refactor!(action): detect when in private branches

This removes the need to use the private-repo-workaround input.

retrieve-old-report.sh

@@ -1,6 +1,23 @@
+#!/bin/sh
+
 . "${GITHUB_ACTION_PATH}/utils.sh"
 
-# USAGE: base_report_url
+repo_info() {
+	curl -X GET \
+		-H "Authorization: token $GITHUB_TOKEN" \
+		-H 'accept: application/json' \
+		"$GITHUB_API_URL/repos/$GITHUB_REPOSITORY"
+}
+
+in_private_repo() {
+	test "$(repo_info | jq --raw-output '.private')" = 'true'
+}
+
+default_branch() {
+	repo_info | jq --raw-output '.default_branch'
+}
+
+# USAGE: base_report_url <BASE_BRANCH>
 base_report_url() {
 	curl -X 'GET' \
 		"$GITHUB_API_URL/repos/$GITHUB_REPOSITORY/actions/tasks" \
@@ -8,9 +25,10 @@ base_report_url() {
 		-H 'accept: application/json' |
 		jq --raw-output \
 			--arg name "$JOB_NAME" \
-			--arg head_branch "$HEAD_BRANCH" \
+			--arg head_branch "$1" \
 			'[.workflow_runs[] | select(.name == $name and .head_branch == $head_branch)] | first | .url'
 }
+
 # USAGE: has_report <REPORT_URL>
 has_report() {
 	http_code=$(curl -X 'GET' -o /dev/null --silent -Iw '%{http_code}' \
@@ -19,23 +37,11 @@ has_report() {
 	test "$http_code" = '200'
 }
 
-# If we have a previous report compare against it
-if [ "$PRIVATE_REPO" = 'true' ]; then
-	log "In a private repo, downloading $HEAD_BRANCH to build the old report"
+# If a base branch is not provided, use the default branch
+base_branch=${BASE_BRANCH-$(default_branch)}
 
-	old=$(mktemp -d)
-	group 'Downloaded files'
-	curl -X 'GET' \
-		"$GITHUB_API_URL/repos/$GITHUB_REPOSITORY/archive/$HEAD_BRANCH.tar.gz" \
-		-H "Authorization: token $GITHUB_TOKEN" |
-		tar -zvx --strip-components=1 -C "$old"
-	endgroup
-
-	(cd "$old" && "$GITHUB_ACTION_PATH/create-report.sh") >old-report.json
-
-	exit 0
-elif [ "$JOB_NAME" ] && [ "$HEAD_BRANCH" ]; then
-	url=$(base_report_url)
+if [ "$(in_private_repo)" != 'true' ] && [ "$JOB_NAME" ]; then
+	url=$(base_report_url "$base_branch")
 
 	log "Found previous run at: $url"
 	report_url="$url/artifacts/$ARTIFACT_NAME"
@@ -46,11 +52,28 @@ elif [ "$JOB_NAME" ] && [ "$HEAD_BRANCH" ]; then
 			"$report_url" \
 			-H "Authorization: token $GITHUB_TOKEN" |
 			gunzip >old-report.json
-		log "Reporting on sizes and comparing to sizes in $HEAD_BRANCH"
+		log "Reporting on sizes and comparing to sizes in $base_branch"
 		exit 0
-	else
-		log "Failed to find previous report, expected at: $report_url"
 	fi
+	error "Failed to find previous report, expected at: $report_url"
 fi
 
-exit 1
+warn "Couldn't retrieve old report:"
+warn '    This usuially happens when running on private repos'
+warn '    or when job-name is not set.'
+warn
+warn '    See the README for more details'
+
+error "Falling back to slow method (checkout $base_branch and generate the report)"
+
+old=$(mktemp -d)
+group "Download files from $base_branch"
+curl -X 'GET' \
+	"$GITHUB_API_URL/repos/$GITHUB_REPOSITORY/archive/$base_branch.tar.gz" \
+	-H "Authorization: token $GITHUB_TOKEN" |
+	tar -zvx --strip-components=1 -C "$old"
+endgroup
+
+(cd "$old" && "$GITHUB_ACTION_PATH/create-report.sh") >old-report.json
+
+exit 0