feat: decide when merge-door releases resume

lib/preflight.sh

@@ -0,0 +1,81 @@
+#!/usr/bin/env bash
+# lib/preflight.sh — the merge door's resume decision, pure and exhaustively
+# tested (issue #273).
+#
+# A merge-door run creates the tag before the artifact hook and release. A
+# failed hook or publish therefore leaves a tag but no release. Re-running the
+# same merge commit must resume after that irreversible step; a published
+# release or a tag naming another commit must still refuse.
+#
+# Pure: no repository or forge reads. The workflow establishes four facts:
+#
+#   VER         the version being released
+#   MERGE_SHA   the commit this door would tag
+#   TAG_SHAS    object names returned for the direct and peeled tag refs,
+#               newline-separated; empty means the tag is absent
+#   RELEASED    yes|no — whether a published release for VER exists
+#
+# Output: resume=yes or resume=no on stdout, notices to stdout, refusals to
+# stderr, return 1 on refusal.
+#
+# The decision table (this IS the spec — issue #273):
+#
+# | # | RELEASED | TAG_SHAS contains MERGE_SHA | result                    |
+# |---|----------|------------------------------|---------------------------|
+# | 1 | yes      | either                       | REFUSE: already released   |
+# | 2 | no       | empty                        | resume=no: ordinary run    |
+# | 3 | no       | yes                          | resume=yes + resume NOTICE |
+# | 4 | no       | non-empty, no                | REFUSE: tag is elsewhere   |
+
+release_preflight() {
+  local tag_sha sha
+
+  if [ -z "${VER:-}" ]; then
+    printf '%s\n' "VER is empty — the caller failed to establish the release version. Refusing to decide — creating nothing." >&2
+    return 1
+  fi
+  if [ -z "${MERGE_SHA:-}" ]; then
+    printf '%s\n' "MERGE_SHA is empty — the caller failed to establish the merge commit. Refusing to decide — creating nothing." >&2
+    return 1
+  fi
+  if [ -z "${RELEASED:-}" ]; then
+    printf '%s\n' "RELEASED is empty — the caller failed to establish whether release '$VER' exists. Refusing to decide — creating nothing." >&2
+    return 1
+  fi
+  case "$RELEASED" in
+    yes | no) ;;
+    *)
+      printf '%s\n' "RELEASED='$RELEASED' — expected yes or no. Refusing to decide — creating nothing." >&2
+      return 1
+      ;;
+  esac
+
+  # Row 1 comes first: deleting a tag under a standing release never makes
+  # that release safe to recreate.
+  if [ "$RELEASED" = yes ]; then
+    printf '%s\n' "release '$VER' already exists — this release already happened; refusing to re-release, creating nothing." >&2
+    return 1
+  fi
+
+  # Row 2: an absent tag is the ordinary first run.
+  if [ -z "${TAG_SHAS:-}" ]; then
+    printf '%s\n' 'resume=no'
+    return 0
+  fi
+
+  # Row 3: compare each object name as a whole line. For an annotated tag the
+  # direct ref names the tag object and the peeled ref names MERGE_SHA.
+  while IFS= read -r sha; do
+    if [ "$sha" = "$MERGE_SHA" ]; then
+      printf '%s\n' "NOTICE: tag '$VER' already stands at this merge commit and no release exists — a previous run of this door tagged and then failed to publish. Resuming: the tag is not recreated; the artifact hook and the publish run."
+      printf '%s\n' 'resume=yes'
+      return 0
+    fi
+  done <<<"$TAG_SHAS"
+
+  # Row 4: the first object name is enough to diagnose the conflicting tag;
+  # MERGE_SHA is printed beside it so the operator sees both sides.
+  tag_sha="${TAG_SHAS%%$'\n'*}"
+  printf '%s\n' "tag '$VER' already exists at $tag_sha but this run would tag $MERGE_SHA — a manual tag won the race, or it names a different commit; refusing to re-release, creating nothing. Delete that tag, or re-tag the merge commit." >&2
+  return 1
+}

test/preflight.test.sh

@@ -18,7 +18,13 @@ FOREIGN_SHA=2222222222222222222222222222222222222222
 # preflight <VER> <MERGE_SHA> <TAG_SHAS> <RELEASED> — run the pure decision
 # with exactly the four gathered facts in its environment.
 preflight() {
-  VER="$1" MERGE_SHA="$2" TAG_SHAS="$3" RELEASED="$4" bash "$PREFLIGHT"
+  (
+    VER="$1" MERGE_SHA="$2" TAG_SHAS="$3" RELEASED="$4"
+    export VER MERGE_SHA TAG_SHAS RELEASED
+    # shellcheck source=lib/preflight.sh
+    . "$PREFLIGHT"
+    release_preflight
+  )
 }
 
 preflight_stdout() {