reimplement build-dep via apts normal resolver

build-dep was implemented by parsing the build-dependencies of a package
and figuring out which packages to install/remove based on this. That
means that for the first level of dependencies build-dep was
implementing its very own resolver with all the benefits (aka: bugs)
this gives us for not using the existing resolver for all levels.

Making this work involves generating a dummy binary package with fitting
Depends and Conflicts and as we can't create them out of thin air the
cache generation needs to be involved so we end up writing a Packages
file which we want to parse – after we have parsed the other Packages
files already. With .dsc/.deb files we could add them before we started
parsing anything.

With a bit of care we can avoid generating too much data we have to
throw away again (as many parts assume that e.g. the count of packages
doesn't change midair), so that on a speed front there shouldn't be
much of a difference, but output can be slightly confusing as if we have
a completely valid cache on disk the "Reading package lists... Done" is
printed two times – but apt is pretty quick about it in that case.

Closes: #137560, #444930, #489911, #583914, #728317, #812173

1 files changed, 44 insertions, 28 deletions

diff --git a/apt-private/private-install.cc b/apt-private/private-install.cc
index 73aebaf2f..3f57b55e2 100644
--- a/apt-private/private-install.cc
+++ b/apt-private/private-install.cc
@@ -41,6 +41,37 @@
 									/*}}}*/
 class pkgSourceList;
 
+bool CheckNothingBroken(CacheFile &Cache)				/*{{{*/
+{
+   // Now we check the state of the packages,
+   if (Cache->BrokenCount() == 0)
+      return true;
+
+   c1out <<
+      _("Some packages could not be installed. This may mean that you have\n"
+	    "requested an impossible situation or if you are using the unstable\n"
+	    "distribution that some required packages have not yet been created\n"
+	    "or been moved out of Incoming.") << std::endl;
+   /*
+   if (Packages == 1)
+   {
+      c1out << std::endl;
+      c1out <<
+	 _("Since you only requested a single operation it is extremely likely that\n"
+	       "the package is simply not installable and a bug report against\n"
+	       "that package should be filed.") << std::endl;
+   }
+   */
+
+   c1out << _("The following information may help to resolve the situation:") << std::endl;
+   c1out << std::endl;
+   ShowBroken(c1out,Cache,false);
+   if (_error->PendingError() == true)
+      return false;
+   else
+      return _error->Error(_("Broken packages"));
+}
+									/*}}}*/
 // InstallPackages - Actually download and install the packages		/*{{{*/
 // ---------------------------------------------------------------------
 /* This displays the informative messages describing what is going to 
@@ -364,7 +395,7 @@ bool InstallPackages(CacheFile &Cache,bool ShwKept,bool Ask, bool Safety)
 // DoAutomaticRemove - Remove all automatic unused packages		/*{{{*/
 // ---------------------------------------------------------------------
 /* Remove unused automatic packages */
-static bool DoAutomaticRemove(CacheFile &Cache)
+bool DoAutomaticRemove(CacheFile &Cache)
 {
    bool Debug = _config->FindI("Debug::pkgAutoRemove",false);
    bool doAutoRemove = _config->FindB("APT::Get::AutomaticRemove", false);
@@ -628,33 +659,8 @@ bool DoCacheManipulationFromCommandLine(CommandLine &CmdL, std::vector<const cha
 	    return false;
       }
 
-      // Now we check the state of the packages,
-      if (Cache->BrokenCount() != 0)
-      {
-	 c1out << 
-	    _("Some packages could not be installed. This may mean that you have\n" 
-	      "requested an impossible situation or if you are using the unstable\n" 
-	      "distribution that some required packages have not yet been created\n"
-	      "or been moved out of Incoming.") << std::endl;
-	 /*
-	 if (Packages == 1)
-	 {
-	    c1out << std::endl;
-	    c1out << 
-	       _("Since you only requested a single operation it is extremely likely that\n"
-		 "the package is simply not installable and a bug report against\n" 
-		 "that package should be filed.") << std::endl;
-	 }
-	 */
-
-	 c1out << _("The following information may help to resolve the situation:") << std::endl;
-	 c1out << std::endl;
-	 ShowBroken(c1out,Cache,false);
-	 if (_error->PendingError() == true)
-	    return false;
-	 else
-	    return _error->Error(_("Broken packages"));
-      }
+      if (CheckNothingBroken(Cache) == false)
+	 return false;
    }
    if (!DoAutomaticRemove(Cache)) 
       return false;
@@ -811,7 +817,17 @@ bool DoInstall(CommandLine &CmdL)
 
 // TryToInstall - Mark a package for installation			/*{{{*/
 void TryToInstall::operator() (pkgCache::VerIterator const &Ver) {
+   if (unlikely(Ver.end()))
+   {
+      _error->Fatal("The given version to TryToInstall is invalid!");
+      return;
+   }
    pkgCache::PkgIterator Pkg = Ver.ParentPkg();
+   if (unlikely(Pkg.end()))
+   {
+      _error->Fatal("The given version to TryToInstall has an invalid parent package!");
+      return;
+   }
 
    Cache->GetDepCache()->SetCandidateVersion(Ver);
    pkgDepCache::StateCache &State = (*Cache)[Pkg];