Use GitHub Actions environment to determine tag name

Author: wjt

endless/src/endless/GenerateVersion.ps1

@@ -19,7 +19,23 @@ $ErrorActionPreference = 'Stop'
 $versionH = $Args[0];
 echo "Generating $versionH..."
 
-$describe = (git describe)
+# When running workflows for a tag, GitHub actions/checkout@v2 doesn't just
+# check out the tag. Instead it does the following:
+#  - pulls the repo
+#  - uses ref-parse to determine the commit object the tag points at
+#  - re-fetches with 'git fetch ... origin +$COMMIT_ID:refs/tags/$TAG'
+#  - checks out that tag
+# As a result it loses the signed tag, which means 'git describe' reports the
+# version as the previous tag, plus a bunch of commits. Really weird.
+#
+# So we can't use 'git describe' and expect to get a bare tag back when we're
+# building that tag. Happily, we can just get the tag name from the GitHub
+# Actions environment and use that directly.
+if (($env:GITHUB_ACTIONS -eq "true") -and ($env:GITHUB_REF_TYPE -eq "tag")) {
+    $describe = $env:GITHUB_REF_NAME
+} else {
+    $describe = (git describe)
+}
 
 # We expect $describe to be of the form:
 #    VERSION_W.X.Y.Z-[number of commits ahead]-[commit hash]