Add --symmetricHEADmaster

Signed-off-by: Mattias Andrée <m@maandree.se>

43 files changed, 876 insertions, 30 deletions

diff --git a/Makefile b/Makefile
index e3fc3df..50591ad 100644
--- a/Makefile
+++ b/Makefile
@@ -86,27 +86,36 @@ TEST =\
 	t/combination-select-head-reduce\
 	t/combination-select-tail-reduce\
 	t/combination-merge-reduce\
+	t/combination-symmetric-reduce\
 	t/combination-remove-base-select-head-reduce\
 	t/combination-remove-base-select-tail-reduce\
 	t/combination-remove-base-merge-reduce\
+	t/combination-remove-base-symmetric-reduce\
 	t/combination-remove-base-reduce\
 	t/all-positive-options-merge\
+	t/all-positive-options-symmetric\
 	t/all-positive-options-select-head\
 	t/all-positive-options-select-tail\
 	t/combination-2-select-head\
 	t/combination-2-select-tail\
 	t/combination-2-merge\
+	t/combination-2-symmetric\
 	t/combination-2-remove-base\
 	t/combination-2-interactive\
 	t/combination-select-head-2-no-select-head\
 	t/combination-select-tail-2-no-select-tail\
 	t/combination-merge-2-no-merge\
+	t/combination-symmetric-2-no-symmetric\
 	t/combination-remove-base-2-no-remove-base\
 	t/combination-interactive-2-no-interactive\
 	t/merge-short-option\
+	t/symmetric-short-option\
+	t/reduce-short-option\
 	t/interactive-short-option\
 	t/no-option-merge-yes-no\
 	t/no-option-merge-no-yes\
+	t/no-option-symmetric-yes-no\
+	t/no-option-symmetric-no-yes\
 	t/no-option-remove-base-yes-no\
 	t/no-option-remove-base-no-yes\
 	t/no-option-select-head-yes-no\
@@ -120,6 +129,7 @@ TEST =\
 	t/no-option-select-head-yes-then-select-tail-yes-no\
 	t/no-option-select-tail-yes-then-select-head-yes-no\
 	t/no-option-merge\
+	t/no-option-symmetric\
 	t/no-option-remove-base\
 	t/no-option-select-head\
 	t/no-option-select-tail\
@@ -172,6 +182,29 @@ TEST =\
 	t/merge-empty-head\
 	t/merge-empty-base\
 	t/merge-empty-tail\
+	t/symmetric-1\
+	t/symmetric-2-different\
+	t/symmetric-2-identical\
+	t/symmetric-3-different-head\
+	t/symmetric-3-different-tail\
+	t/symmetric-3-different-base\
+	t/symmetric-3-all-different\
+	t/symmetric-3-all-identical\
+	t/symmetric-4-different-upper-middle\
+	t/symmetric-4-different-lower-middle\
+	t/symmetric-4-unique-different-middles\
+	t/symmetric-4-same-different-middles\
+	t/symmetric-4-identical\
+	t/symmetric-4-different-head\
+	t/symmetric-4-different-tail\
+	t/symmetric-5-different-upper-middle\
+	t/symmetric-5-different-lower-middle\
+	t/symmetric-no-conflicts\
+	t/symmetric-multiple-conflicts\
+	t/symmetric-multiple-files\
+	t/symmetric-3-empty-head\
+	t/symmetric-3-empty-tail\
+	t/symmetric-3-empty-head-tail\
 	t/marker-size-10\
 	t/marker-size-3\
 	t/marker-size-shorter-ignored\
diff --git a/README b/README
index 0816f27..9940917 100644
--- a/README
+++ b/README
@@ -2,7 +2,8 @@ NAME
 	git-rediff - Reduce partially resolved merge conflicts
 
 SYNOPSIS
-	git rediff [--no-reduce] [--merge|--select-head|--select-tail] [--remove-base] [-i] [<path>...]
+	git rediff [--merge|--symmetric|--select-head|--select-tail]
+	           [--remove-base] [--no-reduce] [-i] [<path>...]
 
 DESCRIPTION
 	git rediff rewrites files containing merge conflicts to
@@ -11,8 +12,8 @@ DESCRIPTION
 OPTIONS
 	-i
 	--interactive
-		Interactively select the action for each merge conflict.
-		See INTERACTIVE COMMANDS.
+		Interactively select the action for each merge
+		conflict. See INTERACTIVE COMMANDS.
 
 		This overrides all other options.
 
@@ -21,24 +22,39 @@ OPTIONS
 
 	-m
 	--merge
-		For conflicts with at least three branches, select the sole branch
-		whose content differs from all other identical branches, but only
-		if that is the top or bottom branch.
+		For conflicts with at least three branches, select
+		the sole branch whose content differs from all other
+		identical branches, but only if that is the top or
+		bottom branch.
 
