[PATCH v2 4/9] mergetools: vimdiff: make vimdiff3 actually work

[Felipe Contreras <felipe.contreras@gmail.com>]

When vimdiff3 was added in 7c147b77d3 (mergetools: add vimdiff3 mode,
2014-04-20), the description made clear the intention:

    It's similar to the default, except that the other windows are
    hidden.  This ensures that removed/added colors are still visible on
    the main merge window, but the other windows not visible.

However, in 0041797449 (vimdiff: new implementation with layout support,
2022-03-30) this was broken by generating a command that never creates
windows, and therefore vim never shows the diff.

In order to show the diff, the windows need to be created first, and
then when they are hidden the diff remains (if hidenoff isn't set).

The layout support implementation broke the whole purpose of vimdiff3,
and simply shows MERGED, which is no different from simply opening the
file with vim.

Setting the `hidden` option makes it work as intended.

Suggested-by: Fernando Ramos <greenfoo@u92.eu>
Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
---
 mergetools/vimdiff | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mergetools/vimdiff b/mergetools/vimdiff
index 103729b6a6..20c61b040b 100644
--- a/mergetools/vimdiff
+++ b/mergetools/vimdiff
@@ -325,7 +325,7 @@ gen_cmd () {
 	if ! echo "$LAYOUT" | grep ",\|/" >/dev/null
 	then
 		buf=$(get_buf "$LAYOUT")
-		FINAL_CMD="-c \"echo | ${buf}b | bufdo diffthis\" -c \"tabfirst\""
+		FINAL_CMD="-c \"echo | set hidden | ${buf}b | bufdo diffthis\" -c \"tabfirst\""
 		return
 	fi
 
@@ -560,7 +560,7 @@ run_unit_tests () {
 	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_04="-c \"echo | set hidden | 4b | bufdo 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\""
-- 
2.37.1.378.g3f95da6bac