feat(rust): port config validate to native Rust (Phase 1.3)

[jd]

First native command. Exercises every piece of the foundations
work so far — HTTP fetch, JSON-schema validation, output
discipline, typed exit codes — and proves the shim-fallback
dispatch pattern.

What ports natively

mergify config validate [-f PATH]:

1. Resolves the config file (explicit --config-file or the
   first of .mergify.yml, .mergify/config.yml,
   .github/mergify.yml).
2. Parses it as YAML via serde_norway. Empty files are treated
   as an empty mapping; non-mapping top-level values are rejected.
3. Fetches the published schema from
   https://docs.mergify.com/mergify-configuration-schema.json
   via the Phase 1.2b HTTP client (30s timeout, retry on 5xx).
4. Validates with the jsonschema crate (draft-07).
5. Emits a human-readable success line or a sorted, path-prefixed
   per-error list via Output::emit.

Exit codes: success → 0, missing / unparseable / schema violations
→ 8 (CONFIGURATION_ERROR), schema-fetch failure → 6
(MERGIFY_API_ERROR).

Dispatch

mergify-cli/src/main.rs inspects argv for a config validate
pair; if present, it parses with clap and runs the native path.
Everything else — including config simulate, every stack
command, the global --version / --help, plus any invalid
invocation — falls through to the Python shim unchanged. Clap is
loaded only when a native match is suspected, so unknown flags on
un-ported commands still produce Python's click error messages
verbatim.

Smoke-tested against the real docs CDN

Missing config → exit 8. Valid config → exit 0. Invalid config →
detailed error list + summary, exit 8. mergify --version still
falls through to Python.

Test coverage

11 unit tests in mergify-config:

• resolve_config_path with explicit, default, and missing paths
• load_yaml happy path, scalar rejection, malformed YAML,
  empty-file-is-empty-mapping
• validate_against_schema happy path + error aggregation
• emit_result for success and failure rendering

Binary size

2.7 MB → 8.0 MB. The jump is jsonschema pulling fancy-regex + the
referencing crate's schema resolver. Still well under the 15 MB
design target; we can trim with features later if needed.

Follow-up

• 1.3b: port config simulate
• 1.4+: ci commands (first CI-facing wins for the port story)

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): port config validate to native Rust (Phase 1.3)	#1282	👈
2	test: add port-inventory guard to catch un-ported Python commands	#1296
3	ci: add Rust release workflow targeting GitHub Release assets	#1297
4	feat(rust): port config simulate to native Rust (Phase 1.3b)	#1298
5	feat(rust): port ci scopes-send to native Rust (Phase 1.4)	#1300
6	feat(rust): port queue pause and unpause to native Rust (Phase 1.5)	#1301
7	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	Reason	Date
1	initial	08627d5	2026-04-21 13:13 UTC
2	rebase	08627d5 → 8b898c2	2026-04-21 13:13 UTC
3	rebase	8b898c2 → 6ee2535		2026-04-22 13:36 UTC
4	rebase	6ee2535 → 538f82f		2026-04-22 18:25 UTC
5	rebase	538f82f → e20964f		2026-04-23 07:32 UTC
6	rebase	e20964f → bdfd8c0		2026-04-23 13:14 UTC
7	rebase	bdfd8c0 → 1bccca9	2026-04-23 19:02 UTC
8	rebase	1bccca9 → db76eee	2026-04-24 13:41 UTC
9	rebase	e40a308 → ce71a83		2026-04-27 07:03 UTC
10	rebase	ce71a83 → 6470fc5		2026-04-28 06:48 UTC
11	rebase	6470fc5 → a286dbf		2026-04-28 14:09 UTC

[mergify]

@jd this pull request is now in conflict 😩

Pull request has been modified.

[mergify]

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• ✅ Entered queue — 2026-04-28 15:01 UTC · Rule: default
• ✅ Checks skipped · PR is already up-to-date
• ✅ Merged — 2026-04-28 15:02 UTC · at a286dbfa4620b07379ff12c715ecf16253728245 · squash

This pull request spent 48 seconds in the queue, including 2 seconds running CI.

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