[PATCH v2] git-jump: pick a mode automatically when invoked without arguments

From: Greg Hurrell <greg.hurrell@datadoghq.com>

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 several situations where we can usefully infer the most valuable and likely mode that a user would want to use, and select it automatically:

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`.

3. In the presence of conflict markers or whitespace errors (as reported
   by `git diff --check`), the user likely wants `git jump ws`.

In this commit we teach `git jump` a new "auto" mode which detects these cases and dispatches to the corresponding mode automatically. The user can either explicitly spell out `git jump auto`, or just leave it at `git jump` (because "auto" is the default).

If none of the interesting cases listed above applies, then auto mode falls back to the existing usage-and-exit behavior.

Signed-off-by: Greg Hurrell <greg.hurrell@datadoghq.com>
---
    git-jump: pick a mode automatically when invoked without arguments
    
    Changes since v0:
    
     * Added explicit "auto" keyword/mode.
     * Updated additional detail to usage info and README.
     * (Bonus) Added ws usage example to README.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-2108%2Fwincent%2Fauto-jump-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-2108/wincent/auto-jump-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/2108

Range-diff vs v1:

 1:  87fa66d233 ! 1:  5fbc8480ef git-jump: pick a mode automatically when invoked without arguments
     @@ Commit message
          arguments after `--stdout`) it currently prints usage and exits with
          status 1.
      
     -    But there are two situations where we can usefully infer the most
     +    But there are several 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:
     +    automatically:
      
          1. When there are unmerged paths in the index, the user likely
             wants `git jump merge`.
     @@ Commit message
          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.
     +    3. In the presence of conflict markers or whitespace errors (as reported
     +       by `git diff --check`), the user likely wants `git jump ws`.
     +
     +    In this commit we teach `git jump` a new "auto" mode which detects these
     +    cases and dispatches to the corresponding mode automatically. The user
     +    can either explicitly spell out `git jump auto`, or just leave it at
     +    `git jump` (because "auto" is the default).
     +
     +    If none of the interesting cases listed above applies, then auto mode
     +    falls back to the existing usage-and-exit behavior.
      
          Signed-off-by: Greg Hurrell <greg.hurrell@datadoghq.com>
      
       ## contrib/git-jump/README ##
     -@@ contrib/git-jump/README: To use it, just drop git-jump in your PATH, and then invoke it like
     - this:
     +@@ contrib/git-jump/README: git jump grep foo_bar
     + # arbitrary grep options
     + git jump grep -i foo_bar
       
     - --------------------------------------------------
     ++# jump to places with conflict markers or whitespace errors
     ++# (as reported by # `git diff --check`)
     ++git jump ws
     ++
     + # use the silver searcher for git jump grep
     + git config jump.grepCmd "ag --column"
     ++
      +# pick a mode automatically: "merge" if there are unmerged paths,
     -+# "diff" if the worktree has unstaged changes, otherwise show usage
     -+git jump
     ++# "diff" if the worktree has unstaged changes, "ws" if there are
     ++# whitespace problems; otherwise show usage
     ++git jump auto
      +
     - # jump to changes not yet staged for commit
     - git jump diff
     ++# with no explicit mode, same as "auto"
     ++git jump
     + --------------------------------------------------
       
     + You can use the optional argument '--stdout' to print the listing to
      
       ## contrib/git-jump/git-jump ##
      @@
     @@ contrib/git-jump/git-jump
      +usage: git jump [--stdout] [<mode>] [<args>]
       
       Jump to interesting elements in an editor.
     - The <mode> parameter is one of:
     -@@ contrib/git-jump/git-jump: while test $# -gt 0; do
     - 	shift
     - done
     - if test $# -lt 1; then
     --	usage >&2
     --	exit 1
     +-The <mode> parameter is one of:
     ++The <mode> parameter is one of the following,
     ++defaulting to "auto" if omitted:
     + 
     + diff: elements are diff hunks. Arguments are given to diff.
     + 
     +@@ contrib/git-jump/git-jump: grep: elements are grep hits. Arguments are given to git grep or, if
     + 
     + ws: elements are whitespace errors. Arguments are given to diff --check.
     + 
     ++auto: select one of the other modes based on worktree state;
     ++      "merge" if there are unmerged paths, "diff" if there are
     ++      unstaged changes, "ws" if there are whitespace errors.
     ++
     + If the optional argument `--stdout` is given, print the quickfix
     + lines to standard output instead of feeding it to the editor.
     + EOF
     +@@ contrib/git-jump/git-jump: mode_ws() {
     + 	git diff --check "$@"
     + }
     + 
     ++mode_auto() {
      +	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
     ++	if test -n "$(git ls-files -u "$@")"; then
     ++		mode_merge "$@"
     ++	elif ! git diff --quiet "$@"; then
     ++		mode_diff "$@"
     ++	elif ! git diff --check >/dev/null 2>&1; then
     ++		mode_ws "$@"
      +	else
      +		usage >&2
      +		exit 1
      +	fi
     ++}
     ++
     + use_stdout=
     + while test $# -gt 0; do
     + 	case "$1" in
     +@@ contrib/git-jump/git-jump: while test $# -gt 0; do
     + 	shift
     + done
     + if test $# -lt 1; then
     +-	usage >&2
     +-	exit 1
     ++	set -- auto
       fi
       mode=$1; shift
       type "mode_$mode" >/dev/null 2>&1 || { usage >&2; exit 1; }

 contrib/git-jump/README   | 12 ++++++++++++
 contrib/git-jump/git-jump | 29 +++++++++++++++++++++++++----
 2 files changed, 37 insertions(+), 4 deletions(-)