diff hgext/automv.py @ 28183:e07daee83029

automv: use 95 as the default similarity threshold

The motivation for the change from 100 to 95 is included in a comment.

* Updated the tests to include a change to a moved file that still should be
  caught as a move.

* Use ui.configint() to non-integer configuration entries more gracefully. Also
  complain if a similarity outside of the acceptable range is set.

--- a/hgext/automv.py	Fri Feb 19 22:28:09 2016 +0100
+++ b/hgext/automv.py	Tue Feb 16 15:58:32 2016 +0000
@@ -11,14 +11,25 @@
 
 The threshold at which a file is considered a move can be set with the
 ``automv.similarity`` config option. This option takes a percentage between 0
-(disabled) and 100 (files must be identical), the default is 100.
+(disabled) and 100 (files must be identical), the default is 95.
 
 """
+
+# Using 95 as a default similarity is based on an analysis of the mercurial
+# repositories of the cpython, mozilla-central & mercurial repositories, as
+# well as 2 very large facebook repositories. At 95 50% of all potential
+# missed moves would be caught, as well as correspond with 87% of all
+# explicitly marked moves.  Together, 80% of moved files are 95% similar or
+# more.
+#
+# See http://markmail.org/thread/5pxnljesvufvom57 for context.
+
 from __future__ import absolute_import
 
 from mercurial import (
     commands,
     copies,
+    error,
     extensions,
     scmutil,
     similar
@@ -37,7 +48,9 @@
     renames = None
     disabled = opts.pop('no_automv', False)
     if not disabled:
-        threshold = float(ui.config('automv', 'similarity', '100'))
+        threshold = ui.configint('automv', 'similarity', 95)
+        if not 0 <= threshold <= 100:
+            raise error.Abort(_('automv.similarity must be between 0 and 100'))
         if threshold > 0:
             match = scmutil.match(repo[None], pats, opts)
             added, removed = _interestingfiles(repo, match)