import-orig: Add new --merge-mode=replace

This allows one to not merge upstream versions into the debian branch
but rather replace the content of the debian branch and only preserve
the debian/ dirs content.

Closes: #778594

3 files changed, 68 insertions, 5 deletions

diff --git a/docs/manpages/gbp-import-orig.sgml b/docs/manpages/gbp-import-orig.sgml
index 809c46aa..ec10d231 100644
--- a/docs/manpages/gbp-import-orig.sgml
+++ b/docs/manpages/gbp-import-orig.sgml
@@ -23,6 +23,7 @@
       &man.common.options.synopsis;
       <arg><option>--upstream-version=</option><replaceable>version</replaceable></arg>
       <arg><option>--[no-]merge</option></arg>
+      <arg><option>--merge-mode=</option><replaceable>[merge|replace]</replaceable></arg>
       <arg><option>--upstream-branch=</option><replaceable>branch_name</replaceable></arg>
       <arg><option>--debian-branch=</option><replaceable>branch_name</replaceable></arg>
       <arg><option>--upstream-vcs-tag=</option><replaceable>tag-format</replaceable></arg>
@@ -84,6 +85,31 @@
         </listitem>
       </varlistentry>
       <varlistentry>
+        <term><option>--merge-mode=</option><replaceable>[merge|replace]</replaceable></term>
+        <listitem>
+          <para>
+            How to fold the newly imported upstream source to the
+            &debian; packaging branch after import.
+	  </para>
+	  <para>
+	    The default mode
+	    <replaceable>merge</replaceable> does a
+	    &git; <command>merge</command> leaving you on your own in
+	    case of merge conflict resolution.
+	  </para>
+	  <para>
+	    <replaceable>replace</replaceable> mode on the
+	    other hand makes the head of the &debian; packaging branch
+	    identical to the newly imported tree but preserves the
+	    content of the <filename>debian/</filename> directory
+	    while keeping the current head as well as the newly
+	    iportant trees as parents of the generated commit. This is
+	    similar to a <option>theirs</option> merge strategy while
+	    preserving <filename>debian/</filename>.
+          </para>
+        </listitem>
+      </varlistentry>
+      <varlistentry>
         <term><option>--upstream-branch</option>=<replaceable>branch_name</replaceable>
         </term>
         <listitem>
diff --git a/gbp/config.py b/gbp/config.py
index 413cb6a8..de8a25ea 100644
--- a/gbp/config.py
+++ b/gbp/config.py
@@ -147,6 +147,7 @@ class GbpOptionParser(OptionParser):
                  'renumber'        : 'False',
                  'notify'          : 'auto',
                  'merge'           : 'True',
+                 'merge-mode'      : 'merge',
                  'track'           : 'True',
                  'author-is-committer': 'False',
                  'author-date-is-committer-date': 'False',
@@ -266,6 +267,9 @@ class GbpOptionParser(OptionParser):
              'merge':
                   ("After the import merge the result to the debian branch, "
                    "default is '%(merge)s'"),
+             'merge-mode':
+                  ("Howto merge the new upstream sources onto the debian branch"
+                   "default is '%(merge-mode)s'"),
              'track':
                   ("Set up tracking for remote branches, "
                    "default is '%(track)s'"),
diff --git a/gbp/scripts/import_orig.py b/gbp/scripts/import_orig.py
index d379466a..16573c31 100644
--- a/gbp/scripts/import_orig.py
+++ b/gbp/scripts/import_orig.py
@@ -174,12 +174,11 @@ def find_source(use_uscan, args):
 
 
 def debian_branch_merge(repo, tag, version, options):
-    gbp.log.info("Merging to '%s'" % options.debian_branch)
-    repo.set_branch(options.debian_branch)
     try:
-        repo.merge(tag)
-    except GitRepositoryError:
-        raise GbpError("Merge failed, please resolve.")
+        func = globals()["debian_branch_merge_by_%s" % options.merge_mode]
+    except KeyError:
+        raise GbpError("%s is not a valid merge mode" % options.merge_mode)
+    func(repo, tag, version, options)
     if options.postimport:
         epoch = ''
         if os.access('debian/changelog', os.R_OK):
@@ -194,6 +193,39 @@ def debian_branch_merge(repo, tag, version, options):
         gbpc.Command(format_str(options.postimport, info), extra_env=env, shell=True)()
 
 
+def debian_branch_merge_by_replace(repo, tag, version, options):
+    gbp.log.info("Replacing upstream source on '%s'" % options.debian_branch)
+
+    tree = [x for x in repo.list_tree("%s^{tree}" % tag)
+            if x[-1] != 'debian']
+    msg = "Updated version %s from '%s'" % (version, tag)
+
+    # Get the current debian/ tree on the debian branch
+    try:
+        deb_sha = [x for x in repo.list_tree("%s^{tree}" % options.debian_branch)
+                   if x[-1] == 'debian' and x[1] == 'tree'][0][2]
+        tree.append(['040000', 'tree', deb_sha, 'debian'])
+        msg += "\n\nwith Debian dir %s" % deb_sha
+    except IndexError:
+        pass  # no debian/ dir is fine
+
+    sha = repo.make_tree(tree)
+    commit = repo.commit_tree(sha, msg, ["%s^{commit}" % options.debian_branch,
+                                         "%s^{commit}" % tag])
+    repo.update_ref("refs/heads/%s" % options.debian_branch, commit,
+                    msg="gbp: Updating %s after import of %s" % (options.debian_branch,
+                                                                 tag))
+    repo.force_head(commit, hard=True)
+
+
+def debian_branch_merge_by_merge(repo, tag, version, options):
+    gbp.log.info("Merging to '%s'" % options.debian_branch)
+    try:
+        repo.merge(tag)
+    except GitRepositoryError:
+        raise GbpError("Merge failed, please resolve.")
+    repo.set_branch(options.debian_branch)
+
 
 def set_bare_repo_options(options):
     """Modify options for import into a bare repository"""
@@ -233,6 +265,7 @@ def build_parser(name):
     branch_group.add_config_file_option(option_name="upstream-vcs-tag", dest="vcs_tag",
                             help="Upstream VCS tag add to the merge commit")
     branch_group.add_boolean_config_file_option(option_name="merge", dest="merge")
+    branch_group.add_config_file_option(option_name="merge-mode", dest="merge_mode")
 
     tag_group.add_boolean_config_file_option(option_name="sign-tags",
                       dest="sign_tags")