commit: refuse to amend during conflict resolution

From: Elijah Newren <[email protected]>

Running git commit --amend during conflict resolution is an ugly foot-gun. For many years, we have rejected amending during conflict resolution in the middle of
- a merge
- a cherry-pick
However, this was never extended to other operations that can also produce conflicts:
- an am operation
- a revert
- a rebase

Extend it to handle these other cases now.

Extending to am, revert, and the apply backend of rebase are fairly straightforward. However, with the merge backend of rebase we have to be more careful, since it powers interactive rebases and
- the interactive machinery internally uses git commit --amend for squash and reword directives
- users are expected to git commit --amend after hitting an edit or break directive
So, we need to be careful with rebase to only reject amending when doing conflict resolution.

A few files under the rebase-merge/ directory provide us the necessary information:

- stopped-sha is written only when the rebase stops and hands control back to the user, so its presence marks a genuine stop -- as opposed to the sequencer's own internal git commit --amend while applying a squash, fixup, or reword, during which no stopped-sha exists.

- amend is written only when the rebase stops with HEAD already pointing at the commit the user is meant to amend: a clean edit, or a fast-forward reword.

Its absence at a stop therefore means
the commit did not apply, so HEAD is the previously-applied commit rather than the one being rebased -- exactly the case we refuse.

So for the merge backend we die when stopped-sha exists and amend does not. This covers a plain conflicted pick as well as a conflicted edit (both leave HEAD on the previously-applied commit), while still allowing a clean edit or reword stop and a break stop (no stopped-sha). stopped-sha is unlinked at the start of the resume loop, so a resumed squash's internal amend is unaffected.

Signed-off-by Elijah Newren <[email protected]>

---
commit: refuse to amend during conflict resolution

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2389%2Fnewren%2Frefuse-amend-during-conflicts-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2389/newren/refuse-amend-during-conflicts-v1
Pull-Request: https://github.com/git/git/pull/2389

  builtin/commit.c                | 41 ++++++++++++++++
  t/t3404-rebase-interactive.sh   | 87 +++++++++++++++++++++++++++++++++
  t/t3507-cherry-pick-conflict.sh | 11 +++++
  t/t4151-am-abort.sh             | 11 +++++
  4 files changed, 150 insertions(+)

builtin/commit.c +1 -0

index 28f6174503..a9fd04366e 100644
@@ -30,6 +30,7 @@
  #include "path.h"
  #include "preload-index.h"
  #include "read-cache.h"
+#include "refs.h"
  #include "repository.h"
  #include "string-list.h"
  #include "rerere.h"

@@ -1336,6 +1337,46 @@ static int parse_and_validate_options(int argc, const char *argv[],
  		else if (whence == FROM_REBASE_PICK)

builtin/commit.c +31 -0

+		/* Check middle of `am` */
+		applying = repo_git_path(the_repository,
+					 "rebase-apply/applying");
+		in_am = file_exists(applying);
+
+		free(applying);
+		if (in_am)
+			die(_("You are in the middle of an am session -- cannot amend."));
+
+		/* Check middle of rebase specifically stopped for conflicts */
+		apply_dir = repo_git_path(the_repository,
+					  "rebase-apply");
+		stopped_sha = repo_git_path(the_repository,
+					    "rebase-merge/stopped-sha");
+		amend_marker = repo_git_path(the_repository,
+					     "rebase-merge/amend");
+		/*
+		 * The apply backend only ever stops for conflicts; the
+		 * merge backend writes stopped-sha but omits `amend`,
+		 * which it writes only at a clean edit/reword stop.
+		 */
+		conflicted_stop =
+			file_exists(apply_dir) ||
+			(file_exists(stopped_sha) && !file_exists(amend_marker));
+
+		free(apply_dir);
+		free(stopped_sha);
+		free(amend_marker);
+		if (conflicted_stop)
+			die(_("You are resolving conflicts during a rebase -- cannot amend."));
+	}
  	if (fixup_message && squash_message)
  		die(_("options '%s' and '%s' cannot be used together"), "--squash", "--fixup");
  	die_for_incompatible_opt4(!!use_message, "-C",

t/t3404-rebase-interactive.sh +87 -0

index ff11abb2f2..01d4735b3b 100755
@@ -1884,6 +1884,93 @@ test_expect_success 'correct error message for commit --amend after empty pick'
  	test_grep "middle of a rebase -- cannot amend." err
  '
 
+test_expect_success 'commit --amend is refused at a rebase conflict stop' '
+	test_when_finished "git rebase --abort" &&
+	git checkout --detach conflict-branch &&
+	(
+		set_fake_editor &&
+		FAKE_LINES="1 3" &&
+		export FAKE_LINES &&
+		test_must_fail git rebase -i A
+	) &&
+	test_path_is_file .git/rebase-merge/patch &&
+	test_path_is_missing .git/rebase-merge/amend &&
+	echo resolved >conflict &&
+	git add conflict &&
+	test_must_fail git commit --amend --no-edit 2>err &&
+	test_grep "You are resolving conflicts during a rebase -- cannot amend" err
+'
+
+test_expect_success 'commit --amend is refused when an "edit" pick conflicts' '
+	test_when_finished "git rebase --abort" &&
+	git checkout --detach conflict-branch &&
+	(
+		set_fake_editor &&
+		FAKE_LINES="1 edit 3" &&
+		export FAKE_LINES &&
+		test_must_fail git rebase -i A
+	) &&
+	test_path_is_file .git/rebase-merge/patch &&
+	test_path_is_missing .git/rebase-merge/amend &&
+	echo resolved >conflict &&
+	git add conflict &&
+	test_must_fail git commit --amend --no-edit 2>err &&
+	test_grep "You are resolving conflicts during a rebase -- cannot amend" err
+'
+
+test_expect_success 'commit --amend is allowed at a rebase edit stop' '
+	test_when_finished "git rebase --abort" &&
+	git checkout --detach no-conflict-branch &&
+	(
+		set_fake_editor &&
+		FAKE_LINES="edit 1 2 3 4" &&
+		export FAKE_LINES &&
+		git rebase -i A
+	) &&
+	test_path_is_file .git/rebase-merge/amend &&
+	echo tweak >fileJ &&
+	git add fileJ &&
+	git commit --amend --no-edit
+'
+
+test_expect_success 'commit --amend is allowed at a rebase break stop' '
+	test_when_finished "git rebase --abort" &&
+	git checkout --detach no-conflict-branch &&
+	(
+		set_fake_editor &&
+		FAKE_LINES="break 1 2 3 4" &&
+		export FAKE_LINES &&
+		git rebase -i A
+	) &&
+	test_must_fail git rev-parse --verify REBASE_HEAD &&
+	echo tweak >fileJ &&
+	git add fileJ &&
+	git commit --amend --no-edit
+'
+
+test_expect_success 'commit --amend is refused at an apply-backend conflict stop' '
+	test_when_finished "rm -rf apply-backend" &&
+	test_create_repo apply-backend &&
+	(
+		cd apply-backend &&
+		test_commit base file &&
+		git branch -M mainline &&
+		test_commit upstream file upstream &&
+		git checkout -b side mainline~1 &&
+		test_commit conflicting file side &&
+		test_commit unrelated other &&
+		test_must_fail git rebase --apply mainline &&
+		# the apply backend only ever stops for conflicts, and
+		# leaves HEAD on the previously-applied commit
+		test_path_is_dir .git/rebase-apply &&
+		test_path_is_missing .git/rebase-apply/applying &&
+		echo resolved >file &&
+		git add file &&
+		test_must_fail git commit --amend --no-edit 2>err &&
+		test_grep "You are resolving conflicts during a rebase -- cannot amend" err
+	)
+'
+
  test_expect_success 'todo has correct onto hash' '
  	GIT_SEQUENCE_EDITOR=cat git rebase -i no-conflict-branch~4 no-conflict-branch >actual &&
  	onto=$(git rev-parse --short HEAD~4) &&

t/t3507-cherry-pick-conflict.sh +11 -0

index 44596cb1e8..42de398f76 100755
@@ -364,6 +364,17 @@ test_expect_success 'failed revert sets REVERT_HEAD' '
  	test_cmp_rev picked REVERT_HEAD
  '
 
+test_expect_success 'commit --amend of revert fails' '
+	pristine_detach initial &&
+
+	test_must_fail git revert picked &&
+	echo resolved >foo &&
+	git add foo &&
+	test_must_fail git commit --amend 2>err &&
+
+	test_grep "in the middle of a revert -- cannot amend." err
+'
+
  test_expect_success 'successful revert does not set REVERT_HEAD' '
  	pristine_detach base &&
  	git revert base &&

t/t4151-am-abort.sh +11 -0

index 8e1ecf8a68..9313a074b2 100755
@@ -63,6 +63,17 @@ do
 
  done
 
+test_expect_success 'commit --amend during a failed am fails' '
+	git reset --hard initial &&
+	cp file-2-expect file-2 &&
+	test_must_fail git am 000[1245]-*.patch &&
+	echo resolved >file-1 &&
+	git add file-1 &&
+	test_must_fail git commit --amend 2>err &&
+	test_grep "in the middle of an am session -- cannot amend." err &&
+	git am --abort
+'
+
  test_expect_success 'am -3 --skip removes otherfile-4' '
  	git reset --hard initial &&
  	test_must_fail git am -3 0003-*.patch &&

base-commit: 2c3adbb2c475981e340c79fdc5e7f4f9b5d9054e

Quoted 9 lines

builtin/commit.c +5 -0

@@ -1336,6 +1337,46 @@ static int parse_and_validate_options(int argc, const char *argv[],
              else if (whence == FROM_REBASE_PICK)
                      die(_("You are in the middle of a rebase -- cannot amend."));
      }
+     if (amend && whence == FROM_COMMIT) {
+             char *applying, *apply_dir, *stopped_sha, *amend_marker;
+             int in_am, conflicted_stop;
+
+             /* Check middle of revert */

builtin/commit.c static int parse_and_validate_options(int argc, const char *argv[], · line 1347

Quoted 3 lines

builtin/commit.c +3 -0

+             if (refs_ref_exists(get_main_ref_store(the_repository),
+                                 "REVERT_HEAD"))
+                     die(_("You are in the middle of a revert -- cannot amend."));

I think it would be much cleaner to move this check and sequencer related ones below into sequencer_determine_whence() so that we don't have to hard code the paths here. It might be worth checking for "am" and the "apply" based rebase in that function as well.

The logic looks sound to me

... However, with the merge backend of rebase we have to
be more careful, since it powers interactive rebases and
- the interactive machinery internally uses git commit --amend for squash and reword directives
- users are expected to git commit --amend after hitting an edit or break directive
So, we need to be careful with rebase to only reject amending when doing conflict resolution.

