rebase -i: add --ignore-whitespace flag

Rebase is implemented with two different backends - 'apply' and
'merge' each of which support a different set of options. In
particular the apply backend supports a number of options implemented
by 'git am' that are not implemented in the merge backend. This means
that the available options are different depending on which backend is
used which is confusing. This patch adds support for the
--ignore-whitespace option to the merge backend. This option treats
lines with only whitespace changes as unchanged and is implemented in
the merge backend by translating it to -Xignore-space-change.

Signed-off-by: Rohit Ashiwal <rohit.ashiwal265@gmail.com>
Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-rebase.txt

@@ -422,8 +422,23 @@ your branch contains commits which were dropped, this option can be used
 with `--keep-base` in order to drop those commits from your branch.
 
 --ignore-whitespace::
+	Ignore whitespace differences when trying to reconcile
+differences. Currently, each backend implements an approximation of
+this behavior:
++
+apply backend: When applying a patch, ignore changes in whitespace in
+context lines. Unfortunately, this means that if the "old" lines being
+replaced by the patch differ only in whitespace from the existing
+file, you will get a merge conflict instead of a successful patch
+application.
++
+merge backend: Treat lines with only whitespace changes as unchanged
+when merging. Unfortunately, this means that any patch hunks that were
+intended to modify whitespace and nothing else will be dropped, even
+if the other side had no changes that conflicted.
+
 --whitespace=<option>::
-	These flags are passed to the 'git apply' program
+	This flag is passed to the 'git apply' program
 	(see linkgit:git-apply[1]) that applies the patch.
 	Implies --apply.
 +
@@ -572,7 +587,6 @@ The following options:
  * --apply
  * --committer-date-is-author-date
  * --ignore-date
- * --ignore-whitespace
  * --whitespace
  * -C
 
@@ -598,6 +612,7 @@ In addition, the following pairs of options are incompatible:
  * --preserve-merges and --signoff
  * --preserve-merges and --rebase-merges
  * --preserve-merges and --empty=
+ * --preserve-merges and --ignore-whitespace
  * --keep-base and --onto
  * --keep-base and --root
 

builtin/rebase.c

@@ -126,6 +126,7 @@ static struct replay_opts get_replay_opts(const struct rebase_options *opts)
 	replay.reschedule_failed_exec = opts->reschedule_failed_exec;
 	replay.gpg_sign = xstrdup_or_null(opts->gpg_sign_opt);
 	replay.strategy = opts->strategy;
+
 	if (opts->strategy_opts)
 		parse_strategy_opts(&replay, opts->strategy_opts);
 
@@ -1466,6 +1467,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	struct strbuf revisions = STRBUF_INIT;
 	struct strbuf buf = STRBUF_INIT;
 	struct object_id merge_base;
+	int ignore_whitespace = 0;
 	enum action action = ACTION_NONE;
 	const char *gpg_sign = NULL;
 	struct string_list exec = STRING_LIST_INIT_NODUP;
@@ -1495,9 +1497,6 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 			PARSE_OPT_NOARG, NULL, REBASE_DIFFSTAT },
 		OPT_BOOL(0, "signoff", &options.signoff,
 			 N_("add a Signed-off-by: line to each commit")),
-		OPT_PASSTHRU_ARGV(0, "ignore-whitespace", &options.git_am_opts,
-				  NULL, N_("passed to 'git am'"),
-				  PARSE_OPT_NOARG),
 		OPT_PASSTHRU_ARGV(0, "committer-date-is-author-date",
 				  &options.git_am_opts, NULL,
 				  N_("passed to 'git am'"), PARSE_OPT_NOARG),
@@ -1505,6 +1504,8 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 				  N_("passed to 'git am'"), PARSE_OPT_NOARG),
 		OPT_PASSTHRU_ARGV('C', NULL, &options.git_am_opts, N_("n"),
 				  N_("passed to 'git apply'"), 0),
+		OPT_BOOL(0, "ignore-whitespace", &ignore_whitespace,
+			 N_("ignore changes in whitespace")),
 		OPT_PASSTHRU_ARGV(0, "whitespace", &options.git_am_opts,
 				  N_("action"), N_("passed to 'git apply'"), 0),
 		OPT_BIT('f', "force-rebase", &options.flags,
@@ -1850,6 +1851,18 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		imply_merge(&options, "--rebase-merges");
 	}
 
+	if (options.type == REBASE_APPLY) {
+		if (ignore_whitespace)
+			argv_array_push(&options.git_am_opts,
+					"--ignore-whitespace");
+	} else {
+		/* REBASE_MERGE and PRESERVE_MERGES */
+		if (ignore_whitespace) {
+			string_list_append(&strategy_options,
+					   "ignore-space-change");
+		}
+	}
+
 	if (strategy_options.nr) {
 		int i;
 

t/t3422-rebase-incompatible-options.sh

@@ -61,7 +61,6 @@ test_rebase_am_only () {
 }
 
 test_rebase_am_only --whitespace=fix
-test_rebase_am_only --ignore-whitespace
 test_rebase_am_only --committer-date-is-author-date
 test_rebase_am_only -C4
 

t/t3436-rebase-more-options.sh

@@ -0,0 +1,60 @@
+#!/bin/sh
+#
+# Copyright (c) 2019 Rohit Ashiwal
+#
+
+test_description='tests to ensure compatibility between am and interactive backends'
+
+. ./test-lib.sh
+
+. "$TEST_DIRECTORY"/lib-rebase.sh
+
+# This is a special case in which both am and interactive backends
+# provide the same output. It was done intentionally because
+# both the backends fall short of optimal behaviour.
+test_expect_success 'setup' '
+	git checkout -b topic &&
+	test_write_lines "line 1" "	line 2" "line 3" >file &&
+	git add file &&
+	git commit -m "add file" &&
+
+	test_write_lines "line 1" "new line 2" "line 3" >file &&
+	git commit -am "update file" &&
+	git tag side &&
+
+	git checkout --orphan master &&
+	test_write_lines "line 1" "        line 2" "line 3" >file &&
+	git commit -am "add file" &&
+	git tag main
+'
+
+test_expect_success '--ignore-whitespace works with apply backend' '
+	test_must_fail git rebase --apply main side &&
+	git rebase --abort &&
+	git rebase --apply --ignore-whitespace main side &&
+	git diff --exit-code side
+'
+
+test_expect_success '--ignore-whitespace works with merge backend' '
+	test_must_fail git rebase --merge main side &&
+	git rebase --abort &&
+	git rebase --merge --ignore-whitespace main side &&
+	git diff --exit-code side
+'
+
+test_expect_success '--ignore-whitespace is remembered when continuing' '
+	(
+		set_fake_editor &&
+		FAKE_LINES="break 1" git rebase -i --ignore-whitespace \
+			main side &&
+		git rebase --continue
+	) &&
+	git diff --exit-code side
+'
+
+# This must be the last test in this file
+test_expect_success '$EDITOR and friends are unchanged' '
+	test_editor_unchanged
+'
+
+test_done