From 7457014be5d095aac55cabd24c82bf0e42641f3b Mon Sep 17 00:00:00 2001
From: Phillip Wood <phillip.wood@dunelm.org.uk>
Date: Thu, 14 Mar 2024 17:05:03 +0000
Subject: [PATCH 1/5] xdiff-interface: refactor parsing of merge.conflictstyle

Factor out the code that parses of conflict style name so it can be
reused in a later commit that wants to parse the name given on the
command line.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 xdiff-interface.c | 29 ++++++++++++++++++-----------
 xdiff-interface.h |  1 +
 2 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/xdiff-interface.c b/xdiff-interface.c
index 3162f51743..16ed8ac492 100644
--- a/xdiff-interface.c
+++ b/xdiff-interface.c
@@ -305,6 +305,22 @@ int xdiff_compare_lines(const char *l1, long s1,
 	return xdl_recmatch(l1, s1, l2, s2, flags);
 }
 
+int parse_conflict_style_name(const char *value)
+{
+	if (!strcmp(value, "diff3"))
+		return XDL_MERGE_DIFF3;
+	else if (!strcmp(value, "zdiff3"))
+		return XDL_MERGE_ZEALOUS_DIFF3;
+	else if (!strcmp(value, "merge"))
+		return 0;
+	/*
+	 * Please update _git_checkout() in git-completion.bash when
+	 * you add new merge config
+	 */
+	else
+		return -1;
+}
+
 int git_xmerge_style = -1;
 
 int git_xmerge_config(const char *var, const char *value,
@@ -313,17 +329,8 @@ int git_xmerge_config(const char *var, const char *value,
 	if (!strcmp(var, "merge.conflictstyle")) {
 		if (!value)
 			return config_error_nonbool(var);
-		if (!strcmp(value, "diff3"))
-			git_xmerge_style = XDL_MERGE_DIFF3;
-		else if (!strcmp(value, "zdiff3"))
-			git_xmerge_style = XDL_MERGE_ZEALOUS_DIFF3;
-		else if (!strcmp(value, "merge"))
-			git_xmerge_style = 0;
-		/*
-		 * Please update _git_checkout() in
-		 * git-completion.bash when you add new merge config
-		 */
-		else
+		git_xmerge_style = parse_conflict_style_name(value);
+		if (git_xmerge_style == -1)
 			return error(_("unknown style '%s' given for '%s'"),
 				     value, var);
 		return 0;
diff --git a/xdiff-interface.h b/xdiff-interface.h
index e6f80df046..38537169b7 100644
--- a/xdiff-interface.h
+++ b/xdiff-interface.h
@@ -51,6 +51,7 @@ int buffer_is_binary(const char *ptr, unsigned long size);
 void xdiff_set_find_func(xdemitconf_t *xecfg, const char *line, int cflags);
 void xdiff_clear_find_func(xdemitconf_t *xecfg);
 struct config_context;
+int parse_conflict_style_name(const char *value);
 int git_xmerge_config(const char *var, const char *value,
 		      const struct config_context *ctx, void *cb);
 extern int git_xmerge_style;

From 412aff7b3379b182e3331ec66c0657ae4e39d576 Mon Sep 17 00:00:00 2001
From: Phillip Wood <phillip.wood@dunelm.org.uk>
Date: Thu, 14 Mar 2024 17:05:04 +0000
Subject: [PATCH 2/5] merge-ll: introduce LL_MERGE_OPTIONS_INIT

Introduce a macro to initialize `struct ll_merge_options` in preparation
for the next commit that will add a new member that needs to be
initialized to a non-zero value.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 builtin/checkout.c | 3 +--
 merge-ll.c         | 2 +-
 merge-ll.h         | 2 ++
 merge-ort.c        | 2 +-
 merge-recursive.c  | 2 +-
 5 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/builtin/checkout.c b/builtin/checkout.c
index a6e30931b5..e9859a1980 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -262,7 +262,7 @@ static int checkout_merged(int pos, const struct checkout *state,
 	mmbuffer_t result_buf;
 	struct object_id threeway[3];
 	unsigned mode = 0;
-	struct ll_merge_options ll_opts;
+	struct ll_merge_options ll_opts = LL_MERGE_OPTIONS_INIT;
 	int renormalize = 0;
 
 	memset(threeway, 0, sizeof(threeway));
@@ -284,7 +284,6 @@ static int checkout_merged(int pos, const struct checkout *state,
 	read_mmblob(&ours, &threeway[1]);
 	read_mmblob(&theirs, &threeway[2]);
 