A few files under the rebase-merge/ directory provide us the necessary information:

- stopped-sha is written only when the rebase stops and hands control back to the user, so its presence marks a genuine stop -- as opposed to the sequencer's own internal git commit --amend while applying a squash, fixup, or reword, during which no stopped-sha exists.

- amend is written only when the rebase stops with HEAD already pointing at the commit the user is meant to amend: a clean edit, or a fast-forward reword. Its absence at a stop therefore means the commit did not apply, so HEAD is the previously-applied commit rather than the one being rebased -- exactly the case we refuse.

So for the merge backend we die when stopped-sha exists and amend does not. This covers a plain conflicted pick as well as a conflicted edit (both leave HEAD on the previously-applied commit), while still allowing a clean edit or reword stop and a break stop (no stopped-sha). stopped-sha is unlinked at the start of the resume loop, so a resumed squash's internal amend is unaffected.

Signed-off-by Elijah Newren <[email protected]>

---

Quoted 8 lines · Elijah Newren via GitGitGadget

... However, with the merge backend of rebase we have to
be more careful, since it powers interactive rebases and
- the interactive machinery internally uses git commit --amend for squash and reword directives
- users are expected to git commit --amend after hitting an edit or break directive
So, we need to be careful with rebase to only reject amending when doing conflict resolution.

True.

In addition, in any and all of these scenarios that lets the user deal with conflicts in his or her working tree files and record the result of conflict resolution in a commit, we should reject not only "git commit --amend" but also "git commit <paths>", shouldn't we?

It may probably be better done in a separate topic, as the guiding principle is slightly different (i.e., "recording the conflict resolution is about recording the state on top of the current HEAD and never about updating the state recorded in the current HEAD" is the theme of the current topic. "recording the conflict resolution is always about the entire tree" is the other topic), so we may want to leave a #leftoverbits marker here.

builtin/commit.c static int parse_and_validate_options(int argc, const char *argv[], · line 1339

Quoted 4 lines · Elijah Newren via GitGitGadget

builtin/commit.c +0 -0

@@ -1336,6 +1337,46 @@ static int parse_and_validate_options(int argc, const char *argv[],
              else if (whence == FROM_REBASE_PICK)
                      die(_("You are in the middle of a rebase -- cannot amend."));
      }

Let's make a mental note that the function receives these parameters:

static int parse_and_validate_options(int argc, const char *argv[],
const struct option *options, const char * const usage[], const char *prefix, struct commit *current_head, struct wt_status *s)

builtin/commit.c static int parse_and_validate_options(int argc, const char *argv[], · line 1347

Quoted 8 lines

builtin/commit.c +8 -0

+     if (amend && whence == FROM_COMMIT) {
+             char *applying, *apply_dir, *stopped_sha, *amend_marker;
+             int in_am, conflicted_stop;
+
+             /* Check middle of revert */
+             if (refs_ref_exists(get_main_ref_store(the_repository),
+                                 "REVERT_HEAD"))
+                     die(_("You are in the middle of a revert -- cannot amend."));

"the_repository" can become "s->repo". The same comment for other checks in this block.

From: Elijah Newren <[email protected]>

When a rebase applies a commit that becomes empty, it stops and asks the user to decide whether to keep it or drop it. HEAD still points at the previously-applied commit at that point, so either amending or creating a partial commit is refused, with one of the following messages:

You are in the middle of a rebase -- cannot amend. cannot do a partial commit during a rebase.

Neither message hints that the real problem is a commit that became empty, and "during a rebase" is overly broad besides -- amending and partial commits are fine at an edit or break stop. Reword both to describe the actual situation.

Signed-off-by Elijah Newren <[email protected]>

---
  builtin/commit.c              | 4 ++--
  t/t3404-rebase-interactive.sh | 4 ++--
  2 files changed, 4 insertions(+), 4 deletions(-)

builtin/commit.c +0 -0

index 28f6174503..0d908d72bb 100644

builtin/commit.c +1 -1

  	}
 
  	if (list_paths(&partial, !current_head ? NULL : "HEAD", &pathspec))

@@ -1334,7 +1334,7 @@ static int parse_and_validate_options(int argc, const char *argv[],
  		else if (is_from_cherry_pick(whence))
  			die(_("You are in the middle of a cherry-pick -- cannot amend."));
  		else if (whence == FROM_REBASE_PICK)
-			die(_("You are in the middle of a rebase -- cannot amend."));
+			die(_("You are resolving a commit that became empty -- cannot amend."));
  	}
  	if (fixup_message && squash_message)
  		die(_("options '%s' and '%s' cannot be used together"), "--squash", "--fixup");

t/t3404-rebase-interactive.sh +2 -2

index ff11abb2f2..1e78dbfd90 100755
@@ -1868,7 +1868,7 @@ test_expect_success 'correct error message for partial commit after empty pick'
  	) &&
  	echo x >file1 &&
  	test_must_fail git commit file1 2>err &&
-	test_grep "cannot do a partial commit during a rebase." err
+	test_grep "cannot do a partial commit while resolving a commit that became empty." err
  '
 
  test_expect_success 'correct error message for commit --amend after empty pick' '

@@ -1881,7 +1881,7 @@ test_expect_success 'correct error message for commit --amend after empty pick'
  	) &&
  	echo x>file1 &&
  	test_must_fail git commit -a --amend 2>err &&
-	test_grep "middle of a rebase -- cannot amend." err
+	test_grep "resolving a commit that became empty -- cannot amend." err
  '
 
  test_expect_success 'todo has correct onto hash' '

builtin/commit.c static const char *prepare_index(const char **argv, const char *prefix, · line 524

Quoted 6 lines

builtin/commit.c +1 -1

@@ -521,7 +521,7 @@ static const char *prepare_index(const char **argv, const char *prefix,
  		else if (is_from_cherry_pick(whence))
  			die(_("cannot do a partial commit during a cherry-pick."));
  		else if (is_from_rebase(whence))
-			die(_("cannot do a partial commit during a rebase."));
+			die(_("cannot do a partial commit while resolving a commit that became empty."));

"while committing a commit that became empty" would be clearer to me, but I what you have is definitely an improvement on the existing message.

Quoted 9 lines · Phillip Wood

builtin/commit.c static const char *prepare_index(const char **argv, const char *prefix, · line 524

Quoted 6 lines

builtin/commit.c +1 -1

@@ -521,7 +521,7 @@ static const char *prepare_index(const char **argv, const char *prefix,
             else if (is_from_cherry_pick(whence))
                     die(_("cannot do a partial commit during a cherry-pick."));
             else if (is_from_rebase(whence))
-                    die(_("cannot do a partial commit during a rebase."));
+                    die(_("cannot do a partial commit while resolving a commit that became empty."));

"while committing a commit that became empty" would be clearer to me, but I what you have is definitely an improvement on the existing message.

A stupid question, but wouldn't a partial commit of an empty commit still an empty commit? IOW, why do we need to reject a partial commit while committing a commit that became empty?

From: Elijah Newren <[email protected]>

When a rebase applies a commit that becomes empty, it stops and asks the user to decide whether to keep it or drop it. HEAD still points at the previously-applied commit at that point, so either amending or creating a partial commit is refused, with one of the following messages:

You are in the middle of a rebase -- cannot amend. cannot do a partial commit during a rebase.

Neither message hints that the real problem is a commit that became empty, and "during a rebase" is overly broad besides -- amending and partial commits are fine at an edit or break stop. Reword both to describe the actual situation.

Signed-off-by Elijah Newren <[email protected]>

---
 builtin/commit.c              | 4 ++--
 t/t3404-rebase-interactive.sh | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

builtin/commit.c +0 -0

index 28f6174503..0d908d72bb 100644

builtin/commit.c static const char *prepare_index(const char **argv, const char *prefix, · line 524

Quoted 1 line

builtin/commit.c +1 -0

+			die(_("cannot do a partial commit while resolving a commit that became empty."));

That is a mouthful. It also is awkward to say "while resolving a commit".

More importantly, I am not sure if whence == FROM_REBASE_PICK at this point in the code flow is a sufficient sign to tell that we were not just in the middle of a rebase, not just a rebase stopped with _some_ conflict, but the way the rebase stopped was because a step in rebase resulted in a commit that is no-op relative to the previous commit. What makes us certain that the rebase-pick is empty?

Quoted 3 lines · Junio C Hamano

Quoted 1 line

+ die(_("cannot do a partial commit while resolving a commit that became empty."));

That is a mouthful. It also is awkward to say "while resolving a commit".

This still stands, but I haven't come up with a better alternative yet.

Quoted 7 lines

More importantly, I am not sure if whence == FROM_REBASE_PICK at this point in the code flow is a sufficient sign to tell that we were not just in the middle of a rebase, not just a rebase stopped with _some_ conflict, but the way the rebase stopped was because a step in rebase resulted in a commit that is no-op relative to the previous commit. What makes us certain that the rebase-pick is empty?

This confusion was because FROM_REBASE_PICK is a misleading name.

sequencer_determine_whence() is the only place that declares the whence is FROM_REBASE_PICK, and it specifically checks if the rebase-head and cherry-pick-head are identical before yielding that value, so by definition we are dealing with an empty-pick situation.

This came from 430b75f720 (commit: give correct advice for empty commit during a rebase, 2019-12-06); interestingly, the name of FROM_REBASE_PICK and is_from_rebase() seem to have confused even the originating commit ;-) The lines in question

(quoted diff) +2 -0

+               else if (is_from_rebase(whence))
+                       die(_("cannot do a partial commit during a rebase."));

are from that commit, which wanted to "give correct advice for empty commit during a rebase".

We may want to

* change the code that does whence == FROM_REBASE_PICK to use is_from_rebase(whence) everywhere (other than the implementation of is_from_rebase() itself, of course).

* give FROM_REBASE_PICK and is_from_rebase() better names that contain "empty" somewhere.

to unconfuse me.

