describe the base and series length in the summary

[bc1cindy]

closes #6: the summary now says whether the base is the same, a descendant or diverged, and the series length before and after.

[github-actions]

range-diff for force push cc74687bdb → 1cfe7d26d0 October 8, 2026 17:07 UTC: 2 unchanged; 2 commits; same base df32adc225

^{reproduce: git range-diff df32adc..cc74687 df32adc..1cfe7d2}

1:  d6502cd215 = 1:  d6502cd215 Find where a series forked from a rewritten base
2:  cc74687bdb = 2:  1cfe7d26d0 Describe the base and series length in the summary

[github-actions]

range-diff for force push 1cfe7d26d0 → 3d03b915a7 October 8, 2026 17:32 UTC: 2 unchanged; 2 commits; same base df32adc225

^{reproduce: git range-diff df32adc..1cfe7d2 df32adc..3d03b91}

1:  d6502cd215 = 1:  d6502cd215 Find where a series forked from a rewritten base
2:  1cfe7d26d0 = 2:  3d03b915a7 Describe the base and series length in the summary

[github-actions]

range-diff for force push 3d03b915a7 → 4fda8c5a5e October 8, 2026 23:23 UTC: 2 modified; 2 commits; same base df32adc225

^{reproduce: git range-diff df32adc..3d03b91 df32adc..4fda8c5}

1:  d6502cd215 ! 1:  04f0bfeccd Find where a series forked from a rewritten base
2:  3d03b915a7 ! 2:  4fda8c5a5e Describe the base and series length in the summary

1: d6502cd215 ! 1: 04f0bfeccd Find where a series forked from a rewritten base

@@ post-range-diff-comment.sh: if git merge-base --is-ancestor "$BEFORE" "$AFTER";
 +# from further back.  GitHub's activity log stands in for the reflog that
 +# `git merge-base --fork-point` reads.
 +base_tips=("origin/$BASE_REF")
-+if rewound="$(gh api --paginate --jq '.[].before' \
-+  "repos/$REPO/activity?ref=refs/heads/$BASE_REF&activity_type=force_push&per_page=100")"; then
++if rewound="$(gh api --paginate --method GET --jq '.[].before' "repos/$REPO/activity" \
++  -f ref="refs/heads/$BASE_REF" -f activity_type=force_push -F per_page=100)"; then
 +  for tip in $rewound; do
 +    if git fetch --quiet --no-tags origin "$tip" 2>/dev/null; then
 +      base_tips+=("$tip")
@@ post-range-diff-comment.sh: if git merge-base --is-ancestor "$BEFORE" "$AFTER";
 +
  # Diff each side against where it forked from the base branch, so a rebase
  # onto a newer base does not drag the base's new commits into the comparison.
- # Fall back to the symmetric difference if either side is unrelated to base.
+-# Fall back to the symmetric difference if either side is unrelated to base.
 -if old_base="$(git merge-base "origin/$BASE_REF" "$BEFORE")" &&
 -  new_base="$(git merge-base "origin/$BASE_REF" "$AFTER")"; then
++# Fall back to the symmetric difference if either side is unrelated to base,
++# or if a tip of the base contains it: its range would be empty, which
++# range-diff rejects.
 +if old_base="$(git merge-base "$BEFORE" "${base_tips[@]}")" &&
-+  new_base="$(git merge-base "$AFTER" "${base_tips[@]}")"; then
++  new_base="$(git merge-base "$AFTER" "${base_tips[@]}")" &&
++  [[ $old_base != "$(git rev-parse "$BEFORE^{commit}")" ]] &&
++  [[ $new_base != "$(git rev-parse "$AFTER^{commit}")" ]]; then
    old_range="$old_base..$BEFORE"
    new_range="$new_base..$AFTER"
  else
+-  echo "::warning::no merge base with $BASE_REF; using $BEFORE...$AFTER"
++  echo "::warning::no fork point from $BASE_REF; using $BEFORE...$AFTER"
+   old_range="$AFTER..$BEFORE"
+   new_range="$BEFORE..$AFTER"
+ fi
 