 		Applied before --remove-base.
 
 	--no-merge
 		Disable --merge.
 
+	-y
+	--symmetric
+		When the top and bottom branches are identical, select
+		their content if all other branches are identical to
+		each other.
+
+		Applied before --reduce.
+
+	--no-symmetric
+		Disable --symmetric.
+
+	-r
 	--reduce
 		Enable reduction of remaining conflicts. (Default)
 
 	--no-reduce
-		Do not reduce remaining conflicts after --merge, --remove-base,
-		--select-head, and --select-tail have been applied.
+		Do not reduce remaining conflicts after --merge,
+		--remove-base, --select-head, and --select-tail have
+		been applied.
 
 	--remove-base
-		Remove the middle branch from three-way merge conflicts.
+		Remove the middle branch from three-way merge
+		conflicts.
 
 		Applied before --reduce.
 
@@ -46,7 +62,8 @@ OPTIONS
 		Disable --remove-base.
 
 	--select-head
-		Resolve each merge conflict by selecting its top branch.
+		Resolve each merge conflict by selecting its top
+		branch.
 
 		Applied before --reduce.
 
@@ -54,7 +71,8 @@ OPTIONS
 		Disable --select-head.
 
 	--select-tail
-		Resolve each merge conflict by selecting its bottom branch.
+		Resolve each merge conflict by selecting its bottom
+		branch.
 
 		Applied before --reduce.
 
@@ -71,15 +89,19 @@ INTERACTIVE COMMANDS
 
 	m	Apply merge selection.
 
+	y	Select symmetric branches.
+
 	r	Reduce the conflict.
 
 	e	Manually edit the conflict.
 
 	s	Skip the conflict.
 
-	d	Skip the conflict and all later conflicts in the current file.
+	d	Skip the conflict and all later conflicts in the
+		current file.
 
-	q	Quit interaction and skip the conflict and all remaining conflicts.
+	q	Quit interaction and skip the conflict and all
+		remaining conflicts.
 
 	?	Display help.
 
diff --git a/git-rediff.1 b/git-rediff.1
index 84598d5..e06a9fb 100644
--- a/git-rediff.1
+++ b/git-rediff.1
@@ -3,9 +3,9 @@
 git-rediff - Reduce partially resolved merge conflicts
 .SH SYNOPSIS
 .B git rediff
-.RB [ --no-reduce ]
-.RB [ --merge | --select-head | --select-tail ]
+.RB [ --merge | --symmetric | --select-head | --select-tail ]
 .RB [ --remove-base ]
+.RB [ --no-reduce ]
 .RB [ -i ]
 .RI [ <path> "...]"
 .SH DESCRIPTION
@@ -40,6 +40,21 @@ Applied before
 Disable
 .BR --merge .
 .TP
+.B -y
+.TQ
+.B --symmetric
+When the top and bottom branches are identical, select their
+content if all other branches are identical to each other.
+
+Applied before
+.BR --reduce .
+.TP
+.B --no-symmetric
+Disable
+.BR --symmetric .
+.TP
+.B -r
+.TQ
 .B --reduce
 Enable reduction of remaining conflicts. (Default)
 .TP
@@ -95,6 +110,9 @@ Remove the middle branch (three-way conflicts only).
 .B m
 Apply merge selection.
 .TP
+.B y
+Select symmetric branches.
+.TP
 .B r
 Reduce the conflict.
 .TP
diff --git a/git-rediff.c b/git-rediff.c
index e856504..0dc68c4 100644
--- a/git-rediff.c
+++ b/git-rediff.c
@@ -8,7 +8,7 @@
 #include <signal.h>
 #include <termios.h>
 
-NUSAGE(2, "[--no-reduce] [--merge|--select-head|--select-tail] [--remove-base] [-i] [<path>...]");
+NUSAGE(2, "[--merge|--symmetric|--select-head|--select-tail] [--remove-base] [--no-reduce] [-i] [<path>...]");
 
