CI: skip publishing nightly build when no new commits since last publish

Attempting to publish an already published version using `sbt-sonatype`
fails with a "Failed to promote the repository" error.

There don't appear to be any configuration settings in `sbt-sontaype`
for avoiding this, so instead we ask for published versions from the
Maven Central metadata and skip the publish step if we find a match.

Author: griggt

.github/workflows/ci.yaml

@@ -447,7 +447,20 @@ jobs:
       - name: Add SBT proxy repositories
         run: cp -vf .github/workflows/repositories /root/.sbt/ ; true
 
+      - name: Get version string for this build
+        run: |
+          ver=$(./project/scripts/sbt "print scala3-compiler-bootstrapped/version" | tail -n1)
+          echo "This build version: $ver"
+          echo "THISBUILD_VERSION=$ver" >> $GITHUB_ENV
+
+      - name: Check whether not yet published
+        id: not_yet_published
+        continue-on-error: true
+        run: |
+          ! ./project/scripts/is-version-published.sh "$THISBUILD_VERSION"
+
       - name: Publish Nightly
+        if: "steps.not_yet_published.outcome == 'success'"
         run: |
           ./project/scripts/sbtPublish ";project scala3-bootstrapped ;publishSigned ;sonatypeBundleRelease"
 

project/scripts/is-version-published.sh

@@ -0,0 +1,47 @@
+#!/usr/bin/env bash
+
+# Check whether a specific version of the Scala 3 compiler is published to Maven Central
+#
+# Usage:
+#   is-version-published.sh <version_string>
+# e.g.
+#   ./is-version-published.sh 3.0.1-RC1-bin-20210411-b44cafa-NIGHTLY
+#
+# Exit status:
+#   zero      if the specified version is published on Maven Central
+#   non-zero  otherwise
+
+ver=$1
+if [[ -z "$ver" ]]; then
+  echo "error: missing version parameter"
+  echo "usage: $0 <version_string>"
+  exit 2
+fi
+
+set -eu
+
+major=${ver%%-bin-*}
+maven_url=https://repo1.maven.org/maven2/org/scala-lang/scala3-compiler_$major/maven-metadata.xml
+
+echo "Checking whether $ver is published"
+echo "at $maven_url"
+echo ""
+
+published=$(curl -s --fail --show-error -L "$maven_url" | sed -ne '/<version>/ s!<version>\(.*\)</version>!\1! p')
+if [[ -n "$published" ]]; then
+  echo "Found published versions:"
+  echo "$published" | xargs -n1
+  echo ""
+
+  for p in $published ; do
+    if [[ "$p" == "$ver" ]]; then
+      echo "Version $ver is already published."
+      exit 0
+    fi
+  done
+  echo "Version $ver is not yet published."
+  exit 10
+else
+  echo "Unable to determine published versions."
+  exit 20
+fi