chore: Add imports_granularity=Module to rustfmt config

.github/actions/bitcoin-int-tests/Dockerfile.rustfmt

@@ -9,4 +9,4 @@ RUN rustup component add rustfmt
 
 COPY . .
 
-RUN cargo fmt --all -- --check
+RUN cargo fmt --all -- --check --config group_imports=StdExternalCrate,imports_granularity=Module

CONTRIBUTING.md

@@ -101,8 +101,8 @@ you push your code. Follow these instruction to set it up:
 2. Change the content of `.git/hooks/pre-commit` to be the following
 ```sh
 #!/bin/sh
-git diff --name-only --staged | grep '\.rs$' | xargs -P 8 -I {} rustfmt {} --edition 2021 --check --config group_imports=StdExternalCrate || (
-  echo 'rustfmt failed: run "cargo fmt --all -- --config group_imports=StdExternalCrate"';
+git diff --name-only --staged | grep '\.rs$' | xargs -P 8 -I {} rustfmt {} --edition 2021 --check --config group_imports=StdExternalCrate,imports_granularity=Module || (
+  echo 'rustfmt failed: run "cargo fmt --all -- --config group_imports=StdExternalCrate,imports_granularity=Module"';
   exit 1
 )
 ```
@@ -384,19 +384,24 @@ A test should be marked `#[ignore]` if:
 
 ## Formatting
 
-This repository uses the default rustfmt formatting style. PRs will be checked against `rustfmt` and will _fail_ if not
-properly formatted.
+PRs will be checked against `rustfmt` and will _fail_ if not properly formatted.
+Unfortunately, some config options that we require cannot currently be set in `.rustfmt` files currently, so arguments must be passed via the command line.
+There is a Makefile target to simplify calling `cargo fmt` with the desired config.
 
 You can check the formatting locally via:
 
 ```bash
-cargo fmt --all -- --check --config group_imports=StdExternalCrate
+cargo fmt --all -- --check --config group_imports=StdExternalCrate,imports_granularity=Module
+# Or
+make fmt-check
 ```
 
 You can automatically reformat your commit via:
 
 ```bash
-cargo fmt --all -- --config group_imports=StdExternalCrate
+cargo fmt --all -- --config group_imports=StdExternalCrate,imports_granularity=Module
+# Or
+make fmt
 ```
 
 ## Comments

Makefile

@@ -0,0 +1,11 @@
+# Shortcuts for common commands
+
+.PHONY: fmt fmt-check
+
+# Run `cargo fmt` with CLI options not available in rustfmt.toml
+fmt:
+	cargo fmt -- --config group_imports=StdExternalCrate,imports_granularity=Module
+
+# Run `cargo fmt` with CLI options not available in rustfmt.toml (check only)
+fmt-check:
+	cargo fmt -- --check --config group_imports=StdExternalCrate,imports_granularity=Module