Downgrade unmerged-usr from error to two warnings

One warning will be issued before the Y/n prompt, the other will
be issued at the end after package installs have been attempted
or if there were other failures, such that the last line you see
is warnings about unmerged-usr

I do not anticipate this to be the final version either, but
there we go.

Closes: #1052058

2 files changed, 33 insertions, 18 deletions

diff --git a/apt-pkg/aptconfiguration.cc b/apt-pkg/aptconfiguration.cc
index 0e4cecd99..dbfa00bb3 100644
--- a/apt-pkg/aptconfiguration.cc
+++ b/apt-pkg/aptconfiguration.cc
@@ -557,7 +557,7 @@ bool Configuration::checkUsrMerged()
       if (stat(dirInUsr.c_str(), &usr))
 	 continue;
       if (root.st_ino != usr.st_ino)
-	 return _error->Error("%s resolved to a different inode than %s", dirInRoot.c_str(), dirInUsr.c_str());
+	 return _error->Warning("%s resolved to a different inode than %s", dirInRoot.c_str(), dirInUsr.c_str()), false;
    }
 
    return true;
diff --git a/apt-private/private-install.cc b/apt-private/private-install.cc
index a195df848..e366634ad 100644
--- a/apt-private/private-install.cc
+++ b/apt-private/private-install.cc
@@ -111,8 +111,39 @@ static void RemoveDownloadNeedingItemsFromFetcher(pkgAcquire &Fetcher, bool &Tra
       I = Fetcher.ItemsBegin();
    }
 }
+#ifdef REQUIRE_MERGED_USR
+// \brief Issues a warning about usrmerge when destructed so we can call it after install finished or failed or whatever.
+struct WarnUsrMerge {
+   CacheFile &Cache;
+   WarnUsrMerge(CacheFile &Cache) : Cache(Cache) {
+
+   }
+   void warn() {
+      auto usrmergePkg = Cache->FindPkg("usrmerge");
+      if (not APT::Configuration::isChroot() && _config->FindDir("Dir") == std::string("/") &&
+	  not usrmergePkg.end() && not usrmergePkg.VersionList().end() &&
+	  not Cache[usrmergePkg].Install() && not APT::Configuration::checkUsrMerged())
+      {
+	 _error->Warning(_("Unmerged usr is no longer supported, use usrmerge to convert to a merged-usr system."));
+	 for (auto VF = usrmergePkg.VersionList().FileList(); not VF.end(); ++VF)
+	    if (VF.File().Origin() != nullptr && VF.File().Origin() == std::string("Debian"))
+	    {
+	       // TRANSLATORS: %s is a url to a page describing merged-usr (bookworm release notes)
+	       _error->Notice(_("See %s for more details."), "https://www.debian.org/releases/bookworm/amd64/release-notes/ch-information.en.html#a-merged-usr-is-now-required");
+	       break;
+	    }
+      }
+   }
+   ~WarnUsrMerge() {
+      warn();
+   }
+};
+#endif
 bool InstallPackages(CacheFile &Cache, APT::PackageVector &HeldBackPackages, bool ShwKept, bool Ask, bool Safety, std::string const &Hook, CommandLine const &CmdL)
 {
+#ifdef REQUIRE_MERGED_USR
+   WarnUsrMerge warnUsrMerge(Cache);
+#endif
    if (not RunScripts("APT::Install::Pre-Invoke"))
       return false;
    if (_config->FindB("APT::Get::Purge", false) == true)
@@ -216,23 +247,7 @@ bool InstallPackages(CacheFile &Cache, APT::PackageVector &HeldBackPackages, boo
       return _error->Error(_("Packages need to be removed but remove is disabled."));
 
 #ifdef REQUIRE_MERGED_USR
-   _error->PushToStack();
-   auto usrmergePkg = Cache->FindPkg("usrmerge");
-   if (not APT::Configuration::isChroot() && _config->FindDir("Dir") == std::string("/") &&
-       not usrmergePkg.end() && not usrmergePkg.VersionList().end() &&
-       not Cache[usrmergePkg].Install() && not APT::Configuration::checkUsrMerged())
-   {
-      _error->Error(_("Unmerged usr is no longer supported, install usrmerge to continue."));
-      for (auto VF = usrmergePkg.VersionList().FileList(); not VF.end(); ++VF)
-	 if (VF.File().Origin() == std::string("Debian"))
-	 {
-	    // TRANSLATORS: %s is a url to a page describing merged-usr (bookworm release notes)
-	    _error->Notice(_("See %s for more details."), "https://www.debian.org/releases/bookworm/amd64/release-notes/ch-information.en.html#a-merged-usr-is-now-required");
-	    break;
-	 }
-      return false;
-   }
-   _error->RevertToStack();
+   warnUsrMerge.warn();
 #endif
 
    // Fail safe check