refactor: enforce line width and import ordering with nightly rustfmt (#2383)

## What changes are proposed in this pull request?
This PR switches our usage of `cargo fmt` to `cargo +nightly fmt` in
order to leverage additional formatter features that are not yet
supported in `stable`. Namely:
1. the ability to break comments at specific line width
2. Re-order imports following consistent grouping pattern

Since this is only for formatting purposes, I believe using `nightly`
cargo is low risk. It does not affect the actual version of Rust we
compile with.

**Note for reviewers:**
It's a large PR but the changes are primarily generated from the
formatter, key changes to review are:
- `.github/workflows/build.yml`
- `rustfmt.toml` (contains the specific formatting rules we desire)

## How was this change tested?
Run tests and clippy

Author: kyli87

.github/workflows/build.yml

@@ -10,7 +10,7 @@ env:
 # enforce the committed Cargo.lock. This prevents CI from silently resolving a newer
 # (potentially compromised) dependency version. If Cargo.lock is out of sync with
 # Cargo.toml, the build fails immediately. Any dependency change must be an explicit,
-# reviewable update to Cargo.lock in the PR. Commands that skip --locked: cargo fmt
+# reviewable update to Cargo.lock in the PR. Commands that skip --locked: cargo +nightly fmt
 # (no dep resolution), cargo msrv verify/show (wrapper tool), cargo miri setup (tooling).
 #
 # Swatinem/rust-cache caches the cargo registry and target directory (~450MB per job).
@@ -41,13 +41,14 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.3.1
-      - name: Install minimal stable with rustfmt
+      - name: Install nightly with rustfmt
         uses: actions-rust-lang/setup-rust-toolchain@150fca883cd4034361b621bd4e6a9d34e5143606 # v1.15.4
         with:
           cache: false
+          toolchain: nightly
           components: rustfmt
       - name: format
-        run: cargo fmt -- --check
+        run: cargo +nightly fmt -- --check
 
   msrv:
     runs-on: ubuntu-latest

CLAUDE.md

@@ -30,7 +30,7 @@ cargo nextest run -p delta_kernel --lib --all-features test_name_here
 cargo nextest run --workspace --all-features test_name_here
 
 # Format, lint, and doc check (always run after code changes)
-cargo fmt \
+cargo +nightly fmt \
   && cargo clippy --workspace --benches --tests --all-features -- -D warnings \
   && cargo doc --workspace --all-features --no-deps
 
@@ -39,7 +39,7 @@ cargo clippy --workspace --no-default-features --features arrow \
   --exclude delta_kernel --exclude delta_kernel_ffi --exclude delta_kernel_derive --exclude delta_kernel_ffi_macros -- -D warnings
 
 # Quick pre-push check (mimics CI)
-cargo fmt \
+cargo +nightly fmt \
   && cargo clippy --workspace --benches --tests --all-features -- -D warnings \
   && cargo doc --workspace --all-features --no-deps \
   && cargo nextest run --workspace --all-features
@@ -226,7 +226,7 @@ and data flow. Keep it concise.
 a newer (potentially compromised) transitive dependency. If `Cargo.lock` is out of sync with
 `Cargo.toml`, the build fails immediately, forcing dependency changes to be explicit and
 reviewable. See the top-level comment in `build.yml` for full rationale. Commands exempt from
-`--locked`: `cargo fmt` (no dep resolution), `cargo msrv verify/show` (wrapper tool),
+`--locked`: `cargo +nightly fmt` (no dep resolution), `cargo msrv verify/show` (wrapper tool),
 `cargo miri setup` (tooling setup).
 
 Ensure that when writing any github action you are considering safety including thinking of

CONTRIBUTING.md

@@ -93,7 +93,7 @@ Our trunk branch is named `main`. Here's the typical workflow:
    # build docs
    cargo doc --workspace --all-features
    # highly recommend editor that automatically formats, but in case you need to:
-   cargo fmt
+   cargo +nightly fmt
 
    # run more tests
    cargo test --workspace --all-features -- --skip read_table_version_hdfs
@@ -116,7 +116,7 @@ Our trunk branch is named `main`. Here's the typical workflow:
 #### General Tips
 
 1. When making your first PR, please read our contributor guidelines: https://github.com/delta-incubator/delta-kernel-rs/blob/main/CONTRIBUTING.md
-2. Run `cargo t --all-features --all-targets` to get started testing, and run `cargo fmt`.
+2. Run `cargo t --all-features --all-targets` to get started testing, and run `cargo +nightly fmt`.
 3. Ensure you have added or run the appropriate tests for your PR.
 4. If the PR is unfinished, add '[WIP]' in your PR title, e.g., '[WIP] Your PR title ...'.
 5. Be sure to keep the PR description updated to reflect all changes.

acceptance/src/acceptance_workloads/mod.rs

@@ -19,7 +19,6 @@
 //!       expected_metadata/    # Expected add files after data skipping as Parquet files
 //!         part-aaaaa.parquet
 //!         part-bbbbb.parquet
-//!
 //! ```
 //!
 //! ## Expected Data Format

acceptance/src/acceptance_workloads/validation.rs

@@ -7,20 +7,18 @@
 use std::fs::{self, File};
 use std::path::Path;
 