 #if defined(__clang__)
 # pragma clang diagnostic ignored "-Wunsafe-buffer-usage"
@@ -41,6 +41,7 @@ static int ttyfd_out = -1;
 #endif
 static struct stat tty_st;
 static int merge = 0;
+static int symmetric = 0;
 static int remove_base = 0;
 static int select_head = 0;
 static int select_tail = 0;
@@ -552,6 +553,7 @@ display_help(size_t nsubhunks)
 	if (nsubhunks == 3U)
 		dprintf(ttyfd_out, "b - remove base\n");
 	dprintf(ttyfd_out, "m - merge\n");
+	dprintf(ttyfd_out, "y - select symmetric branches\n");
 	dprintf(ttyfd_out, "r - reduce\n");
 	dprintf(ttyfd_out, "e - manually edit this hunk\n");
 	dprintf(ttyfd_out, "s - skip this hunk\n");
@@ -627,7 +629,7 @@ get_command(size_t nsubhunks, size_t number, size_t total)
 	int matched = 0;
 
 again:
-	dprintf(ttyfd_out, "\033[1;34m(%zu/%zu) Resolve this conflict [h,t,b,m,r,e,s,d,q,?]? \033[0m", number, total);
+	dprintf(ttyfd_out, "\033[1;34m(%zu/%zu) Resolve this conflict [h,t,b,m,y,r,e,s,d,q,?]? \033[0m", number, total);
 
 	for (;;) {
 		n = read(ttyfd_in, &c, 1);
@@ -653,6 +655,7 @@ again:
 	matched |= select_head = c == 'h';
 	matched |= select_tail = c == 't';
 	matched |= merge       = c == 'm';
+	matched |= symmetric   = c == 'y';
 	matched |= reduce      = c == 'r';
 	matched |= remove_base = c == 'b';
 	matched |= /* skip = */  c == 's';
@@ -806,6 +809,14 @@ rediff_hunk(struct text *resp, const struct hunk *hunk, const struct line *tail)
 		else
 			goto genuine_conflict;
 		return MERGED;
+	} else if (symmetric) {
+		if (!texts_equal(&hunk->subs[0].text, &hunk->subs[hunk->nsubs - 1U].text))
+			goto genuine_conflict;
+		for (i = 2U; i < hunk->nsubs - 1U; i++)
+			if (!texts_equal(&hunk->subs[i].text, &hunk->subs[1U].text))
+				goto genuine_conflict;
+		append_text(resp, &hunk->subs[0].text);
+		return MERGED;
 	}
 genuine_conflict:
 
@@ -1134,8 +1145,12 @@ main(int argc, char *argv[])
 			case 'm': merge = 1;
 		else if (TESTLONG("--no-merge", 0))
 			merge = 0;
+		else if (TESTLONG("--symmetric", 0))
+			case 'y': symmetric = 1;
+		else if (TESTLONG("--no-symmetric", 0))
+			symmetric = 0;
 		else if (TESTLONG("--reduce", 0))
-			reduce = 1;
+			case 'r': reduce = 1;
 		else if (TESTLONG("--no-reduce", 0))
 			reduce = 0;
 		else if (TESTLONG("--remove-base", 0))
@@ -1157,7 +1172,7 @@ main(int argc, char *argv[])
 		usage();
 	} ARGEND;
 
-	if (merge + select_head + select_tail > 1)
+	if (merge + symmetric + select_head + select_tail > 1)
 		usage();
 
