[PATCH 1/2] mergetools: vimdiff3: make it work as intended

[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.

We could restore the correct behavior by modifying gen_cmd to open all
the windows, and then hide them, but there's no need to do that when the
-d option of vim (vimdiff) does precisely that.

So let's skip the whole gen_cmd function for vimdiff3, and hide the
windows, therefore restoring the previous intended behavior.

Cc: Fernando Ramos <greenfoo@u92.eu>
Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
---
 mergetools/vimdiff | 38 ++++++++++++++++++++++++--------------
 1 file changed, 24 insertions(+), 14 deletions(-)

diff --git a/mergetools/vimdiff b/mergetools/vimdiff
index f770b8fe24..f4c3bf6d11 100644
--- a/mergetools/vimdiff
+++ b/mergetools/vimdiff
@@ -388,26 +388,36 @@ merge_cmd () {
 	layout=$(git config mergetool.vimdiff.layout)
 
 	case "$1" in
-	*vimdiff)
-		if test -z "$layout"
+	*vimdiff3)
+		if $base_present
 		then
-			# Default layout when none is specified
-			layout="(LOCAL,BASE,REMOTE)/MERGED"
+			CMD='hid | hid | hid'
+		else
+			CMD='hid | hid'
 		fi
+		FINAL_CMD="-d -c '$CMD'"
 		;;
-	*vimdiff1)
-		layout="@LOCAL,REMOTE"
-		;;
-	*vimdiff2)
-		layout="LOCAL,MERGED,REMOTE"
-		;;
-	*vimdiff3)
-		layout="MERGED"
+	*)
+		case "$1" in
+		*vimdiff)
+			if test -z "$layout"
+			then
+				# Default layout when none is specified
+				layout="(LOCAL,BASE,REMOTE)/MERGED"
+			fi
+			;;
+		*vimdiff1)
+			layout="@LOCAL,REMOTE"
+			;;
+		*vimdiff2)
+			layout="LOCAL,MERGED,REMOTE"
+			;;
+		esac
+
+		gen_cmd "$layout"
 		;;
 	esac
 
-	gen_cmd "$layout"
-
 	debug_print ""
 	debug_print "FINAL CMD : $FINAL_CMD"
 	debug_print "FINAL TAR : $FINAL_TARGET"
-- 
2.37.1.313.ge269dbcbc5