From: Elijah Newren <[email protected]>

builtin/commit.c +6 -4

index 0d908d72bb..4a6054aae0 100644
@@ -1326,15 +1326,30 @@ static int parse_and_validate_options(int argc, const char *argv[],
  		use_editor = 0;
 
  	/* Sanity check options */
-	if (amend && !current_head)
-		die(_("You have nothing to amend."));
-	if (amend && whence != FROM_COMMIT) {
-		if (whence == FROM_MERGE)
+	if (amend) {
+		if (!current_head)
+			die(_("You have nothing to amend."));
+		/*
+		 * Refuse to amend in the middle of any operation that is
+		 * meant to record its result as a new commit on top of HEAD

sequencer.c +10 -0

index 65afd100d9..bd4a724410 100644
@@ -6966,6 +6966,71 @@ int sequencer_determine_whence(struct repository *r, enum commit_whence *whence)
  	return 0;
  }
 
+enum ongoing_operation sequencer_ongoing_operation(struct repository *r,
+						   enum commit_whence whence)
+{
[...]
+	/*
+	 * In the middle of a rebase that stopped for conflict resolution?
+	 * The apply backend only ever stops for conflicts, so the presence
+	 * of its state directory is enough.  The merge backend writes
+	 * stopped-sha whenever it hands control back to the user, but omits
+	 * `amend` unless it stopped with HEAD already pointing at the commit
+	 * to be amended (a clean edit/reword stop); its absence therefore

sequencer.c +9 -0

+		free(stopped_sha);
+		free(amend_marker);
+	}
+	if (found)
+		return ONGOING_REBASE_CONFLICT;
+
+	return ONGOING_NONE;
+}
+
  int sequencer_get_update_refs_state(const char *wt_dir,
  				    struct string_list *refs)
  {

sequencer.h +23 -0

index 64a9c7fb1b..3a4bd97db1 100644
@@ -277,6 +277,29 @@ int sequencer_get_last_command(struct repository* r,
  			       enum replay_action *action);
  int sequencer_determine_whence(struct repository *r, enum commit_whence *whence);
 
+/*
+ * An in-progress operation that records its result (often a conflict
+ * resolution) as a new commit on top of HEAD, during which amending
+ * HEAD via "git commit --amend" is almost always a mistake.
+ */
+enum ongoing_operation {
+	ONGOING_NONE = 0,
+	ONGOING_MERGE,
+	ONGOING_CHERRY_PICK,
+	ONGOING_REBASE_EMPTY,
+	ONGOING_REVERT,
+	ONGOING_AM,
+	ONGOING_REBASE_CONFLICT
+};
+
+/*
+ * Return which in-progress operation, if any, is underway; see enum
+ * ongoing_operation.  'whence' is the origin already computed for the
+ * pending commit.
+ */
+enum ongoing_operation sequencer_ongoing_operation(struct repository *r,
+						   enum commit_whence whence);
+
  /**
   * Append the set of ref-OID pairs that are currently stored for the 'git
   * rebase --update-refs' feature if such a rebase is currently happening.

t/t3404-rebase-interactive.sh +87 -0

index 1e78dbfd90..7cf06e5f9a 100755
@@ -1884,6 +1884,93 @@ test_expect_success 'correct error message for commit --amend after empty pick'
  	test_grep "resolving a commit that became empty -- cannot amend." err
  '
 
+test_expect_success 'commit --amend is refused at a rebase conflict stop' '
+	test_when_finished "git rebase --abort" &&
+	git checkout --detach conflict-branch &&
+	(
+		set_fake_editor &&
+		FAKE_LINES="1 3" &&
+		export FAKE_LINES &&
+		test_must_fail git rebase -i A
+	) &&
+	test_path_is_file .git/rebase-merge/patch &&
+	test_path_is_missing .git/rebase-merge/amend &&
+	echo resolved >conflict &&
+	git add conflict &&
+	test_must_fail git commit --amend --no-edit 2>err &&
+	test_grep "You are resolving conflicts during a rebase -- cannot amend" err
+'
+
+test_expect_success 'commit --amend is refused when an "edit" pick conflicts' '
+	test_when_finished "git rebase --abort" &&
+	git checkout --detach conflict-branch &&
+	(
+		set_fake_editor &&
+		FAKE_LINES="1 edit 3" &&
+		export FAKE_LINES &&
+		test_must_fail git rebase -i A
+	) &&
+	test_path_is_file .git/rebase-merge/patch &&
+	test_path_is_missing .git/rebase-merge/amend &&
+	echo resolved >conflict &&
+	git add conflict &&
+	test_must_fail git commit --amend --no-edit 2>err &&
+	test_grep "You are resolving conflicts during a rebase -- cannot amend" err
+'
+
+test_expect_success 'commit --amend is allowed at a rebase edit stop' '
+	test_when_finished "git rebase --abort" &&
+	git checkout --detach no-conflict-branch &&
+	(
+		set_fake_editor &&
+		FAKE_LINES="edit 1 2 3 4" &&
+		export FAKE_LINES &&
+		git rebase -i A
+	) &&
+	test_path_is_file .git/rebase-merge/amend &&
+	echo tweak >fileJ &&
+	git add fileJ &&
+	git commit --amend --no-edit
+'
+
+test_expect_success 'commit --amend is allowed at a rebase break stop' '
+	test_when_finished "git rebase --abort" &&
+	git checkout --detach no-conflict-branch &&
+	(
+		set_fake_editor &&
+		FAKE_LINES="break 1 2 3 4" &&
+		export FAKE_LINES &&
+		git rebase -i A
+	) &&
+	test_must_fail git rev-parse --verify REBASE_HEAD &&
+	echo tweak >fileJ &&
+	git add fileJ &&
+	git commit --amend --no-edit
+'
+
+test_expect_success 'commit --amend is refused at an apply-backend conflict stop' '
+	test_when_finished "rm -rf apply-backend" &&
+	test_create_repo apply-backend &&
+	(
+		cd apply-backend &&
+		test_commit base file &&
+		git branch -M mainline &&
+		test_commit upstream file upstream &&
+		git checkout -b side mainline~1 &&
+		test_commit conflicting file side &&
+		test_commit unrelated other &&
+		test_must_fail git rebase --apply mainline &&
+		# the apply backend only ever stops for conflicts, and
+		# leaves HEAD on the previously-applied commit
+		test_path_is_dir .git/rebase-apply &&
+		test_path_is_missing .git/rebase-apply/applying &&
+		echo resolved >file &&
+		git add file &&
+		test_must_fail git commit --amend --no-edit 2>err &&
+		test_grep "You are resolving conflicts during a rebase -- cannot amend" err
+	)
+'
+
  test_expect_success 'todo has correct onto hash' '
  	GIT_SEQUENCE_EDITOR=cat git rebase -i no-conflict-branch~4 no-conflict-branch >actual &&
  	onto=$(git rev-parse --short HEAD~4) &&

t/t3507-cherry-pick-conflict.sh +11 -0

index 44596cb1e8..42de398f76 100755
@@ -364,6 +364,17 @@ test_expect_success 'failed revert sets REVERT_HEAD' '
  	test_cmp_rev picked REVERT_HEAD
  '
 
+test_expect_success 'commit --amend of revert fails' '
+	pristine_detach initial &&
+
+	test_must_fail git revert picked &&
+	echo resolved >foo &&
+	git add foo &&
+	test_must_fail git commit --amend 2>err &&
+
+	test_grep "in the middle of a revert -- cannot amend." err
+'
+
  test_expect_success 'successful revert does not set REVERT_HEAD' '
  	pristine_detach base &&
  	git revert base &&

t/t4151-am-abort.sh +11 -0

index 8e1ecf8a68..9313a074b2 100755
@@ -63,6 +63,17 @@ do
 
  done
 
+test_expect_success 'commit --amend during a failed am fails' '
+	git reset --hard initial &&
+	cp file-2-expect file-2 &&
+	test_must_fail git am 000[1245]-*.patch &&
+	echo resolved >file-1 &&
+	git add file-1 &&
+	test_must_fail git commit --amend 2>err &&
+	test_grep "in the middle of an am session -- cannot amend." err &&
+	git am --abort
+'
+
  test_expect_success 'am -3 --skip removes otherfile-4' '
  	git reset --hard initial &&
  	test_must_fail git am -3 0003-*.patch &&

From: Elijah Newren <[email protected]>

Similar to the previous commit, just as git commit --amend is a foot-gun during conflict resolution, so is a partial commit (git commit <paths>). Recording a conflict resolution is about capturing the state of the entire tree on top of HEAD, not a subset of paths. For many years we have rejected partial commits in the middle of
- a merge
- a cherry-pick
- a rebase that stopped at a pick

but, just like amending, this was never extended to the other operations that can also leave conflicts to resolve:
- an am operation
- a revert
- a rebase that stopped for conflict resolution

Reuse sequencer_ongoing_operation(), introduced for the analogous --amend check, to detect all of these and refuse the partial commit.

Signed-off-by Elijah Newren <[email protected]>

---
  builtin/commit.c                | 22 ++++++++++++++-------
  sequencer.h                     |  5 +++--
  t/t3404-rebase-interactive.sh   | 34 +++++++++++++++++++++++++++++++++
  t/t3507-cherry-pick-conflict.sh | 11 +++++++++++
  t/t4151-am-abort.sh             | 11 +++++++++++
  5 files changed, 74 insertions(+), 9 deletions(-)

builtin/commit.c +15 -7

index 4a6054aae0..9da3f1191b 100644
@@ -515,13 +515,21 @@ static const char *prepare_index(const char **argv, const char *prefix,
  	 */
  	commit_style = COMMIT_PARTIAL;
 
-	if (whence != FROM_COMMIT) {
-		if (whence == FROM_MERGE)
-			die(_("cannot do a partial commit during a merge."));
-		else if (is_from_cherry_pick(whence))
-			die(_("cannot do a partial commit during a cherry-pick."));
-		else if (is_from_rebase(whence))
-			die(_("cannot do a partial commit while resolving a commit that became empty."));
+	switch (sequencer_ongoing_operation(the_repository, whence)) {
+	case ONGOING_NONE:
+		break;
+	case ONGOING_MERGE:
+		die(_("cannot do a partial commit during a merge."));
+	case ONGOING_CHERRY_PICK:
+		die(_("cannot do a partial commit during a cherry-pick."));
+	case ONGOING_REBASE_EMPTY:
+		die(_("cannot do a partial commit while resolving a commit that became empty."));
+	case ONGOING_REVERT:
+		die(_("cannot do a partial commit during a revert."));
+	case ONGOING_AM:
+		die(_("cannot do a partial commit during an am session."));
+	case ONGOING_REBASE_CONFLICT:
+		die(_("cannot do a partial commit while resolving conflicts during a rebase."));
  	}
 
  	if (list_paths(&partial, !current_head ? NULL : "HEAD", &pathspec))

sequencer.h +3 -2

index 3a4bd97db1..634d1ddcb3 100644
@@ -279,8 +279,9 @@ int sequencer_determine_whence(struct repository *r, enum commit_whence *whence)
 
  /*
   * An in-progress operation that records its result (often a conflict
- * resolution) as a new commit on top of HEAD, during which amending
- * HEAD via "git commit --amend" is almost always a mistake.
+ * resolution) as a new commit on top of HEAD.  Some ways of invoking
+ * "git commit" -- amending HEAD, or a partial commit -- are almost
+ * always a mistake during such an operation.
   */
  enum ongoing_operation {
  	ONGOING_NONE = 0,

t/t3404-rebase-interactive.sh +34 -0

index 7cf06e5f9a..1314b0fd05 100755
@@ -1971,6 +1971,40 @@ test_expect_success 'commit --amend is refused at an apply-backend conflict stop
  	)
  '
 