 	originally_interactive = interactive;
diff --git a/t/all-positive-options-symmetric b/t/all-positive-options-symmetric
new file mode 100755
index 0000000..eb53cb9
--- /dev/null
+++ b/t/all-positive-options-symmetric
@@ -0,0 +1,23 @@
+#!/bin/sh -e
+. t/common.sh
+interactive
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	same \
+	ours \
+	"${PARENT} base" \
+	same \
+	base \
+	"${TAIL}" \
+	same \
+	theirs \
+	"${END} theirs"
+
+printf '%s\n' > file.expected \
+	same \
+	ours
+
+printf '%s' h > input
+normal --symmetric --remove-base --reduce --interactive file 8<input 9>output
+test -s output
diff --git a/t/combination-2-symmetric b/t/combination-2-symmetric
new file mode 100755
index 0000000..059897d
--- /dev/null
+++ b/t/combination-2-symmetric
@@ -0,0 +1,22 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	same \
+	new \
+	"${PARENT} base" \
+	same \
+	old \
+	"${TAIL}" \
+	same \
+	new \
+	"${END} theirs"
+
+printf '%s\n' > file.expected \
+	same \
+	new
+
+normal --symmetric --symmetric --no-reduce file
+
+also_interactive y
diff --git a/t/combination-remove-base-symmetric-reduce b/t/combination-remove-base-symmetric-reduce
new file mode 100755
index 0000000..c4b1cf9
--- /dev/null
+++ b/t/combination-remove-base-symmetric-reduce
@@ -0,0 +1,34 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	first \
+	"${PARENT} base" \
+	not-first \
+	"${TAIL}" \
+	first \
+	"${END} theirs" \
+	"${HEAD} ours" \
+	ours \
+	common \
+	"${PARENT} base" \
+	base \
+	common \
+	"${TAIL}" \
+	theirs \
+	common \
+	"${END} theirs"
+
+printf '%s\n' > file.expected \
+	first \
+	"${HEAD} ours" \
+	ours \
+	"${TAIL}" \
+	theirs \
+	"${END} theirs" \
+	common
+
+conflict --remove-base --symmetric --reduce file
+
+also_interactive yy
diff --git a/t/combination-symmetric-2-no-symmetric b/t/combination-symmetric-2-no-symmetric
new file mode 100755
index 0000000..6aaf0e0
--- /dev/null
+++ b/t/combination-symmetric-2-no-symmetric
@@ -0,0 +1,28 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	same \
+	new \
+	"${PARENT} base" \
+	same \
+	old \
+	"${TAIL}" \
+	same \
+	new \
+	"${END} theirs"
+
+printf '%s\n' > file.expected \
+	same \
+	"${HEAD} ours" \
+	new \
+	"${PARENT} base" \
+	old \
+	"${TAIL}" \
+	new \
+	"${END} theirs"
+
+conflict --symmetric --no-symmetric --no-symmetric file
+
+also_interactive r
diff --git a/t/combination-symmetric-reduce b/t/combination-symmetric-reduce
new file mode 100755
index 0000000..e5e370a
--- /dev/null
+++ b/t/combination-symmetric-reduce
@@ -0,0 +1,36 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	first \
+	"${PARENT} base" \
+	not-first \
+	"${TAIL}" \
+	first \
+	"${END} theirs" \
+	"${HEAD} ours" \
+	ours \
+	common \
+	"${PARENT} base" \
+	base \
+	common \
+	"${TAIL}" \
+	theirs \
+	common \
+	"${END} theirs"
+
+printf '%s\n' > file.expected \
+	first \
+	"${HEAD} ours" \
+	ours \
+	"${PARENT} base" \
+	base \
+	"${TAIL}" \
+	theirs \
+	"${END} theirs" \
+	common
+
+conflict --symmetric --reduce file
+
+also_interactive yr
diff --git a/t/common.sh b/t/common.sh
index 30e4b6e..38d2845 100644
--- a/t/common.sh
+++ b/t/common.sh
@@ -141,7 +141,7 @@ interactive_filename () {
 
 interactive_prompt () {
 	test $# = 2
-	printf '\e[1;34m(%s/%s) Resolve this conflict [h,t,b,m,r,e,s,d,q,?]? \e[0m\n' "$1" "$2"
+	printf '\e[1;34m(%s/%s) Resolve this conflict [h,t,b,m,y,r,e,s,d,q,?]? \e[0m\n' "$1" "$2"
 }
 
 interactive_help () {
@@ -155,6 +155,7 @@ interactive_help () {
 	fi
 	printf '%s\n' \
 		'm - merge' \
+		'y - select symmetric branches' \
 		'r - reduce' \
 		'e - manually edit this hunk' \
 		's - skip this hunk' \
diff --git a/t/invalid-option-combinations b/t/invalid-option-combinations
index 527ce63..1a75005 100755
--- a/t/invalid-option-combinations
+++ b/t/invalid-option-combinations
@@ -16,5 +16,54 @@ error --select-head --merge --select-tail file
 error --select-head --select-tail --merge file
 error --select-tail --merge --select-head file
 error --select-tail --select-head --merge file
+error --symmetric --merge file
+error --merge --symmetric file
+error --symmetric --select-head file
+error --select-head --symmetric file
+error --symmetric --select-tail file
+error --select-tail --symmetric file
+error --symmetric --merge --select-head file
+error --symmetric --select-head --merge file
+error --symmetric --merge --select-tail file
+error --symmetric --select-tail --merge file
+error --symmetric --select-head --select-tail file
+error --symmetric --select-tail --select-head file
+error --merge --symmetric --select-head file
+error --select-head --symmetric --merge file
+error --merge --symmetric --select-tail file
+error --select-tail --symmetric --merge file
+error --select-head --symmetric --select-tail file
+error --select-tail --symmetric --select-head file
+error --merge --select-head --symmetric file
+error --select-head --merge --symmetric file
+error --merge --select-tail --symmetric file
+error --select-tail --merge --symmetric file
+error --select-head --select-tail --symmetric file
+error --select-tail --select-head --symmetric file
+error --symmetric --merge --select-head --select-tail file
+error --symmetric --merge --select-tail --select-head file
+error --symmetric --select-head --merge --select-tail file
+error --symmetric --select-head --select-tail --merge file
+error --symmetric --select-tail --merge --select-head file
+error --symmetric --select-tail --select-head --merge file
+error --merge --symmetric --select-head --select-tail file
+error --merge --symmetric --select-tail --select-head file
+error --select-head --symmetric --merge --select-tail file
+error --select-head --symmetric --select-tail --merge file
+error --select-tail --symmetric --merge --select-head file
+error --select-tail --symmetric --select-head --merge file
+error --merge --select-head --symmetric --select-tail file
+error --merge --select-tail --symmetric --select-head file
+error --select-head --merge --symmetric --select-tail file
+error --select-head --select-tail --symmetric --merge file
+error --select-tail --merge --symmetric --select-head file
+error --select-tail --select-head --symmetric --merge file
+error --merge --select-head --select-tail --symmetric file
+error --merge --select-tail --select-head --symmetric file
+error --select-head --merge --select-tail --symmetric file
+error --select-head --select-tail --merge --symmetric file
+error --select-tail --merge --select-head --symmetric file
+error --select-tail --select-head --merge --symmetric file
+
 error --unknown-option file
 error '-$' file
diff --git a/t/no-option-merge b/t/no-option-merge
index 5f55d74..8f9a63e 100755
--- a/t/no-option-merge
+++ b/t/no-option-merge
@@ -4,23 +4,23 @@
 printf '%s\n' > file \
 	"${HEAD} ours" \
 	same \
-	ours \
+	new \
 	"${PARENT} base" \
 	same \
-	base \
+	old \
 	"${TAIL}" \
 	same \
-	theirs \
+	old \
 	"${END} theirs"
 
