diff: Integrate libdiff from OpenBSD GoT.

This adds support for two new diff algorithms, Myers diff and Patience
diff.

These algorithms perform a different form of search compared to the
classic Stone algorithm and support escapes when worst case scenarios
are encountered.

Add the -A flag to allow selection of the algorithm, but default to
using the new Myers diff implementation.

The libdiff implementation currently only supports a subset of input and
output options supported by diff. When these options are used, but the
algorithm is not selected, automatically fallback to the classic Stone
algorithm until support for these modes can be added.

Based on work originally done by thj@ with contributions from kevans@.

Sponsored by: Klara, Inc.
Reviewed by: thj
Differential Revision: https://reviews.freebsd.org/D44302

diff: Improve history section.

Reviewed by: gbe
Differential Revision: https://reviews.freebsd.org/D44409

diff(1) add FreeBSD HISTORY

diff: Bump manual page date.

Sponsored by: Klara, Inc.

diff: Fix --expand-tabs and --side-by-side.

* Overhaul column width and padding calculation.
* Rewrite print_space() so it is now a) correct and b) understandable.
* Rewrite tab expansion in fetch() for the same reason.

This brings us in line with GNU diff for all cases I could think of.

Sponsored by: Klara, Inc.
Reviewed by: imp
Differential Revision: https://reviews.freebsd.org/D44014

diff(1): fix a typo

On the manpage of diff(1), "when" is mistyped to "wen".

Event: Advanced UNIX Programming Course (Fall'23) at NTHU.
Signed-off-by: Pin-Yi Kuo <kuokuoyiyi@gapp.nthu.edu.tw>
Reviewed by: imp, zlei
Pull Request: https://github.com/freebsd/freebsd-src/pull/943

usr.bin: Remove ancient SCCS tags.

Remove ancient SCCS tags from the tree, automated scripting, with two
minor fixup to keep things compiling. All the common forms in the tree
were removed with a perl script.

Sponsored by: Netflix

Remove $FreeBSD$: one-line nroff pattern

Remove /^\.\\"\s*\$FreeBSD\$$\n/

diff: add support for --help and --version

Add support for --help and --version to be compatible with gnu diff.

gnu diff --help writes to stdout, do the same to be compatible

Reviewed by: bapt, pstef, debrup, Pau Amma
Sponsored by: Klara Inc.
Differential Revision: https://reviews.freebsd.org/D34508

diff: Detect Objective-C methods

When searching back for function definitions, consider lines starting
with '+' and '-', this allows us to pick up Objective-C methods as well
as C style function definitions.

Reviewed by: bapt
Sponsored by: Klara Inc.
Differential Revision: https://reviews.freebsd.org/D34202

diff: implement option -F (--show-function-line)

With unified and context diffs, show the last line that matches the
provided pattern before the context.

Reviewed by: bapt
Differential Revision: https://reviews.freebsd.org/D31714

diff(1): Add --color support

Adds a --color flag to diff(1) that supports the same options as GNU's
diff(1). The colors are customizable with the env var DIFFCOLORS in
a format similar to grep(1)'s GREPCOLORS. An example would be 04;36:41
for additions to be underlined light blue, and deletions have a red
background.

Differential Revision: https://reviews.freebsd.org/D30545

diff(1): Add EXAMPLES section

Add examples for -r, -u, -N, -x, -q and -I

Approved by: 0mp@
Differential Revision: https://reviews.freebsd.org/D25345

Document long version of -b option

PR: 234195
Submitted by: Fehmi Noyan Isi <fnoyanisi@yahoo.com>
Reported by: Andras Farkas <deepbluemistake@gmail.com>
MFC after: 3 days

diff: fix segfault with --tabsize and no/malformed argument

--tabsize was previously listed as optional_argument, but didn't account for
the optionality of it in the argument handling. This is irrelevant -- the
manpage doesn't indicate that the argument is optional, and indeed there's
no clear interpretation of omitting the argument because there's no other
side effect of --tabsize.

The "malformed" argument part of the header on this message is simply
referring to usage like this:

% diff --tabsize 4 A B

With an optional_argument, the argument must be attached to the parameter
directly (e.g. --tabsize=4), so the argument is effectively NULL with the
above invocation as if no argument had been passed.

PR: 243974
Submitted by: fehmi noyan isi <fnoyanisi yahoo com> (diff.c portion)
MFC after: 3 days

diff.1: Fix style & document -y as extension to POSIX

- Long options must be stylized with the Fl macro as well.

Reviewed by: bapt
Approved by: bcr (mentor)
Differential Revision: https://reviews.freebsd.org/D23642

Fix most of the style warnings

diff: implement -y (--side-by-side) along with -W and --suppress-common-lines

PR: 219933
Submitted by: fehmi noyan isi <fnoyanisi@yahoo.com>
MFC after: 3 weeks

diff(1): Implement -B/--ignore-blank-lines

As noted by cem in r338035, coccinelle invokes diff(1) with the -B flag.
This was not previously implemented here, so one was forced to create a link
for GNU diff to /usr/local/bin/diff

Implement the -B flag and add some primitive tests for it. It is implemented
in the same fashion that -I is implemented; each chunk's lines are scanned,
and if a non-blank line is encountered then the chunk will be output.
Otherwise, it's skipped.

MFC after: 2 weeks

Cross reference pr(1) which diff might call with -l option

Document all long options

Implement a basic --changed-group-format

etcupdate(8) requires that option, while GNU diff supports many more variation
of that options, their behaviour beside the simple verion implemented here are
quite inconsistent as such I do not plan to implement those.

The only special keyword supported by this implementation are: %< and %>
%= is not implemented as the documentation of GNU diff says: common lines, but
it actually when tested print the changes from the first file

add a stub --speed-large-files for compatibility with GNU diff

There is no intention to implement it, but lots of scripts/tools using
diff(1) passes GNU diff option

diff(1): document remaining long options

While here, try and tie together some of the short options with
their long option equivalents, where possible.

Sponsored by: Dell EMC Isilon

diff(1): fix SYNOPSIS section noting non-existent option, --no-ignore-case

`--no-ignore-case` should be `--no-ignore-file-name-case` per code for
compatibility with [g]diff(1).

Sponsored by: Dell EMC Isilon

diff(1): add --strip-trailing-cr to last example in the SYNOPSIS

This syncs the last example in the SYNOPSIS with the other examples.

Reviewed by: bapt
Sponsored by: Dell EMC Isilon
Differential Revision: D10017

diff(1): sort long options under -D example in SYNOPSYS

Sponsored by: Dell EMC Isilon

Fix wrong date in diff(1)

Reported by: rgrimes

Import diff from OpenBSD and remove GNU diff

Some of the modifications from the previous summer of code has been integrated
Modification for compatibility with GNU diff output has been added

Main difference with OpenBSD:
Implement multiple GNU diff options:
* --ignore-file-name-case
* --no-ignore-file-name-case
* --normal
* --tabsize
* --strip-trailing-cr
Make diff -p compatible with GNU diff
Implement diff -l
Make diff -r compatible with GNU diff

Capsicumize diffing 2 regular files
Add a simple test suite

Approved by: AsiaBSDcon devsummit
Obtained from: OpenBSD, GSoC
Relnotes: yes