rustfmt: Add CI scripts and format onion_utils.rs

.github/workflows/build.yml

@@ -216,3 +216,20 @@ jobs:
       - name: Run default clippy linting
         run: |
           cargo clippy -- -Aclippy::erasing_op -Aclippy::never_loop -Aclippy::if_same_then_else -Dclippy::try_err
+
+  rustfmt:
+    runs-on: ubuntu-latest
+    env:
+      TOOLCHAIN: 1.63.0
+    steps:
+      - name: Checkout source code
+        uses: actions/checkout@v3
+      - name: Install Rust ${{ env.TOOLCHAIN }} toolchain
+        run: |
+          curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --profile=minimal --default-toolchain ${{ env.TOOLCHAIN }}
+          rustup override set ${{ env.TOOLCHAIN }}
+      - name: Install rustfmt
+        run: |
+          rustup component add rustfmt
+      - name: Run rustfmt checks
+        run: ci/rustfmt.sh

CONTRIBUTING.md

@@ -120,7 +120,15 @@ Coding Conventions
 ------------------
 
 Use tabs. If you want to align lines, use spaces. Any desired alignment should
-display fine at any tab-length display setting.
+display fine at any tab-length display setting. We use `rustfmt` to establish
+uniform coding standards throughout the codebase. Please run
+
+```bash
+./ci/rustfmt.sh
+```
+
+before committing and pushing any changes, as compliance will also be checked
+and enforced by our CI scripts.
 
 Our CI enforces [clippy's](https://github.com/rust-lang/rust-clippy) default
 linting

ci/rustfmt.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+set -eox pipefail
+
+# Generate initial exclusion list
+#find . -name '*.rs' -type f |sort >rustfmt_excluded_files
+
+# Run fmt
+TMP_FILE=$(mktemp)
+find . -name '*.rs' -type f |sort >$TMP_FILE
+for file in $(comm -23 $TMP_FILE rustfmt_excluded_files); do
+	echo "Checking formatting of $file"
+	rustfmt +1.63.0 --check $file
+done