Adding a configlet formatting check (#265)

* Adding a configlet formatting check.

.travis.yml

@@ -49,5 +49,6 @@ install:
 script:
   - bin/fetch-configlet
   - bin/configlet lint .
+  - bin/check-configlet-fmt.sh
   - cmake -G Ninja
   - ninja

bin/check-configlet-fmt.sh

@@ -0,0 +1,27 @@
+#!/usr/bin/env bash
+
+# This ensures that the track configuration files are formatted correctly.
+
+repo=$(cd "$(dirname "$0")/.." && pwd)
+configlet="${repo}/bin/configlet"
+
+if ! cfg=$($configlet fmt .); then
+    echo "configlet fmt returned non-0 exit code with output:"
+    echo "$cfg"
+    exit 1
+fi
+
+if git diff-index --quiet HEAD --; then
+    # No changes detected
+    echo "configlet fmt: no changes needed"
+    exit 0
+else
+    # Changes needed
+    echo "configlet fmt: changes needed"
+    echo "Run 'bin/fetch-configlet && bin/configlet fmt .' to apply these changes."
+    echo ""
+    git diff
+    exit 1
+fi
+
+exit 0