Add a script to automatically rustfmt all required files

As we now require `rustfmt` pass on a subset of our files, its
helpful to have a script which will automatically format any
required files so that contributors don't need to think too hard
about it.

CONTRIBUTING.md

@@ -124,7 +124,7 @@ 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
+./contrib/run-rustfmt.sh
 ```
 
 before committing and pushing any changes, as compliance will also be checked

contrib/run-rustfmt.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+set -eo pipefail
+
+# Generate initial exclusion list
+#find . -name '*.rs' -type f |sort >rustfmt_excluded_files
+
+# The +rustversion syntax only works with rustup-installed rust toolchains,
+# not with any distro-provided ones. Thus, we check for a rustup install and
+# only pass +1.63.0 if we find one.
+VERS=""
+[ "$(which rustup)" != "" ] && VERS="+1.63.0"
+
+# Run fmt
+TMP_FILE=$(mktemp)
+find . -name '*.rs' -type f |sort >$TMP_FILE
+for file in $(comm -23 $TMP_FILE rustfmt_excluded_files); do
+	echo "Formatting $file..."
+	rustfmt $VERS --edition 2021 $file
+done