Add a C++ rpmdb-diff API wrapping the C one, bind in Rust

I'd like to compute diffs in apply-live to differentiate
between "pure layering" versus modifications/removals.

Makefile-libpriv.am

@@ -42,6 +42,7 @@ librpmostreepriv_sources = \
 	src/libpriv/rpmostree-refsack.cxx \
 	src/libpriv/rpmostree-rpm-util.cxx \
 	src/libpriv/rpmostree-rpm-util.h \
+	src/libpriv/rpmostree-diff.cxx \
 	src/libpriv/rpmostree-importer.cxx \
 	src/libpriv/rpmostree-importer.h \
 	src/libpriv/rpmostree-unpacker-core.cxx \

rust/src/lib.rs

@@ -265,6 +265,15 @@ pub mod ffi {
         fn main_print_error(msg: &str);
     }
 
+    unsafe extern "C++" {
+        include!("rpmostree-diff.hpp");
+        type RPMDiff;
+        fn n_removed(&self) -> i32;
+        fn n_added(&self) -> i32;
+        fn n_modified(&self) -> i32;
+            dest: &CxxString,
+    }
+
     unsafe extern "C++" {
         include!("rpmostree-output.h");
         type Progress;

src/libpriv/rpmostree-diff.cxx

@@ -0,0 +1,61 @@
+/*
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation; either version 2 of the licence or (at
+ * your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General
+ * Public License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place, Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+#include <memory>
+
+#include "rpmostree-diff.hpp"
+#include "rpmostree-db.h"
+#include "rpmostree-util.h"
+
+namespace rpmostreecxx {
+
+RPMDiff::RPMDiff(GPtrArray *removed, GPtrArray *added, GPtrArray *modified_old, GPtrArray *modified_new) {
+  removed_ = g_ptr_array_ref(removed);
+  added_ = g_ptr_array_ref(added);
+  modified_old_ = g_ptr_array_ref(modified_old);
+  modified_new_ = g_ptr_array_ref(modified_new);
+}
+
+RPMDiff::~RPMDiff() {
+  g_ptr_array_unref(removed_);
+  g_ptr_array_unref(added_);
+  g_ptr_array_unref(modified_old_);
+  g_ptr_array_unref(modified_new_);
+}
+
+std::unique_ptr<RPMDiff>
+rpmdb_diff(OstreeRepo &repo, const std::string &from, const std::string &to) {
+  g_autoptr(GPtrArray) removed = NULL;
+  g_autoptr(GPtrArray) added = NULL;
+  g_autoptr(GPtrArray) modified_old = NULL;
+  g_autoptr(GPtrArray) modified_new = NULL;
+  g_autoptr(GError) local_error = NULL;
+  if (!rpm_ostree_db_diff(&repo, from.c_str(), to.c_str(),
+                          &removed, &added, &modified_old, &modified_new,
+                          NULL, &local_error))
+    util::throw_gerror(local_error);
+  return std::make_unique<RPMDiff>(removed, added, modified_old, modified_new);
+}
+
+void
+RPMDiff::print() const
+{
+  rpmostree_diff_print_formatted (RPMOSTREE_DIFF_PRINT_FORMAT_FULL_MULTILINE, NULL, 0,
+                                  removed_, added_, modified_old_, modified_new_);
+}
+
+} /* namespace */

src/libpriv/rpmostree-diff.hpp

@@ -0,0 +1,57 @@
+/*
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation; either version 2 of the licence or (at
+ * your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General
+ * Public License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place, Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+#pragma once
+
+#include <string>
+#include <exception>
+#include <sstream>
+#include <memory>
+
+#include <ostree.h>
+
+#include "rust/cxx.h"
+
+namespace rpmostreecxx {
+
+class RPMDiff final {
+public:
+    int n_removed() const {
+        return removed_->len;
+    }
+    int n_added() const {
+        return added_->len;
+    }
+    int n_modified() const {
+        return modified_old_->len + modified_new_->len;
+    }
+    ~RPMDiff();
+    RPMDiff(GPtrArray *removed, GPtrArray *added, GPtrArray *modified_old, GPtrArray *modified_new);
+
+    // TODO(cgwalters) enhance this with options
+    void print() const;
+
+private:
+    GPtrArray *removed_;
+    GPtrArray *added_;
+    GPtrArray *modified_old_;
+    GPtrArray *modified_new_;
+};
+
+std::unique_ptr<RPMDiff> rpmdb_diff(OstreeRepo &repo, const std::string &src, const std::string &dest);
+
+} /* namespace */