+test_expect_success 'partial commit is refused at a rebase conflict stop' '
+	test_when_finished "git rebase --abort" &&
+	git checkout --detach conflict-branch &&
+	(
+		set_fake_editor &&
+		FAKE_LINES="1 3" &&
+		export FAKE_LINES &&
+		test_must_fail git rebase -i A
+	) &&
+	echo resolved >conflict &&
+	git add conflict &&
+	test_must_fail git commit conflict 2>err &&
+	test_grep "cannot do a partial commit while resolving conflicts during a rebase." err
+'
+
+test_expect_success 'partial commit is refused at an apply-backend conflict stop' '
+	test_when_finished "rm -rf apply-backend" &&
+	test_create_repo apply-backend &&
+	(
+		cd apply-backend &&
+		test_commit base file &&
+		git branch -M mainline &&
+		test_commit upstream file upstream &&
+		git checkout -b side mainline~1 &&
+		test_commit conflicting file side &&
+		test_commit unrelated other &&
+		test_must_fail git rebase --apply mainline &&
+		echo resolved >file &&
+		git add file &&
+		test_must_fail git commit file 2>err &&
+		test_grep "cannot do a partial commit while resolving conflicts during a rebase." err
+	)
+'
+
  test_expect_success 'todo has correct onto hash' '
  	GIT_SEQUENCE_EDITOR=cat git rebase -i no-conflict-branch~4 no-conflict-branch >actual &&
  	onto=$(git rev-parse --short HEAD~4) &&

t/t3507-cherry-pick-conflict.sh +11 -0

index 42de398f76..c3d024c97f 100755
@@ -375,6 +375,17 @@ test_expect_success 'commit --amend of revert fails' '
  	test_grep "in the middle of a revert -- cannot amend." err
  '
 
+test_expect_success 'partial commit during a revert fails' '
+	pristine_detach initial &&
+
+	test_must_fail git revert picked &&
+	echo resolved >foo &&
+	git add foo &&
+	test_must_fail git commit foo 2>err &&
+
+	test_grep "cannot do a partial commit during a revert." err
+'
+
  test_expect_success 'successful revert does not set REVERT_HEAD' '
  	pristine_detach base &&
  	git revert base &&

t/t4151-am-abort.sh +11 -0

index 9313a074b2..c80269e015 100755
@@ -74,6 +74,17 @@ test_expect_success 'commit --amend during a failed am fails' '
  	git am --abort
  '
 
+test_expect_success 'partial commit during a failed am fails' '
+	git reset --hard initial &&
+	cp file-2-expect file-2 &&
+	test_must_fail git am 000[1245]-*.patch &&
+	echo resolved >file-1 &&
+	git add file-1 &&
+	test_must_fail git commit file-1 2>err &&
+	test_grep "cannot do a partial commit during an am session." err &&
+	git am --abort
+'
+
  test_expect_success 'am -3 --skip removes otherfile-4' '
  	git reset --hard initial &&
  	test_must_fail git am -3 0003-*.patch &&

Both git commit --amend and a partial commit (git commit <paths>) are foot-guns while the user is in the middle of an operation that resolves conflicts on top of HEAD: recording a conflict resolution is about capturing the state of the whole tree as a new commit, not about rewriting HEAD or committing a subset of paths.

Historically we only rejected these during a merge or a cherry-pick or when resolving an empty pick during a rebase. The same hazard exists for am, revert, and rebase conflict stops, none of which were covered. This series extends the refusal to all of them.

The three patches:

1. reword the two pre-existing "empty commit" rebase messages, which were misleadingly generic
2. refuse git commit --amend during these additional operations
3. refuse partial commits during the same operations.

Elijah Newren (3):
commit: reword the empty-commit rebase errors
commit: refuse to amend during conflict resolution
commit: refuse partial commits during conflict resolution

  builtin/commit.c                |  51 +++++++++----
  sequencer.c                     |  65 +++++++++++++++++
  sequencer.h                     |  24 ++++++
  t/t3404-rebase-interactive.sh   | 125 +++++++++++++++++++++++++++++++-
  t/t3507-cherry-pick-conflict.sh |  22 ++++++
  t/t4151-am-abort.sh             |  22 ++++++
  6 files changed, 293 insertions(+), 16 deletions(-)

base-commit: 2c3adbb2c475981e340c79fdc5e7f4f9b5d9054e
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2389%2Fnewren%2Frefuse-amend-during-conflicts-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2389/newren/refuse-amend-during-conflicts-v2
Pull-Request: https://github.com/git/git/pull/2389

Range-diff vs v1:

  -:  ---------- > 1:  65c48ed3cb commit: reword the empty-commit rebase errors
  1:  a3d6b059c6 ! 2:  4a1461e527 commit: refuse to amend during conflict resolution
      @@ Commit message
           Signed-off-by: Elijah Newren <[email protected]>
       
        ## builtin/commit.c ##
      -@@
      - #include "path.h"
      - #include "preload-index.h"
      - #include "read-cache.h"
      -+#include "refs.h"
      - #include "repository.h"
      - #include "string-list.h"
      - #include "rerere.h"
       @@ builtin/commit.c: static int parse_and_validate_options(int argc, const char *argv[],
      - 		else if (whence == FROM_REBASE_PICK)
      - 			die(_("You are in the middle of a rebase -- cannot amend."));
      + 		use_editor = 0;
      +
      + 	/* Sanity check options */
      +-	if (amend && !current_head)
      +-		die(_("You have nothing to amend."));
      +-	if (amend && whence != FROM_COMMIT) {
      +-		if (whence == FROM_MERGE)
      ++	if (amend) {
      ++		if (!current_head)
      ++			die(_("You have nothing to amend."));
      ++		/*
      ++		 * Refuse to amend in the middle of any operation that is
      ++		 * meant to record its result as a new commit on top of HEAD
      ++		 * rather than by rewriting HEAD.
      ++		 */
      ++		switch (sequencer_ongoing_operation(s->repo, whence)) {
      ++		case ONGOING_NONE:
      ++			break;
      ++		case ONGOING_MERGE:
      + 			die(_("You are in the middle of a merge -- cannot amend."));
      +-		else if (is_from_cherry_pick(whence))
      ++		case ONGOING_CHERRY_PICK:
      + 			die(_("You are in the middle of a cherry-pick -- cannot amend."));
      +-		else if (whence == FROM_REBASE_PICK)
      ++		case ONGOING_REBASE_EMPTY:
      + 			die(_("You are resolving a commit that became empty -- cannot amend."));
      ++		case ONGOING_REVERT:
      ++			die(_("You are in the middle of a revert -- cannot amend."));
      ++		case ONGOING_AM:
      ++			die(_("You are in the middle of an am session -- cannot amend."));
      ++		case ONGOING_REBASE_CONFLICT:
      ++			die(_("You are resolving conflicts during a rebase -- cannot amend."));
      ++		}
        	}
      -+	if (amend && whence == FROM_COMMIT) {
      -+		char *applying, *apply_dir, *stopped_sha, *amend_marker;
      -+		int in_am, conflicted_stop;
      + 	if (fixup_message && squash_message)
      + 		die(_("options '%s' and '%s' cannot be used together"), "--squash", "--fixup");
      +
      + ## sequencer.c ##
      +@@ sequencer.c: int sequencer_determine_whence(struct repository *r, enum commit_whence *whence)
      + 	return 0;
      + }
      +
      ++enum ongoing_operation sequencer_ongoing_operation(struct repository *r,
      ++						   enum commit_whence whence)
      ++{
      ++	char *path;
      ++	int found;
       +
      -+		/* Check middle of revert */
      -+		if (refs_ref_exists(get_main_ref_store(the_repository),
      -+				    "REVERT_HEAD"))
      -+			die(_("You are in the middle of a revert -- cannot amend."));
      ++	/*
      ++	 * The merge, cherry-pick, and (empty) rebase-pick stops are already
      ++	 * distinguished by 'whence'.
      ++	 */
      ++	switch (whence) {
      ++	case FROM_MERGE:
      ++		return ONGOING_MERGE;
      ++	case FROM_CHERRY_PICK_SINGLE:
      ++	case FROM_CHERRY_PICK_MULTI:
      ++		return ONGOING_CHERRY_PICK;
      ++	case FROM_REBASE_PICK:
      ++		return ONGOING_REBASE_EMPTY;
      ++	case FROM_COMMIT:
      ++		break;
      ++	}
       +
      -+		/* Check middle of `am` */
      -+		applying = repo_git_path(the_repository,
      -+					 "rebase-apply/applying");
      -+		in_am = file_exists(applying);
      ++	/*
      ++	 * 'whence' is FROM_COMMIT, but we may still be in the middle of an
      ++	 * operation that records its result on top of HEAD; detect those
      ++	 * from their on-disk state.
      ++	 */
       +
      -+		free(applying);
      -+		if (in_am)
      -+			die(_("You are in the middle of an am session -- cannot amend."));
      ++	/* In the middle of a revert? */
      ++	if (refs_ref_exists(get_main_ref_store(r), "REVERT_HEAD"))
      ++		return ONGOING_REVERT;
       +
      -+		/* Check middle of rebase specifically stopped for conflicts */
      -+		apply_dir = repo_git_path(the_repository,
      -+					  "rebase-apply");
      -+		stopped_sha = repo_git_path(the_repository,
      -+					    "rebase-merge/stopped-sha");
      -+		amend_marker = repo_git_path(the_repository,
      -+					     "rebase-merge/amend");
      -+		/*
      -+		 * The apply backend only ever stops for conflicts; the
      -+		 * merge backend writes stopped-sha but omits `amend`,
      -+		 * which it writes only at a clean edit/reword stop.
      -+		 */
      -+		conflicted_stop =
      -+			file_exists(apply_dir) ||
      -+			(file_exists(stopped_sha) && !file_exists(amend_marker));
      ++	/* In the middle of an `am`? */
      ++	path = repo_git_path(r, "rebase-apply/applying");
      ++	found = file_exists(path);
      ++	free(path);
      ++	if (found)
      ++		return ONGOING_AM;
      ++
      ++	/*
      ++	 * In the middle of a rebase that stopped for conflict resolution?
      ++	 * The apply backend only ever stops for conflicts, so the presence
      ++	 * of its state directory is enough.  The merge backend writes
      ++	 * stopped-sha whenever it hands control back to the user, but omits
      ++	 * `amend` unless it stopped with HEAD already pointing at the commit
      ++	 * to be amended (a clean edit/reword stop); its absence therefore
      ++	 * marks a conflicted stop.
      ++	 */
      ++	path = repo_git_path(r, "rebase-apply");
      ++	found = file_exists(path);
      ++	free(path);
      ++	if (!found) {
      ++		char *stopped_sha = repo_git_path(r, "rebase-merge/stopped-sha");
      ++		char *amend_marker = repo_git_path(r, "rebase-merge/amend");
       +
      -+		free(apply_dir);
      ++		found = file_exists(stopped_sha) && !file_exists(amend_marker);
       +		free(stopped_sha);
       +		free(amend_marker);
      -+		if (conflicted_stop)
      -+			die(_("You are resolving conflicts during a rebase -- cannot amend."));
       +	}
      - 	if (fixup_message && squash_message)
      - 		die(_("options '%s' and '%s' cannot be used together"), "--squash", "--fixup");
      - 	die_for_incompatible_opt4(!!use_message, "-C",
      ++	if (found)
      ++		return ONGOING_REBASE_CONFLICT;
      ++
      ++	return ONGOING_NONE;
      ++}
      ++
      + int sequencer_get_update_refs_state(const char *wt_dir,
      + 				    struct string_list *refs)
      + {
      +
      + ## sequencer.h ##
      +@@ sequencer.h: int sequencer_get_last_command(struct repository* r,
      + 			       enum replay_action *action);
      + int sequencer_determine_whence(struct repository *r, enum commit_whence *whence);
      +
      ++/*
      ++ * An in-progress operation that records its result (often a conflict
      ++ * resolution) as a new commit on top of HEAD, during which amending
      ++ * HEAD via "git commit --amend" is almost always a mistake.
      ++ */
      ++enum ongoing_operation {
      ++	ONGOING_NONE = 0,
      ++	ONGOING_MERGE,
      ++	ONGOING_CHERRY_PICK,
      ++	ONGOING_REBASE_EMPTY,
      ++	ONGOING_REVERT,
      ++	ONGOING_AM,
      ++	ONGOING_REBASE_CONFLICT
      ++};
      ++
      ++/*
      ++ * Return which in-progress operation, if any, is underway; see enum
      ++ * ongoing_operation.  'whence' is the origin already computed for the
      ++ * pending commit.
      ++ */
      ++enum ongoing_operation sequencer_ongoing_operation(struct repository *r,
      ++						   enum commit_whence whence);
      ++
      + /**
      +  * Append the set of ref-OID pairs that are currently stored for the 'git
      +  * rebase --update-refs' feature if such a rebase is currently happening.
       
