rustfmt

Q: Format tests directory?

Yes - cargo fmt --all includes tests and benches.

Q: How ignore one file?

ignore = ["src/ffi/generated.rs"] in rustfmt.toml.

Q: CI on Windows?

Set newline_style = "Unix" for consistent line endings in snapshots and fmt.

Q: Format before commit?

pre-commit hook or editor format-on-save; CI --check as backstop.

Q: Workspace member override?

Nested rustfmt.toml in member crate overrides root for that crate only.

Q: fmt in merge conflicts?

Re-run cargo fmt after resolving; avoid hand-aligning braces.

rustfmt (via cargo fmt) enforces consistent Rust formatting so reviews focus on behavior, not brace placement.

Recipe

cargo fmt
cargo fmt --check

# rustfmt.toml
edition = "2024"
max_width = 100
imports_granularity = "Module"

When to reach for this: Every Rust project; run on save locally and --check in CI.

Working Example

# rustfmt.toml at repo root
edition = "2024"
max_width = 100
newline_style = "Unix"
use_small_heuristics = "Max"

- run: cargo fmt --all -- --check

What this demonstrates:

edition aligns formatter with language edition
--check fails CI on drift without writing files
rustfmt.toml applies workspace-wide when at root
cargo fmt --all includes workspace members

Deep Dive

Common Options

Option	Effect
`max_width`	Line wrap column
`chain_width`	Method chain breaking
`format_code_in_doc_comments`	Format doctests
`group_imports`	Merge/use import style

Editor Integration

rust-analyzer rust-analyzer.rustfmt.extraArgs
Format on save in VS Code / Cursor with rust-analyzer
Pre-commit hook: cargo fmt --check

Gotchas

Different rustfmt versions - CI vs local diff noise. Fix: pin toolchain in rust-toolchain.toml to 1.97.0.
Generated files formatted - merge pain. Fix: exclude in rustfmt.toml ignore paths or do not commit generated sources.
Macro-heavy code ugly - rustfmt limitations. Fix: #[rustfmt::skip] sparingly with comment why.
Skipping fmt in PR - style debates return. Fix: zero tolerance --check on main.
Edition mismatch - wrong import reorder rules. Fix: edition = "2024" in rustfmt.toml matches Cargo.toml.

Alternatives

Alternative	Use When	Don't Use When
Manual style guide	Never for Rust teams	Always - use rustfmt
`dprint` with rust plugin	Polyglot repos	Pure Rust workspace
`#[rustfmt::skip]`	FFI layout-critical blocks	Entire modules

FAQs

Where put rustfmt.toml?

Repo root for workspaces; applies to all members unless overridden per crate.

fmt vs clippy?

fmt is style only; clippy is lint logic. Run both in CI.

Format tests directory?

Yes - cargo fmt --all includes tests and benches.

How ignore one file?

ignore = ["src/ffi/generated.rs"] in rustfmt.toml.

Does fmt change semantics?

No - only whitespace and import order; still run tests after large reformats.

rustfmt on stable?

Ships with Rust 1.97 toolchain; no separate install.

CI on Windows?

Set newline_style = "Unix" for consistent line endings in snapshots and fmt.

Format before commit?

pre-commit hook or editor format-on-save; CI --check as backstop.

Workspace member override?

Nested rustfmt.toml in member crate overrides root for that crate only.

fmt in merge conflicts?

Re-run cargo fmt after resolving; avoid hand-aligning braces.

Clippy - linting companion
Pre-commit & Editor Setup - local workflow
Linting in CI - pipeline
Linting & Formatting Best Practices - team policy

Stack versions: This page was written for Rust 1.97.0 (edition 2024), Tokio 1.x, Axum 0.8, serde 1.0, sqlx 0.8, clap 4, and Polars 0.46+.

Recipe

cargo fmt
cargo fmt --check

# rustfmt.toml
edition = "2024"
max_width = 100
imports_granularity = "Module"

When to reach for this: Every Rust project; run on save locally and --check in CI.

Working Example

# rustfmt.toml at repo root
edition = "2024"
max_width = 100
newline_style = "Unix"
use_small_heuristics = "Max"

- run: cargo fmt --all -- --check

What this demonstrates:

edition aligns formatter with language edition
--check fails CI on drift without writing files
rustfmt.toml applies workspace-wide when at root
cargo fmt --all includes workspace members

Deep Dive

Common Options

Option	Effect
`max_width`	Line wrap column
`chain_width`	Method chain breaking
`format_code_in_doc_comments`	Format doctests
`group_imports`	Merge/use import style

Editor Integration

rust-analyzer rust-analyzer.rustfmt.extraArgs
Format on save in VS Code / Cursor with rust-analyzer
Pre-commit hook: cargo fmt --check

Gotchas

Different rustfmt versions - CI vs local diff noise. Fix: pin toolchain in rust-toolchain.toml to 1.97.0.
Generated files formatted - merge pain. Fix: exclude in rustfmt.toml ignore paths or do not commit generated sources.
Macro-heavy code ugly - rustfmt limitations. Fix: #[rustfmt::skip] sparingly with comment why.
Skipping fmt in PR - style debates return. Fix: zero tolerance --check on main.
Edition mismatch - wrong import reorder rules. Fix: edition = "2024" in rustfmt.toml matches Cargo.toml.

Alternatives

Alternative	Use When	Don't Use When
Manual style guide	Never for Rust teams	Always - use rustfmt
`dprint` with rust plugin	Polyglot repos	Pure Rust workspace
`#[rustfmt::skip]`	FFI layout-critical blocks	Entire modules

FAQs

Where put rustfmt.toml?

Repo root for workspaces; applies to all members unless overridden per crate.

fmt vs clippy?

fmt is style only; clippy is lint logic. Run both in CI.

Format tests directory?

Yes - cargo fmt --all includes tests and benches.

How ignore one file?

ignore = ["src/ffi/generated.rs"] in rustfmt.toml.

Does fmt change semantics?

No - only whitespace and import order; still run tests after large reformats.

rustfmt on stable?

Ships with Rust 1.97 toolchain; no separate install.

CI on Windows?

Set newline_style = "Unix" for consistent line endings in snapshots and fmt.

Format before commit?

pre-commit hook or editor format-on-save; CI --check as backstop.

Workspace member override?

Nested rustfmt.toml in member crate overrides root for that crate only.

fmt in merge conflicts?

Re-run cargo fmt after resolving; avoid hand-aligning braces.

Clippy - linting companion
Pre-commit & Editor Setup - local workflow
Linting in CI - pipeline
Linting & Formatting Best Practices - team policy

Stack versions: This page was written for Rust 1.97.0 (edition 2024), Tokio 1.x, Axum 0.8, serde 1.0, sqlx 0.8, clap 4, and Polars 0.46+.

rustfmt

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