fix(cargo): raise MSRV to 1.88 to match let-chain usage

[JulianMaurin]

The workspace declares rust-version = "1.85", but the code uses
let-chains (if let … && …) — stabilized in Rust 1.88 — in
revision_history.rs, notes_push.rs, and approvals.rs. Building on
1.85–1.87 fails deep in compilation with E0658, so the declared
floor was a misleading contract.

Raise the floor to the honest minimum. Cargo now rejects older
toolchains up front ("requires rustc 1.88") instead of failing
mid-build. Prebuilt wheels are unaffected — no rustc is involved.

Raising the floor unlocks two clippy suggestions previously gated
below 1.85, applied here so the bump lands clippy-clean: collapsing
nested if let { if … } into let-chains (clippy::collapsible_if),
and OsStr::display() (stable since 1.87) instead of {:?} on the
editor path in stack note (clippy::unnecessary_debug_formatting).

Co-Authored-By: Claude Opus 4.8 (1M context) noreply@anthropic.com

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[JulianMaurin]

This pull request is part of a Mergify stack:

#	Pull Request	Link
1	fix(cargo): raise MSRV to 1.88 to match let-chain usage	#1647	👈
2	ci: harden the PR pipeline with MSRV, supply-chain, and lint gates	#1648
3	ci(release): pin action SHAs and add build/publish attestations	#1649
4	chore(deps): centralize shared dependencies in [workspace.dependencies]	#1650
5	fix(ci): resolve junit-process token via the shared auth helper	#1651
6	refactor(cli): model stack as a native clap subcommand tree	#1652
7	refactor(core): preserve error sources and print the cause chain	#1653
8	fix(self-update): exit with the GitHub-API code and retry transients	#1654
9	feat(http): honor GitHub rate limits and bound connect time	#1655
10	feat(cli): add a global --color flag and fix queue-show glyphs	#1656
11	feat(cli): add a -v/-vv verbosity ladder backed by tracing	#1657
12	feat(cli): generate shell completions and a man page	#1658
13	test: golden-snapshot the CLI surface and guard schema drift	#1659
14	refactor: dedupe the GIT_SEQUENCE_EDITOR lookup and drop port cruft	#1660
15	docs(agents): rewrite AGENTS.md for the Rust workspace	#1661

[Copilot]

Pull request overview

This pull request updates the workspace MSRV to match Rust language features now used across the codebase (notably if/while let-chains), ensuring older toolchains fail fast via Cargo’s rust-version check rather than during compilation.

Changes:

• Bump workspace rust-version from 1.85 to 1.88.
• Refactor multiple nested if let { if ... } patterns into let-chains for clippy cleanliness and readability.
• Improve stack note editor error output by using OsStr::display() instead of debug formatting.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
Cargo.toml	Raises workspace MSRV to 1.88 and documents the rationale.
crates/mergify-stack/src/stack_context.rs	Converts env-var override logic to a let-chain.
crates/mergify-stack/src/rebase_todo.rs	Converts optional exec injection check to a let-chain.
crates/mergify-stack/src/progress.rs	Collapses detail-highlighting conditions into a let-chain.
crates/mergify-stack/src/git.rs	Collapses merge-base fork-point fallback check into a let-chain.
crates/mergify-stack/src/commands/note.rs	Uses display() for editor path in error message.
crates/mergify-core/src/auth.rs	Collapses gh auth token fallback check into a let-chain.
crates/mergify-ci/src/scopes_detect/outputs.rs	Uses let-chains to combine stdin take + write failure handling.
crates/mergify-ci/src/scopes_detect/mod.rs	Uses let-chains for optional debug file listing.
crates/mergify-ci/src/junit_process/junit.rs	Collapses nested testcase mutation + guard checks into let-chains.
crates/mergify-ci/src/junit_process/command.rs	Collapses silent-failure detection condition into a let-chain.
crates/mergify-ci/src/git_refs.rs	Collapses several nested event-structure checks into let-chains.
crates/mergify-ci/src/detector.rs	Collapses GHA PR-head-SHA detection into a let-chain.

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Queued — the merge queue status continues in this comment ↓.

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Merge Queue Status

• ✅ Entered queue — 2026-06-19 07:47 UTC · Rule: default
• ✅ Checks skipped · PR is already up-to-date
• ✅ Merged — 2026-06-19 07:47 UTC · at fc4d9a6c13418972212f615305422a4e8a58e662 · squash

This pull request spent 11 seconds in the queue, including 2 seconds running CI.

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