Streamline access to barbarian architecture functionality

APT is not the place this information should be stored at, but it is a
good place to experiment and see what will be (not) needed in the future
for a proper implementation higher up the stack.

This is why "BarbarianArchitectures" is chosen instead of a more neutral
and/or sensible "VeryForeign" and isn't readily exported in the API to
other clients for this PoC as a to be drawn up standard will likely
require potentially incompatible changes. Having a then outdated and
slightly different implementation block a "good" name would be bad.

The functionality itself mostly exists (ignoring bugs) since the
introduction of MultiArch as we always had the risk of encountering
packages of architectures not known to dpkg (forced onto the system,
potentially before MultiArch) we had to deal with somehow and other
edge cases.

All this commit really does is allowing what could previously only be
achieved with editing sources.list and some conf options via a single
config option: -o APT::BarbarianArchitectures=foo,bar

8 files changed, 219 insertions, 24 deletions

diff --git a/apt-pkg/aptconfiguration.cc b/apt-pkg/aptconfiguration.cc
index 671c3d553..00a97a0e7 100644
--- a/apt-pkg/aptconfiguration.cc
+++ b/apt-pkg/aptconfiguration.cc
@@ -315,13 +315,11 @@ bool Configuration::checkLanguage(std::string Lang, bool const All) {
 									/*}}}*/
 // getArchitectures - Return Vector of preferred Architectures		/*{{{*/
 std::vector<std::string> const Configuration::getArchitectures(bool const &Cached) {
-	using std::string;
-
-	std::vector<string> static archs;
+	std::vector<std::string> static archs;
 	if (likely(Cached == true) && archs.empty() == false)
 		return archs;
 
-	string const arch = _config->Find("APT::Architecture");
+	std::string const arch = _config->Find("APT::Architecture");
 	archs = _config->FindVector("APT::Architectures");
 
 	if (archs.empty() == true && _system != nullptr)
@@ -331,15 +329,13 @@ std::vector<std::string> const Configuration::getArchitectures(bool const &Cache
 	    std::find(archs.begin(), archs.end(), arch) == archs.end())
 		archs.insert(archs.begin(), arch);
 
-	// erase duplicates and empty strings
-	for (std::vector<string>::reverse_iterator a = archs.rbegin();
-	     a != archs.rend(); ++a) {
-		if (a->empty() == true || std::find(a + 1, archs.rend(), *a) != archs.rend())
-			archs.erase(a.base()-1);
-		if (a == archs.rend())
-			break;
-	}
-
+	// erase duplicates, empty strings and very foreign architectures
+	auto newend = std::remove_if(archs.begin(), archs.end(), [](auto const &a) { return a.empty(); });
+	for (auto a = archs.begin(); a != newend; ++a)
+		newend = std::remove(std::next(a), newend, *a);
+	for (auto const &f : _config->FindVector("APT::BarbarianArchitectures"))
+		newend = std::remove(archs.begin(), newend, f);
+	archs.erase(newend, archs.end());
 	return archs;
 }
 									/*}}}*/
diff --git a/apt-pkg/deb/debmetaindex.cc b/apt-pkg/deb/debmetaindex.cc
index f24a5e79e..d78cea758 100644
--- a/apt-pkg/deb/debmetaindex.cc
+++ b/apt-pkg/deb/debmetaindex.cc
@@ -18,6 +18,7 @@
 
 #include <algorithm>
 #include <map>
+#include <optional>
 #include <sstream>
 #include <string>
 #include <utility>
@@ -966,13 +967,13 @@ pkgCache::RlsFileIterator debReleaseIndex::FindInCache(pkgCache &Cache, bool con
 
