# HG changeset patch
# User Pierre-Yves David <pierre-yves.david@ens-lyon.org>
# Date 1490675008 -7200
# Node ID 472d726c1afdfa0c47694305de2a41e7a97e3b55
# Parent  510267cf6c586d8d085135af8ef6c8b5b9973085
tags: extract filenode filtering into its own function

We'll also need to reuse this logic so we extract it into its own function. We
document some of the logic in the process.

diff -r 510267cf6c58 -r 472d726c1afd mercurial/tags.py
--- a/mercurial/tags.py	Tue Mar 28 06:08:12 2017 +0200
+++ b/mercurial/tags.py	Tue Mar 28 06:23:28 2017 +0200
@@ -95,17 +95,10 @@
         _updatetags(cachetags, alltags)
         return alltags
 
-    seen = set()  # set of fnode
-    fnodes = []
     for head in reversed(heads):  # oldest to newest
         assert head in repo.changelog.nodemap, \
                "tag cache returned bogus head %s" % short(head)
-
-        fnode = tagfnode.get(head)
-        if fnode and fnode not in seen:
-            seen.add(fnode)
-            fnodes.append(fnode)
-
+    fnodes = _filterfnodes(tagfnode, reversed(heads))
     alltags = _tagsfromfnodes(ui, repo, fnodes)
 
     # and update the cache (if necessary)
@@ -113,6 +106,21 @@
         _writetagcache(ui, repo, valid, alltags)
     return alltags
 
+def _filterfnodes(tagfnode, nodes):
+    """return a list of unique fnodes
+
+    The order of this list matches the order of "nodes". Preserving this order
+    is important as reading tags in different order provides different
+    results."""
+    seen = set()  # set of fnode
+    fnodes = []
+    for no in nodes:  # oldest to newest
+        fnode = tagfnode.get(no)
+        if fnode and fnode not in seen:
+            seen.add(fnode)
+            fnodes.append(fnode)
+    return fnodes
+
 def _tagsfromfnodes(ui, repo, fnodes):
     """return a tagsmap from a list of file-node