Bug#992116: release-notes: Add breakage from merged-/usr-via-aliased-dirs

[Guillem Jover <guillem@debian.org>]

Package: release-notes
Severity: important

Hi,

While this breakage is apparently not going to be reverted, the users
deserve to know what they are getting into, to avoid hard to track
bugs and misbehavior.

To me this would be worth mentioning on its own in addition to the
note I added to the "deprecation" entry, but repetition is not ideal
and I can see push back on that too, so I'd rather have it listed
just once than not at all.

Thanks,
Guillem

From 134021b9dff9ad4e52a7446ce57dbfc0339b4754 Mon Sep 17 00:00:00 2001
From: Guillem Jover <guillem@debian.org>
Date: Wed, 11 Aug 2021 21:24:59 +0200
Subject: [PATCH] issues.dbk: Add breakage from merged-/usr-via-aliased-dirs

While this breakage is apparently not going to be reverted, the users
deserve to know what they are getting into, to avoid hard to track
bugs and misbehavior. In particular dpkg has *never* supported this
layout.
---
 en/issues.dbk | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/en/issues.dbk b/en/issues.dbk
index d3321953..bbd772ad 100644
--- a/en/issues.dbk
+++ b/en/issues.dbk
@@ -893,6 +893,25 @@ Environment=SYSTEMD_SULOGIN_FORCE=1
             role="package">usrmerge</systemitem> package exists to do
             the conversion if desired.
           </para>
+          <para>
+            Take into account that this layout has never been supported by
+            the dpkg suite and breaks several of its core assumptions. Included
+            among these are: not being able to notice file conflicts thus
+            causing silent overwrites, disappearing pathnames on upgrades,
+            failing to apply stat-overrides, missed trigger activations, failing
+            to find pathnames on search queries, etc.
+            For more information see the <ulink
+            url="https://wiki.debian.org/Teams/Dpkg/FAQ#unsupported-merged-usr-via-aliased-dirs";>
+            dpkg FAQ entry</ulink>.
+          </para>
+          <para>
+            It can also cause problems with any other software or subsystem
+            that tracks filesystem objects, and might be doing string-wise
+            comparisons. An example of such interfaces is
+            <filename>/etc/shells</filename>, where the entries need to be
+            duplicated or programs using that file directly or indirectly
+            might fail to match them.
+          </para>
 	</listitem>
 
         <listitem>
-- 
2.32.0