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

6 files changed, 114 insertions, 2 deletions

diff --git a/apt-pkg/cachefile.cc b/apt-pkg/cachefile.cc
index 92a3b201b..3e3540bbd 100644
--- a/apt-pkg/cachefile.cc
+++ b/apt-pkg/cachefile.cc
@@ -26,6 +26,7 @@
 #include <apt-pkg/depcache.h>
 #include <apt-pkg/mmap.h>
 #include <apt-pkg/pkgcache.h>
+#include <apt-pkg/indexfile.h>
 
 #include <string.h>
 #include <unistd.h>
@@ -186,6 +187,60 @@ bool pkgCacheFile::Open(OpProgress *Progress, bool WithLock)
    return true;
 }
 									/*}}}*/
+bool pkgCacheFile::AddIndexFile(pkgIndexFile * const File)		/*{{{*/
+{
+   if (SrcList == NULL)
+      if (BuildSourceList() == false)
+	 return false;
+   SrcList->AddVolatileFile(File);
+
+   if (Cache == nullptr || File->HasPackages() == false || File->Exists() == false)
+      return true;
+
+   if (File->FindInCache(*Cache).end() == false)
+      return _error->Warning("Duplicate sources.list entry %s",
+	    File->Describe().c_str());
+
+   if (ExternOwner == false)
+   {
+      delete DCache;
+      delete Cache;
+   }
+   delete Policy;
+   DCache = NULL;
+   Policy = NULL;
+   Cache = NULL;
+
+   if (ExternOwner == false)
+   {
+      // a dynamic mmap means that we have build at least parts of the cache
+      // in memory – which we might or might not have written to disk.
+      // Throwing away would therefore be a very costly operation we want to avoid
+      DynamicMMap * dynmmap = dynamic_cast<DynamicMMap*>(Map);
+      if (dynmmap != nullptr)
+      {
+	 {
+	    pkgCacheGenerator Gen(dynmmap, nullptr);
+	    if (File->Merge(Gen, nullptr) == false)
+	       return false;
+	 }
+	 Cache = new pkgCache(Map);
+	 return _error->PendingError() == false;
+      }
+      else
+      {
+	 delete Map;
+	 Map = NULL;
+      }
+   }
+   else
+   {
+      ExternOwner = false;
+      Map = NULL;
+   }
+   return true;
+}
+									/*}}}*/
 // CacheFile::RemoveCaches - remove all cache files from disk		/*{{{*/
 // ---------------------------------------------------------------------
 /* */
diff --git a/apt-pkg/cachefile.h b/apt-pkg/cachefile.h
index df724ff45..e23f37675 100644
--- a/apt-pkg/cachefile.h
+++ b/apt-pkg/cachefile.h
@@ -32,6 +32,7 @@
 class MMap;
 class pkgPolicy;
 class pkgSourceList;
+class pkgIndexFile;
 class OpProgress;
 
 class pkgCacheFile
@@ -74,6 +75,8 @@ class pkgCacheFile
    static void RemoveCaches();
    void Close();
 
