Merge branch 'nd/magic-pathspec-from-root'

When giving arguments without "--" disambiguation, object names
that come  earlier on the command line must not be interpretable as
pathspecs and pathspecs that come later on the command line must
not be interpretable as object names.  Tweak the disambiguation
rule so that ":/" (no other string before or after) is always
interpreted as a pathspec, to avoid having to say "git cmd -- :/".

* nd/magic-pathspec-from-root:
grep: avoid accepting ambiguous revision
Update :/abc ambiguity check

diff --combined setup.c
index 1ccfafaa7a85875338a49953518207b74dca62c4,47acc1186f0b06e239ecbd8ed32885a66240fa1f..2e1521b09e5e6a0de585225293805b1d30a03cd4
--- 1/setup.c
--- 2/setup.c
+++ b/setup.c
@@@ -66,7 -66,14 +66,14 @@@ int check_filename(const char *prefix, 
        const char *name;
        struct stat st;
  
-       name = prefix ? prefix_filename(prefix, strlen(prefix), arg) : arg;
+       if (!prefixcmp(arg, ":/")) {
+               if (arg[2] == '\0') /* ":/" is root dir, always exists */
+                       return 1;
+               name = arg + 2;
+       } else if (prefix)
+               name = prefix_filename(prefix, strlen(prefix), arg);
+       else
+               name = arg;
        if (!lstat(name, &st))
                return 1; /* file exists */
        if (errno == ENOENT || errno == ENOTDIR)
@@@ -246,25 -253,6 +253,25 @@@ static const char *prefix_pathspec(cons
                return prefix_path(prefix, prefixlen, copyfrom);
  }
  
 +/*
 + * N.B. get_pathspec() is deprecated in favor of the "struct pathspec"
 + * based interface - see pathspec_magic above.
 + *
 + * Arguments:
 + *  - prefix - a path relative to the root of the working tree
 + *  - pathspec - a list of paths underneath the prefix path
 + *
 + * Iterates over pathspec, prepending each path with prefix,
 + * and return the resulting list.
 + *
 + * If pathspec is empty, return a singleton list containing prefix.
 + *
 + * If pathspec and prefix are both empty, return an empty list.
 + *
 + * This is typically used by built-in commands such as add.c, in order
 + * to normalize argv arguments provided to the built-in into a list of
 + * paths to process, all relative to the root of the working tree.
 + */
  const char **get_pathspec(const char *prefix, const char **pathspec)
  {
        const char *entry = *pathspec;