contrib: add git-jump script

This is a small script for helping your editor jump to
specific points of interest. See the README for details.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/git-jump/README

@@ -0,0 +1,92 @@
+git-jump
+========
+
+Git-jump is a script for helping you jump to "interesting" parts of your
+project in your editor. It works by outputting a set of interesting
+spots in the "quickfix" format, which editors like vim can use as a
+queue of places to visit (this feature is usually used to jump to errors
+produced by a compiler). For example, given a diff like this:
+
+------------------------------------
+diff --git a/foo.c b/foo.c
+index a655540..5a59044 100644
+--- a/foo.c
++++ b/foo.c
+@@ -1,3 +1,3 @@
+ int main(void) {
+-  printf("hello word!\n");
++  printf("hello world!\n");
+ }
+-----------------------------------
+
+git-jump will feed this to the editor:
+
+-----------------------------------
+foo.c:2: printf("hello word!\n");
+-----------------------------------
+
+Obviously this trivial case isn't that interesting; you could just open
+`foo.c` yourself. But when you have many changes scattered across a
+project, you can use the editor's support to "jump" from point to point.
+
+Git-jump can generate three types of interesting lists:
+
+  1. The beginning of any diff hunks.
+
+  2. The beginning of any merge conflict markers.
+
+  3. Any grep matches.
+
+
+Using git-jump
+--------------
+
+To use it, just drop git-jump in your PATH, and then invoke it like
+this:
+
+--------------------------------------------------
+# jump to changes not yet staged for commit
+git jump diff
+
+# jump to changes that are staged for commit; you can give
+# arbitrary diff options
+git jump diff --cached
+
+# jump to merge conflicts
+git jump merge
+
+# jump to all instances of foo_bar
+git jump grep foo_bar
+
+# same as above, but case-insensitive; you can give
+# arbitrary grep options
+git jump grep -i foo_bar
+--------------------------------------------------
+
+
+Related Programs
+----------------
+
+You can accomplish some of the same things with individual tools. For
+example, you can use `git mergetool` to start vimdiff on each unmerged
+file. `git jump merge` is for the vim-wielding luddite who just wants to
+jump straight to the conflict text with no fanfare.
+
+As of git v1.7.2, `git grep` knows the `--open-files-in-pager` option,
+which does something similar to `git jump grep`. However, it is limited
+to positioning the cursor to the correct line in only the first file,
+leaving you to locate subsequent hits in that file or other files using
+the editor or pager. By contrast, git-jump provides the editor with a
+complete list of files and line numbers for each match.
+
+
+Limitations
+-----------
+
+This scripts was written and tested with vim. Given that the quickfix
+format is the same as what gcc produces, I expect emacs users have a
+similar feature for iterating through the list, but I know nothing about
+how to activate it.
+
+The shell snippets to generate the quickfix lines will almost certainly
+choke on filenames with exotic characters (like newlines).

contrib/git-jump/git-jump

@@ -0,0 +1,69 @@
+#!/bin/sh
+
+usage() {
+	cat <<\EOF
+usage: git jump <mode> [<args>]
+
+Jump to interesting elements in an editor.
+The <mode> parameter is one of:
+
+diff: elements are diff hunks. Arguments are given to diff.
+
+merge: elements are merge conflicts. Arguments are ignored.
+
+grep: elements are grep hits. Arguments are given to grep.
+EOF
+}
+
+open_editor() {
+	editor=`git var GIT_EDITOR`
+	eval "$editor -q \$1"
+}
+
+mode_diff() {
+	git diff --relative "$@" |
+	perl -ne '
+	if (m{^\+\+\+ b/(.*)}) { $file = $1; next }
+	defined($file) or next;
+	if (m/^@@ .*\+(\d+)/) { $line = $1; next }
+	defined($line) or next;
+	if (/^ /) { $line++; next }
+	if (/^[-+]\s*(.*)/) {
+		print "$file:$line: $1\n";
+		$line = undef;
+	}
+	'
+}
+
+mode_merge() {
+	git ls-files -u |
+	perl -pe 's/^.*?\t//' |
+	sort -u |
+	while IFS= read fn; do
+		grep -Hn '^<<<<<<<' "$fn"
+	done
+}
+
+# Grep -n generates nice quickfix-looking lines by itself,
+# but let's clean up extra whitespace, so they look better if the
+# editor shows them to us in the status bar.
+mode_grep() {
+	git grep -n "$@" |
+	perl -pe '
+	s/[ \t]+/ /g;
+	s/^ *//;
+	'
+}
+
+if test $# -lt 1; then
+	usage >&2
+	exit 1
+fi
+mode=$1; shift
+
+trap 'rm -f "$tmp"' 0 1 2 3 15
+tmp=`mktemp -t git-jump.XXXXXX` || exit 1
+type "mode_$mode" >/dev/null 2>&1 || { usage >&2; exit 1; }
+"mode_$mode" "$@" >"$tmp"
+test -s "$tmp" || exit 0
+open_editor "$tmp"