 class APT_HIDDEN debSLTypeDebian : public pkgSourceList::Type		/*{{{*/
 {
-   static std::vector<std::string> getDefaultSetOf(std::string const &Name,
-	 std::map<std::string, std::string> const &Options, std::vector<std::string> const &defaultValues)
+   static std::optional<std::vector<std::string>> getDefaultSetOf(std::string const &Name,
+	 std::map<std::string, std::string> const &Options)
    {
       auto const val = Options.find(Name);
       if (val != Options.end())
 	 return VectorizeString(val->second, ',');
-      return defaultValues;
+      return {};
    }
    static std::vector<std::string> applyPlusMinusOptions(std::string const &Name,
 	 std::map<std::string, std::string> const &Options, std::vector<std::string> &&Values)
@@ -997,12 +998,21 @@ class APT_HIDDEN debSLTypeDebian : public pkgSourceList::Type		/*{{{*/
    static std::vector<std::string> parsePlusMinusOptions(std::string const &Name,
 	 std::map<std::string, std::string> const &Options, std::vector<std::string> const &defaultValues)
    {
-      return applyPlusMinusOptions(Name, Options, getDefaultSetOf(Name, Options, defaultValues));
+      return applyPlusMinusOptions(Name, Options, getDefaultSetOf(Name, Options).value_or(defaultValues));
    }
    static std::vector<std::string> parsePlusMinusArchOptions(std::string const &Name,
 	 std::map<std::string, std::string> const &Options)
    {
-      auto Values = getDefaultSetOf(Name, Options, APT::Configuration::getArchitectures());
+      std::vector<std::string> Values;
+     if (auto opt = getDefaultSetOf(Name, Options); opt.has_value())
+        Values = opt.value();
+     else
+     {
+	Values = APT::Configuration::getArchitectures();
+	auto veryforeign = _config->FindVector("APT::BarbarianArchitectures");
+	Values.reserve(Values.size() + veryforeign.size());
+	std::move(veryforeign.begin(), veryforeign.end(), std::back_inserter(Values));
+     }
       // all is a very special architecture users shouldn't be concerned with explicitly
       // but if the user does, do not override the choice
       auto const val = Options.find(Name + "-");
diff --git a/apt-pkg/edsp.cc b/apt-pkg/edsp.cc
index 5bf23044b..b7c0d28d2 100644
--- a/apt-pkg/edsp.cc
+++ b/apt-pkg/edsp.cc
@@ -208,7 +208,10 @@ static bool WriteScenarioLimitedDependency(FileFd &output,
 									/*}}}*/
 static bool checkKnownArchitecture(std::string const &arch)		/*{{{*/
 {
-   return APT::Configuration::checkArchitecture(arch);
+   if (APT::Configuration::checkArchitecture(arch))
+      return true;
+   static auto const veryforeign = _config->FindVector("APT::BarbarianArchitectures");
+   return std::find(veryforeign.begin(), veryforeign.end(), arch) != veryforeign.end();
 }
 									/*}}}*/
 static bool WriteGenericRequestHeaders(FileFd &output, APT::StringView const head)/*{{{*/
@@ -217,6 +220,8 @@ static bool WriteGenericRequestHeaders(FileFd &output, APT::StringView const hea
 	 "Architectures:");
    for (auto const &a : APT::Configuration::getArchitectures())
        WriteOkay(Okay, output, " ", a);
+   for (auto const &a : _config->FindVector("APT::BarbarianArchitectures"))
+       WriteOkay(Okay, output, " ", a);
    return WriteOkay(Okay, output, "\n");
 }
 									/*}}}*/
diff --git a/apt-private/private-source.cc b/apt-private/private-source.cc
index 7eb5a8f4a..db96cb17f 100644
--- a/apt-private/private-source.cc
+++ b/apt-private/private-source.cc
@@ -638,11 +638,14 @@ static void WriteBuildDependencyPackage(std::ostringstream &buildDepsPkgFile,
 bool DoBuildDep(CommandLine &CmdL)
 {
    std::string hostArch = _config->Find("APT::Get::Host-Architecture");
-   if (hostArch.empty() == false)
+   if (not hostArch.empty())
    {
-      std::vector<std::string> archs = APT::Configuration::getArchitectures();
-      if (std::find(archs.begin(), archs.end(), hostArch) == archs.end())
-	 return _error->Error(_("No architecture information available for %s. See apt.conf(5) APT::Architectures for setup"), hostArch.c_str());
+      if (not APT::Configuration::checkArchitecture(hostArch))
+      {
+	 auto const veryforeign = _config->FindVector("APT::BarbarianArchitectures");
+	 if (std::find(veryforeign.begin(), veryforeign.end(), hostArch) == veryforeign.end())
+	    _error->Warning(_("No architecture information available for %s. See apt.conf(5) APT::Architectures for setup"), hostArch.c_str());
+      }
    }
    auto const nativeArch = _config->Find("APT::Architecture");
    std::string const pseudoArch = hostArch.empty() ? nativeArch : hostArch;
diff --git a/doc/examples/configure-index b/doc/examples/configure-index
index 4eca100f5..f3f7f5ebc 100644
--- a/doc/examples/configure-index
+++ b/doc/examples/configure-index
@@ -49,6 +49,7 @@ APT
 {
   Architecture "<STRING>"; // debian architecture like amd64, i386, powerpc, armhf, mips, …
   Architectures "<LIST>"; // a list of (foreign) debian architectures, defaults to: dpkg --print-foreign-architectures
+  BarbarianArchitectures "<LIST>"; // a list of architectures considered too foreign to satisfy M-A:foreign
 