+   bool AddIndexFile(pkgIndexFile * const File);
+
    inline pkgCache* GetPkgCache() { BuildCaches(NULL, false); return Cache; };
    inline pkgDepCache* GetDepCache() { BuildDepCache(); return DCache; };
    inline pkgPolicy* GetPolicy() { BuildPolicy(); return Policy; };
diff --git a/apt-pkg/deb/debindexfile.cc b/apt-pkg/deb/debindexfile.cc
index c11efd0ae..84dabc06b 100644
--- a/apt-pkg/deb/debindexfile.cc
+++ b/apt-pkg/deb/debindexfile.cc
@@ -297,6 +297,39 @@ std::string debDebianSourceDirIndex::GetComponent() const
    return "local-control";
 }
 									/*}}}*/
+// String Package Index - a string of Packages file content		/*{{{*/
+std::string debStringPackageIndex::GetArchitecture() const
+{
+   return std::string();
+}
+std::string debStringPackageIndex::GetComponent() const
+{
+   return "apt-tmp-index";
+}
+uint8_t debStringPackageIndex::GetIndexFlags() const
+{
+   return pkgCache::Flag::NotSource;
+}
+const pkgIndexFile::Type *debStringPackageIndex::GetType() const
+{
+   return pkgIndexFile::Type::GetType("Debian Package Index");
+}
+debStringPackageIndex::debStringPackageIndex(std::string const &content) :
+   pkgDebianIndexRealFile("", false), d(NULL)
+{
+   char fn[1024];
+   std::string const tempdir = GetTempDir();
+   snprintf(fn, sizeof(fn), "%s/%s.XXXXXX", tempdir.c_str(), "apt-tmp-index");
+   int const fd = mkstemp(fn);
+   File = fn;
+   FileFd::Write(fd, content.data(), content.length());
+   close(fd);
+}
+debStringPackageIndex::~debStringPackageIndex()
+{
+   RemoveFile("~debStringPackageIndex", File);
+}
+									/*}}}*/
 
 // Index File types for Debian						/*{{{*/
 class APT_HIDDEN debIFTypeSrc : public pkgIndexFile::Type
diff --git a/apt-pkg/deb/debindexfile.h b/apt-pkg/deb/debindexfile.h
index 890141dff..3652f631c 100644
--- a/apt-pkg/deb/debindexfile.h
+++ b/apt-pkg/deb/debindexfile.h
@@ -176,4 +176,23 @@ public:
    virtual const Type *GetType() const APT_OVERRIDE APT_CONST;
 };
 
+class debStringPackageIndex : public pkgDebianIndexRealFile
+{
+   void * const d;
+protected:
+   virtual std::string GetArchitecture() const APT_OVERRIDE;
+   virtual std::string GetComponent() const APT_OVERRIDE;
+   virtual uint8_t GetIndexFlags() const APT_OVERRIDE;
+
+public:
+   virtual const Type *GetType() const APT_OVERRIDE APT_CONST;
+
+   // Interface for the Cache Generator
+   virtual bool HasPackages() const APT_OVERRIDE {return true;};
+   // Abort if the file does not exist.
+   virtual bool Exists() const APT_OVERRIDE {return true;};
+
+   debStringPackageIndex(std::string const &content);
+   virtual ~debStringPackageIndex();
+};
 #endif
diff --git a/apt-pkg/indexfile.cc b/apt-pkg/indexfile.cc
index dfd482c04..657cdfb36 100644
--- a/apt-pkg/indexfile.cc
+++ b/apt-pkg/indexfile.cc
@@ -267,7 +267,9 @@ std::string pkgDebianIndexTargetFile::GetProgressDescription() const
 pkgDebianIndexRealFile::pkgDebianIndexRealFile(std::string const &pFile, bool const Trusted) :/*{{{*/
    pkgDebianIndexFile(Trusted), d(NULL)
 {
-   if (pFile == "/nonexistent/stdin")
+   if (pFile.empty())
+      ;
+   else if (pFile == "/nonexistent/stdin")
       File = pFile;
    else
       File = flAbsPath(pFile);
diff --git a/apt-pkg/pkgcachegen.cc b/apt-pkg/pkgcachegen.cc
index 0dbac3df8..120b0c414 100644
--- a/apt-pkg/pkgcachegen.cc
+++ b/apt-pkg/pkgcachegen.cc
@@ -1735,7 +1735,7 @@ bool pkgCacheGenerator::MakeStatusCache(pkgSourceList &List,OpProgress *Progress
    }
 
    if (Debug == true)
-      std::clog << "Caches done. Now bring in the volatile files (if any)" << std::endl;
+      std::clog << "Caches done. " << (volatile_fine ? "No volatile files, so we are done here." : "Now bring in the volatile files") << std::endl;
 
    if (volatile_fine == false)
    {