[PATCH v3] 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 two 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`.

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 v2; all of these in response to feedback from Junio:
    
     * Removed stray # from README.
     * Don't both teaching "auto" to select "ws" mode, because it is always
       subsumed by "diff".
     * Update usage string to make clear that git jump --stdout foo is not a
       synonym for git jump --stdout auto foo, because distinguishing
       between foo as <mode> and foo as <arg> is fraught with ambiguity.
    
    In answer to Junio's question:
    
    > If more than one interesting cases apply, what happens, and what
    > should happen?
    
    it's an ordered choice (merge > diff).

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-2108%2Fwincent%2Fauto-jump-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-2108/wincent/auto-jump-v3
Pull-Request: https://github.com/gitgitgadget/git/pull/2108

Range-diff vs v2:

 1:  5fbc8480ef ! 1:  af758dcfd2 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 several situations where we can usefully infer the most
     +    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:
      
     @@ Commit message
          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
     @@ contrib/git-jump/README: git jump grep foo_bar
       git jump grep -i foo_bar
       
      +# jump to places with conflict markers or whitespace errors
     -+# (as reported by # `git diff --check`)
     ++# (as reported by `git diff --check`)
      +git jump ws
      +
       # use the silver searcher for git jump grep
     @@ contrib/git-jump/README: git jump grep foo_bar
      +# whitespace problems; otherwise show usage
      +git jump auto
      +
     -+# with no explicit mode, same as "auto"
     ++# with no explicit mode and no args, same as "auto"
      +git jump
       --------------------------------------------------
       
     @@ contrib/git-jump/README: git jump grep foo_bar
      
       ## contrib/git-jump/git-jump ##
      @@
     - 
       usage() {
       	cat <<\EOF
     --usage: git jump [--stdout] <mode> [<args>]
     -+usage: git jump [--stdout] [<mode>] [<args>]
     + usage: git jump [--stdout] <mode> [<args>]
     ++   or: git jump [--stdout]
       
       Jump to interesting elements in an editor.
      -The <mode> parameter is one of:
     -+The <mode> parameter is one of the following,
     -+defaulting to "auto" if omitted:
     ++The <mode> parameter is one of the following.
     ++With no <mode> and no <args>, it defaults to "auto".
       
       diff: elements are diff hunks. Arguments are given to diff.
       
     @@ contrib/git-jump/git-jump: mode_ws() {
      +		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

 contrib/git-jump/README   | 12 ++++++++++++
 contrib/git-jump/git-jump | 26 +++++++++++++++++++++++---
 2 files changed, 35 insertions(+), 3 deletions(-)