 printf '%s\n' > file.expected \
 	same \
 	"${HEAD} ours" \
-	ours \
+	new \
 	"${PARENT} base" \
-	base \
+	old \
 	"${TAIL}" \
-	theirs \
+	old \
 	"${END} theirs"
 
 conflict --no-merge file
diff --git a/t/no-option-merge-yes-no b/t/no-option-merge-yes-no
index f351e7c..af35ed8 100755
--- a/t/no-option-merge-yes-no
+++ b/t/no-option-merge-yes-no
@@ -3,11 +3,11 @@
 
 printf '%s\n' > file \
 	"${HEAD} ours" \
-	ours \
+	old \
 	"${PARENT} base" \
-	base \
+	old \
 	"${TAIL}" \
-	theirs \
+	new \
 	"${END} theirs"
 
 cp -- file file.expected
diff --git a/t/no-option-reduce-no-yes b/t/no-option-reduce-no-yes
index e6a7d8c..9078a9b 100755
--- a/t/no-option-reduce-no-yes
+++ b/t/no-option-reduce-no-yes
@@ -3,14 +3,25 @@
 
 printf '%s\n' > file \
 	"${HEAD} ours" \
+	same \
 	ours \
 	"${PARENT} base" \
+	same \
 	base \
 	"${TAIL}" \
+	same \
 	theirs \
 	"${END} theirs"
 
-cp -- file file.expected
+printf '%s\n' > file.expected \
+	same \
+	"${HEAD} ours" \
+	ours \
+	"${PARENT} base" \
+	base \
+	"${TAIL}" \
+	theirs \
+	"${END} theirs"
 
 conflict --no-reduce --reduce file
 
diff --git a/t/no-option-reduce-yes-no b/t/no-option-reduce-yes-no
index 82fa7bd..8a55b15 100755
--- a/t/no-option-reduce-yes-no
+++ b/t/no-option-reduce-yes-no
@@ -3,10 +3,13 @@
 
 printf '%s\n' > file \
 	"${HEAD} ours" \
+	same \
 	ours \
 	"${PARENT} base" \
+	same \
 	base \
 	"${TAIL}" \
+	same \
 	theirs \
 	"${END} theirs"
 
