tags-cache: add a dedicated warm cache function to hgtagsfnodescache

Having a dedicated API point will help to optimize that specific usage. Right
doing a full phases weam takes a long time, even when the cache is already
filled.

mercurial/localrepo.py

@@ -2959,7 +2959,7 b' class localrepository:'
 
         if repository.CACHE_FILE_NODE_TAGS in caches:
             # accessing fnode cache warms the cache
-            tagsmod.fnoderevs(self.ui, unfi, unfi.changelog.revs())
+            tagsmod.warm_cache(self)
 
         if repository.CACHE_TAGS_DEFAULT in caches:
             # accessing tags warm the cache

mercurial/tags.py

@@ -80,6 +80,12 b' from .utils import stringutil'
 # setting it) for each tag is last.
 
 
+def warm_cache(repo):
+    """ensure the cache is properly filled"""
+    unfi = repo.unfiltered()
+    fnoderevs(repo.ui, unfi, unfi.changelog.revs())
+
+
 def fnoderevs(ui, repo, revs):
     """return the list of '.hgtags' fnodes used in a set revisions