 1
        if "N" not in match.group(2):
            installed += 1
        atoms.append(match.group(3))
    return total, installed, atoms


def pretend_counts(atom, cache):
    """(dependency-count, installed-dependency-count) for a solo emerge.

    None means the atom cannot be resolved against the tree at all (no
    ebuilds, masked, conflicting): exception-table candidates then fall
    back to not-found; installed candidates degrade to (1, 1).
    """
    if atom in cache:
        return cache[atom]
    returncode, stdout, stderr = emerge_pretend([atom])
    if returncode != 0:
        cache[atom] = None
        return None
    total, installed, _ = parse_merge_list(stdout)
    counts = (total, installed) if total else (1, 1)
    cache[atom] = counts
    return counts


def cmd_query(args):
    try:
        return run_query(args)
    except SystemExit:
        raise
    except Exception as e:
        fail_plain("query failed: %s" % e, EXIT_RESOLVE)


def run_query(args):
    index = build_vdb_index()
    refs = list(dict.fromkeys(args.refs))

    candidates = {}
    resolved_ref = {}
    for ref in refs:
        cpv = resolve_installed(ref, index)
        if cpv is not None:
            name = category_package(cpv)
        else:
            name = EXCEPTIONS.get(ref)
            if name is None:
                if ref.partition(":")[0] not in TRANSLATED_PREFIXES:
                    sys.stderr.write(
                        "usm-spm-emerge: resource type of \"%s\" has no "
                        "system-package-manager translation\n" % ref)
                continue
        resolved_ref[ref] = name
        entry = candidates.setdefault(name, {"resources": [], "installed": False})
        entry["resources"].append(ref)
        if cpv is not None:
            entry["installed"] = True

    counts_cache = {}
    package_counts = {}
    for name, entry in candidates.items():
        counts = pretend_counts(name, counts_cache)
        if counts is None and entry["installed"]:
            sys.stderr.write(
                "usm-spm-emerge: %s is installed but emerge cannot resolve "
                "its atom; estimating dependency counts as installed-only\n"
                % name)
            counts = (1, 1)
        package_counts[name] = counts

    not_found = []
    for ref in refs:
        name = resolved_ref.get(ref)
        if name is None or package_counts[name] is None:
            not_found.append(ref)

    packages = []
    for name in sorted(candidates):
        if package_counts[name] is None:
            continue
        dependency_count, installed_dependency_count = package_counts[name]
        packages.append({
            "name": name,
            "resources": candidates[name]["resources"],
            "dependency-count": dependency_count,
            "installed-dependency-count": installed_dependency_count,
        })

    sys.stdout.write(json.dumps({
        "not-found": not_found,
        "packages": packages,
    }) + "\n")
    sys.stdout.flush()
    return EXIT_OK


EMERGING_LINE = re.compile(r">>> Emerging \((\d+) of (\d+)\) (\S+)")
INSTALLING_LINE = re.compile(r">>> Installing \((\d+) of (\d+)\) (\S+)")


def classify_failure(output):
    """Map an emerge failure transcript onto a contract exit code."""
    lowered = output.lower()
    if ("all ebuilds that could satisfy" in lowered
            or "dependency conflict" in lowered
            or "conflicting requests" in lowered
            or "blocked" in lowered
            or "no ebuilds to satisfy" in lowered):
        return EXIT_RESOLVE
    if ("couldn't download" in lowered
            or "fetch instructions" in lowered
            or "failed to fetch" in lowered):
        return EXIT_DOWNLOAD
    return EXIT_TRANSACTION


NOISE_LINE = re.compile(r"^\s*\*\s+(IMPORTANT:|Use eselect news)")


def failure_message(lines, limit=15):
    """Last few meaningful output lines as a terminal error message."""
    meaningful = [line.strip() for line in lines
                  if line.strip() and not NOISE_LINE.match(line)]
    tail = meaningful[-limit:]
    message = " | ".join(tail)
    return message[:800] if message else "emerge exited non-zero"