  ## tests/test_action.py ##
 @@ tests/test_action.py: class ActionTest(unittest.TestCase):
@@ tests/test_action.py: class ActionTest(unittest.TestCase):
 +        self.assertIn(f"git range-diff {old_parent[:7]}", out)
 +        self.assertIn(f"{new_parent[:7]}..{self.after[:7]}</code>", out)
 +        self.assertIn(": 1 unchanged</summary>", out)
++
++    def test_series_an_old_base_tip_contained(self):
++        self.git("checkout", "-q", "-b", "child")
++        self.before = self.commit("child\n", "child", path="child")
++        self.git("branch", "merged", self.before)
++        self.after = self.commit("child again\n", "child", amend=True, path="child")
++        self.run_action(base_ref="topic", rewound=[self.before])
 +
      def test_force_push_shallow_checkout(self):
          self.run_action(shallow=True)

2: 3d03b915a7 ! 2: 4fda8c5a5e Describe the base and series length in the summary

@@ README.md: jobs:
 
  ## post-range-diff-comment.sh ##
 @@ post-range-diff-comment.sh: if old_base="$(git merge-base "$BEFORE" "${base_tips[@]}")" &&
-   new_base="$(git merge-base "$AFTER" "${base_tips[@]}")"; then
+   [[ $new_base != "$(git rev-parse "$AFTER^{commit}")" ]]; then
    old_range="$old_base..$BEFORE"
    new_range="$new_base..$AFTER"
 +  read -r base_behind base_ahead < <(git rev-list --left-right --count "$old_base...$new_base")
  else
-   echo "::warning::no merge base with $BASE_REF; using $BEFORE...$AFTER"
+   echo "::warning::no fork point from $BASE_REF; using $BEFORE...$AFTER"
    old_range="$AFTER..$BEFORE"
    new_range="$BEFORE..$AFTER"
 +  old_base="" new_base="" base_behind=0 base_ahead=0
@@ tests/test_action.py: class ActionTest(unittest.TestCase):
 +        self.after = self.git("rev-parse", "HEAD")
 +        self.assertNotIn("base <a", self.run_action())
  
-     def test_force_push_shallow_checkout(self):
-         self.run_action(shallow=True)
+     def test_series_an_old_base_tip_contained(self):
+         self.git("checkout", "-q", "-b", "child")
 
  ## tests/test_render.py ##
 @@ tests/test_render.py: FIXTURES = pathlib.Path(__file__).parent / "fixtures"

[github-actions]

range-diff for force push 4fda8c5a5e → 2b03757377 October 9, 2026 11:59 UTC: 1 modified, 1 unchanged; 2 commits; same base df32adc225

^{reproduce: git range-diff df32adc..4fda8c5 df32adc..2b03757}

1:  04f0bfeccd = 1:  04f0bfeccd Find where a series forked from a rewritten base
2:  4fda8c5a5e ! 2:  2b03757377 Describe the base and series length in the summary

2: 4fda8c5a5e ! 2: 2b03757377 Describe the base and series length in the summary

@@ Metadata
  ## Commit message ##
     Describe the base and series length in the summary
 
-    Says whether a force push kept the base, moved to a descendant or to a
-    diverged one, and how many commits the series had before and after.
+    Says whether a force push kept the base or moved it to a descendant, an
+    ancestor or a diverged one, and how many commits the series had before
+    and after.
 
  ## README.md ##
 @@ README.md: jobs:
@@ README.md: jobs:
 -recognized from its force pushes in the repository's activity log. Inputs and
 -outputs are described in [action.yml](action.yml).
 +changes. The summary line says how many commits the series had before and
-+after, and whether its base is the same, a descendant of the old one, or
-+diverged from it. A base branch that was itself rewritten, as a parent in a
-+stack, is recognized from its force pushes in the repository's activity log.
-+Inputs and outputs are described in [action.yml](action.yml).
++after, and whether its base is the same, a descendant or an ancestor of the
++old one, or diverged from it. A base branch that was itself rewritten, as a
++parent in a stack, is recognized from its force pushes in the repository's
++activity log. Inputs and outputs are described in [action.yml](action.yml).
  
  `pull_request_target` gives fork PRs a token that can comment. It is safe here
  because nothing from the PR runs: the checkout is the base branch, the action

[oakagent]

ACK 2b03757 (automated): reviewed 2 commits 04f0bfe..2b03757; no findings.