        ## t/t3404-rebase-interactive.sh ##
       @@ t/t3404-rebase-interactive.sh: test_expect_success 'correct error message for commit --amend after empty pick'
      - 	test_grep "middle of a rebase -- cannot amend." err
      + 	test_grep "resolving a commit that became empty -- cannot amend." err
        '
        
       +test_expect_success 'commit --amend is refused at a rebase conflict stop' '

-: ---------- > 3: e0be8cdf63 commit: refuse partial commits during conflict resolution

Quoted 7 lines

The three patches:

1. reword the two pre-existing "empty commit" rebase messages, which were misleadingly generic
2. refuse git commit --amend during these additional operations
3. refuse partial commits during the same operations.

Thanks for working on this, it is a useful improvement to our UI. I've left a couple of comments but this all looks pretty sound to me.

From: Elijah Newren <[email protected]>

Commit 430b75f7209c (commit: give correct advice for empty commit during a rebase, 2019-12-06) introduced a FROM_REBASE_PICK enum value and an is_from_rebase() function. Those names failed to convey that they were specifically about hitting a commit that becomes empty when rebasing. Clarify their names now.

While at it, change whence == FROM_REBASE_EMPTY to use is_from_rebase_empty(whence).

Quoted 7 lines · Elijah Newren via GitGitGadget

From: Elijah Newren <[email protected]>

Commit 430b75f7209c (commit: give correct advice for empty commit during a rebase, 2019-12-06) introduced a FROM_REBASE_PICK enum value and an is_from_rebase() function. Those names failed to convey that they were specifically about hitting a commit that becomes empty when rebasing. Clarify their names now.

Becomes empty is different from picking an empty commit, right. I am not sure if "is_from_rebase_empty()" conveys the difference and more importantly, I am afraid it hints the latter. I have a feeling that EMPTY_REBASE (instead of REBASE_EMPTY) may match what we want to express slightly better, but not by a large margin to make a difference. Perhaps Phillip has a better idea?

Quoted 3 lines

While at it, change whence == FROM_REBASE_EMPTY to use is_from_rebase_empty(whence).

Very much appreciated.

From: Elijah Newren <[email protected]>

For years, we disallowed partial commits during merges or cherry-picks. In commit 430b75f7209c (commit: give correct advice for empty commit during a rebase, 2019-12-06) it was noted that the "cannot do a partial commit during a cherry-pick" message was also printed when rebasing a commit that became empty, and rather than drop the check in that case, that commit opted to make the message print the actual operation that was in progress.

Since a commit that has become empty comes without conflicts, a new partial commit poses no problems; remove the error in that case.

Signed-off-by Elijah Newren <[email protected]>

---
 builtin/commit.c              | 2 --
 t/t3404-rebase-interactive.sh | 5 ++---
 2 files changed, 2 insertions(+), 5 deletions(-)

builtin/commit.c +0 -2

index 569e31fb60..610820c99f 100644
@@ -520,8 +520,6 @@ static const char *prepare_index(const char **argv, const char *prefix,
 			die(_("cannot do a partial commit during a merge."));
 		else if (is_from_cherry_pick(whence))
 			die(_("cannot do a partial commit during a cherry-pick."));
-		else if (is_from_rebase_empty(whence))
-			die(_("cannot do a partial commit during a rebase."));
 	}
 
 	if (list_paths(&partial, !current_head ? NULL : "HEAD", &pathspec))

t/t3404-rebase-interactive.sh +2 -3

index ff11abb2f2..3588e16543 100755
@@ -1858,7 +1858,7 @@ test_expect_success 'post-commit hook is called' '
 	test_cmp expect actual
 '
 
-test_expect_success 'correct error message for partial commit after empty pick' '
+test_expect_success 'partial commit is allowed when a rebase pick becomes empty' '
 	test_when_finished "git rebase --abort" &&
 	(
 		set_fake_editor &&

@@ -1867,8 +1867,7 @@ test_expect_success 'correct error message for partial commit after empty pick'
 		test_must_fail git rebase -i A D
 	) &&
 	echo x >file1 &&
-	test_must_fail git commit file1 2>err &&
-	test_grep "cannot do a partial commit during a rebase." err
+	git commit file1
 '
 
 test_expect_success 'correct error message for commit --amend after empty pick' '

From: Elijah Newren <[email protected]>

When a rebase applies a commit that becomes empty, it stops and asks the user to decide whether to keep it or drop it. HEAD still points at the previously-applied commit at that point, so amending is refused, with:

You are in the middle of a rebase -- cannot amend.

That message would suggest that amending is not allowed during an 'edit' or 'break' stop, which is misleading, plus it lacks the specificity that might help the user know why their particular case is a problem: the commit they intended to amend became empty and was dropped, so amending would affect the wrong commit. Reword the error accordingly.

Signed-off-by Elijah Newren <[email protected]>

---
 builtin/commit.c              | 2 +-
 t/t3404-rebase-interactive.sh | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

builtin/commit.c +0 -0

index 610820c99f..774fb8299d 100644

builtin/commit.c +0 -0

 	}
 	if (fixup_message && squash_message)
 		die(_("options '%s' and '%s' cannot be used together"), "--squash", "--fixup");

t/t3404-rebase-interactive.sh +1 -1

index 3588e16543..81f4844950 100755
@@ -1880,7 +1880,7 @@ test_expect_success 'correct error message for commit --amend after empty pick'
 	) &&
 	echo x>file1 &&
 	test_must_fail git commit -a --amend 2>err &&
-	test_grep "middle of a rebase -- cannot amend." err
+	test_grep "now-empty commit has been dropped -- cannot amend." err
 '
 
 test_expect_success 'todo has correct onto hash' '

builtin/commit.c +10 -5

-	if (whence != FROM_COMMIT) {
-		if (whence == FROM_MERGE)
-			die(_("cannot do a partial commit during a merge."));
-		else if (is_from_cherry_pick(whence))
-			die(_("cannot do a partial commit during a cherry-pick."));
+	switch (sequencer_ongoing_operation(the_repository, whence)) {
+	case ONGOING_NONE:
+		break;
+	case ONGOING_MERGE:
+		die(_("cannot do a partial commit during a merge."));
+	case ONGOING_CHERRY_PICK:
+		die(_("cannot do a partial commit during a cherry-pick."));
+	case ONGOING_REBASE_EMPTY:
+		/*
+		 * A pick that became empty is not a conflict, and creating

From: Elijah Newren <[email protected]>

Commit 430b75f7209c (commit: give correct advice for empty commit during a rebase, 2019-12-06) introduced a FROM_REBASE_PICK enum value and an is_from_rebase() function. Those names failed to convey that they were specifically about hitting a commit that becomes empty when rebasing. Clarify their names now.

While at it, change whence == FROM_REBASE_NOW_EMPTY to use is_from_rebase_now_empty(whence).

Signed-off-by Elijah Newren <[email protected]>

---
  builtin/commit.c | 14 +++++++-------
  sequencer.c      |  2 +-
  wt-status.h      |  6 +++---
  3 files changed, 11 insertions(+), 11 deletions(-)

builtin/commit.c +7 -7

index 28f6174503..17cc27e53e 100644
@@ -520,7 +520,7 @@ static const char *prepare_index(const char **argv, const char *prefix,
  			die(_("cannot do a partial commit during a merge."));
  		else if (is_from_cherry_pick(whence))
  			die(_("cannot do a partial commit during a cherry-pick."));
-		else if (is_from_rebase(whence))
+		else if (is_from_rebase_now_empty(whence))
  			die(_("cannot do a partial commit during a rebase."));
  	}
 

@@ -893,7 +893,7 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
  	 */
  	else if (whence == FROM_MERGE)
  		hook_arg1 = "merge";
-	else if (is_from_cherry_pick(whence) || whence == FROM_REBASE_PICK) {
+	else if (is_from_cherry_pick(whence) || is_from_rebase_now_empty(whence)) {
  		hook_arg1 = "commit";
  		hook_arg2 = "CHERRY_PICK_HEAD";
  	}

@@ -1086,7 +1086,7 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
  		if (amend)
  			fputs(_(empty_amend_advice), stderr);
  		else if (is_from_cherry_pick(whence) ||
-			 whence == FROM_REBASE_PICK) {
+			 is_from_rebase_now_empty(whence)) {
  			fputs(_(empty_cherry_pick_advice), stderr);
  			if (whence == FROM_CHERRY_PICK_SINGLE)
  				fputs(_(empty_cherry_pick_advice_single), stderr);

