feat(rust): add mergify-py-shim with embedded Python fallback

[jd]

Adds the Python shim that lets the Rust binary dispatch every
command to the existing Python implementation. Phase 1.1's
deliverable: a Rust binary that, from a user's perspective,
behaves identically to the Python CLI.

What the shim does

1. Embeds the full mergify_cli/ Python source at compile time
   via include_dir!. Today the payload is ~400KB of .py files
   plus tests; Phase 1.5 will add a build-time filter to drop the
   tests tree and any __pycache__ directories.
2. On first invocation, extracts to
   ~/.cache/mergify/py/<CARGO_PKG_VERSION>/mergify_cli/ under a
   file lock. Extraction is atomic: write to a temp dir, rename,
   then write a .complete sentinel. Concurrent first-runs
   serialize safely; the fast path (sentinel present) touches only
   one exists() syscall.
3. Invokes python3 -m mergify_cli <args> with the extracted
   directory prepended to PYTHONPATH and PYTHONSAFEPATH=1
   so the cwd never shadows the extracted tree. Exit code and
   stdin/stdout/stderr are forwarded transparently.

Cache keying

Today the cache is keyed on CARGO_PKG_VERSION. Since that's
0.0.0 during dev, the cache is shared across builds — clear
~/.cache/mergify/py/ by hand when iterating on Python source
in a worktree. Phase 1.5 stamps a real version + git SHA, after
which every build invalidates cleanly.

Binary wire-up

crates/mergify-cli/src/main.rs now delegates every argv tail
to mergify_py_shim::run. When Phase 1.3+ ports the first
command, native Rust dispatch intercepts it before falling back
to the shim for un-ported commands. Phase 6 deletes the shim
crate entirely.

Known gap

python3 on PATH must have mergify_cli's runtime dependencies
(httpx, rich, pydantic, etc.) importable — the shim
embeds only the source, not site-packages. Locally you get this
via uv run; in production the Python deps have to come from
somewhere (PyPI install, a bootstrap venv, or a pip-backed
first-run step). Phase 1.5 decides the mechanism. For Phase 1.1
the shim mechanics are validated in isolation.

Tests

Three unit tests in the shim crate cover the extraction logic:
files get written, nested directories preserved, second call is
idempotent (sentinel fast-path). End-to-end smoke: uv run ./target/release/mergify --help extracts and produces Python's
help output.

Binary size: 2.6 MB. Well under the 15 MB design target.

Co-Authored-By: Claude Opus 4.7 (1M context) noreply@anthropic.com

[jd]

This pull request is part of a Mergify stack:

#	Pull Request	Link
1	feat(rust): add mergify-py-shim with embedded Python fallback	#1272	👈
2	feat(rust): add mergify-core foundation types (Phase 1.2a)	#1280
3	feat(rust): add mergify-core::http with retry + typed errors (Phase 1.2b)	#1281
4	feat(rust): port config validate to native Rust (Phase 1.3)	#1282
5	test: add port-inventory guard to catch un-ported Python commands	#1296
6	ci: add Rust release workflow targeting GitHub Release assets	#1297
7	feat(rust): port config simulate to native Rust (Phase 1.3b)	#1298
8	feat(rust): port ci scopes-send to native Rust (Phase 1.4)	#1300
9	feat(rust): port queue pause and unpause to native Rust (Phase 1.5)	#1301
10	feat(rust): port ci git-refs and ci queue-info to native Rust (Phase 1.6)	#1302

[mergify]

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[jd]

Revision history

#	Type	Changes	Date
1	initial	c7daf9b	2026-04-21 08:00 UTC
2	rebase	c7daf9b → b187fb4	2026-04-21 08:00 UTC
3	rebase	b187fb4 → 8f404aa	2026-04-21 09:10 UTC
4	rebase	8f404aa → 27194e6	2026-04-21 13:13 UTC
5	rebase	27194e6 → 1823ce5
6	rebase	1823ce5 → 7617830
7	content	7617830 → 6c4294a
8	rebase	6c4294a → 91c97d0
9	rebase	91c97d0 → b10a54b	2026-04-23 19:02 UTC

[mergify]

@jd this pull request is now in conflict 😩

[Copilot]

Pull request overview

Introduces a new Rust “Python shim” crate that embeds the existing mergify_cli/ Python sources, extracts them to a per-user cache on first run, and forwards all CLI invocations to python3 -m mergify_cli so the Rust binary behaves like the Python CLI during the port.

Changes:

• Added crates/mergify-py-shim to embed, extract (locked + atomic), and invoke the Python CLI, with unit tests for extraction behavior.
• Updated crates/mergify-cli’s main.rs to delegate all args to the shim and propagate the Python exit code.
• Wired the new shim crate into the Rust workspace dependency graph (Cargo.toml + Cargo.lock).

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
crates/mergify-py-shim/src/lib.rs	Implements embedding/extraction/invocation logic and adds unit tests.
crates/mergify-py-shim/Cargo.toml	Defines the new shim crate and its dependencies.
crates/mergify-cli/src/main.rs	Delegates CLI execution to the shim and forwards exit status/errors.
crates/mergify-cli/Cargo.toml	Adds dependency on mergify-py-shim.
Cargo.lock	Records new Rust dependency resolution for the shim crate.

---

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[kozlek]

Really impressive ! Impatient to see how you will deal with the python runtime dependencies !
What about relying on uv to install them at runtime ? (uv needs to be installed though...)

Pull request has been modified.

[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-04-24 09:21 UTC · Rule: default
• ✅ Checks passed · on draft merge queue: embarking main (f6dcf95) and #1272 together #1303
• ✅ Merged — 2026-04-24 09:28 UTC · at b10a54b4c670a056fc5837fcb1ff2a3a9a5e536c · squash

This pull request spent 6 minutes 46 seconds in the queue, including 6 minutes 24 seconds running CI.

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