git-jump: pick a mode automatically when invoked without arguments

When `git jump` is invoked with no positional arguments (and no
arguments after `--stdout`) it currently prints usage and exits with
status 1.

But there are two situations where we can usefully infer the most
valuable and likely mode that a user would want to use, and select it
automatically when they run `git jump` without arguments:

1. When there are unmerged paths in the index, the user likely
   wants `git jump merge`.

2. When the working tree has unstaged changes, the user likely
   wants `git jump diff`.

Detect these two cases and dispatch to the corresponding mode
automatically, falling back to the existing usage-and-exit behavior
when neither holds.

Signed-off-by: Greg Hurrell <greg.hurrell@datadoghq.com>

Author: wincent

contrib/git-jump/README

@@ -55,6 +55,10 @@ To use it, just drop git-jump in your PATH, and then invoke it like
 this:
 
 --------------------------------------------------
+# pick a mode automatically: "merge" if there are unmerged paths,
+# "diff" if the worktree has unstaged changes, otherwise show usage
+git jump
+
 # jump to changes not yet staged for commit
 git jump diff
 

contrib/git-jump/git-jump

@@ -2,7 +2,7 @@
 
 usage() {
 	cat <<\EOF
-usage: git jump [--stdout] <mode> [<args>]
+usage: git jump [--stdout] [<mode>] [<args>]
 
 Jump to interesting elements in an editor.
 The <mode> parameter is one of:
@@ -99,8 +99,18 @@ while test $# -gt 0; do
 	shift
 done
 if test $# -lt 1; then
-	usage >&2
-	exit 1
+	if test "$(git rev-parse --is-inside-work-tree 2>/dev/null)" != "true"; then
+		usage >&2
+		exit 1
+	fi
+	if test -n "$(git ls-files -u)"; then
+		set -- merge
+	elif ! git diff --quiet; then
+		set -- diff
+	else
+		usage >&2
+		exit 1
+	fi
 fi
 mode=$1; shift
 type "mode_$mode" >/dev/null 2>&1 || { usage >&2; exit 1; }