Use sparse-checkout

action.yml

@@ -5,6 +5,19 @@ inputs:
   github_token:
     description: 'GITHUB_TOKEN'
     default: '${{ github.token }}'
+  filter:
+    description: >
+      Partially clone against a given filter.
+    default: ""
+  use_sparse_checkout:
+    description: >
+      Wheter to use sparse-checkout
+    default: false
+  sparse_checkout:
+    description: >
+      Do a sparse checkout on given patterns.
+      Each pattern should be separated with a space.
+    default: ""
   merge:
     description: >
       Whether to actually merge the pull request or only check whether
@@ -57,6 +70,9 @@ runs:
         export GITHUB_TOKEN=${{ inputs.github_token }}
         export DEBUG=${{ inputs.debug }}
         export COMMENT=${{ inputs.comment }}
+        export FILTER=${{ inputs.filter }}
+        export USE_SPARSE_CHECKOUT=${{ inputs.use_sparse_checkout}}
+        export SPARSE_CHECKOUT="${{ inputs.sparse_checkout }}"
 
         # github.action_path is set to $REPO.
         if test "x${{ inputs.merge }}" = xtrue

src/fast-forward.sh

@@ -34,6 +34,21 @@ case "${DEBUG:-0}" in
         ;;
 esac
 
+filter_string=""
+if [[ -n "${FILTER:-}" ]]
+then
+  filter_string="--filter=${FILTER}"
+fi
+
+case "${USE_SPARSE_CHECKOUT:-false}" in
+  0 | false | False| FALSE) USE_SPARSE_CHECKOUT=false;;
+  1 | true | True | TRUE) USE_SPARSE_CHECKOUT=true;;
+  *)
+      echo "Warning: Invalid value ('$USE_SPARSE_CHECKOUT') for USE_SPARSE_CHECKOUT." >&2;
+      USE_SPARSE_CHECKOUT=false
+      ;;
+esac
+
 # Set to true to post a comment to the issue.
 case "${COMMENT:-true}" in
     0 | never | false | FALSE) COMMENT=never;;
@@ -180,8 +195,18 @@ LOG=$(mktemp)
         } | git credential approve
 
         CLONE_URL="${CLONE_URL%://*}://${GITHUB_ACTOR}@${CLONE_URL#*://}"
-        git clone --quiet --single-branch --filter=blob:none --branch "$BASE_REF" "$CLONE_URL" .
+        git clone --quiet ${filter_string} --no-checkout "$CLONE_URL" .
 
+        if [[ ${USE_SPARSE_CHECKOUT} == true ]]
+        then
+          echo "Initialize sparse-checkout"
+          git sparse-checkout init
+          if [[ -n "${SPARSE_CHECKOUT}" ]]
+          then
+            git sparse-checkout add ${SPARSE_CHECKOUT}
+          fi
+        fi
+        git checkout "$BASE_REF"
         BASE_SHA="$(git rev-parse origin/$BASE_REF 2>/dev/null)"
     fi