* src/diff.h (no_dereference_symlinks): New variable.
* src/diff.c: Include xreadlink.h.
(longopts): Add --no-dereference option.
(main): Accept --no-dereference option.
(option_help_msgid): Mention the --no-dereference option.
(compare_files): If no_dereference_symlinks is true, use lstat()
instead of stat(). Compare symbolic links by comparing their values.
* bootstrap.conf (gnulib_modules): Add lstat, stat, xreadlink.
* doc/diffutils.texi (Comparing Directories, diff Options): Mention the
--no-dereference option.
* tests/no-dereference: New file.
* tests/Makefile.am (TESTS): Add it.

Run "make update-copyright".

* tests/binary: Reverse arguments to compare to avoid failure of
new syntax-check rule.
* configure.ac: Use -Wno-format-nonliteral.
Mark functions as pure of const, per recommendations enabled by
new gcc -W options.  Use _GL_ATTRIBUTE_PURE and _GL_ATTRIBUTE_CONST.
* lib/cmpbuf.h (buffer_lcm, block_compare):
Apply pure and/or const attributes.
* src/cmp.c (block_compare): Likewise.
* src/context.c (find_hunk): Likewise.
* src/diff.h (lines_differ): Likewise.
* src/diff3.c (skipwhite): Likewise.
* src/dir.c (dir_loop): Likewise.
* src/util.c (find_change, find_reverse_change): Likewise.
(translate_line_number): Likewise.

Likewise, when an empty file is expected, use "compare /dev/null out",
not "compare out /dev/null". I.e., specify the expected/desired contents
via the first file name.  Prompted by a suggestion from Bruno Haible
in http://thread.gmane.org/gmane.comp.gnu.grep.bugs/4020/focus=29154

Run these commands:

  git grep -l -E 'compare [^ ]+ exp' \
    |xargs perl -pi -e 's/\b(compare) (\S+) (exp\S*)/$1 $3 $2/'
  git grep -l -E 'compare [^ ]+ /dev/null' \
    |xargs perl -pi -e 's,\b(compare) (\S+) (/dev/null),$1 $3 $2,'

But manually convert this one:

  -compare out exp-$(echo $opt|tr ' ' _)
  +compare exp-$(echo $opt|tr ' ' _) out

and avoid an inappropriate change to cfg.mk.

* tests/Makefile.am (TESTS_ENVIRONMENT): Redirection with `exec 9>&2'
is not portable to various Korn shells, and to (at least) HP-UX 11
/bin/sh.  Use a more portable idiom.
See http://thread.gmane.org/gmane.comp.gnu.coreutils.bugs/22488 for
lots of discussion.

All the test scripts in the diffutils testsuite are shell scripts,
so the current definition of TESTS_ENVIRONMENT, which adaptively
run tests using either perl or the shell depending on their kind,
is an overkill.

Moreover, this change is required in order for the testsuite to
continue to work with the new testsuite harness that is planned
to be introduced in Automake 1.12 (which, as of the writing date,
is still under development and in late alpha state).

See also related discussion on bug-coreutils:
 <http://debbugs.gnu.org/cgi/bugreport.cgi?bug=8887>

* tests/Makefile.am (TESTS_ENVIRONMENT): Remove definition of the
`shell_or_perl_' shell function, which is not required anymore.
(LOG_COMPILER): New, define to `$(SHELL)'.
* tests/binary: Make executable.
* tests/colliding-file-names: Likewise.
* tests/excess-slash: Likewise.
* tests/no-newline-at-eof: Likewise.

* bootstrap: Update from gnulib.
* tests/init.sh: Likewise.

* tests/init.sh: Update from gnulib.

* tests/function-line-vs-leading-space: Use sed -n '3,$p' rather than
tail -n+3.  Older versions of tail do not accept that newer syntax.
Reported by Sudhakara Peram.

On most systems, like-named files were compared, by luck.
However, on others, different-named files would be compared
since their names were being treated as equal -- but they had
different content, so the test would fail.
* tests/colliding-file-names: Use different sets of file names
in d1 and d2 so that they cannot accidentally match.
Put the same line in each test file.  This is required
when files named e.g., abc and ABC are compared.
This test was failing on a NixOS 86_64-darwin system.