matcher: make e.g. 'relpath:.' lead to fast paths

Several commands take the fast path when match.always() is
true. However, when the user passes "." on the command line, that
results in a matcher for which match.always() == False. Let's make it
so such matchers return True, and have an empty list of .files(). This
makes e.g. "hg log ." as fast as "hg log" and "hg revert ." as fast as
"hg revert --all" (when run from repo root).

mercurial/match.py

@@ -34,6 +34,15 b' def _expandsets(kindpats, ctx):'
         other.append((kind, pat))
     return fset, other
 
+def _kindpatsalwaysmatch(kindpats):
+    """"Checks whether the kindspats match everything, as e.g.
+    'relpath:.' does.
+    """
+    for kind, pat in kindpats:
+        if pat != '' or kind not in ['relpath', 'glob']:
+            return False
+    return True
+
 class match(object):
     def __init__(self, root, cwd, patterns, include=[], exclude=[],
                  default='glob', exact=False, auditor=None, ctx=None):
@@ -84,10 +93,11 b' class match(object):'
             matchfns.append(self.exact)
         elif patterns:
             kindpats = _normalize(patterns, default, root, cwd, auditor)
-            self._files = _roots(kindpats)
-            self._anypats = self._anypats or _anypats(kindpats)
-            self.patternspat, pm = _buildmatch(ctx, kindpats, '$')
-            matchfns.append(pm)
+            if not _kindpatsalwaysmatch(kindpats):
+                self._files = _roots(kindpats)
+                self._anypats = self._anypats or _anypats(kindpats)
+                self.patternspat, pm = _buildmatch(ctx, kindpats, '$')
+                matchfns.append(pm)
 
         if not matchfns:
             m = util.always

mercurial/scmutil.py

@@ -725,6 +725,8 b' def matchandpats(ctx, pats=[], opts={}, '
     def badfn(f, msg):
         ctx.repo().ui.warn("%s: %s\n" % (m.rel(f), msg))
     m.bad = badfn
+    if m.always():
+        pats = []
     return m, pats
 
 def match(ctx, pats=[], opts={}, globbed=False, default='relpath'):