   Build-Essential "<LIST>"; // list of package names
   Build-Profiles "<STRING_OR_LIST>";
diff --git a/test/integration/test-apt-get-build-dep-barbarian b/test/integration/test-apt-get-build-dep-barbarian
new file mode 100755
index 000000000..688f7a54b
--- /dev/null
+++ b/test/integration/test-apt-get-build-dep-barbarian
@@ -0,0 +1,140 @@
+#!/bin/sh
+set -e
+
+TESTDIR="$(readlink -f "$(dirname "$0")")"
+. "$TESTDIR/framework"
+setupenvironment
+configarchitecture 'amd64' 'i386' 'armel' 'mipsel'
+
+insertinstalledpackage 'build-essential' 'all' '1'
+insertpackage 'unstable' 'samey' 'amd64,i386,armel,mipsel' '1' 'Multi-Arch: same'
+insertinstalledpackage 'samey' 'unknown' '1' 'Multi-Arch: same'
+
+insertsource 'unstable' 'cool-foo' 'any' '1' 'Build-Depends: foo, samey'
+insertsource 'unstable' 'bad-amd64-foo' 'any' '1' 'Build-Depends: foo, samey
+Build-Conflicts: foo:amd64'
+insertsource 'unstable' 'bad-armel-foo' 'any' '1' 'Build-Depends: foo, samey
+Build-Conflicts: foo:armel'
+insertsource 'unstable' 'bad-amd64-armel-foo' 'any' '1' 'Build-Depends: foo, samey
+Build-Conflicts: foo:amd64, foo:armel'
+insertsource 'unstable' 'bad-amd64-i386-foo' 'any' '1' 'Build-Depends: foo, samey
+Build-Conflicts: foo:amd64, foo:i386'
+insertsource 'unstable' 'bad-amd64-i386-armel-foo' 'any' '1' 'Build-Depends: foo, samey
+Build-Conflicts: foo:amd64, foo:i386, foo:armel'
+insertpackage 'unstable' 'foo' 'amd64,i386,armel,mipsel' '1' 'Multi-Arch: foreign'
+
+setupaptarchive
+
+installsfoosamey() {
+	local FOO="foo:$1"
+	local SAMEY="samey:$2"
+	if [ "$1" = 'amd64' ]; then FOO='foo'; fi
+	if [ "$2" = 'amd64' ]; then SAMEY='samey'; fi
+	echo "Reading package lists...
+Reading package lists...
+Building dependency tree...
+The following NEW packages will be installed:
+  $FOO $SAMEY
+0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded.
+Inst $FOO (1 unstable [$1])
+Inst $SAMEY (1 unstable [$2])
+Conf $FOO (1 unstable [$1])
+Conf $SAMEY (1 unstable [$2])"
+}
+
+testdpkginstalled 'samey:unknown'
+
+testsuccessequal "$(installsfoosamey 'amd64' 'amd64')" apt build-dep cool-foo -s
+testsuccessequal "$(installsfoosamey 'amd64' 'amd64')" apt build-dep cool-foo -s -a amd64
+testsuccessequal "$(installsfoosamey 'amd64' 'i386')" apt build-dep cool-foo -s -a i386
+testsuccessequal "$(installsfoosamey 'amd64' 'armel')" apt build-dep cool-foo -s -a armel
+
+testsuccessequal "$(installsfoosamey 'i386' 'amd64')" apt build-dep bad-amd64-foo -s
+testsuccessequal "$(installsfoosamey 'i386' 'amd64')" apt build-dep bad-amd64-foo -s -a amd64
+testsuccessequal "$(installsfoosamey 'i386' 'i386')" apt build-dep bad-amd64-foo -s -a i386
+testsuccessequal "$(installsfoosamey 'i386' 'armel')" apt build-dep bad-amd64-foo -s -a armel
+
+testsuccessequal "$(installsfoosamey 'amd64' 'amd64')" apt build-dep bad-armel-foo -s
+testsuccessequal "$(installsfoosamey 'amd64' 'amd64')" apt build-dep bad-armel-foo -s -a amd64
+testsuccessequal "$(installsfoosamey 'amd64' 'i386')" apt build-dep bad-armel-foo -s -a i386
+testsuccessequal "$(installsfoosamey 'amd64' 'armel')" apt build-dep bad-armel-foo -s -a armel
+
+testsuccessequal "$(installsfoosamey 'i386' 'amd64')" apt build-dep bad-amd64-armel-foo -s
+testsuccessequal "$(installsfoosamey 'i386' 'amd64')" apt build-dep bad-amd64-armel-foo -s -a amd64
+testsuccessequal "$(installsfoosamey 'i386' 'i386')" apt build-dep bad-amd64-armel-foo -s -a i386
+testsuccessequal "$(installsfoosamey 'i386' 'armel')" apt build-dep bad-amd64-armel-foo -s -a armel
+
+testsuccessequal "$(installsfoosamey 'armel' 'amd64')" apt build-dep bad-amd64-i386-foo -s
+testsuccessequal "$(installsfoosamey 'armel' 'amd64')" apt build-dep bad-amd64-i386-foo -s -a amd64
+testsuccessequal "$(installsfoosamey 'armel' 'i386')" apt build-dep bad-amd64-i386-foo -s -a i386
+testsuccessequal "$(installsfoosamey 'armel' 'armel')" apt build-dep bad-amd64-i386-foo -s -a armel
+
+testsuccessequal "$(installsfoosamey 'mipsel' 'amd64')" apt build-dep bad-amd64-i386-armel-foo -s
+testsuccessequal "$(installsfoosamey 'mipsel' 'amd64')" apt build-dep bad-amd64-i386-armel-foo -s -a amd64
+testsuccessequal "$(installsfoosamey 'mipsel' 'i386')" apt build-dep bad-amd64-i386-armel-foo -s -a i386
