repoview: add a 'devel.debug.repo-filter' option

If set, there will be debug message when a filter computation is triggered.

This is going to be useful to remove various filtering trigger and to test they
do not get reintroduced.

Differential Revision: https://phab.mercurial-scm.org/D7476

mercurial/configitems.py

@@ -433,6 +433,9 coreconfigitem(
     b'devel', b'debug.extensions', default=False,
 )
 coreconfigitem(
+    b'devel', b'debug.repo-filters', default=False,
+)
+coreconfigitem(
     b'devel', b'debug.peer-request', default=False,
 )
 coreconfigitem(

mercurial/repoview.py

@@ -217,6 +217,9 def filterrevs(repo, filtername, visibil
     hidden-state and must be visible. They are dynamic and hence we should not
     cache it's result"""
     if filtername not in repo.filteredrevcache:
+        if repo.ui.configbool(b'devel', b'debug.repo-filters'):
+            msg = b'debug.filters: computing revision filter for "%s"\n'
+            repo.ui.debug(msg % filtername)
         func = filtertable[filtername]
         if visibilityexceptions:
             return func(repo.unfiltered, visibilityexceptions)