@@ -1333,7 +1333,7 @@ static int parse_and_validate_options(int argc, const char *argv[],
  			die(_("You are in the middle of a merge -- cannot amend."));
  		else if (is_from_cherry_pick(whence))
  			die(_("You are in the middle of a cherry-pick -- cannot amend."));
-		else if (whence == FROM_REBASE_PICK)
+		else if (is_from_rebase_now_empty(whence))
  			die(_("You are in the middle of a rebase -- cannot amend."));
  	}
  	if (fixup_message && squash_message)

@@ -1353,7 +1353,7 @@ static int parse_and_validate_options(int argc, const char *argv[],
  	if (amend && !use_message && !fixup_message)
  		use_message = "HEAD";
  	if (!use_message && !is_from_cherry_pick(whence) &&
-	    !is_from_rebase(whence) && renew_authorship)
+	    !is_from_rebase_now_empty(whence) && renew_authorship)
  		die(_("--reset-author can be used only with -C, -c or --amend."));
  	if (use_message) {
  		use_message_buffer = read_commit_message(use_message);

@@ -1362,7 +1362,7 @@ static int parse_and_validate_options(int argc, const char *argv[],
  			author_message_buffer = use_message_buffer;
  		}
  	}
-	if ((is_from_cherry_pick(whence) || whence == FROM_REBASE_PICK) &&
+	if ((is_from_cherry_pick(whence) || is_from_rebase_now_empty(whence)) &&
  	    !renew_authorship) {
  		author_message = "CHERRY_PICK_HEAD";
  		author_message_buffer = read_commit_message(author_message);

@@ -1887,7 +1887,7 @@ int cmd_commit(int argc,
  		if (!reflog_msg)
  			reflog_msg = is_from_cherry_pick(whence)
  					? "commit (cherry-pick)"
-					: is_from_rebase(whence)
+					: is_from_rebase_now_empty(whence)
  					? "commit (rebase)"
  					: "commit";
  		commit_list_insert(current_head, &parents);

sequencer.c +1 -1

index 65afd100d9..d336c309ca 100644
@@ -6956,7 +6956,7 @@ int sequencer_determine_whence(struct repository *r, enum commit_whence *whence)
  		    !repo_get_oid(r, "REBASE_HEAD", &rebase_head) &&
  		    !repo_get_oid(r, "CHERRY_PICK_HEAD", &cherry_pick_head) &&
  		    oideq(&rebase_head, &cherry_pick_head))
-			*whence = FROM_REBASE_PICK;
+			*whence = FROM_REBASE_NOW_EMPTY;
  		else
  			*whence = FROM_CHERRY_PICK_SINGLE;
 

wt-status.h +3 -3

index e9fe32e98c..2143f50b49 100644
@@ -41,7 +41,7 @@ enum commit_whence {
  	FROM_MERGE,      /* commit came from merge */
  	FROM_CHERRY_PICK_SINGLE, /* commit came from cherry-pick */
  	FROM_CHERRY_PICK_MULTI, /* commit came from a sequence of cherry-picks */
-	FROM_REBASE_PICK /* commit came from a pick/reword/edit */
+	FROM_REBASE_NOW_EMPTY /* rebase applied a pick that became empty */
  };
 
  static inline int is_from_cherry_pick(enum commit_whence whence)

@@ -50,9 +50,9 @@ static inline int is_from_cherry_pick(enum commit_whence whence)
  		whence == FROM_CHERRY_PICK_MULTI;
  }
 
-static inline int is_from_rebase(enum commit_whence whence)
+static inline int is_from_rebase_now_empty(enum commit_whence whence)
  {
-	return whence == FROM_REBASE_PICK;
+	return whence == FROM_REBASE_NOW_EMPTY;
  }
 
  struct wt_status_change_data {

From: Elijah Newren <[email protected]>

For years, we disallowed partial commits during merges or cherry-picks. In commit 430b75f7209c (commit: give correct advice for empty commit during a rebase, 2019-12-06) it was noted that the "cannot do a partial commit during a cherry-pick" message was also printed when rebasing a commit that became empty, and rather than drop the check in that case, that commit opted to make the message print the actual operation that was in progress.

Since a commit that has become empty comes without conflicts, a new partial commit poses no problems; remove the error in that case.

Signed-off-by Elijah Newren <[email protected]>

---
  builtin/commit.c              | 2 --
  t/t3404-rebase-interactive.sh | 5 ++---
  2 files changed, 2 insertions(+), 5 deletions(-)

builtin/commit.c +0 -2

index 17cc27e53e..01b79185e7 100644
@@ -520,8 +520,6 @@ static const char *prepare_index(const char **argv, const char *prefix,
  			die(_("cannot do a partial commit during a merge."));
  		else if (is_from_cherry_pick(whence))
  			die(_("cannot do a partial commit during a cherry-pick."));
-		else if (is_from_rebase_now_empty(whence))
-			die(_("cannot do a partial commit during a rebase."));
  	}
 
  	if (list_paths(&partial, !current_head ? NULL : "HEAD", &pathspec))

t/t3404-rebase-interactive.sh +2 -3

index ff11abb2f2..3588e16543 100755
@@ -1858,7 +1858,7 @@ test_expect_success 'post-commit hook is called' '
  	test_cmp expect actual
  '
 
-test_expect_success 'correct error message for partial commit after empty pick' '
+test_expect_success 'partial commit is allowed when a rebase pick becomes empty' '
  	test_when_finished "git rebase --abort" &&
  	(
  		set_fake_editor &&

@@ -1867,8 +1867,7 @@ test_expect_success 'correct error message for partial commit after empty pick'
  		test_must_fail git rebase -i A D
  	) &&
  	echo x >file1 &&
-	test_must_fail git commit file1 2>err &&
-	test_grep "cannot do a partial commit during a rebase." err
+	git commit file1
  '
 
  test_expect_success 'correct error message for commit --amend after empty pick' '

From: Elijah Newren <[email protected]>

When a rebase applies a commit that becomes empty, it stops and asks the user to decide whether to keep it or drop it. HEAD still points at the previously-applied commit at that point, so amending is refused, with:

You are in the middle of a rebase -- cannot amend.

That message would suggest that amending is not allowed during an 'edit' or 'break' stop, which is misleading, plus it lacks the specificity that might help the user know why their particular case is a problem: the commit they intended to amend became empty and was dropped, so amending would affect the wrong commit. Reword the error accordingly.

Signed-off-by Elijah Newren <[email protected]>

---
  builtin/commit.c              | 2 +-
  t/t3404-rebase-interactive.sh | 2 +-
  2 files changed, 2 insertions(+), 2 deletions(-)

builtin/commit.c +1 -1

index 01b79185e7..9b6eaa3c72 100644
@@ -1332,7 +1332,7 @@ static int parse_and_validate_options(int argc, const char *argv[],
  		else if (is_from_cherry_pick(whence))
  			die(_("You are in the middle of a cherry-pick -- cannot amend."));
  		else if (is_from_rebase_now_empty(whence))
-			die(_("You are in the middle of a rebase -- cannot amend."));
+			die(_("The now-empty commit has been dropped -- cannot amend."));
  	}
  	if (fixup_message && squash_message)
  		die(_("options '%s' and '%s' cannot be used together"), "--squash", "--fixup");

t/t3404-rebase-interactive.sh +1 -1

index 3588e16543..81f4844950 100755
@@ -1880,7 +1880,7 @@ test_expect_success 'correct error message for commit --amend after empty pick'
  	) &&
  	echo x>file1 &&
  	test_must_fail git commit -a --amend 2>err &&
-	test_grep "middle of a rebase -- cannot amend." err
+	test_grep "now-empty commit has been dropped -- cannot amend." err
  '
 
  test_expect_success 'todo has correct onto hash' '

From: Elijah Newren <[email protected]>

Running git commit --amend during conflict resolution is an ugly foot-gun. For many years, we have rejected amending during conflict resolution in the middle of
- a merge
- a cherry-pick
However, this was never extended to other operations that can also produce conflicts:
- an am operation
- a revert
- a rebase

Extend it to handle these other cases now.

Extending to am, revert, and the apply backend of rebase are fairly straightforward. However, with the merge backend of rebase we have to be more careful, since it powers interactive rebases and
- the interactive machinery internally uses git commit --amend for squash and reword directives
- users are expected to git commit --amend after hitting an edit or break directive
So, we need to be careful with rebase to only reject amending when doing conflict resolution.

A few files under the rebase-merge/ directory provide us the necessary information:

- stopped-sha is written only when the rebase stops and hands control back to the user, so its presence marks a genuine stop -- as opposed to the sequencer's own internal git commit --amend while applying a squash, fixup, or reword, during which no stopped-sha exists.

- amend is written only when the rebase stops with HEAD already pointing at the commit the user is meant to amend: a clean edit, or a fast-forward reword. Its absence at a stop therefore means the commit did not apply, so HEAD is the previously-applied commit rather than the one being rebased -- exactly the case we refuse.

So for the merge backend we die when stopped-sha exists and amend does not. This covers a plain conflicted pick as well as a conflicted edit (both leave HEAD on the previously-applied commit), while still allowing a clean edit or reword stop and a break stop (no stopped-sha). stopped-sha is unlinked at the start of the resume loop, so a resumed squash's internal amend is unaffected.

Signed-off-by Elijah Newren <[email protected]>

---
  builtin/commit.c                | 27 +++++++---
  sequencer.c                     | 57 +++++++++++++++++++++
  sequencer.h                     | 23 +++++++++
  t/t3404-rebase-interactive.sh   | 87 +++++++++++++++++++++++++++++++++
  t/t3507-cherry-pick-conflict.sh | 11 +++++
  t/t4151-am-abort.sh             | 11 +++++
  6 files changed, 210 insertions(+), 6 deletions(-)

builtin/commit.c +21 -6

index 9b6eaa3c72..284fc7fdc6 100644
@@ -1324,15 +1324,30 @@ static int parse_and_validate_options(int argc, const char *argv[],
  		use_editor = 0;
 
  	/* Sanity check options */
-	if (amend && !current_head)
-		die(_("You have nothing to amend."));
-	if (amend && whence != FROM_COMMIT) {
-		if (whence == FROM_MERGE)
+	if (amend) {
+		if (!current_head)
+			die(_("You have nothing to amend."));
+		/*
+		 * Refuse to amend in the middle of any operation that is
+		 * meant to record its result as a new commit on top of HEAD
+		 * rather than by rewriting HEAD.
+		 */
+		switch (sequencer_ongoing_operation(s->repo, whence)) {
+		case ONGOING_NONE:
+			break;
+		case ONGOING_MERGE:
  			die(_("You are in the middle of a merge -- cannot amend."));
-		else if (is_from_cherry_pick(whence))
+		case ONGOING_CHERRY_PICK:
  			die(_("You are in the middle of a cherry-pick -- cannot amend."));
-		else if (is_from_rebase_now_empty(whence))
+		case ONGOING_REBASE_NOW_EMPTY:
  			die(_("The now-empty commit has been dropped -- cannot amend."));
+		case ONGOING_REVERT:
+			die(_("You are in the middle of a revert -- cannot amend."));
+		case ONGOING_AM:
+			die(_("You are in the middle of an am session -- cannot amend."));
+		case ONGOING_REBASE_CONFLICT:
+			die(_("You are resolving conflicts during a rebase -- cannot amend."));
+		}
  	}
  	if (fixup_message && squash_message)
  		die(_("options '%s' and '%s' cannot be used together"), "--squash", "--fixup");

sequencer.c +57 -0

index d336c309ca..6a28e0dd9a 100644
@@ -142,6 +142,13 @@ static GIT_PATH_FUNC(rebase_path_author_script, "rebase-merge/author-script")
   * command is processed, this file is deleted.
   */
  static GIT_PATH_FUNC(rebase_path_amend, "rebase-merge/amend")
+/*
+ * The apply ("am") backend keeps its state in the rebase-apply directory;
+ * the "applying" file within it marks a plain `git am` (as opposed to an
+ * apply-based rebase).
+ */
+static GIT_PATH_FUNC(apply_dir, "rebase-apply")
+static GIT_PATH_FUNC(apply_path_applying, "rebase-apply/applying")
  /*
   * When we stop at a given patch via the "edit" command, this file contains
   * the commit object name of the corresponding patch.

