From ea4b7921b7e3eadb42be1deab5f343dbba8f29df Mon Sep 17 00:00:00 2001
From: Julian Andres Klode <julian.klode@canonical.com>
Date: Thu, 16 Jan 2020 10:53:05 +0100
Subject: NewProvidesAllArch: Check if group is empty before using it

APT 1.9.6 introduced empty groups by making use of groups to
deduplicate package names. This is not normally a problem, but
here we assumed that every group has at least one package.

This caused a problem because automake was providing automake-1.16
while having the source package automake-1.16. So we found the
automake-1.16 group, iterated over its empty package list, trying
to store the provides (which hence never happened).

LP: #1859952
---
 apt-pkg/pkgcachegen.cc                  |  2 +-
 test/integration/test-provides-arch-all | 28 ++++++++++++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)
 create mode 100755 test/integration/test-provides-arch-all

diff --git a/apt-pkg/pkgcachegen.cc b/apt-pkg/pkgcachegen.cc
index 75bd4c853..8e0301151 100644
--- a/apt-pkg/pkgcachegen.cc
+++ b/apt-pkg/pkgcachegen.cc
@@ -1203,7 +1203,7 @@ bool pkgCacheListParser::NewProvidesAllArch(pkgCache::VerIterator &Ver, StringVi
    Dynamic<StringView> DynPackage(Package);
    Dynamic<StringView> DynVersion(Version);
 
-   if (Grp.end() == true)
+   if (Grp.end() == true || Grp->FirstPackage == 0)
       return NewProvides(Ver, Package, Cache.NativeArch(), Version, Flags);
    else
    {
diff --git a/test/integration/test-provides-arch-all b/test/integration/test-provides-arch-all
new file mode 100755
index 000000000..f212b513c
--- /dev/null
+++ b/test/integration/test-provides-arch-all
@@ -0,0 +1,28 @@
+#!/bin/sh
+#
+# In apt 1.9.6, this test would have failed, outputting:
+#   The following packages will be REMOVED:
+#    libltdl-dev
+#   0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
+#   Remv libltdl-dev [1]
+#
+# Because we started inserting groups without packages, and then could not
+# properly insert the provides.
+
+set -e
+
+TESTDIR="$(readlink -f "$(dirname "$0")")"
+. "$TESTDIR/framework"
+setupenvironment
+configarchitecture "i386"
+
+insertinstalledpackage 'automake' 'i386' '1' 'Provides: automake-1.16
+Source: automake-1.16
+Multi-Arch: foreign'
+insertinstalledpackage 'libltdl-dev' 'i386' '1' 'Depends: automake-1.16'
+
+setupaptarchive
+
+testsuccessequal 'Reading package lists...
+Building dependency tree...
+0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.' aptget install -f -s
-- 
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