reintegrate: learn --allow-empty

I was initially torn about adding this flag, since it's just a
convoluted way to spell `git reset --hard master`. But in practice, time
and again I found myself annoyed at going "okay, time to reintegrate..."
then hitting a wall where I have to go "oh yeah, no actual branches,
guess I'll have to reset by hand". It's conceptually simpler to keep it
all in the same subcommand, and also not difficult to add, so may as
well toss it in there.

Fun side note: looking back at my code let me discover the dead
`in_progress()` function.

completions/bash/git-topics

@@ -55,7 +55,7 @@ __git_topics_reintegrate() {
     return
   fi
   case "$cur" in
-    --*) __gitcomp "--onto" ;;
+    --*) __gitcomp "--onto --allow-empty" ;;
     *) __git_complete_refs ;;
   esac
 }

completions/zsh/_git-topics

@@ -79,6 +79,7 @@ __git_topics_list() {
 __git_topics_reintegrate() {
   _arguments -C -S -s \
     "--onto=[merge topics onto this branch]:branches:__git_branches" \
+    "--allow-empty[do not abort due to empty todo list]" \
     "--continue[continue after resolving a merge conflict]" \
     "--skip[skip the current merge and continue]" \
     "--abort[abort and reset the original branch]" \

libexec/lib/reintegrate

@@ -173,29 +173,26 @@ if test -d "$state"; then
   OPTIONS="(--continue | --skip | --abort | --quit | --edit-todo)"
 else
   in_progress=
-  OPTIONS="[--onto <branch>]"
+  OPTIONS="[--onto <branch>] [--allow-empty]"
 fi
 
 OPTIONS_SPEC="\
-$dashless $command [--onto <branch>]
+$dashless $command [--onto <branch>] [--allow-empty]
 $dashless $command (--continue | --skip | --abort | --quit | --edit-todo)
 --
  Options
-onto=!     merge topics onto this branch (default: $DEVELOP)
+onto=!       merge topics onto this branch (default: $DEVELOP)
+allow-empty! do not abort due to empty todo list
  Actions
-continue!  continue after resolving a merge conflict
-skip!      skip the current merge and continue
-abort!     abort and reset the original branch
-quit!      abort but keep the branch where it is
-edit-todo! edit the todo list
+continue!    continue after resolving a merge conflict
+skip!        skip the current merge and continue
+abort!       abort and reset the original branch
+quit!        abort but keep the branch where it is
+edit-todo!   edit the todo list
 "
 
 eval "$(parsed_options "$@")"
 
-in_progress() {
-  test -n "$in_progress"
-}
-
 assert_in_progress() {
   test -n "$in_progress" || {
     echo >&2 "There doesn't appear to be a reintegration in progress. Try"
@@ -242,6 +239,11 @@ while test -n "$1"; do
       branch="${1##--onto=}"
       shift
       ;;
+    --allow-empty)
+      refute_in_progress
+      allow_empty="true"
+      shift
+      ;;
     --)
       shift
       ;;

libexec/lib/reintegrate--onto

@@ -22,14 +22,23 @@ echo "$(
   sed "s/^- /drop /"
 )" >"$todo"
 
-EXTRA_INSTRUCTIONS="
+if test -z "$allow_empty"; then
+  EXTRA_INSTRUCTIONS="
 If you drop every line, the reintegration will be aborted without any effect on
 the $branch branch.
 "
+else
+  EXTRA_INSTRUCTIONS="
+If you drop every line, the reintegration will still rewind the $branch branch,
+making it even with the $MASTER branch.
+"
+fi
 
 edit_todo
 
-test -s "$todo" || finished "Reintegration aborted due to empty todo list"
+if test -z "$allow_empty"; then
+  test -s "$todo" || finished "Reintegration aborted due to empty todo list"
+fi
 
 git checkout --quiet "$branch" || exit "$?"
 ensure_correct_branch

ronn/git-topics-reintegrate.1.md

@@ -2,7 +2,7 @@
 
 ## SYNOPSIS
 
-`git topics reintegrate` [--onto <branch>]
+`git topics reintegrate` [--onto <branch>] [--allow-empty]
 
 `git topics reintegrate` (--continue | --skip | --abort | --quit | --edit-todo)
 
@@ -50,15 +50,24 @@ created and based off of _master_.
 
 Merge conflicts and other errors might interrupt the execution of the todo
 list. When this happens, it's your responsibility to resolve the issue and
-resume the reintegration using the "action" flags of this command (i.e., any
-option other than `--onto`).
+resume the reintegration using the flags listed in the [ACTIONS][] section
+below.
 
 ## OPTIONS
 
 * --onto <branch>:
   Reintegrate topics onto the specified branch. If not supplied, the target
   branch will default to _develop_.
 
+* --allow-empty:
+  Normally, you can abort a reintegration by saving an empty todo list (whether
+  literally empty or containing nothing but `drop` instructions). However, if
+  you give this option, the reintegration will still run without re-merging any
+  topics. Effectively, this is equivalent to just doing `git reset --hard
+  <master>` by hand.
+
+## ACTIONS
+
 * --continue:
   Resumes executing the todo list after you've resolved a merge conflict.