remove "first package seen is native package" assumption

The fix for #777760 causes packages of foreign (and the native)
architectures, to be created correctly, but invalidates (like the
previously existing, but policy-forbidden architecture-less packages
we had to support for some upgrade scenarios) the assumption that the
first (and only) package in the cache for a single architecture system
must be the package for the native architecture (as, where should the
other architectures come from, right? Wrong.).

Depending on the order of parsing sources more or less packages can be
effected by this. The effects are strange (for apt it mostly effects
simulation/debug output, but also apt-mark on these specific packages),
which complicates debugging, but relatively harmless if understood as
most actions do not need direct named access to packages.

The problem is fixed by removing the single-arch special casing in the
paths who had them (Cache.FindPkg), so they use the same code as
multi-arch systems, which use them as a wrapper for Grp.FindPkg.

Note that single-arch system code was using Grp.FindPkg before as well
if a Grp structure was handily available, so we don't introduce new
untested code here: We remove more brittle special cases which are less
tested instead (this was planed to be done for Stretch anyhow).

Note further that the method with the assumption itself isn't fixed. As
it is a private method I opted for declaring it deprecated instead and
remove all its call positions. As it is private no-one can call this
method legally (thanks to how c++ works by default its still an exported
symbol through) and fixing it basically means reimplementing code we
already have in Grp.FindPkg.

Removing rather than fixing seems hence like a good solution.

Closes: 782777
Thanks: Axel Beckert for testing

apt-pkg/pkgcache.cc

@@ -230,12 +230,7 @@ pkgCache::PkgIterator pkgCache::SingleArchFindPkg(const string &Name)
 pkgCache::PkgIterator pkgCache::FindPkg(const string &Name) {
 	size_t const found = Name.find(':');
 	if (found == string::npos)
-	{
-		if (MultiArchCache() == false)
-			return SingleArchFindPkg(Name);
-		else
-			return FindPkg(Name, "native");
-	}
+	   return FindPkg(Name, "native");
 	string const Arch = Name.substr(found+1);
 	/* Beware: This is specialcased to handle pkg:any in dependencies as
 	   these are linked to virtual pkg:any named packages with all archs.
@@ -249,13 +244,6 @@ pkgCache::PkgIterator pkgCache::FindPkg(const string &Name) {
 // ---------------------------------------------------------------------
 /* Returns 0 on error, pointer to the package otherwise */
 pkgCache::PkgIterator pkgCache::FindPkg(const string &Name, string const &Arch) {
-	if (MultiArchCache() == false && Arch != "none") {
-		if (Arch == "native" || Arch == "all" || Arch == "any" ||
-		    Arch == NativeArch())
-			return SingleArchFindPkg(Name);
-		else
-			return PkgIterator(*this,0);
-	}
 	/* We make a detour via the GrpIterator here as
 	   on a multi-arch environment a group is easier to
 	   find than a package (less entries in the buckets) */

apt-pkg/pkgcache.h

@@ -218,7 +218,7 @@ class pkgCache								/*{{{*/
 
 private:
    bool MultiArchEnabled;
-   PkgIterator SingleArchFindPkg(const std::string &Name);
+   APT_DEPRECATED PkgIterator SingleArchFindPkg(const std::string &Name);
 };
 									/*}}}*/
 // Header structure							/*{{{*/

test/integration/test-bug-782777-single-arch-weirdness

@@ -0,0 +1,72 @@
+#!/bin/sh
+# Ensure that the order in which packages are in the binary cache
+# does not effect if they can be found or not
+set -e
+
+TESTDIR=$(readlink -f $(dirname $0))
+. $TESTDIR/framework
+setupenvironment
+configarchitecture 'i386'
+
+insertpackage 'unstable' 'abar' 'i386' '1'
+insertpackage 'unstable' 'foobar' 'i386' '1' 'Depends: abar:amd64, zfoo:amd64'
+insertpackage 'unstable' 'zfoo' 'i386' '1'
+
+setupaptarchive
+
+testrun() {
+	rm -f rootdir/var/lib/apt/extended_states
+
+	testequal 'Reading package lists...
+Building dependency tree...
+The following NEW packages will be installed:
+  abar zfoo
+0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded.
+Inst abar (1 unstable [i386])
+Inst zfoo (1 unstable [i386])
+Conf abar (1 unstable [i386])
+Conf zfoo (1 unstable [i386])' aptget install abar zfoo -s
+
+	testequal 'Reading package lists...
+Building dependency tree...
+The following NEW packages will be installed:
+  abar zfoo
+0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded.
+Inst abar (1 unstable [i386])
+Inst zfoo (1 unstable [i386])
+Conf abar (1 unstable [i386])
+Conf zfoo (1 unstable [i386])' aptget install abar:i386 zfoo:i386 -s
+
+	testequal "Reading package lists...
+Building dependency tree...
+Package abar:amd64 is not available, but is referred to by another package.
+This may mean that the package is missing, has been obsoleted, or
+is only available from another source
+
+Package zfoo:amd64 is not available, but is referred to by another package.
+This may mean that the package is missing, has been obsoleted, or
+is only available from another source
+
+E: Package 'abar:amd64' has no installation candidate
+E: Package 'zfoo:amd64' has no installation candidate" aptget install abar:amd64 zfoo:amd64 -s
+
+	cp -f rootdir/var/lib/dpkg/status status.backup
+	insertinstalledpackage 'abar' 'i386' '1'
+	insertinstalledpackage 'zfoo' 'i386' '1'
+
+	testequal 'abar
+zfoo' aptmark showmanual abar zfoo
+	testequal 'abar set to automatically installed.
+zfoo set to automatically installed.' aptmark auto abar zfoo
+	testempty aptmark showmanual abar zfoo
+	testequal 'abar
+zfoo' aptmark showauto abar zfoo
+
+	mv -f status.backup rootdir/var/lib/dpkg/status
+}
+
+msgmsg 'Single-Arch testrun'
+testrun
+msgmsg 'Multi-Arch testrun'
+configarchitecture 'i386' 'amd64'
+testrun