-use delta_kernel::arrow::datatypes::Schema as ArrowSchema;
-use delta_kernel::engine::arrow_conversion::TryFromKernel;
-use itertools::Itertools;
-use tracing::debug;
-
 use delta_kernel::arrow::array::RecordBatch;
 use delta_kernel::arrow::compute::concat_batches;
+use delta_kernel::arrow::datatypes::Schema as ArrowSchema;
+use delta_kernel::engine::arrow_conversion::TryFromKernel;
 use delta_kernel::parquet::arrow::arrow_reader::ParquetRecordBatchReaderBuilder;
 use delta_kernel::DeltaResult;
 use delta_kernel_benchmarks::models::{ReadExpected, SnapshotExpected};
-
-use crate::data::assert_data_matches;
+use itertools::Itertools;
+use tracing::debug;
 
 use super::workload::{ReadResult, SnapshotResult};
+use crate::data::assert_data_matches;
 
 /// Read expected data from parquet files in expected_dir/expected_data/.
 fn read_expected_data(expected_dir: &Path) -> Result<RecordBatch, String> {

acceptance/src/acceptance_workloads/workload.rs

@@ -2,7 +2,6 @@
 
 use std::sync::Arc;
 
-use super::validation::{validate_read_result, validate_snapshot};
 use delta_kernel::actions::{Metadata, Protocol};
 use delta_kernel::arrow::array::RecordBatch;
 use delta_kernel::arrow::compute::filter_record_batch;
@@ -17,6 +16,8 @@ use delta_kernel_benchmarks::predicate_parser::parse_predicate;
 use itertools::Itertools;
 use url::Url;
 
+use super::validation::{validate_read_result, validate_snapshot};
+
 /// Result of executing a read workload.
 #[derive(Debug)]
 pub struct ReadResult {

acceptance/src/data.rs

@@ -1,18 +1,20 @@
-use std::{path::Path, sync::Arc};
+use std::path::Path;
+use std::sync::Arc;
 
 use delta_kernel::arrow::array::RecordBatch;
 use delta_kernel::arrow::compute::concat_batches;
 use delta_kernel::arrow::datatypes::{DataType, Field, Fields, Schema, SchemaRef};
 use delta_kernel::arrow::util::pretty::pretty_format_batches;
-
 use delta_kernel::engine::arrow_data::EngineDataArrowExt as _;
-use delta_kernel::object_store::{local::LocalFileSystem, ObjectStore};
+use delta_kernel::object_store::local::LocalFileSystem;
+use delta_kernel::object_store::ObjectStore;
 use delta_kernel::parquet::arrow::async_reader::{
     ParquetObjectReader, ParquetRecordBatchStreamBuilder,
 };
 use delta_kernel::snapshot::Snapshot;
 use delta_kernel::{DeltaResult, Engine, Error};
-use futures::{stream::TryStreamExt, StreamExt};
+use futures::stream::TryStreamExt;
+use futures::StreamExt;
 use itertools::Itertools;
 
 use crate::{TestCaseInfo, TestResult};

acceptance/src/meta.rs

@@ -3,13 +3,14 @@ use std::fs::File;
 use std::path::{Path, PathBuf};
 use std::sync::Arc;
 
-use delta_kernel::object_store::{local::LocalFileSystem, path::Path as ObjectPath, ObjectStore};
+use delta_kernel::object_store::local::LocalFileSystem;
+use delta_kernel::object_store::path::Path as ObjectPath;
+use delta_kernel::object_store::ObjectStore;
+use delta_kernel::{Engine, Error, Snapshot, Version};
 use futures::stream::TryStreamExt;
 use serde::{Deserialize, Serialize};
 use url::Url;
 
-use delta_kernel::{Engine, Error, Snapshot, Version};
-
 #[derive(Debug, thiserror::Error)]
 pub enum AssertionError {
     #[error("Invalid test case data")]

acceptance/tests/acceptance_workloads_reader.rs

@@ -5,7 +5,8 @@
 
 use std::path::Path;
 
-use acceptance::acceptance_workloads::{workload::execute_and_validate_workload, TestCase};
+use acceptance::acceptance_workloads::workload::execute_and_validate_workload;
+use acceptance::acceptance_workloads::TestCase;
 
 /// Tests that cannot be executed due to test harness limitations.
 /// These fail at parse time or cause infrastructure issues (OOM, hang).

benchmarks/benches/workload_bench.rs

@@ -2,7 +2,6 @@ use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::Arc;
 
 use criterion::{criterion_group, criterion_main, Criterion};
-
 use delta_kernel_benchmarks::models::{
     default_read_configs, ParallelScan, ReadConfig, ReadOperation, Spec,
 };
@@ -77,7 +76,8 @@ fn run_benchmark(c: &mut Criterion, runner: &dyn WorkloadRunner, reporter: &Coun
 
 fn build_read_configs(table_name: &str) -> Vec<ReadConfig> {
     // Choose which benchmark configurations to run for a given table
-    // TODO: This function will take in table info to choose the appropriate configs for a given table
+    // TODO: This function will take in table info to choose the appropriate configs for a given
+    // table
     let mut configs = default_read_configs();
     if table_name.contains("V2Chkpt") {
         configs.push(ReadConfig {