@@ -6966,6 +6973,56 @@ int sequencer_determine_whence(struct repository *r, enum commit_whence *whence)
  	return 0;
  }
 
+enum ongoing_operation sequencer_ongoing_operation(struct repository *r,
+						   enum commit_whence whence)
+{
+	/*
+	 * The merge, cherry-pick, and (empty) rebase-pick stops are already
+	 * distinguished by 'whence'.
+	 */
+	switch (whence) {
+	case FROM_MERGE:
+		return ONGOING_MERGE;
+	case FROM_CHERRY_PICK_SINGLE:
+	case FROM_CHERRY_PICK_MULTI:
+		return ONGOING_CHERRY_PICK;
+	case FROM_REBASE_NOW_EMPTY:
+		return ONGOING_REBASE_NOW_EMPTY;
+	case FROM_COMMIT:
+		break;
+	}
+
+	/*
+	 * 'whence' is FROM_COMMIT, but we may still be in the middle of an
+	 * operation that records its result on top of HEAD; detect those
+	 * from their on-disk state.
+	 */
+
+	/* In the middle of a revert? */
+	if (refs_ref_exists(get_main_ref_store(r), "REVERT_HEAD"))
+		return ONGOING_REVERT;
+
+	/* In the middle of an `am`? */
+	if (file_exists(apply_path_applying()))
+		return ONGOING_AM;
+
+	/*
+	 * In the middle of a rebase that stopped for conflict resolution?
+	 * The apply backend only ever stops for conflicts, so the presence
+	 * of its state directory is enough.  The merge backend writes
+	 * stopped-sha whenever it hands control back to the user, but omits
+	 * `amend` unless it stopped with HEAD already pointing at the commit
+	 * to be amended (a clean edit/reword stop); its absence therefore
+	 * marks a conflicted stop.
+	 */
+	if (file_exists(apply_dir()) ||
+	    (file_exists(rebase_path_stopped_sha()) &&
+	     !file_exists(rebase_path_amend())))
+		return ONGOING_REBASE_CONFLICT;
+
+	return ONGOING_NONE;
+}
+
  int sequencer_get_update_refs_state(const char *wt_dir,
  				    struct string_list *refs)
  {

sequencer.h +23 -0

index 64a9c7fb1b..fb4a744208 100644
@@ -277,6 +277,29 @@ int sequencer_get_last_command(struct repository* r,
  			       enum replay_action *action);
  int sequencer_determine_whence(struct repository *r, enum commit_whence *whence);
 
+/*
+ * An in-progress operation that records its result (often a conflict
+ * resolution) as a new commit on top of HEAD, during which amending
+ * HEAD via "git commit --amend" is almost always a mistake.
+ */
+enum ongoing_operation {
+	ONGOING_NONE = 0,
+	ONGOING_MERGE,
+	ONGOING_CHERRY_PICK,
+	ONGOING_REBASE_NOW_EMPTY,
+	ONGOING_REVERT,
+	ONGOING_AM,
+	ONGOING_REBASE_CONFLICT
+};
+
+/*
+ * Return which in-progress operation, if any, is underway; see enum
+ * ongoing_operation.  'whence' is the origin already computed for the
+ * pending commit.
+ */
+enum ongoing_operation sequencer_ongoing_operation(struct repository *r,
+						   enum commit_whence whence);
+
  /**
   * Append the set of ref-OID pairs that are currently stored for the 'git
   * rebase --update-refs' feature if such a rebase is currently happening.

t/t3404-rebase-interactive.sh +87 -0

index 81f4844950..4e6c3e2f19 100755
@@ -1883,6 +1883,93 @@ test_expect_success 'correct error message for commit --amend after empty pick'
  	test_grep "now-empty commit has been dropped -- cannot amend." err
  '
 
+test_expect_success 'commit --amend is refused at a rebase conflict stop' '
+	test_when_finished "git rebase --abort" &&
+	git checkout --detach conflict-branch &&
+	(
+		set_fake_editor &&
+		FAKE_LINES="1 3" &&
+		export FAKE_LINES &&
+		test_must_fail git rebase -i A
+	) &&
+	test_path_is_file .git/rebase-merge/patch &&
+	test_path_is_missing .git/rebase-merge/amend &&
+	echo resolved >conflict &&
+	git add conflict &&
+	test_must_fail git commit --amend --no-edit 2>err &&
+	test_grep "You are resolving conflicts during a rebase -- cannot amend" err
+'
+
+test_expect_success 'commit --amend is refused when an "edit" pick conflicts' '
+	test_when_finished "git rebase --abort" &&
+	git checkout --detach conflict-branch &&
+	(
+		set_fake_editor &&
+		FAKE_LINES="1 edit 3" &&
+		export FAKE_LINES &&
+		test_must_fail git rebase -i A
+	) &&
+	test_path_is_file .git/rebase-merge/patch &&
+	test_path_is_missing .git/rebase-merge/amend &&
+	echo resolved >conflict &&
+	git add conflict &&
+	test_must_fail git commit --amend --no-edit 2>err &&
+	test_grep "You are resolving conflicts during a rebase -- cannot amend" err
+'
+
+test_expect_success 'commit --amend is allowed at a rebase edit stop' '
+	test_when_finished "git rebase --abort" &&
+	git checkout --detach no-conflict-branch &&
+	(
+		set_fake_editor &&
+		FAKE_LINES="edit 1 2 3 4" &&
+		export FAKE_LINES &&
+		git rebase -i A
+	) &&
+	test_path_is_file .git/rebase-merge/amend &&
+	echo tweak >fileJ &&
+	git add fileJ &&
+	git commit --amend --no-edit
+'
+
+test_expect_success 'commit --amend is allowed at a rebase break stop' '
+	test_when_finished "git rebase --abort" &&
+	git checkout --detach no-conflict-branch &&
+	(
+		set_fake_editor &&
+		FAKE_LINES="break 1 2 3 4" &&
+		export FAKE_LINES &&
+		git rebase -i A
+	) &&
+	test_must_fail git rev-parse --verify REBASE_HEAD &&
+	echo tweak >fileJ &&
+	git add fileJ &&
+	git commit --amend --no-edit
+'
+
+test_expect_success 'commit --amend is refused at an apply-backend conflict stop' '
+	test_when_finished "rm -rf apply-backend" &&
+	test_create_repo apply-backend &&
+	(
+		cd apply-backend &&
+		test_commit base file &&
+		git branch -M mainline &&
+		test_commit upstream file upstream &&
+		git checkout -b side mainline~1 &&
+		test_commit conflicting file side &&
+		test_commit unrelated other &&
+		test_must_fail git rebase --apply mainline &&
+		# the apply backend only ever stops for conflicts, and
+		# leaves HEAD on the previously-applied commit
+		test_path_is_dir .git/rebase-apply &&
+		test_path_is_missing .git/rebase-apply/applying &&
+		echo resolved >file &&
+		git add file &&
+		test_must_fail git commit --amend --no-edit 2>err &&
+		test_grep "You are resolving conflicts during a rebase -- cannot amend" err
+	)
+'
+
  test_expect_success 'todo has correct onto hash' '
  	GIT_SEQUENCE_EDITOR=cat git rebase -i no-conflict-branch~4 no-conflict-branch >actual &&
  	onto=$(git rev-parse --short HEAD~4) &&

t/t3507-cherry-pick-conflict.sh +11 -0

index 44596cb1e8..42de398f76 100755
@@ -364,6 +364,17 @@ test_expect_success 'failed revert sets REVERT_HEAD' '
  	test_cmp_rev picked REVERT_HEAD
  '
 
+test_expect_success 'commit --amend of revert fails' '
+	pristine_detach initial &&
+
+	test_must_fail git revert picked &&
+	echo resolved >foo &&
+	git add foo &&
+	test_must_fail git commit --amend 2>err &&
+
+	test_grep "in the middle of a revert -- cannot amend." err
+'
+
  test_expect_success 'successful revert does not set REVERT_HEAD' '
  	pristine_detach base &&
  	git revert base &&

t/t4151-am-abort.sh +11 -0

index 8e1ecf8a68..9313a074b2 100755
@@ -63,6 +63,17 @@ do
 
  done
 
+test_expect_success 'commit --amend during a failed am fails' '
+	git reset --hard initial &&
+	cp file-2-expect file-2 &&
+	test_must_fail git am 000[1245]-*.patch &&
+	echo resolved >file-1 &&
+	git add file-1 &&
+	test_must_fail git commit --amend 2>err &&
+	test_grep "in the middle of an am session -- cannot amend." err &&
+	git am --abort
+'
+
  test_expect_success 'am -3 --skip removes otherfile-4' '
  	git reset --hard initial &&
  	test_must_fail git am -3 0003-*.patch &&

Changes since v3:

* Just a clarifying rename, but applied in 3 places:
* FROM_REBASE_EMPTY -> FROM_REBASE_NOW_EMPTY
* is_from_rebase_empty() -> is_from_rebase_now_empty()
* ONGOING_REBASE_EMPTY -> ONGOING_REBASE_NOW_EMPTY

Changes since v2:

* Two new preparatory patches:
* Rename FROM_REBASE_PICK and is_from_rebase() to point out they are about empty commits
* Allow a partial commit when a rebase pick becomes empty
* Tweaked the error message for attempted amend on now-dropped empty commit (suggestions for further improvements welcome)
* Used the path accessor functions within sequencer.c to simplify the new helper function

Both git commit --amend and a partial commit (git commit <paths>) are foot-guns while the user is in the middle of an operation that resolves conflicts on top of HEAD: recording a conflict resolution is about capturing the state of the whole tree as a new commit, not about rewriting HEAD or committing a subset of paths.