diff --git a/t/no-option-symmetric b/t/no-option-symmetric
new file mode 100755
index 0000000..82d6b73
--- /dev/null
+++ b/t/no-option-symmetric
@@ -0,0 +1,28 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	same \
+	new \
+	"${PARENT} base" \
+	same \
+	old \
+	"${TAIL}" \
+	same \
+	new \
+	"${END} theirs"
+
+printf '%s\n' > file.expected \
+	same \
+	"${HEAD} ours" \
+	new \
+	"${PARENT} base" \
+	old \
+	"${TAIL}" \
+	new \
+	"${END} theirs"
+
+conflict --no-symmetric file
+
+also_interactive r
diff --git a/t/no-option-symmetric-no-yes b/t/no-option-symmetric-no-yes
new file mode 100755
index 0000000..45954cb
--- /dev/null
+++ b/t/no-option-symmetric-no-yes
@@ -0,0 +1,18 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	new \
+	"${PARENT} base" \
+	old \
+	"${TAIL}" \
+	new \
+	"${END} theirs"
+
+printf '%s\n' > file.expected \
+	new
+
+normal --no-symmetric --symmetric --no-reduce file
+
+also_interactive y
diff --git a/t/no-option-symmetric-yes-no b/t/no-option-symmetric-yes-no
new file mode 100755
index 0000000..415467c
--- /dev/null
+++ b/t/no-option-symmetric-yes-no
@@ -0,0 +1,17 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	same \
+	"${PARENT} base" \
+	base \
+	"${TAIL}" \
+	same \
+	"${END} theirs"
+
+cp -- file file.expected
+
+conflict --symmetric --no-symmetric --no-reduce file
+
+also_interactive r
diff --git a/t/reduce-short-option b/t/reduce-short-option
new file mode 100755
index 0000000..0e2b5b7
--- /dev/null
+++ b/t/reduce-short-option
@@ -0,0 +1,26 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} 1" \
+	common-first \
+	head-second \
+	common-third \
+	"${TAIL} 2" \
+	common-first \
+	tail-second \
+	common-third \
+	"${END} 2"
+
+printf '%s\n' > file.expected \
+	common-first \
+	"${HEAD} 1" \
+	head-second \
+	"${TAIL} 2" \
+	tail-second \
+	"${END} 2" \
+	common-third
+
+conflict -r file
+
+also_interactive r
diff --git a/t/symmetric-1 b/t/symmetric-1
new file mode 100755
index 0000000..f0d1a4b
--- /dev/null
+++ b/t/symmetric-1
@@ -0,0 +1,11 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} only" \
+	only \
+	"${END} only"
+
+cp -- file file.expected
+
+error --symmetric --no-reduce file
diff --git a/t/symmetric-2-different b/t/symmetric-2-different
new file mode 100755
index 0000000..889e4ed
--- /dev/null
+++ b/t/symmetric-2-different
@@ -0,0 +1,15 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	ours \
+	"${TAIL}" \
+	theirs \
+	"${END} theirs"
+
+cp -- file file.expected
+
+conflict --symmetric --no-reduce file
+
+also_interactive y
diff --git a/t/symmetric-2-identical b/t/symmetric-2-identical
new file mode 100755
index 0000000..90f8369
--- /dev/null
+++ b/t/symmetric-2-identical
@@ -0,0 +1,16 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	same \
+	"${TAIL}" \
+	same \
+	"${END} theirs"
+
+printf '%s\n' > file.expected \
+	same
+
+normal --symmetric --no-reduce file
+
+also_interactive y
diff --git a/t/symmetric-3-all-different b/t/symmetric-3-all-different
new file mode 100755
index 0000000..0693a80
--- /dev/null
+++ b/t/symmetric-3-all-different
@@ -0,0 +1,17 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	first \
+	"${PARENT} 2" \
+	second \
+	"${TAIL}" \
+	third \
+	"${END} theirs"
+
+cp -- file file.expected
+
+conflict --symmetric --no-reduce file
+
+also_interactive y
diff --git a/t/symmetric-3-all-identical b/t/symmetric-3-all-identical
new file mode 100755
index 0000000..986d367
--- /dev/null
+++ b/t/symmetric-3-all-identical
@@ -0,0 +1,18 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	same \
+	"${PARENT} 2" \
+	same \
+	"${TAIL}" \
+	same \
+	"${END} theirs"
+
+printf '%s\n' > file.expected \
+	same
+
+normal --symmetric --no-reduce file
+
+also_interactive y
diff --git a/t/symmetric-3-different-base b/t/symmetric-3-different-base
new file mode 100755
index 0000000..176c212
--- /dev/null
+++ b/t/symmetric-3-different-base
@@ -0,0 +1,18 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	same \
+	"${PARENT} 2" \
+	different \
+	"${TAIL}" \
+	same \
+	"${END} theirs"
+
+printf '%s\n' > file.expected \
+	same
+
+normal --symmetric --no-reduce file
+
+also_interactive y
