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

2 files changed, 52 insertions, 0 deletions

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