Implement clean: input

.github/workflows/checkout.yml

@@ -42,6 +42,9 @@ jobs:
       - uses: ./.github/tmp/checkout
         with:
           fetch-depth: 3
+          # "Error: Can't find 'action.yml', 'action.yaml' or 'Dockerfile' under '/home/runner/work/tianon-actions/tianon-actions/.github/tmp/checkout'. Did you forget to run actions/checkout before running your local action?" 😂
+          clean: false
+          # (if we let this "checkout" run the "clean" bits, it deletes our original checkout and thus the post-run step fails 🤦)
       - run: ls -laFh
       - run: git log --oneline
       - run: touch is-it-writeable checkout/is-it-writeable
@@ -66,3 +69,13 @@ jobs:
             echo >&2 'error: depth is busted'
             exit 1
           fi
+      # test clean:
+      - uses: ./checkout
+        with:
+          fetch-depth: 1
+          path: test/checkout/subdirectory
+      - run: |
+          if [ -e test/checkout/subdirectory/is-it-writeable ]; then
+            echo >&2 'error: clean is busted'
+            exit 1
+          fi

checkout/action.yml

@@ -15,6 +15,9 @@ inputs:
 
   path: {}
 
+  clean:
+    default: true
+
   fetch-depth:
     description: 'number of commits; 0 for all'
     default: 1

checkout/checkout.sh

@@ -27,9 +27,20 @@ case "${INPUT_SET_SAFE_DIRECTORY,,}" in
 	true|yes|1) git config --global --add safe.directory "$path" ;;
 esac
 
+: clean "${INPUT_CLEAN=true}"
+case "${INPUT_CLEAN,,}" in
+	true|yes|1)
+		# https://github.com/actions/checkout/blob/cbb722410c2e876e24abbe8de2cc27693e501dcb/src/git-directory-helper.ts#L90-L124
+		if [ -e "$path" ] && { ! git -C "$path" clean -ffdx || ! git -C "$path" reset --hard HEAD; }; then
+			find "$path" -mindepth 1 -delete
+		fi
+		;;
+esac
+
 mkdir --parents --verbose "$path"
 git init --quiet "$path"
 cd "$path"
+git remote remove origin || :
 git remote add origin "$host/${INPUT_REPOSITORY%.git}.git"
 git config --local gc.auto 0