feat(py): add apt_base() factory for cross-toolchain apt sharing

Author: markovejnovic

dsls/harmont-py/harmont/__init__.py

@@ -34,6 +34,7 @@
 from ._envelope import dump_registry_json
 from ._step import Step, scratch, wait
 from ._target import clear_target_cache, target  # noqa: F401  clear_target_cache used by tests
+from ._toolchain import apt_base
 from ._typing import BaseImage, Dep, Target
 from .cache import (
     CacheCompose,
@@ -140,6 +141,7 @@ def sh(
     "Pipeline",
     "Step",
     "Target",
+    "apt_base",
     "cmake",
     "compose",
     "composer",

dsls/harmont-py/harmont/_toolchain.py

@@ -77,3 +77,18 @@ def make_install_chain(
         label=f":{lang_tag}: {install_tag}",
         cache=install_cache,
     )
+
+
+def apt_base(
+    *,
+    packages: tuple[str, ...],
+    image: str | None = None,
+    label: str = ":apt: base",
+) -> Step:
+    """Create a standalone apt-base step sharable across toolchains via ``base=``."""
+    return scratch().sh(
+        apt_install_cmd(packages),
+        label=label,
+        image=image,
+        cache=CacheTTL(duration=APT_TTL),
+    )

dsls/harmont-py/tests/test_toolchain_compose.py

@@ -82,3 +82,55 @@ def test_mixed_pipeline_compiles():
     )
     assert p["version"] == "0"
     assert len(p["graph"]["nodes"]) > 0
+
+
+def _step_by_substring(p: dict, needle: str) -> dict:
+    for n in p["graph"]["nodes"]:
+        if needle in (n["step"].get("cmd") or ""):
+            return n["step"]
+    msg = f"no command step containing {needle!r}"
+    raise AssertionError(msg)
+
+
+def test_apt_base_shared_across_toolchains():
+    """Single apt-base feeds both rust and python toolchains."""
+    base = hm.apt_base(
+        packages=(
+            "curl",
+            "ca-certificates",
+            "build-essential",
+            "pkg-config",
+            "libssl-dev",
+            "python3",
+            "python3-venv",
+        ),
+    )
+    rust = hm.rust(path=".", base=base)
+    py = hm.py.uv(path="dsls/harmont-py", base=base)
+    p = hm.pipeline(
+        rust.build(),
+        py.test(),
+        default_image="ubuntu:24.04",
+    )
+    cmds = _cmds(p)
+    assert len([c for c in cmds if "apt-get install" in c]) == 1
+    assert any("sh.rustup.rs" in c for c in cmds)
+    assert any("uv" in c for c in cmds)
+
+
+def test_apt_base_default_label():
+    base = hm.apt_base(packages=("curl",))
+    assert base.label == ":apt: base"
+
+
+def test_apt_base_custom_image():
+    base = hm.apt_base(packages=("curl",), image="debian:bookworm")
+    rust = hm.rust(path=".", base=base)
+    p = hm.pipeline(rust.build(), default_image="ubuntu:24.04")
+    apt_step = _step_by_substring(p, "apt-get install")
+    assert apt_step.get("image") == "debian:bookworm"
+
+
+def test_apt_base_custom_label():
+    base = hm.apt_base(packages=("curl",), label=":lock: deps")
+    assert base.label == ":lock: deps"