Add SPM Caching Action

.gitignore

@@ -0,0 +1,2 @@
+
+.DS_Store

bin/install_swiftpm_dependencies

@@ -1,9 +1,67 @@
 #!/bin/bash -eu
 
+CUSTOM_PACKAGE_RESOLVED_PATH=${1-}
+BUILD_TYPE=${2-}
+SPM_CACHE_LOCATION="$HOME/spm"
+
+WORKSPACE_PACKAGE_RESOLVED_PATH=(*.xcworkspace/xcshareddata/swiftpm/Package.resolved)
+ROOT_PACKAGE_RESOLVED_PATH=Package.resolved
+
+# Find where Package.resolved is located
+if [[ -n "$CUSTOM_PACKAGE_RESOLVED_PATH" ]]; then
+  PACKAGE_RESOLVED_LOCATION=$CUSTOM_PACKAGE_RESOLVED_PATH
+elif  [[ -f ${WORKSPACE_PACKAGE_RESOLVED_PATH[0]} ]]; then
+  BUILD_TYPE="XCODEBUILD"
+  PACKAGE_RESOLVED_LOCATION=${WORKSPACE_PACKAGE_RESOLVED_PATH[0]}
+elif  [[ -f $ROOT_PACKAGE_RESOLVED_PATH ]]; then
+  BUILD_TYPE="SWIFT"
+  PACKAGE_RESOLVED_LOCATION=$ROOT_PACKAGE_RESOLVED_PATH
+else
+  echo "Unable to find Package.resolved"
+fi
+
+PACKAGE_RESOLVED_HASH=$(hash_file "$PACKAGE_RESOLVED_LOCATION")
+CACHE_KEY="$BUILDKITE_PIPELINE_SLUG-spm-cache-$PACKAGE_RESOLVED_HASH"
+
+# Restore SPM cache if it's available
+mkdir -p "$SPM_CACHE_LOCATION"
+cd "$SPM_CACHE_LOCATION"
+restore_cache "$CACHE_KEY"
+cd -
+
+# This will let Xcode use the system SSH config for downloading packages
 sudo defaults write com.apple.dt.Xcode IDEPackageSupportUseBuiltinSCM YES
 
 # Trust all GitHub.com and BitBucket.org keys – this allows checking out dependencies via SSH
 add_host_to_ssh_known_hosts bitbucket.org
 add_host_to_ssh_known_hosts github.com
 
-xcodebuild -resolvePackageDependencies
+# Based on the project type, resolve the packages using the correct build type
+if [[ "$BUILD_TYPE" == "XCODEBUILD" ]]; then
+  echo "	Resolving packages with \`xcodebuild\`"
+  xcodebuild \
+  -resolvePackageDependencies \
+  -clonedSourcePackagesDirPath "$SPM_CACHE_LOCATION"
+elif [[ "$BUILD_TYPE" == "SWIFT" ]]; then
+  echo "	Resolving packages with \`swift\`"
+  swift package resolve \
+  --cache-path "$SPM_CACHE_LOCATION" \
+  --verbose
+else 
+  echo "BUILD_TYPE is not set"
+fi
+
+# `checkouts` can be removed because the system can quickly generate them 
+# instead of needing to download them in the cache each time.
+# 
+# `artifacts` should be removed because it causes issues when downloading 
+# certain packages to have the artifacts already present after extracting 
+# cache
+echo "	Cleaning up cache files before saving cache"
+rm -rf "$SPM_CACHE_LOCATION/checkouts" "$SPM_CACHE_LOCATION/artifacts"
+
+# If this is the first time we've seen this particular cache key, save it for the future
+echo "	Saving SPM Cache"
+save_cache "$SPM_CACHE_LOCATION" "$CACHE_KEY" false --use_alternate_tar_config
+
+

bin/save_cache

@@ -48,7 +48,17 @@ if ! aws s3api head-object --bucket "$S3_BUCKET_NAME" --key "$CACHE_KEY" > /dev/
 	echo "No existing cache entry for $CACHE_KEY – storing in cache"
 
 	echo "	Compressing"
-	tar -czf "$CACHE_KEY" "$CACHE_FILE"
+	TAR_CONFIG=${4-}
+	if [[ "$TAR_CONFIG" == '--use_alternate_tar_config' ]]; then
+		# This is used by actions such as `install_swiftpm_dependencies`
+		# This configuration allows the tar to not include the full system path of the
+		# directory that's being archived. For example, this will save only the 
+		# "DIRECTORY_BEING_ARCHIVED" in `/User/builder/DIRECTORY_BEING_ARCHIVED` 
+		# instead of also creating `/User/builder` when extracting the archive
+		tar -czf "$CACHE_KEY" -C "$CACHE_FILE" .		
+	else
+		tar -czf "$CACHE_KEY" "$CACHE_FILE"
+	fi
 
 	echo "	Uploading"
 	# If the bucket has transfer acceleration enabled, use it!