# Gentoo installs some tool binaries under versioned names only (vala's
# ebuild ships valac-0.56 without an unversioned valac), while USM
# manifests reference the unversioned bin:. After a transaction that
# installed one of these atoms, link each unversioned name to the newest
# versioned binary so bin: refs resolve on the filesystem.
UNVERSIONED_TOOL_LINKS = {
    "dev-lang/vala": ["valac", "vala-gen-introspect", "vapigen"],
}


def link_unversioned_tools(atoms):
    """Ensure unversioned tool symlinks exist for versioned ebuild tools."""
    wanted = set()
    for atom in atoms:
        for prefix, tools in UNVERSIONED_TOOL_LINKS.items():
            if atom == prefix or atom.startswith(prefix + ":"):
                wanted.update(tools)
    for tool in sorted(wanted):
        target = os.path.join("/usr/bin", tool)
        if os.path.exists(target):
            continue
        candidates = sorted(glob.glob("/usr/bin/%s-[0-9]*" % tool))
        if candidates:
            try:
                os.symlink(os.path.basename(candidates[-1]), target)
            except OSError:
                pass


def cmd_install(args):
    returncode, stdout, stderr = emerge_pretend(args.names)
    if returncode != 0:
        fail("dependency resolution failed: %s"
             % failure_message((stdout + "\n" + stderr).splitlines()),
             EXIT_RESOLVE)
    total, _, atoms = parse_merge_list(stdout)
    emit_event({"type": "begin", "total": total})
    if args.test:
        emit_event({"type": "complete", "status": "ok", "installed": 0})
        return EXIT_OK

    command = [EMERGE, "--ask=n", "--quiet=y"] + list(args.names)
    try:
        proc = subprocess.Popen(
            command, stdout=subprocess.PIPE, stderr=subprocess.PIPE,
            text=True, errors="replace", bufsize=1)
    except OSError as e:
        fail("could not run emerge: %s" % e, EXIT_FAILURE)

    transcript = []

    def drain_stderr():
        for line in proc.stderr:
            transcript.append(line)
            sys.stderr.write(line)
            sys.stderr.flush()

    reader = threading.Thread(target=drain_stderr)
    reader.daemon = True
    reader.start()

    completed = []
    for line in proc.stdout:
        transcript.append(line)
        sys.stderr.write(line)
        sys.stderr.flush()
        emerging = EMERGING_LINE.match(line)
        if emerging:
            emit_event({
                "type": "package",
                "name": category_package(emerging.group(3)),
                "current": int(emerging.group(1)),
                "total": int(emerging.group(2)),
                "progress": 0.0,
            })
            continue
        installing = INSTALLING_LINE.match(line)
        if installing:
            name = category_package(installing.group(3))
            completed.append(name)
            emit_event({"type": "package-complete", "name": name})

    returncode = proc.wait()
    reader.join(timeout=5)
    if returncode != 0:
        fail("emerge failed (%s): %s" % (returncode, failure_message(transcript)),
             classify_failure("".join(transcript)))

    link_unversioned_tools(args.names)

    emit_event({
        "type": "complete",
        "status": "ok",
        "installed": len(completed),
    })
    return EXIT_OK


def main():
    parser = argparse.ArgumentParser(
        prog="usm-spm-emerge",
        description="USM system-package-manager helper for Portage (Gentoo)")
    subparsers = parser.add_subparsers(dest="command", required=True)

    query_parser = subparsers.add_parser(
        "query", help="resolve USM resource refs to system packages")
    query_parser.add_argument(
        "refs", nargs="+", metavar="USM-REF",
        help="resource ref, e.g. bin:valac or pc:glib-2.0.pc")
    query_parser.set_defaults(handler=cmd_query)

    install_parser = subparsers.add_parser(
        "install", help="install system packages, streaming progress events")
    install_parser.add_argument(
        "--test", action="store_true",
        help="resolve only (emerge --pretend); no packages are built")
    install_parser.add_argument(
        "names", nargs="+", metavar="ATOM",
        help="native gentoo package atom, e.g. dev-build/meson")
    install_parser.set_defaults(handler=cmd_install)

    args = parser.parse_args()
    try:
        return args.handler(args)
    except HelperError as e:
        fail(str(e), e.exit_code)
    except SystemExit:
        raise
    except Exception as e:
        message = "unexpected failure: %s" % e
        if args.command == "install":
            fail(message, EXIT_FAILURE)
        fail_plain(message, EXIT_FAILURE)


if __name__ == "__main__":
    sys.exit(main())