From 7bec6d3d7008dcfde1d999776102bf5ab2e86381 Mon Sep 17 00:00:00 2001
From: Julian Andres Klode <julian.klode@canonical.com>
Date: Sun, 27 Dec 2020 13:56:22 +0100
Subject: Implement ?reverse-depends/~R and friends

This was easy.
---
 apt-pkg/cachefilter-patterns.cc | 28 ++++++++++++++++++++++++++++
 apt-pkg/cachefilter-patterns.h  | 21 +++++++++++++++++++++
 doc/apt-patterns.7.xml          |  8 ++++++++
 3 files changed, 57 insertions(+)

diff --git a/apt-pkg/cachefilter-patterns.cc b/apt-pkg/cachefilter-patterns.cc
index 4a99635db..471e698d6 100644
--- a/apt-pkg/cachefilter-patterns.cc
+++ b/apt-pkg/cachefilter-patterns.cc
@@ -39,6 +39,16 @@ static const constexpr struct
    {"DBreaks:"_sv, "?breaks"_sv, true},
    {"DEnhances:"_sv, "?enhances"_sv, true},
    {"D"_sv, "?depends"_sv, true},
+   {"RDepends:"_sv, "?reverse-depends"_sv, true},
+   {"RPre-Depends:"_sv, "?reverse-pre-depends"_sv, true},
+   {"RSuggests:"_sv, "?reverse-suggests"_sv, true},
+   {"RRecommends:"_sv, "?reverse-recommends"_sv, true},
+   {"RConflicts:"_sv, "?reverse-conflicts"_sv, true},
+   {"RReplaces:"_sv, "?reverse-replaces"_sv, true},
+   {"RObsoletes:"_sv, "?reverse-obsoletes"_sv, true},
+   {"RBreaks:"_sv, "?reverse-breaks"_sv, true},
+   {"REnhances:"_sv, "?reverse-enhances"_sv, true},
+   {"R"_sv, "?reverse-depends"_sv, true},
    {"E"_sv, "?essential"_sv, false},
    {"F"_sv, "?false"_sv, false},
    {"g"_sv, "?garbage"_sv, false},
@@ -447,6 +457,24 @@ std::unique_ptr<APT::CacheFilter::Matcher> PatternParser::aPattern(std::unique_p
       return std::make_unique<Patterns::VersionDepends>(aPattern(node->arguments[0]), pkgCache::Dep::DpkgBreaks);
    if (node->matches("?enhances", 1, 1))
       return std::make_unique<Patterns::VersionDepends>(aPattern(node->arguments[0]), pkgCache::Dep::Enhances);
+   if (node->matches("?reverse-depends", 1, 1))
+      return std::make_unique<Patterns::PackageReverseDepends>(aPattern(node->arguments[0]));
+   if (node->matches("?reverse-predepends", 1, 1))
+      return std::make_unique<Patterns::PackageReverseDepends>(aPattern(node->arguments[0]), pkgCache::Dep::PreDepends);
+   if (node->matches("?reverse-suggests", 1, 1))
+      return std::make_unique<Patterns::PackageReverseDepends>(aPattern(node->arguments[0]), pkgCache::Dep::Suggests);
+   if (node->matches("?reverse-recommends", 1, 1))
+      return std::make_unique<Patterns::PackageReverseDepends>(aPattern(node->arguments[0]), pkgCache::Dep::Recommends);
+   if (node->matches("?reverse-conflicts", 1, 1))
+      return std::make_unique<Patterns::PackageReverseDepends>(aPattern(node->arguments[0]), pkgCache::Dep::Conflicts);
+   if (node->matches("?reverse-replaces", 1, 1))
+      return std::make_unique<Patterns::PackageReverseDepends>(aPattern(node->arguments[0]), pkgCache::Dep::Replaces);
+   if (node->matches("?reverse-obsoletes", 1, 1))
+      return std::make_unique<Patterns::PackageReverseDepends>(aPattern(node->arguments[0]), pkgCache::Dep::Obsoletes);
+   if (node->matches("?reverse-breaks", 1, 1))
+      return std::make_unique<Patterns::PackageReverseDepends>(aPattern(node->arguments[0]), pkgCache::Dep::DpkgBreaks);
+   if (node->matches("?reverse-enhances", 1, 1))
+      return std::make_unique<Patterns::PackageReverseDepends>(aPattern(node->arguments[0]), pkgCache::Dep::Enhances);
    if (node->matches("?essential", 0, 0))
       return std::make_unique<Patterns::PackageIsEssential>();
    if (node->matches("?exact-name", 1, 1))
diff --git a/apt-pkg/cachefilter-patterns.h b/apt-pkg/cachefilter-patterns.h
index 048c7041f..e0c48dd12 100644
--- a/apt-pkg/cachefilter-patterns.h
+++ b/apt-pkg/cachefilter-patterns.h
@@ -317,6 +317,27 @@ struct APT_HIDDEN VersionDepends : public VersionAnyMatcher
    }
 };
 
+struct APT_HIDDEN PackageReverseDepends : public PackageMatcher
+{
+   std::unique_ptr<APT::CacheFilter::Matcher> base;
+   pkgCache::Dep::DepType type;
+   PackageReverseDepends(std::unique_ptr<APT::CacheFilter::Matcher> base, pkgCache::Dep::DepType type = pkgCache::Dep::Depends) : base(std::move(base)), type(type) {}
+   bool operator()(pkgCache::PkgIterator const &Pkg) override
+   {
+      for (auto D = Pkg.RevDependsList(); not D.end(); D++)
+      {
+	 if (D.IsImplicit())
+	    continue;
+	 if (D->Type != type)
+	    continue;
+	 if ((*base)(D.ParentVer()))
+	    return true;
+      }
+
+      return false;
+   }
+};
+
 struct APT_HIDDEN VersionIsAnyVersion : public VersionAnyMatcher
 {
    std::unique_ptr<APT::CacheFilter::Matcher> base;
diff --git a/doc/apt-patterns.7.xml b/doc/apt-patterns.7.xml
index 06a60285b..0d2e79f88 100644
--- a/doc/apt-patterns.7.xml
+++ b/doc/apt-patterns.7.xml
@@ -167,6 +167,14 @@
      <term><code>?enhances(PATTERN)</code></term><term><code>~DEnhances:PATTERN</code></term>
      <listitem><para>Selects versions depending/pre-depending/suggesting/conflicting/etc on/with/ packages matching PATTERN.</para></listitem>
      </varlistentry>
+     <varlistentry>
+       <term><code>?reverse-<emphasis>depType</emphasis>(PATTERN)</code></term>
+       <term><code>~R<emphasis>DepType</emphasis>:PATTERN</code></term>
+       <listitem><para>Opposite of <code>?depends</code> and friends - selects all packages that have reverse-dependencies (versions) matching PATTERN.</para>
+         <para><emphasis>depType</emphasis> is one of the dependency types such as <code>depends</code>, so that we don't have to repeat the entire list from the first paragraph here.</para>
+       </listitem>
+     </varlistentry>
+
   </variablelist>
 
  </refsect1>
-- 
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