bug#58958: 29.0.50; overlays fail to evaporate across indirect buffers

[Matt Armstrong]

This bug is inspired by bug#58928, but not the same, and repros after
Stefan's fix for that bug.  In fact, it repros in Emacs 27 as well.

See attached patch for repro steps as an ert test.  Essentially, either:

1) Create an overlay in an indirect buffer, set its 'evaporate property
   to t.
2) Delete text from the base buffer such that the overlay is empty.
3) Verify it is no longer in the indirect buffer (in fact, it remains as
   an empty overlay).

Repeat the above swapping the indirect and base buffers.  The bug goes
both ways.

>From 3da7e442467d5dad3c875d5bfb7e68017400a14b Mon Sep 17 00:00:00 2001
From: Matt Armstrong <matt@rfc20.org>
Date: Tue, 1 Nov 2022 19:40:20 -0700
Subject: [PATCH] Add a test for overlay evaporation across indirect buffers

* test/src/buffer-tests.el (buffer-tests--overlays-indirect-evaporate):
Test evaporation of overlays triggered by deleting text in base
and in indirect buffers.  Test doesn't pass at the moment.
---
 test/src/buffer-tests.el | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/test/src/buffer-tests.el b/test/src/buffer-tests.el
index b96a8dcacd2..a4a1f609fd2 100644
--- a/test/src/buffer-tests.el
+++ b/test/src/buffer-tests.el
@@ -296,6 +296,42 @@ buffer-tests--overlays-indirect-bug58928
       (should (equal (overlay-start ol1) (overlay-start ol2)))
       (should (equal (overlay-end ol1) (overlay-end ol2))))))
 
+(ert-deftest buffer-tests--overlays-indirect-evaporate ()
+  "Verify that deleting text evaporates overlays in every related buffer.
+
+Deleting characters from either a base or an indirect buffer
+should evaporate overlays in both."
+  :expected-result :failed
+  ;; Loop twice, erasing from the base buffer the first time and the
+  ;; indirect buffer the second.
+  (dolist (erase-where '(base indirect))
+    (ert-info ((format "erase-where %S" erase-where))
+      (with-temp-buffer
+        (insert "xxx")
+        (let* ((beg 2)
+               (end 3)
+               (base (current-buffer))
+               (base-overlay (make-overlay beg end base))
+               (indirect (make-indirect-buffer
+                          base
+                          (generate-new-buffer-name
+                           (concat (buffer-name base) "-indirect"))))
+               (indirect-overlay (make-overlay beg end indirect)))
+          (overlay-put base-overlay 'evaporate t)
+          (overlay-put indirect-overlay 'evaporate t)
+          (with-current-buffer (pcase-exhaustive erase-where
+                                 (`base base)
+                                 (`indirect indirect))
+            (delete-region beg end))
+          (ert-info ((prin1-to-string
+                      `(,base ,base-overlay ,indirect ,indirect-overlay)))
+            (should (not (buffer-live-p (overlay-buffer base-overlay))))
+            (should (not (buffer-live-p (overlay-buffer indirect-overlay))))
+            (should (equal nil (with-current-buffer base
+                                 (overlays-in (point-min) (point-max)))))
+            (should (equal nil (with-current-buffer indirect
+                                 (overlays-in (point-min) (point-max)))))))))))
+
 (ert-deftest overlay-evaporation-after-killed-buffer ()
   (let* ((ols (with-temp-buffer
                 (insert "toto")
-- 
2.35.1


In GNU Emacs 29.0.50 (build 3, x86_64-pc-linux-gnu, GTK+ Version
 3.24.34, cairo version 1.16.0) of 2022-10-30 built on naz
Repository revision: 73953b23aad5af80275838cd3b1c88e045e1856e
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12201003
System Description: Debian GNU/Linux bookworm/sid

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