From 08762e0e4e2923360339eeb4d8ed26a00d7f1de5 Mon Sep 17 00:00:00 2001
From: Julian Andres Klode <julian.klode@canonical.com>
Date: Thu, 15 Aug 2019 13:35:01 +0200
Subject: Add ?essential pattern

This matches all packages where at least one of the versions
is marked essential; or well, whenver apt considers a package
essential.
---
 apt-pkg/cachefilter-patterns.cc    | 2 ++
 apt-pkg/cachefilter-patterns.h     | 7 +++++++
 doc/apt-patterns.7.xml             | 3 +++
 test/integration/test-apt-patterns | 3 +++
 4 files changed, 15 insertions(+)

diff --git a/apt-pkg/cachefilter-patterns.cc b/apt-pkg/cachefilter-patterns.cc
index a180cf78e..ea35b9c46 100644
--- a/apt-pkg/cachefilter-patterns.cc
+++ b/apt-pkg/cachefilter-patterns.cc
@@ -216,6 +216,8 @@ std::unique_ptr<APT::CacheFilter::Matcher> PatternParser::aPattern(std::unique_p
       return std::make_unique<Patterns::PackageIsBroken>(file);
    if (node->matches("?config-files", 0, 0))
       return std::make_unique<Patterns::PackageIsConfigFiles>();
+   if (node->matches("?essential", 0, 0))
+      return std::make_unique<Patterns::PackageIsEssential>();
    if (node->matches("?false", 0, 0))
       return std::make_unique<APT::CacheFilter::FalseMatcher>();
    if (node->matches("?garbage", 0, 0))
diff --git a/apt-pkg/cachefilter-patterns.h b/apt-pkg/cachefilter-patterns.h
index c219e5bcd..17f1fc752 100644
--- a/apt-pkg/cachefilter-patterns.h
+++ b/apt-pkg/cachefilter-patterns.h
@@ -158,6 +158,13 @@ struct PackageIsGarbage : public PackageMatcher
       return (*Cache)[Pkg].Garbage;
    }
 };
+struct PackageIsEssential : public PackageMatcher
+{
+   bool operator()(pkgCache::PkgIterator const &Pkg) override
+   {
+      return (Pkg->Flags & pkgCache::Flag::Essential) != 0;
+   }
+};
 
 struct PackageIsInstalled : public PackageMatcher
 {
diff --git a/doc/apt-patterns.7.xml b/doc/apt-patterns.7.xml
index e1c64de8e..11031be95 100644
--- a/doc/apt-patterns.7.xml
+++ b/doc/apt-patterns.7.xml
@@ -78,6 +78,9 @@
      <varlistentry><term><code>?config-files</code></term>
      <listitem><para>Selects packages that are not fully installed, but have solely residual configuration files left.</para></listitem>
      </varlistentry>
+     <varlistentry><term><code>?essential</code></term>
+     <listitem><para>Selects packages that have Essential: yes set in their control file.</para></listitem>
+     </varlistentry>
      <varlistentry><term><code>?garbage</code></term>
      <listitem><para>Selects packages that can be removed automatically.</para></listitem>
      </varlistentry>
diff --git a/test/integration/test-apt-patterns b/test/integration/test-apt-patterns
index e566c6bd2..1efb10d2d 100755
--- a/test/integration/test-apt-patterns
+++ b/test/integration/test-apt-patterns
@@ -122,6 +122,9 @@ broken/now 1.0 i386 [installed,local]" apt list '?broken'
 testsuccessequal "Listing...
 conf-only/now 1.0 i386 [residual-config]" apt list '?config-files'
 
+testsuccessequal "Listing...
+essential/now 1.0 i386 [installed,local]" apt list '?essential'
+
 testsuccessequal "Listing...
 automatic2/now 1.0 i386 [installed,local]" apt list '?garbage'
 
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