-	memset(&ll_opts, 0, sizeof(ll_opts));
 	git_config_get_bool("merge.renormalize", &renormalize);
 	ll_opts.renormalize = renormalize;
 	merge_status = ll_merge(&result_buf, path, &ancestor, "base",
diff --git a/merge-ll.c b/merge-ll.c
index 5ffb045efb..ef200e4497 100644
--- a/merge-ll.c
+++ b/merge-ll.c
@@ -401,7 +401,7 @@ enum ll_merge_result ll_merge(mmbuffer_t *result_buf,
 	     const struct ll_merge_options *opts)
 {
 	struct attr_check *check = load_merge_attributes();
-	static const struct ll_merge_options default_opts;
+	static const struct ll_merge_options default_opts = LL_MERGE_OPTIONS_INIT;
 	const char *ll_driver_name = NULL;
 	int marker_size = DEFAULT_CONFLICT_MARKER_SIZE;
 	const struct ll_merge_driver *driver;
diff --git a/merge-ll.h b/merge-ll.h
index e4a20e81a3..af1ee36abd 100644
--- a/merge-ll.h
+++ b/merge-ll.h
@@ -82,6 +82,8 @@ struct ll_merge_options {
 	long xdl_opts;
 };
 
+#define LL_MERGE_OPTIONS_INIT {0}
+
 enum ll_merge_result {
 	LL_MERGE_ERROR = -1,
 	LL_MERGE_OK = 0,
diff --git a/merge-ort.c b/merge-ort.c
index 8617babee4..4a02c3ecd9 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -1956,7 +1956,7 @@ static int merge_3way(struct merge_options *opt,
 		      mmbuffer_t *result_buf)
 {
 	mmfile_t orig, src1, src2;
-	struct ll_merge_options ll_opts = {0};
+	struct ll_merge_options ll_opts = LL_MERGE_OPTIONS_INIT;
 	char *base, *name1, *name2;
 	enum ll_merge_result merge_status;
 
diff --git a/merge-recursive.c b/merge-recursive.c
index a0c3e7a2d9..02b7b584f9 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -1047,7 +1047,7 @@ static int merge_3way(struct merge_options *opt,
 		      const int extra_marker_size)
 {
 	mmfile_t orig, src1, src2;
-	struct ll_merge_options ll_opts = {0};
+	struct ll_merge_options ll_opts = LL_MERGE_OPTIONS_INIT;
 	char *base, *name1, *name2;
 	enum ll_merge_result merge_status;
 

From 135cc712c39fa7ccf25b9b2b55d1d07fc85c85a4 Mon Sep 17 00:00:00 2001
From: Phillip Wood <phillip.wood@dunelm.org.uk>
Date: Thu, 14 Mar 2024 17:05:05 +0000
Subject: [PATCH 3/5] merge options: add a conflict style member

Add a conflict_style member to `struct merge_options` and `struct
ll_merge_options` to allow callers to override the default conflict
style. This will be used in the next commit.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 merge-ll.c        | 4 +++-
 merge-ll.h        | 5 ++++-
 merge-ort.c       | 1 +
 merge-recursive.c | 3 +++
 merge-recursive.h | 1 +
 5 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/merge-ll.c b/merge-ll.c
index ef200e4497..34514e8bc6 100644
--- a/merge-ll.c
+++ b/merge-ll.c
@@ -128,7 +128,9 @@ static enum ll_merge_result ll_xdl_merge(const struct ll_merge_driver *drv_unuse
 	xmp.level = XDL_MERGE_ZEALOUS;
 	xmp.favor = opts->variant;
 	xmp.xpp.flags = opts->xdl_opts;
-	if (git_xmerge_style >= 0)
+	if (opts->conflict_style >= 0)
+		xmp.style = opts->conflict_style;
+	else if (git_xmerge_style >= 0)
 		xmp.style = git_xmerge_style;
 	if (marker_size > 0)
 		xmp.marker_size = marker_size;
diff --git a/merge-ll.h b/merge-ll.h
index af1ee36abd..d038ee0c1e 100644
--- a/merge-ll.h
+++ b/merge-ll.h
@@ -78,11 +78,14 @@ struct ll_merge_options {
 	 */
 	unsigned extra_marker_size;
 
+	/* Override the global conflict style. */
+	int conflict_style;
+
 	/* Extra xpparam_t flags as defined in xdiff/xdiff.h. */
 	long xdl_opts;
 };
 
-#define LL_MERGE_OPTIONS_INIT {0}
+#define LL_MERGE_OPTIONS_INIT { .conflict_style = -1 }
 
 enum ll_merge_result {
 	LL_MERGE_ERROR = -1,
diff --git a/merge-ort.c b/merge-ort.c
index 4a02c3ecd9..a9ab403145 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -1966,6 +1966,7 @@ static int merge_3way(struct merge_options *opt,
 	ll_opts.renormalize = opt->renormalize;
 	ll_opts.extra_marker_size = extra_marker_size;
 	ll_opts.xdl_opts = opt->xdl_opts;
+	ll_opts.conflict_style = opt->conflict_style;
 
 	if (opt->priv->call_depth) {
 		ll_opts.virtual_ancestor = 1;
diff --git a/merge-recursive.c b/merge-recursive.c
index 02b7b584f9..33b5f9384e 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -1054,6 +1054,7 @@ static int merge_3way(struct merge_options *opt,
 	ll_opts.renormalize = opt->renormalize;
 	ll_opts.extra_marker_size = extra_marker_size;
 	ll_opts.xdl_opts = opt->xdl_opts;
+	ll_opts.conflict_style = opt->conflict_style;
 
 	if (opt->priv->call_depth) {
 		ll_opts.virtual_ancestor = 1;
@@ -3899,6 +3900,8 @@ void init_merge_options(struct merge_options *opt,
 
 	opt->renormalize = 0;
 
+	opt->conflict_style = -1;
+
 	merge_recursive_config(opt);
 	merge_verbosity = getenv("GIT_MERGE_VERBOSITY");
 	if (merge_verbosity)
diff --git a/merge-recursive.h b/merge-recursive.h
index 3d3b3e3c29..e67d38c303 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -31,6 +31,7 @@ struct merge_options {
 
 	/* xdiff-related options (patience, ignore whitespace, ours/theirs) */
 	long xdl_opts;
+	int conflict_style;
 	enum {
 		MERGE_VARIANT_NORMAL = 0,
 		MERGE_VARIANT_OURS,

From dbeaf8e8c0ada5ba6a8c379e2ad7bab7e815ba79 Mon Sep 17 00:00:00 2001
From: Phillip Wood <phillip.wood@dunelm.org.uk>
Date: Thu, 14 Mar 2024 17:05:06 +0000
Subject: [PATCH 4/5] checkout: cleanup --conflict=<style> parsing

Passing an invalid conflict style name such as "--conflict=bad" gives
the error message

    error: unknown style 'bad' given for 'merge.conflictstyle'

which is unfortunate as it talks about a config setting rather than
the option given on the command line. This happens because the
implementation calls git_xmerge_config() to set the conflict style
using the value given on the command line. Use the newly added
parse_conflict_style_name() instead and pass the value down the call
chain to override the config setting. This also means we can avoid
setting up a struct config_context required for calling
git_xmerge_config().

The option is now parsed in a callback to avoid having to store the
option name. This is a change in behavior as now

    git checkout --conflict=bad --conflict=diff3

will error out when parsing "--conflict=bad" whereas before this change
it would succeed because it would only try to parse the value of the
last "--conflict" option given on the command line.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 builtin/checkout.c | 51 +++++++++++++++++++++++++++++-----------------
 t/t7201-co.sh      |  6 ++++++
 2 files changed, 38 insertions(+), 19 deletions(-)

diff --git a/builtin/checkout.c b/builtin/checkout.c
index e9859a1980..0e5d1af75b 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -91,7 +91,7 @@ struct checkout_opts {
 	int new_branch_log;
 	enum branch_track track;
 	struct diff_options diff_options;
-	char *conflict_style;
+	int conflict_style;
 
 	int branch_exists;
 	const char *prefix;
@@ -100,6 +100,8 @@ struct checkout_opts {
 	struct tree *source_tree;
 };
 
+#define CHECKOUT_OPTS_INIT { .conflict_style = -1 }
+
 struct branch_info {
 	char *name; /* The short name used */
 	char *path; /* The full name of a real branch */
@@ -251,7 +253,8 @@ static int checkout_stage(int stage, const struct cache_entry *ce, int pos,
 }
 
 static int checkout_merged(int pos, const struct checkout *state,
-			   int *nr_checkouts, struct mem_pool *ce_mem_pool)
+			   int *nr_checkouts, struct mem_pool *ce_mem_pool,
+			   int conflict_style)
 {
 	struct cache_entry *ce = the_index.cache[pos];
 	const char *path = ce->name;
@@ -286,6 +289,7 @@ static int checkout_merged(int pos, const struct checkout *state,
 
 	git_config_get_bool("merge.renormalize", &renormalize);
 	ll_opts.renormalize = renormalize;
+	ll_opts.conflict_style = conflict_style;
 	merge_status = ll_merge(&result_buf, path, &ancestor, "base",
 				&ours, "ours", &theirs, "theirs",
 				state->istate, &ll_opts);
@@ -416,7 +420,8 @@ static int checkout_worktree(const struct checkout_opts *opts,
 			else if (opts->merge)
 				errs |= checkout_merged(pos, &state,
 							&nr_unmerged,
-							&ce_mem_pool);
+							&ce_mem_pool,
+							opts->conflict_style);
 			pos = skip_same_name(ce, pos) - 1;
 		}
 	}
@@ -886,6 +891,7 @@ static int merge_working_tree(const struct checkout_opts *opts,
 			}
 			o.branch1 = new_branch_info->name;
 			o.branch2 = "local";
+			o.conflict_style = opts->conflict_style;
 			ret = merge_trees(&o,
 					  new_tree,
 					  work,
@@ -1616,6 +1622,21 @@ static int checkout_branch(struct checkout_opts *opts,
 	return switch_branches(opts, new_branch_info);
 }
 
+static int parse_opt_conflict(const struct option *o, const char *arg, int unset)
+{
+	struct checkout_opts *opts = o->value;
+
+	if (unset) {
+		opts->conflict_style = -1;
+		return 0;
+	}
+	opts->conflict_style = parse_conflict_style_name(arg);
+	if (opts->conflict_style < 0)
+		return error(_("unknown conflict style '%s'"), arg);
+
+	return 0;
+}
+
 static struct option *add_common_options(struct checkout_opts *opts,
 					 struct option *prevopts)
 {
@@ -1626,8 +1647,9 @@ static struct option *add_common_options(struct checkout_opts *opts,
 			    PARSE_OPT_OPTARG, option_parse_recurse_submodules_worktree_updater),
 		OPT_BOOL(0, "progress", &opts->show_progress, N_("force progress reporting")),
 		OPT_BOOL('m', "merge", &opts->merge, N_("perform a 3-way merge with the new branch")),
-		OPT_STRING(0, "conflict", &opts->conflict_style, N_("style"),
-			   N_("conflict style (merge, diff3, or zdiff3)")),
+		OPT_CALLBACK(0, "conflict", opts, N_("style"),
+			     N_("conflict style (merge, diff3, or zdiff3)"),
+			     parse_opt_conflict),
 		OPT_END()
 	};
 	struct option *newopts = parse_options_concat(prevopts, options);
@@ -1718,15 +1740,9 @@ static int checkout_main(int argc, const char **argv, const char *prefix,
 			opts->show_progress = isatty(2);
 	}
 
-	if (opts->conflict_style) {
-		struct key_value_info kvi = KVI_INIT;
-		struct config_context ctx = {
-			.kvi = &kvi,
-		};
+	if (opts->conflict_style >= 0)
 		opts->merge = 1; /* implied */
-		git_xmerge_config("merge.conflictstyle", opts->conflict_style,
-				  &ctx, NULL);
-	}
+
 	if (opts->force) {
 		opts->discard_changes = 1;
 		opts->ignore_unmerged_opt = "--force";
@@ -1891,7 +1907,7 @@ static int checkout_main(int argc, const char **argv, const char *prefix,
 
 int cmd_checkout(int argc, const char **argv, const char *prefix)
 {
-	struct checkout_opts opts;
+	struct checkout_opts opts = CHECKOUT_OPTS_INIT;
 	struct option *options;
 	struct option checkout_options[] = {
 		OPT_STRING('b', NULL, &opts.new_branch, N_("branch"),
@@ -1907,7 +1923,6 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 	int ret;
 	struct branch_info new_branch_info = { 0 };
 
-	memset(&opts, 0, sizeof(opts));
 	opts.dwim_new_local_branch = 1;
 	opts.switch_branch_doing_nothing_is_ok = 1;
 	opts.only_merge_on_switching_branches = 0;
@@ -1946,7 +1961,7 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 
 int cmd_switch(int argc, const char **argv, const char *prefix)
 {
-	struct checkout_opts opts;
+	struct checkout_opts opts = CHECKOUT_OPTS_INIT;
 	struct option *options = NULL;
 	struct option switch_options[] = {
 		OPT_STRING('c', "create", &opts.new_branch, N_("branch"),
@@ -1962,7 +1977,6 @@ int cmd_switch(int argc, const char **argv, const char *prefix)
 	int ret;
 	struct branch_info new_branch_info = { 0 };
 
-	memset(&opts, 0, sizeof(opts));
 	opts.dwim_new_local_branch = 1;
 	opts.accept_ref = 1;
 	opts.accept_pathspec = 0;
@@ -1988,7 +2002,7 @@ int cmd_switch(int argc, const char **argv, const char *prefix)
 
 int cmd_restore(int argc, const char **argv, const char *prefix)
 {
-	struct checkout_opts opts;
+	struct checkout_opts opts = CHECKOUT_OPTS_INIT;
 	struct option *options;
 	struct option restore_options[] = {
 		OPT_STRING('s', "source", &opts.from_treeish, "<tree-ish>",
@@ -2005,7 +2019,6 @@ int cmd_restore(int argc, const char **argv, const char *prefix)
 	int ret;
 	struct branch_info new_branch_info = { 0 };
 
-	memset(&opts, 0, sizeof(opts));
 	opts.accept_ref = 0;
 	opts.accept_pathspec = 1;
 	opts.empty_pathspec_ok = 0;
diff --git a/t/t7201-co.sh b/t/t7201-co.sh
index 10cc6c4605..e1f85a9156 100755
--- a/t/t7201-co.sh
+++ b/t/t7201-co.sh
@@ -631,6 +631,12 @@ test_expect_success 'checkout --conflict=diff3' '
 	test_cmp merged file
 '
 
+test_expect_success 'checkout with invalid conflict style' '
+	test_must_fail git checkout --conflict=bad 2>actual -- file &&
+	echo "error: unknown conflict style ${SQ}bad${SQ}" >expect &&
+	test_cmp expect actual
+'
+
 test_expect_success 'failing checkout -b should not break working tree' '
 	git clean -fd &&  # Remove untracked files in the way
 	git reset --hard main &&

From 5a99c1ac1a9640f7ee0374e9b90523f500bdbb5a Mon Sep 17 00:00:00 2001
From: Phillip Wood <phillip.wood@dunelm.org.uk>
Date: Thu, 14 Mar 2024 17:05:07 +0000
Subject: [PATCH 5/5] checkout: fix interaction between --conflict and --merge

When using "git checkout" to recreate merge conflicts or merge
uncommitted changes when switching branch "--conflict" sensibly implies
"--merge". Unfortunately the way this is implemented means that "git
checkout --conflict=diff3 --no-merge" implies "--merge" violating the
usual last-one-wins rule. Fix this by only overriding the value of
opts->merge if "--conflicts" comes after "--no-merge" or "-[-no]-merge"
is not given on the command line.

The behavior of "git checkout --merge --no-conflict" is unchanged and
will still merge on the basis that the "-[-no]-conflict" options are
primarily intended to affect the conflict style and so "--no-conflict"
should cancel a previous "--conflict" but not override "--merge".

Of the four new tests the second one tests the behavior change
introduced by this commit, the other three check that this commit does
not regress the existing behavior.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 builtin/checkout.c | 10 +++++---
 t/t7201-co.sh      | 60 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 67 insertions(+), 3 deletions(-)

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 0e5d1af75b..30d13c9e14 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -100,7 +100,7 @@ struct checkout_opts {
 	struct tree *source_tree;
 };
 
-#define CHECKOUT_OPTS_INIT { .conflict_style = -1 }
+#define CHECKOUT_OPTS_INIT { .conflict_style = -1, .merge = -1 }
 
 struct branch_info {
 	char *name; /* The short name used */
@@ -1633,6 +1633,9 @@ static int parse_opt_conflict(const struct option *o, const char *arg, int unset
 	opts->conflict_style = parse_conflict_style_name(arg);
 	if (opts->conflict_style < 0)
 		return error(_("unknown conflict style '%s'"), arg);
+	/* --conflict overrides a previous --no-merge */
+	if (!opts->merge)
+		opts->merge = -1;
 
 	return 0;
 }
@@ -1740,8 +1743,9 @@ static int checkout_main(int argc, const char **argv, const char *prefix,
 			opts->show_progress = isatty(2);
 	}
 
-	if (opts->conflict_style >= 0)
-		opts->merge = 1; /* implied */
+	/* --conflicts implies --merge */
+	if (opts->merge == -1)
+		opts->merge = opts->conflict_style >= 0;
 
 	if (opts->force) {
 		opts->discard_changes = 1;
diff --git a/t/t7201-co.sh b/t/t7201-co.sh
index e1f85a9156..42352dc0db 100755
--- a/t/t7201-co.sh
+++ b/t/t7201-co.sh
@@ -631,6 +631,66 @@ test_expect_success 'checkout --conflict=diff3' '
 	test_cmp merged file
 '
 
+test_expect_success 'checkout --conflict=diff3 --no-conflict does not merge' '
+	setup_conflicting_index &&
+	echo "none of the above" >expect &&
+	cat expect >fild &&
+	cat expect >file &&
+	test_must_fail git checkout --conflict=diff3 --no-conflict -- fild file 2>err &&
+	test_cmp expect file &&
+	test_cmp expect fild &&
+	echo "error: path ${SQ}file${SQ} is unmerged" >expect &&
+	test_cmp expect err
+'
+
+test_expect_success 'checkout --conflict=diff3 --no-merge does not merge' '
+	setup_conflicting_index &&
+	echo "none of the above" >expect &&
+	cat expect >fild &&
+	cat expect >file &&
+	test_must_fail git checkout --conflict=diff3 --no-merge -- fild file 2>err &&
+	test_cmp expect file &&
+	test_cmp expect fild &&
+	echo "error: path ${SQ}file${SQ} is unmerged" >expect &&
+	test_cmp expect err
+'
+
+test_expect_success 'checkout --no-merge --conflict=diff3 does merge' '
+	setup_conflicting_index &&
+	echo "none of the above" >fild &&
+	echo "none of the above" >file &&
+	git checkout --no-merge --conflict=diff3 -- fild file &&
+	echo "ourside" >expect &&
+	test_cmp expect fild &&
+	cat >expect <<-\EOF &&
+	<<<<<<< ours
+	ourside
+	||||||| base
+	original
+	=======
+	theirside
+	>>>>>>> theirs
+	EOF
+	test_cmp expect file
+'
+
+test_expect_success 'checkout --merge --conflict=diff3 --no-conflict does merge' '
+	setup_conflicting_index &&
+	echo "none of the above" >fild &&
+	echo "none of the above" >file &&
+	git checkout --merge --conflict=diff3 --no-conflict -- fild file &&
+	echo "ourside" >expect &&
+	test_cmp expect fild &&
+	cat >expect <<-\EOF &&
+	<<<<<<< ours
+	ourside
+	=======
+	theirside
+	>>>>>>> theirs
+	EOF
+	test_cmp expect file
+'
+
 test_expect_success 'checkout with invalid conflict style' '
 	test_must_fail git checkout --conflict=bad 2>actual -- file &&
 	echo "error: unknown conflict style ${SQ}bad${SQ}" >expect &&