diff --git a/t/symmetric-3-different-head b/t/symmetric-3-different-head
new file mode 100755
index 0000000..435d828
--- /dev/null
+++ b/t/symmetric-3-different-head
@@ -0,0 +1,17 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	different \
+	"${PARENT} 2" \
+	same \
+	"${TAIL}" \
+	same \
+	"${END} theirs"
+
+cp -- file file.expected
+
+conflict --symmetric --no-reduce file
+
+also_interactive y
diff --git a/t/symmetric-3-different-tail b/t/symmetric-3-different-tail
new file mode 100755
index 0000000..733c7d3
--- /dev/null
+++ b/t/symmetric-3-different-tail
@@ -0,0 +1,17 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	same \
+	"${PARENT} 2" \
+	same \
+	"${TAIL}" \
+	different \
+	"${END} theirs"
+
+cp -- file file.expected
+
+conflict --symmetric --no-reduce file
+
+also_interactive y
diff --git a/t/symmetric-3-empty-head b/t/symmetric-3-empty-head
new file mode 100755
index 0000000..af61802
--- /dev/null
+++ b/t/symmetric-3-empty-head
@@ -0,0 +1,16 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	"${PARENT} 2" \
+	2 \
+	"${TAIL}" \
+	2 \
+	"${END} theirs"
+
+cp -- file file.expected
+
+conflict --symmetric --no-reduce file
+
+also_interactive y
diff --git a/t/symmetric-3-empty-head-tail b/t/symmetric-3-empty-head-tail
new file mode 100755
index 0000000..f93cd84
--- /dev/null
+++ b/t/symmetric-3-empty-head-tail
@@ -0,0 +1,15 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	"${PARENT} 2" \
+	base \
+	"${TAIL}" \
+	"${END} theirs"
+
+: > file.expected
+
+normal --symmetric --no-reduce file
+
+also_interactive y
diff --git a/t/symmetric-3-empty-tail b/t/symmetric-3-empty-tail
new file mode 100755
index 0000000..bbd4e7a
--- /dev/null
+++ b/t/symmetric-3-empty-tail
@@ -0,0 +1,16 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	1 \
+	"${PARENT} 2" \
+	1 \
+	"${TAIL}" \
+	"${END} theirs"
+
+cp -- file file.expected
+
+conflict --symmetric --no-reduce file
+
+also_interactive y
diff --git a/t/symmetric-4-different-head b/t/symmetric-4-different-head
new file mode 100755
index 0000000..0d4d704
--- /dev/null
+++ b/t/symmetric-4-different-head
@@ -0,0 +1,19 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	different \
+	"${PARENT} 2" \
+	same \
+	"${PARENT} 3" \
+	same \
+	"${TAIL}" \
+	same \
+	"${END} theirs"
+
+cp -- file file.expected
+
+conflict --symmetric --no-reduce file
+
+also_interactive y
diff --git a/t/symmetric-4-different-lower-middle b/t/symmetric-4-different-lower-middle
new file mode 100755
index 0000000..f8c334e
--- /dev/null
+++ b/t/symmetric-4-different-lower-middle
@@ -0,0 +1,19 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	same \
+	"${PARENT} 2" \
+	same \
+	"${PARENT} 3" \
+	different \
+	"${TAIL}" \
+	same \
+	"${END} theirs"
+
+cp -- file file.expected
+
+conflict --symmetric --no-reduce file
+
+also_interactive y
diff --git a/t/symmetric-4-different-tail b/t/symmetric-4-different-tail
new file mode 100755
index 0000000..1bf80ff
--- /dev/null
+++ b/t/symmetric-4-different-tail
@@ -0,0 +1,19 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	same \
+	"${PARENT} 2" \
+	same \
+	"${PARENT} 3" \
+	same \
+	"${TAIL}" \
+	different \
+	"${END} theirs"
+
+cp -- file file.expected
+
+conflict --symmetric --no-reduce file
+
+also_interactive y
diff --git a/t/symmetric-4-different-upper-middle b/t/symmetric-4-different-upper-middle
new file mode 100755
index 0000000..d78a5a2
--- /dev/null
+++ b/t/symmetric-4-different-upper-middle
@@ -0,0 +1,19 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	same \
+	"${PARENT} 2" \
+	different \
+	"${PARENT} 3" \
+	same \
+	"${TAIL}" \
+	same \
+	"${END} theirs"
+
+cp -- file file.expected
+
+conflict --symmetric --no-reduce file
+
+also_interactive y
diff --git a/t/symmetric-4-identical b/t/symmetric-4-identical
new file mode 100755
index 0000000..40c82d7
--- /dev/null
+++ b/t/symmetric-4-identical
@@ -0,0 +1,20 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	same \
+	"${PARENT} 2" \
+	same \
+	"${PARENT} 3" \
+	same \
+	"${TAIL}" \
+	same \
+	"${END} theirs"
+
+printf '%s\n' > file.expected \
+	same
+
+normal --symmetric --no-reduce file
+
+also_interactive y
