# HG changeset patch
# User Gregory Szorc <gregory.szorc@gmail.com>
# Date 1432596263 25200
# Node ID eaa456c5e6995f687178fb897181c7722a804b0a
# Parent  894bcdbb9e7a8a9cd975cc563c9dc5d92e253a3b
tags: support reading tags cache without populating

An upcoming patch will teach the bundle2 protocol to transfer .hgtags
fnodes to the client. We don't want this to incur any extra work
at serve time. Create an optional cache query mode that doesn't
populate the cache as a side-effect.

diff -r 894bcdbb9e7a -r eaa456c5e699 mercurial/tags.py
--- a/mercurial/tags.py	Sun May 31 17:41:35 2015 -0700
+++ b/mercurial/tags.py	Mon May 25 16:24:23 2015 -0700
@@ -442,11 +442,13 @@
                 self._raw.pop()
             self._dirtyoffset = len(self._raw)
 
-    def getfnode(self, node):
+    def getfnode(self, node, computemissing=True):
         """Obtain the filenode of the .hgtags file at a specified revision.
 
         If the value is in the cache, the entry will be validated and returned.
-        Otherwise, the filenode will be computed and returned.
+        Otherwise, the filenode will be computed and returned unless
+        "computemissing" is False, in which case None will be returned without
+        any potentially expensive computation being performed.
 
         If an .hgtags does not exist at the specified revision, nullid is
         returned.
@@ -470,7 +472,12 @@
 
             # Fall through.
 
-        # If we get here, the entry is either missing or invalid. Populate it.
+        # If we get here, the entry is either missing or invalid.
+
+        if not computemissing:
+            return None
+
+        # Populate missing entry.
         try:
             fnode = ctx.filenode('.hgtags')
         except error.LookupError: