Handle publishing of packages using Yarn Classic / NPM (#87)

* feat: fall back to NPM_TOKEN if YARN_NPM_AUTH_TOKEN not set
* fix: use npm for publish when yarn berry not available
* ci: add missing PUBLISH_NPM_TAG env var

---------

Co-authored-by: Elliot Winkler <elliot.winkler@gmail.com>

.github/workflows/test-monorepo.yml

@@ -42,4 +42,4 @@ jobs:
           cd skunkworks
           yarn install --immutable
           yarn plugin import workspace-tools
-          NPM_TOKEN="test" ../action-npm-publish/scripts/main.sh
+          PUBLISH_NPM_TAG="latest" NPM_TOKEN="test" ../action-npm-publish/scripts/main.sh

scripts/publish.sh

@@ -1,15 +1,38 @@
 #!/usr/bin/env bash
 
-set -x
 set -e
 set -o pipefail
 
+export YARN_NPM_AUTH_TOKEN="${YARN_NPM_AUTH_TOKEN:-$NPM_TOKEN}"
+
+YARN_MAJOR="$(yarn --version | sed 's/\..*//' || true)"
+if [[ "$YARN_MAJOR" -ge "3" ]]; then
+  PUBLISH_CMD="yarn npm publish --tag $PUBLISH_NPM_TAG"
+  PACK_CMD="yarn pack --out /tmp/%s-%v.tgz"
+  # install is handled by yarn berry pack/publish
+  INSTALL_CMD=""
+  LOGIN_CMD=""
+else
+  echo "Warning: Did not detect compatible yarn version. This action officially supports Yarn v3 and newer. Falling back to using npm." >&2
+  echo "//registry.npmjs.org/:_authToken=${YARN_NPM_AUTH_TOKEN}" >> $HOME/.npmrc
+  PUBLISH_CMD="npm publish --tag $PUBLISH_NPM_TAG"
+  PACK_CMD="npm pack --pack-destination=/tmp/"
+  if [[ -f 'yarn.lock' ]]; then
+    INSTALL_CMD="yarn install --frozen-lockfile"
+  else
+    INSTALL_CMD="npm ci"
+  fi
+fi
+
 if [[ -z $YARN_NPM_AUTH_TOKEN ]]; then
-  echo "Notice: 'npm-token' not set. Running 'yarn pack'."
-  yarn pack --out /tmp/%s-%v.tgz
+  echo "Notice: 'npm-token' not set. Running '$PACK_CMD'."
+  $INSTALL_CMD
+  $PACK_CMD
   exit 0
 fi
 
+set -x
+
 if [[ -z $PUBLISH_NPM_TAG ]]; then
   echo "Notice: 'npm-tag' not set."
   exit 1
@@ -34,4 +57,6 @@ if [[ -n "$1" ]]; then
   fi
 fi
 
-yarn npm publish --tag "$PUBLISH_NPM_TAG"
+$INSTALL_CMD
+$PUBLISH_CMD
+rm -f $HOME/.npmrc