diff --git a/t/symmetric-4-same-different-middles b/t/symmetric-4-same-different-middles
new file mode 100755
index 0000000..9d95e43
--- /dev/null
+++ b/t/symmetric-4-same-different-middles
@@ -0,0 +1,25 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	new \
+	new \
+	"${PARENT} 2" \
+	old \
+	old \
+	"${PARENT} 3" \
+	old \
+	old \
+	"${TAIL}" \
+	new \
+	new \
+	"${END} theirs"
+
+printf '%s\n' > file.expected \
+	new \
+	new
+
+normal --symmetric --no-reduce file
+
+also_interactive y
diff --git a/t/symmetric-4-unique-different-middles b/t/symmetric-4-unique-different-middles
new file mode 100755
index 0000000..1b76187
--- /dev/null
+++ b/t/symmetric-4-unique-different-middles
@@ -0,0 +1,23 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	same \
+	"${PARENT} 2" \
+	common \
+	first \
+	common \
+	"${PARENT} 3" \
+	common \
+	second \
+	common \
+	"${TAIL}" \
+	same \
+	"${END} theirs"
+
+cp -- file file.expected
+
+conflict --symmetric --no-reduce file
+
+also_interactive y
diff --git a/t/symmetric-5-different-lower-middle b/t/symmetric-5-different-lower-middle
new file mode 100755
index 0000000..530ea01
--- /dev/null
+++ b/t/symmetric-5-different-lower-middle
@@ -0,0 +1,21 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	same \
+	"${PARENT} 2" \
+	same \
+	"${PARENT} 3" \
+	same \
+	"${PARENT} 4" \
+	different \
+	"${TAIL}" \
+	same \
+	"${END} theirs"
+
+cp -- file file.expected
+
+conflict --symmetric --no-reduce file
+
+also_interactive y
diff --git a/t/symmetric-5-different-upper-middle b/t/symmetric-5-different-upper-middle
new file mode 100755
index 0000000..b2fe2dd
--- /dev/null
+++ b/t/symmetric-5-different-upper-middle
@@ -0,0 +1,21 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	same \
+	"${PARENT} 2" \
+	different \
+	"${PARENT} 3" \
+	add \
+	"${PARENT} 4" \
+	add \
+	"${TAIL}" \
+	same \
+	"${END} theirs"
+
+cp -- file file.expected
+
+conflict --symmetric --no-reduce file
+
+also_interactive y
diff --git a/t/symmetric-multiple-conflicts b/t/symmetric-multiple-conflicts
new file mode 100755
index 0000000..713a96c
--- /dev/null
+++ b/t/symmetric-multiple-conflicts
@@ -0,0 +1,42 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	before \
+	"${HEAD} ours" \
+	same \
+	"${PARENT} base" \
+	different-interior \
+	"${TAIL}" \
+	same \
+	"${END} theirs" \
+	between \
+	"${HEAD} ours" \
+	different-head \
+	"${PARENT} base" \
+	interior \
+	"${PARENT} other" \
+	interior \
+	"${TAIL}" \
+	same \
+	"${END} theirs" \
+	after
+
+printf '%s\n' > file.expected \
+	before \
+	same \
+	between \
+	"${HEAD} ours" \
+	different-head \
+	"${PARENT} base" \
+	interior \
+	"${PARENT} other" \
+	interior \
+	"${TAIL}" \
+	same \
+	"${END} theirs" \
+	after
+
+conflict --symmetric --no-reduce file
+
+also_interactive yy
diff --git a/t/symmetric-multiple-files b/t/symmetric-multiple-files
new file mode 100755
index 0000000..86d2235
--- /dev/null
+++ b/t/symmetric-multiple-files
@@ -0,0 +1,29 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > first \
+	"${HEAD} ours" \
+	same \
+	"${PARENT} base" \
+	different \
+	"${TAIL}" \
+	same \
+	"${END} theirs"
+
+printf '%s\n' > first.expected \
+	same
+
+printf '%s\n' > second \
+	"${HEAD} ours" \
+	different \
+	"${PARENT} base" \
+	interior \
+	"${TAIL}" \
+	same \
+	"${END} theirs"
+
+cp -- second second.expected
+
+conflict --symmetric --no-reduce first second
+
+also_interactive yy
diff --git a/t/symmetric-no-conflicts b/t/symmetric-no-conflicts
new file mode 100755
index 0000000..d7c8c7f
--- /dev/null
+++ b/t/symmetric-no-conflicts
@@ -0,0 +1,11 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	no conflicts in this file
+
+cp -- file file.expected
+
+normal --symmetric --no-reduce file
+
+also_interactive ''
diff --git a/t/symmetric-short-option b/t/symmetric-short-option
new file mode 100755
index 0000000..66c257a
--- /dev/null
+++ b/t/symmetric-short-option
@@ -0,0 +1,18 @@
+#!/bin/sh -e
+. t/common.sh
+
+printf '%s\n' > file \
+	"${HEAD} ours" \
+	same \
+	"${PARENT} base" \
+	different \
+	"${TAIL}" \
+	same \
+	"${END} theirs"
+
+printf '%s\n' > file.expected \
+	same
+
+normal -y --no-reduce file
+
+also_interactive y