grep: search working directory files by default if --all-files is specified

The default was -rtip:0 before, but "--all-files -rtip:0" would be the most
useless combination, and it isn't supported yet. Let's change the default to
something useful.

This isn't flagged as BC since --all-files isn't released.

Differential Revision: https://phab.mercurial-scm.org/D3917

mercurial/commands.py

@@ -2535,6 +2535,8 b' def grep(ui, repo, pattern, *pats, **opt'
     diff = opts.get('all') or opts.get('diff')
     if diff and opts.get('all_files'):
         raise error.Abort(_('--diff and --all-files are mutually exclusive'))
+    if opts.get('all_files') and not opts.get('rev'):
+        opts['rev'] = ['wdir()']
 
     reflags = re.M
     if opts.get('ignore_case'):

tests/test-grep.t

@@ -412,6 +412,18 b' Test for showing working of allfiles fla'
   $ hg grep -r "." "unmod" --all-files
   um:1:unmod
 
+With --all-files, the working directory is searched by default
+
+  $ echo modified >> new
+  $ hg grep --all-files mod
+  new:2147483647:modified
+  um:2147483647:unmod
+
+ which can be overridden by -rREV
+
+  $ hg grep --all-files -r. mod
+  um:1:unmod
+
 --diff --all-files makes no sense since --diff is the option to grep history
 
   $ hg grep --diff --all-files um