+testsuccessequal "$(installsfoosamey 'mipsel' 'armel')" apt build-dep bad-amd64-i386-armel-foo -s -a armel
+
+
+msgmsg 'BarbarianArchitectures' 'config'
+echo 'APT::BarbarianArchitectures { "mipsel"; "armel"; };' > rootdir/etc/apt/apt.conf.d/99barbarianarchs
+testsuccess aptcache gencaches
+
+testsuccessequal "$(installsfoosamey 'amd64' 'i386')" apt build-dep cool-foo -s -a i386
+testsuccessequal "$(installsfoosamey 'i386' 'i386')" apt build-dep bad-amd64-foo -s -a i386
+testsuccessequal "$(installsfoosamey 'amd64' 'i386')" apt build-dep bad-armel-foo -s -a i386
+testsuccessequal "$(installsfoosamey 'i386' 'i386')" apt build-dep bad-amd64-armel-foo -s -a i386
+testfailureequal 'Reading package lists...
+Reading package lists...
+Building dependency tree...
+Some packages could not be installed. This may mean that you have
+requested an impossible situation or if you are using the unstable
+distribution that some required packages have not yet been created
+or been moved out of Incoming.
+The following information may help to resolve the situation:
+
+The following packages have unmet dependencies:
+ builddeps:bad-amd64-i386-foo:i386 : Depends: foo:i386
+E: Unable to correct problems, you have held broken packages.' apt build-dep bad-amd64-i386-foo -s -a i386
+testfailureequal 'Reading package lists...
+Reading package lists...
+Building dependency tree...
+Some packages could not be installed. This may mean that you have
+requested an impossible situation or if you are using the unstable
+distribution that some required packages have not yet been created
+or been moved out of Incoming.
+The following information may help to resolve the situation:
+
+The following packages have unmet dependencies:
+ builddeps:bad-amd64-i386-armel-foo:i386 : Depends: foo:i386
+E: Unable to correct problems, you have held broken packages.' apt build-dep bad-amd64-i386-armel-foo -s -a i386
+
+testsuccessequal "$(installsfoosamey 'amd64' 'armel')" apt build-dep cool-foo -s -a armel
+testsuccessequal "$(installsfoosamey 'i386' 'armel')" apt build-dep bad-amd64-foo -s -a armel
+testsuccessequal "$(installsfoosamey 'amd64' 'armel')" apt build-dep bad-armel-foo -s -a armel
+testsuccessequal "$(installsfoosamey 'i386' 'armel')" apt build-dep bad-amd64-armel-foo -s -a armel
+testsuccessequal "$(installsfoosamey 'armel' 'armel')" apt build-dep bad-amd64-i386-foo -s -a armel
+FAILURE='Reading package lists...
+Building dependency tree...
+Some packages could not be installed. This may mean that you have
+requested an impossible situation or if you are using the unstable
+distribution that some required packages have not yet been created
+or been moved out of Incoming.
+The following information may help to resolve the situation:
+
+The following packages have unmet dependencies:
+ builddeps:bad-amd64-i386-armel-foo:armel : Depends: foo:armel
+E: Unable to correct problems, you have held broken packages.'
+testfailureequal "Reading package lists...
+$FAILURE" apt build-dep bad-amd64-i386-armel-foo -s -a armel
+
+msgmsg 'BarbarianArchitectures' 'cmdline options'
+rm rootdir/etc/apt/apt.conf.d/99barbarianarchs
+testsuccess aptcache gencaches
+
+testsuccessequal "$(installsfoosamey 'mipsel' 'armel')" apt build-dep bad-amd64-i386-armel-foo -s -a armel
+testsuccess aptcache gencaches -o APT::BarbarianArchitectures::=armel
+testsuccessequal "$(installsfoosamey 'mipsel' 'armel')" apt build-dep bad-amd64-i386-armel-foo -s -a armel -o APT::BarbarianArchitectures::=armel
+testfailureequal "$FAILURE" apt build-dep bad-amd64-i386-armel-foo -s -a armel -o APT::BarbarianArchitectures::=mipsel
+testfailureequal "$FAILURE" apt build-dep bad-amd64-i386-armel-foo -s -a armel -o APT::BarbarianArchitectures::=mipsel -o APT::BarbarianArchitectures::=armel
+testfailureequal "Reading package lists...
+$FAILURE" apt build-dep bad-amd64-i386-armel-foo -s -a armel -o APT::BarbarianArchitectures=mipsel,armel
diff --git a/test/integration/test-apt-get-build-dep-file b/test/integration/test-apt-get-build-dep-file
index c4b6947bf..88bf10b0f 100755
--- a/test/integration/test-apt-get-build-dep-file
+++ b/test/integration/test-apt-get-build-dep-file
@@ -158,7 +158,19 @@ testsuccess aptget build-dep --simulate '..'
 cd ../..
 