Historically we only rejected these during a merge or a cherry-pick or when resolving an empty pick during a rebase. The same hazard exists for am, revert, and rebase conflict stops, none of which were covered. This series extends the refusal to all of them.

The three patches:

1. reword the two pre-existing "empty commit" rebase messages, which were misleadingly generic
2. refuse git commit --amend during these additional operations
3. refuse partial commits during the same operations.

Elijah Newren (5):
commit: clarify FROM_REBASE_PICK and is_from_rebase() names
commit: allow a partial commit when a rebase pick becomes empty
commit: reword the empty-commit rebase amend error
commit: refuse to amend during conflict resolution
commit: refuse partial commits during conflict resolution

  builtin/commit.c                |  65 +++++++++++-----
  sequencer.c                     |  59 ++++++++++++++-
  sequencer.h                     |  24 ++++++
  t/t3404-rebase-interactive.sh   | 128 +++++++++++++++++++++++++++++++-
  t/t3507-cherry-pick-conflict.sh |  22 ++++++
  t/t4151-am-abort.sh             |  22 ++++++
  wt-status.h                     |   6 +-
  7 files changed, 299 insertions(+), 27 deletions(-)

base-commit: 2c3adbb2c475981e340c79fdc5e7f4f9b5d9054e
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2389%2Fnewren%2Frefuse-amend-during-conflicts-v4
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2389/newren/refuse-amend-during-conflicts-v4
Pull-Request: https://github.com/git/git/pull/2389

Range-diff vs v3:

1: 7e198a20fa ! 1: bd361679b9 commit: clarify FROM_REBASE_PICK and is_from_rebase() names

      @@ Commit message
           specifically about hitting a commit that becomes empty when rebasing.
           Clarify their names now.
       
      -    While at it, change `whence == FROM_REBASE_EMPTY` to use
      -    `is_from_rebase_empty(whence)`.
      +    While at it, change `whence == FROM_REBASE_NOW_EMPTY` to use
      +    `is_from_rebase_now_empty(whence)`.
       
           Signed-off-by: Elijah Newren <[email protected]>
       
      @@ builtin/commit.c: static const char *prepare_index(const char **argv, const char
        		else if (is_from_cherry_pick(whence))
        			die(_("cannot do a partial commit during a cherry-pick."));
       -		else if (is_from_rebase(whence))
      -+		else if (is_from_rebase_empty(whence))
      ++		else if (is_from_rebase_now_empty(whence))
        			die(_("cannot do a partial commit during a rebase."));
        	}
        
      @@ builtin/commit.c: static int prepare_to_commit(const char *index_file, const cha
        	else if (whence == FROM_MERGE)
        		hook_arg1 = "merge";
       -	else if (is_from_cherry_pick(whence) || whence == FROM_REBASE_PICK) {
      -+	else if (is_from_cherry_pick(whence) || is_from_rebase_empty(whence)) {
      ++	else if (is_from_cherry_pick(whence) || is_from_rebase_now_empty(whence)) {
        		hook_arg1 = "commit";
        		hook_arg2 = "CHERRY_PICK_HEAD";
        	}
      @@ builtin/commit.c: static int prepare_to_commit(const char *index_file, const cha
        			fputs(_(empty_amend_advice), stderr);
        		else if (is_from_cherry_pick(whence) ||
       -			 whence == FROM_REBASE_PICK) {
      -+			 is_from_rebase_empty(whence)) {
      ++			 is_from_rebase_now_empty(whence)) {
        			fputs(_(empty_cherry_pick_advice), stderr);
        			if (whence == FROM_CHERRY_PICK_SINGLE)
        				fputs(_(empty_cherry_pick_advice_single), stderr);
      @@ builtin/commit.c: static int parse_and_validate_options(int argc, const char *ar
        		else if (is_from_cherry_pick(whence))
        			die(_("You are in the middle of a cherry-pick -- cannot amend."));
       -		else if (whence == FROM_REBASE_PICK)
      -+		else if (is_from_rebase_empty(whence))
      ++		else if (is_from_rebase_now_empty(whence))
        			die(_("You are in the middle of a rebase -- cannot amend."));
        	}
        	if (fixup_message && squash_message)
      @@ builtin/commit.c: static int parse_and_validate_options(int argc, const char *ar
        		use_message = "HEAD";
        	if (!use_message && !is_from_cherry_pick(whence) &&
       -	    !is_from_rebase(whence) && renew_authorship)
      -+	    !is_from_rebase_empty(whence) && renew_authorship)
      ++	    !is_from_rebase_now_empty(whence) && renew_authorship)
        		die(_("--reset-author can be used only with -C, -c or --amend."));
        	if (use_message) {
        		use_message_buffer = read_commit_message(use_message);
      @@ builtin/commit.c: static int parse_and_validate_options(int argc, const char *ar
        		}
        	}
       -	if ((is_from_cherry_pick(whence) || whence == FROM_REBASE_PICK) &&
      -+	if ((is_from_cherry_pick(whence) || is_from_rebase_empty(whence)) &&
      ++	if ((is_from_cherry_pick(whence) || is_from_rebase_now_empty(whence)) &&
        	    !renew_authorship) {
        		author_message = "CHERRY_PICK_HEAD";
        		author_message_buffer = read_commit_message(author_message);
      @@ builtin/commit.c: int cmd_commit(int argc,
        			reflog_msg = is_from_cherry_pick(whence)
        					? "commit (cherry-pick)"
       -					: is_from_rebase(whence)
      -+					: is_from_rebase_empty(whence)
      ++					: is_from_rebase_now_empty(whence)
        					? "commit (rebase)"
        					: "commit";
        		commit_list_insert(current_head, &parents);
      @@ sequencer.c: int sequencer_determine_whence(struct repository *r, enum commit_wh
        		    !repo_get_oid(r, "CHERRY_PICK_HEAD", &cherry_pick_head) &&
        		    oideq(&rebase_head, &cherry_pick_head))
       -			*whence = FROM_REBASE_PICK;
      -+			*whence = FROM_REBASE_EMPTY;
      ++			*whence = FROM_REBASE_NOW_EMPTY;
        		else
        			*whence = FROM_CHERRY_PICK_SINGLE;
        
      @@ wt-status.h: enum commit_whence {
        	FROM_CHERRY_PICK_SINGLE, /* commit came from cherry-pick */
        	FROM_CHERRY_PICK_MULTI, /* commit came from a sequence of cherry-picks */
       -	FROM_REBASE_PICK /* commit came from a pick/reword/edit */
      -+	FROM_REBASE_EMPTY /* rebase applied a pick that became empty */
      ++	FROM_REBASE_NOW_EMPTY /* rebase applied a pick that became empty */
        };
        
        static inline int is_from_cherry_pick(enum commit_whence whence)
      @@ wt-status.h: static inline int is_from_cherry_pick(enum commit_whence whence)
        }
        
       -static inline int is_from_rebase(enum commit_whence whence)
      -+static inline int is_from_rebase_empty(enum commit_whence whence)
      ++static inline int is_from_rebase_now_empty(enum commit_whence whence)
        {
       -	return whence == FROM_REBASE_PICK;
      -+	return whence == FROM_REBASE_EMPTY;
      ++	return whence == FROM_REBASE_NOW_EMPTY;
        }
        
        struct wt_status_change_data {
  2:  e169303619 ! 2:  a0b9900437 commit: allow a partial commit when a rebase pick becomes empty
      @@ builtin/commit.c: static const char *prepare_index(const char **argv, const char
        			die(_("cannot do a partial commit during a merge."));
        		else if (is_from_cherry_pick(whence))
        			die(_("cannot do a partial commit during a cherry-pick."));
      --		else if (is_from_rebase_empty(whence))
      +-		else if (is_from_rebase_now_empty(whence))
       -			die(_("cannot do a partial commit during a rebase."));
        	}

3: 0850a999da ! 3: c4511a9887 commit: reword the empty-commit rebase amend error

      @@ builtin/commit.c
       @@ builtin/commit.c: static int parse_and_validate_options(int argc, const char *argv[],
        		else if (is_from_cherry_pick(whence))
        			die(_("You are in the middle of a cherry-pick -- cannot amend."));
      - 		else if (is_from_rebase_empty(whence))
      + 		else if (is_from_rebase_now_empty(whence))
       -			die(_("You are in the middle of a rebase -- cannot amend."));
       +			die(_("The now-empty commit has been dropped -- cannot amend."));
        	}

4: 9f80d8a00d ! 4: e77b34c1cf commit: refuse to amend during conflict resolution
@@ builtin/commit.c: static int parse_and_validate_options(int argc, const char *ar
- else if (is_from_cherry_pick(whence))
+ case ONGOING_CHERRY_PICK:
die(_("You are in the middle of a cherry-pick -- cannot amend."));
-- else if (is_from_rebase_empty(whence))
-+ case ONGOING_REBASE_EMPTY:
+- else if (is_from_rebase_now_empty(whence))
++ case ONGOING_REBASE_NOW_EMPTY:
die(_("The now-empty commit has been dropped -- cannot amend."));
+ case ONGOING_REVERT:
+ die(_("You are in the middle of a revert -- cannot amend."));
@@ sequencer.c: int sequencer_determine_whence(struct repository *r, enum commit_wh
+ case FROM_CHERRY_PICK_SINGLE:
+ case FROM_CHERRY_PICK_MULTI:
+ return ONGOING_CHERRY_PICK;
-+ case FROM_REBASE_EMPTY:
-+ return ONGOING_REBASE_EMPTY;
++ case FROM_REBASE_NOW_EMPTY:
++ return ONGOING_REBASE_NOW_EMPTY;
+ case FROM_COMMIT:
+ break;
+ }
@@ sequencer.h: int sequencer_get_last_command(struct repository* r,
+ ONGOING_NONE = 0,
+ ONGOING_MERGE,
+ ONGOING_CHERRY_PICK,
-+ ONGOING_REBASE_EMPTY,
++ ONGOING_REBASE_NOW_EMPTY,
+ ONGOING_REVERT,
+ ONGOING_AM,
+ ONGOING_REBASE_CONFLICT
5: 050b9e8a52 ! 5: b93b26ed9f commit: refuse partial commits during conflict resolution
@@ builtin/commit.c: static const char *prepare_index(const char **argv, const char
+ die(_("cannot do a partial commit during a merge."));
+ case ONGOING_CHERRY_PICK:
+ die(_("cannot do a partial commit during a cherry-pick."));
-+ case ONGOING_REBASE_EMPTY:
++ case ONGOING_REBASE_NOW_EMPTY:
+ /*
+ * A pick that became empty is not a conflict, and creating
+ * a new commit (partial or not) poses no problem.