[PATCH v3 0/4] history: add squash subcommand to fold a range

Adds git history squash <revision-range> to fold a range of commits into its oldest one, reusing that commit's message and replaying any descendants on top.

Changes in v3:

 * Moved the feature out of git rebase and into a new git history squash
   <revision-range> subcommand, per the list discussion. git rebase --squash
   is dropped.
 * Takes an arbitrary range (git history squash @~3.., git history squash
   @~5..@~2), folding it into the oldest commit and replaying any
   descendants on top.
 * Implemented as a single tree operation rather than picking each commit,
   so there are no repeated conflict stops (addresses Phillip's efficiency
   point).
 * A merge inside the range is folded fine, only a range with more than one
   base is rejected.
 * --reedit-message seeds the editor with every folded-in message, not just
   the oldest.

Harald Nordgren (4):
  history: extract helper for a commit's parent tree
  history: give commit_tree_ext a message template
  history: add squash subcommand to fold a range
  history: re-edit a squash with every message

 Documentation/git-history.adoc |  21 +++
 builtin/history.c              | 287 ++++++++++++++++++++++++++++-----
 t/meson.build                  |   1 +
 t/t3454-history-squash.sh      | 250 ++++++++++++++++++++++++++++
 4 files changed, 521 insertions(+), 38 deletions(-)
 create mode 100755 t/t3454-history-squash.sh

base-commit: 95e20213faefeb95df29277c58ac1980ab68f701
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2337%2FHaraldNordgren%2Frebase-fixup-fold-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2337/HaraldNordgren/rebase-fixup-fold-v3
Pull-Request: https://github.com/git/git/pull/2337

Range-diff vs v2:

 1:  c55b9cd6f7 < -:  ---------- t3415: remove prepare-commit-msg hook after use
 2:  22d4276ff5 < -:  ---------- rebase: add --squash to fold a range
 -:  ---------- > 1:  1e31474ef6 history: extract helper for a commit's parent tree
 -:  ---------- > 2:  498da64046 history: give commit_tree_ext a message template
 -:  ---------- > 3:  66b2f49fb4 history: add squash subcommand to fold a range
 -:  ---------- > 4:  43e4270614 history: re-edit a squash with every message