 testfailureequal 'E: Must specify at least one package to check builddeps for' aptget build-dep
-testfailureequal 'E: No architecture information available for armel. See apt.conf(5) APT::Architectures for setup' aptget build-dep --simulate ./foo-1.0 -a armel
+testfailureequal "Note, using directory './foo-1.0' to get the build dependencies
+Reading package lists...
+Building dependency tree...
+Some packages could not be installed. This may mean that you have
+requested an impossible situation or if you are using the unstable
+distribution that some required packages have not yet been created
+or been moved out of Incoming.
+The following information may help to resolve the situation:
+
+The following packages have unmet dependencies:
+ builddeps:./foo-1.0:armel : Depends: debhelper:armel (>= 7) but it is not installable
+W: No architecture information available for armel. See apt.conf(5) APT::Architectures for setup
+E: Unable to correct problems, you have held broken packages." aptget build-dep --simulate ./foo-1.0 -a armel
 testfailureequal 'Reading package lists...
 E: Unable to find a source package for foo' aptget build-dep --simulate foo
 
diff --git a/test/libapt/getarchitectures_test.cc b/test/libapt/getarchitectures_test.cc
index 57e9a5f2f..4f767226f 100644
--- a/test/libapt/getarchitectures_test.cc
+++ b/test/libapt/getarchitectures_test.cc
@@ -75,3 +75,31 @@ TEST(ArchitecturesTest,Duplicates)
 
    _config->Clear();
 }
+TEST(ArchitecturesTest,VeryForeign)
+{
+   _config->Clear();
+   _config->Set("APT::Architectures::", "i386");
+   _config->Set("APT::Architectures::", "amd64");
+   _config->Set("APT::Architectures::", "armel");
+
+   auto vec = APT::Configuration::getArchitectures(false);
+   ASSERT_EQ(3u, vec.size());
+   EXPECT_EQ("i386", vec[0]);
+   EXPECT_EQ("amd64", vec[1]);
+   EXPECT_EQ("armel", vec[2]);
+
+   _config->Set("APT::BarbarianArchitectures::", "mipsel");
+   vec = APT::Configuration::getArchitectures(false);
+   ASSERT_EQ(3u, vec.size());
+   EXPECT_EQ("i386", vec[0]);
+   EXPECT_EQ("amd64", vec[1]);
+   EXPECT_EQ("armel", vec[2]);
+
+   _config->Set("APT::BarbarianArchitectures::", "armel");
+   vec = APT::Configuration::getArchitectures(false);
+   ASSERT_EQ(2u, vec.size());
+   EXPECT_EQ("i386", vec[0]);
+   EXPECT_EQ("amd64", vec[1]);
+
+   _config->Clear();
+}