vimdiff: make layout engine more robust against user vim settings

'vim' has two configuration options ('splitbelow' and 'splitright') that
change the way the 'split' command behaves. When they are set, the
commands that the layout engine generates no longer work as expected.

In order to fix this we can append special keyword 'leftabove' to each
'split' and 'vertical split' subcommand found inside the command string
generated by the layout engine.

This works because whatever comes after 'leftabove' will temporally
ignore settings 'splitbelow' and 'splitright'.

Reported-by: Matthew Klein <[email protected]>
Signed-off-by: Fernando Ramos <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: greenfoo

mergetools/vimdiff

@@ -228,14 +228,14 @@ gen_cmd_aux () {
 
 	elif ! test -z "$index_horizontal_split"
 	then
-		before="split"
+		before="leftabove split"
 		after="wincmd j"
 		index=$index_horizontal_split
 		terminate="true"
 
 	elif ! test -z "$index_vertical_split"
 	then
-		before="vertical split"
+		before="leftabove vertical split"
 		after="wincmd l"
 		index=$index_vertical_split
 		terminate="true"
@@ -310,7 +310,7 @@ gen_cmd () {
 	#
 	#     gen_cmd "@LOCAL , REMOTE"
 	#     |
-	#     `-> FINAL_CMD    == "-c \"echo | vertical split | 1b | wincmd l | 3b | tabdo windo diffthis\" -c \"tabfirst\""
+	#     `-> FINAL_CMD    == "-c \"echo | leftabove vertical split | 1b | wincmd l | 3b | tabdo windo diffthis\" -c \"tabfirst\""
 	#         FINAL_TARGET == "LOCAL"
 
 	LAYOUT=$1
@@ -555,22 +555,22 @@ run_unit_tests () {
 	TEST_CASE_15="  ((  (LOCAL , BASE , REMOTE) / MERGED))   +(BASE)   , LOCAL+ BASE , REMOTE+ (((LOCAL / BASE / REMOTE)) ,    MERGED   )  "
 	TEST_CASE_16="LOCAL,BASE,REMOTE / MERGED + BASE,LOCAL + BASE,REMOTE + (LOCAL / BASE / REMOTE),MERGED"
 
