Index: tracdarcs/components.py
===================================================================
--- tracdarcs/components.py	(revision 185)
+++ tracdarcs/components.py	(revision 195)
@@ -20,5 +20,5 @@
 from trac.db import Column, DatabaseManager, Index, Table
 from trac.env import IEnvironmentSetupParticipant
-from trac.util.text import shorten_line
+from trac.util.text import shorten_line, to_unicode
 from trac.versioncontrol import IRepositoryConnector, NoSuchChangeset
 from trac.versioncontrol.web_ui import IPropertyRenderer, RenderedProperty
@@ -86,14 +86,42 @@
 
     def _format_link(self, formatter, ns, rev, label):
-
-        repos = self.env.get_repository()
-        try:
-            chgset = repos.get_changeset(rev)
-            return tag.a(chgset.rev, class_="changeset",
-                         title=shorten_line(chgset.message),
-                         href=formatter.href.changeset(chgset.rev))
-        except NoSuchChangeset, e:
-            return tag.a(label, class_="missing changeset",
-                         title="No changeset for %s" % rev, rel="nofollow")
+        reponame = None
+
+        # See if the context carries a repository...
+        context = formatter.context
+        while context:
+            if context.resource.realm in ('source', 'changeset'):
+                reponame = context.resource.parent.id
+                break
+            context = context.parent
+
+        # If it does not, take the first repository containing the
+        # specified revision, if any. We can do this assuming that
+        #   a) we are dealing with full darcs hashes and
+        #   b) darcs hashes are globally unique
+        if reponame is None:
+            db = self.env.get_db_cnx()
+            c = db.cursor()
+            c.execute('SELECT r.value '
+                      'FROM darcs_changesets c JOIN repository r ON c.repo_id = r.id '
+                      'WHERE c.hash = %s AND r.name = %s '
+                      'ORDER BY r.id '
+                      'LIMIT 1', (rev, 'name',))
+            row = c.fetchone()
+            reponame = row and row[0] or ''
+
+        repos = self.env.get_repository(reponame)
+        if repos:
+            try:
+                chgset = repos.get_changeset(rev)
+                return tag.a(chgset.rev, class_="changeset",
+                             title=shorten_line(chgset.message),
+                             href=formatter.href.changeset(chgset.rev, reponame))
+            except NoSuchChangeset, e:
+                errmsg = to_unicode(e)
+        else:
+            errmsg = 'Repository "%s" not found' % reponame
+
+        return tag.a(label, class_="missing changeset", title=errmsg, rel="nofollow")
 
 class DarcsSetup(Component):