actions: adding a workflow to check for stale hints

.github/workflows/stale_hints.yml

@@ -0,0 +1,19 @@
+name: Check for stale hints
+on:
+  pull_request:
+  workflow_dispatch:
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        shell: bash
+    steps:
+      - uses: actions/checkout@v4
+      - run: |
+          L=$(.scripts/remove_stale_hints.sh list)
+          if [ "$L" != "" ]; then
+            echo "There are stale hints:"
+            echo "$L"
+            false
+          fi

.scripts/remove_stale_hints.sh

@@ -2,6 +2,11 @@
 
 set -eu
 
+list=false
+if [ $# -gt 0 ] && [ $1 == "list" ]; then
+	list=true
+fi
+
 declare -A files # Store all basenames in repo
 declare -A hints # Store all paths of hints in repo
 
@@ -27,7 +32,11 @@ for h0 in "${!hints[@]}"; do
 	# Given a/b/c/Foo.Bar.fst.hints, if there is no Foo.Bar.fst
 	# anywhere, then delete the hint file.
 	if ! [ -v "files[$h]" ]; then
-		echo "DELETING HINT $h0"
-		rm -f "${h0}"
+		if $list; then
+			echo "$h0"
+		else
+			echo "DELETING HINT $h0"
+			rm -f "${h0}"
+		fi
 	fi
 done