-	EXPECTED_CMD_01="-c \"echo | split | vertical split | 1b | wincmd l | vertical split | 2b | wincmd l | 3b | wincmd j | 4b | tabdo windo diffthis\" -c \"tabfirst\""
-	EXPECTED_CMD_02="-c \"echo | vertical split | 1b | wincmd l | 3b | tabdo windo diffthis\" -c \"tabfirst\""
-	EXPECTED_CMD_03="-c \"echo | vertical split | 1b | wincmd l | vertical split | 4b | wincmd l | 3b | tabdo windo diffthis\" -c \"tabfirst\""
+	EXPECTED_CMD_01="-c \"echo | leftabove split | leftabove vertical split | 1b | wincmd l | leftabove vertical split | 2b | wincmd l | 3b | wincmd j | 4b | tabdo windo diffthis\" -c \"tabfirst\""
+	EXPECTED_CMD_02="-c \"echo | leftabove vertical split | 1b | wincmd l | 3b | tabdo windo diffthis\" -c \"tabfirst\""
+	EXPECTED_CMD_03="-c \"echo | leftabove vertical split | 1b | wincmd l | leftabove vertical split | 4b | wincmd l | 3b | tabdo windo diffthis\" -c \"tabfirst\""
 	EXPECTED_CMD_04="-c \"echo | 4b | bufdo diffthis\" -c \"tabfirst\""
-	EXPECTED_CMD_05="-c \"echo | split | 1b | wincmd j | split | 4b | wincmd j | 3b | tabdo windo diffthis\" -c \"tabfirst\""
-	EXPECTED_CMD_06="-c \"echo | vertical split | split | 1b | wincmd j | 3b | wincmd l | 4b | tabdo windo diffthis\" -c \"tabfirst\""
-	EXPECTED_CMD_07="-c \"echo | vertical split | 4b | wincmd l | split | 1b | wincmd j | 3b | tabdo windo diffthis\" -c \"tabfirst\""
-	EXPECTED_CMD_08="-c \"echo | split | vertical split | 1b | wincmd l | 3b | wincmd j | 4b | tabdo windo diffthis\" -c \"tabfirst\""
-	EXPECTED_CMD_09="-c \"echo | split | 4b | wincmd j | vertical split | 1b | wincmd l | 3b | tabdo windo diffthis\" -c \"tabfirst\""
-	EXPECTED_CMD_10="-c \"echo | vertical split | split | 1b | wincmd j | split | 2b | wincmd j | 3b | wincmd l | 4b | tabdo windo diffthis\" -c \"tabfirst\""
-	EXPECTED_CMD_11="-c \"echo | -tabnew | split | vertical split | 1b | wincmd l | vertical split | 2b | wincmd l | 3b | wincmd j | 4b | tabnext | -tabnew | vertical split | 2b | wincmd l | 1b | tabnext | -tabnew | vertical split | 2b | wincmd l | 3b | tabnext | vertical split | split | 1b | wincmd j | split | 2b | wincmd j | 3b | wincmd l | 4b | tabdo windo diffthis\" -c \"tabfirst\""
-	EXPECTED_CMD_12="-c \"echo | vertical split | split | vertical split | 1b | wincmd l | 3b | wincmd j | 2b | wincmd l | 4b | tabdo windo diffthis\" -c \"tabfirst\""
-	EXPECTED_CMD_13="-c \"echo | vertical split | split | vertical split | 1b | wincmd l | 3b | wincmd j | 2b | wincmd l | vertical split | split | 1b | wincmd j | 3b | wincmd l | 4b | tabdo windo diffthis\" -c \"tabfirst\""
-	EXPECTED_CMD_14="-c \"echo | -tabnew | vertical split | 2b | wincmd l | 3b | tabnext | vertical split | 2b | wincmd l | 1b | tabdo windo diffthis\" -c \"tabfirst\""
-	EXPECTED_CMD_15="-c \"echo | -tabnew | split | vertical split | 1b | wincmd l | vertical split | 2b | wincmd l | 3b | wincmd j | 4b | tabnext | -tabnew | vertical split | 2b | wincmd l | 1b | tabnext | -tabnew | vertical split | 2b | wincmd l | 3b | tabnext | vertical split | split | 1b | wincmd j | split | 2b | wincmd j | 3b | wincmd l | 4b | tabdo windo diffthis\" -c \"tabfirst\""
-	EXPECTED_CMD_16="-c \"echo | -tabnew | split | vertical split | 1b | wincmd l | vertical split | 2b | wincmd l | 3b | wincmd j | 4b | tabnext | -tabnew | vertical split | 2b | wincmd l | 1b | tabnext | -tabnew | vertical split | 2b | wincmd l | 3b | tabnext | vertical split | split | 1b | wincmd j | split | 2b | wincmd j | 3b | wincmd l | 4b | tabdo windo diffthis\" -c \"tabfirst\""
+	EXPECTED_CMD_05="-c \"echo | leftabove split | 1b | wincmd j | leftabove split | 4b | wincmd j | 3b | tabdo windo diffthis\" -c \"tabfirst\""
+	EXPECTED_CMD_06="-c \"echo | leftabove vertical split | leftabove split | 1b | wincmd j | 3b | wincmd l | 4b | tabdo windo diffthis\" -c \"tabfirst\""
+	EXPECTED_CMD_07="-c \"echo | leftabove vertical split | 4b | wincmd l | leftabove split | 1b | wincmd j | 3b | tabdo windo diffthis\" -c \"tabfirst\""
+	EXPECTED_CMD_08="-c \"echo | leftabove split | leftabove vertical split | 1b | wincmd l | 3b | wincmd j | 4b | tabdo windo diffthis\" -c \"tabfirst\""
+	EXPECTED_CMD_09="-c \"echo | leftabove split | 4b | wincmd j | leftabove vertical split | 1b | wincmd l | 3b | tabdo windo diffthis\" -c \"tabfirst\""
+	EXPECTED_CMD_10="-c \"echo | leftabove vertical split | leftabove split | 1b | wincmd j | leftabove split | 2b | wincmd j | 3b | wincmd l | 4b | tabdo windo diffthis\" -c \"tabfirst\""
+	EXPECTED_CMD_11="-c \"echo | -tabnew | leftabove split | leftabove vertical split | 1b | wincmd l | leftabove vertical split | 2b | wincmd l | 3b | wincmd j | 4b | tabnext | -tabnew | leftabove vertical split | 2b | wincmd l | 1b | tabnext | -tabnew | leftabove vertical split | 2b | wincmd l | 3b | tabnext | leftabove vertical split | leftabove split | 1b | wincmd j | leftabove split | 2b | wincmd j | 3b | wincmd l | 4b | tabdo windo diffthis\" -c \"tabfirst\""
+	EXPECTED_CMD_12="-c \"echo | leftabove vertical split | leftabove split | leftabove vertical split | 1b | wincmd l | 3b | wincmd j | 2b | wincmd l | 4b | tabdo windo diffthis\" -c \"tabfirst\""
+	EXPECTED_CMD_13="-c \"echo | leftabove vertical split | leftabove split | leftabove vertical split | 1b | wincmd l | 3b | wincmd j | 2b | wincmd l | leftabove vertical split | leftabove split | 1b | wincmd j | 3b | wincmd l | 4b | tabdo windo diffthis\" -c \"tabfirst\""
+	EXPECTED_CMD_14="-c \"echo | -tabnew | leftabove vertical split | 2b | wincmd l | 3b | tabnext | leftabove vertical split | 2b | wincmd l | 1b | tabdo windo diffthis\" -c \"tabfirst\""
+	EXPECTED_CMD_15="-c \"echo | -tabnew | leftabove split | leftabove vertical split | 1b | wincmd l | leftabove vertical split | 2b | wincmd l | 3b | wincmd j | 4b | tabnext | -tabnew | leftabove vertical split | 2b | wincmd l | 1b | tabnext | -tabnew | leftabove vertical split | 2b | wincmd l | 3b | tabnext | leftabove vertical split | leftabove split | 1b | wincmd j | leftabove split | 2b | wincmd j | 3b | wincmd l | 4b | tabdo windo diffthis\" -c \"tabfirst\""
+	EXPECTED_CMD_16="-c \"echo | -tabnew | leftabove split | leftabove vertical split | 1b | wincmd l | leftabove vertical split | 2b | wincmd l | 3b | wincmd j | 4b | tabnext | -tabnew | leftabove vertical split | 2b | wincmd l | 1b | tabnext | -tabnew | leftabove vertical split | 2b | wincmd l | 3b | tabnext | leftabove vertical split | leftabove split | 1b | wincmd j | leftabove split | 2b | wincmd j | 3b | wincmd l | 4b | tabdo windo diffthis\" -c \"tabfirst\""
 
 	EXPECTED_TARGET_01="MERGED"
 	EXPECTED_TARGET_02="LOCAL"