Merge branch 'km/mergetool-vimdiff-layout-fallback'

Variants of vimdiff learned to honor mergetool.<variant>.layout settings.

* km/mergetool-vimdiff-layout-fallback:
  mergetools: vimdiff: use correct tool's name when reading mergetool config

Documentation/config/mergetool.txt

@@ -45,14 +45,21 @@ mergetool.meld.useAutoMerge::
 	value of `false` avoids using `--auto-merge` altogether, and is the
 	default value.
 
-mergetool.vimdiff.layout::
-	The vimdiff backend uses this variable to control how its split
-	windows appear. Applies even if you are using Neovim (`nvim`) or
-	gVim (`gvim`) as the merge tool. See BACKEND SPECIFIC HINTS section
-ifndef::git-mergetool[]
-	in linkgit:git-mergetool[1].
+mergetool.<vimdiff variant>.layout::
+	Configure the split window layout for vimdiff's `<variant>`, which is any of `vimdiff`,
+	`nvimdiff`, `gvimdiff`.
+	Upon launching `git mergetool` with `--tool=<variant>` (or without `--tool`
+	if `merge.tool` is configured as `<variant>`), Git will consult
+	`mergetool.<variant>.layout` to determine the tool's layout. If the
+	variant-specific configuration is not available, `vimdiff`'s is used as
+	fallback.  If that too is not available, a default layout with 4 windows
+	will be used.  To configure the layout, see the `BACKEND SPECIFIC HINTS`
+ifdef::git-mergetool[]
+	section.
+endif::[]
+ifndef::git-mergetool[]
+	section in linkgit:git-mergetool[1].
 endif::[]
-	for details.
 
 mergetool.hideResolved::
 	During a merge, Git will automatically resolve as many conflicts as

Documentation/mergetools/vimdiff.txt

@@ -177,7 +177,8 @@ Instead of `--tool=vimdiff`, you can also use one of these other variants:
 
 When using these variants, in order to specify a custom layout you will have to
 set configuration variables `mergetool.gvimdiff.layout` and
-`mergetool.nvimdiff.layout` instead of `mergetool.vimdiff.layout`
+`mergetool.nvimdiff.layout` instead of `mergetool.vimdiff.layout` (though the
+latter will be used as fallback if the variant-specific one is not set).
 
 In addition, for backwards compatibility with previous Git versions, you can
 also append `1`, `2` or `3` to either `vimdiff` or any of the variants (ex:

mergetools/vimdiff

@@ -371,9 +371,17 @@ diff_cmd_help () {
 
 
 merge_cmd () {
-	layout=$(git config mergetool.vimdiff.layout)
+	TOOL=$1
 
-	case "$1" in
+	layout=$(git config "mergetool.$TOOL.layout")
+
+	# backward compatibility:
+	if test -z "$layout"
+	then
+		layout=$(git config mergetool.vimdiff.layout)
+	fi
+
+	case "$TOOL" in
 	*vimdiff)
 		if test -z "$layout"
 		then