merge(3p/git): Merge git subtree at v2.29.2

This also bumps the stable nixpkgs to 20.09 as of 2020-11-21, because
there is some breakage in the git build related to the netrc
credentials helper which someone has taken care of in nixpkgs.

The stable channel is not used for anything other than git, so this
should be fine.

Change-Id: I3575a19dab09e1e9556cf8231d717de9890484fb

third_party/git/mergetools/bc

@@ -21,3 +21,8 @@ translate_merge_tool_path() {
 		echo bcompare
 	fi
 }
+
+list_tool_variants () {
+	echo bc
+	echo bc3
+}

third_party/git/mergetools/bc3

@@ -1 +0,0 @@
-. "$MERGE_TOOLS_DIR/bc"

third_party/git/mergetools/gvimdiff3

@@ -1 +0,0 @@
-. "$MERGE_TOOLS_DIR/vimdiff"

third_party/git/mergetools/meld

@@ -3,34 +3,87 @@ diff_cmd () {
 }
 
 merge_cmd () {
-	if test -z "${meld_has_output_option:+set}"
+	check_meld_for_features
+
+	option_auto_merge=
+	if test "$meld_use_auto_merge_option" = true
 	then
-		check_meld_for_output_version
+		option_auto_merge="--auto-merge"
 	fi
 
 	if test "$meld_has_output_option" = true
 	then
-		"$merge_tool_path" --output="$MERGED" \
+		"$merge_tool_path" $option_auto_merge --output="$MERGED" \
 			"$LOCAL" "$BASE" "$REMOTE"
 	else
-		"$merge_tool_path" "$LOCAL" "$MERGED" "$REMOTE"
+		"$merge_tool_path" $option_auto_merge "$LOCAL" "$MERGED" "$REMOTE"
 	fi
 }
 
-# Check whether we should use 'meld --output <file>'
-check_meld_for_output_version () {
-	meld_path="$(git config mergetool.meld.path)"
-	meld_path="${meld_path:-meld}"
-
-	if meld_has_output_option=$(git config --bool mergetool.meld.hasOutput)
+# Get meld help message
+init_meld_help_msg () {
+	if test -z "$meld_help_msg"
 	then
-		: use configured value
-	elif "$meld_path" --help 2>&1 |
-		grep -e '--output=' -e '\[OPTION\.\.\.\]' >/dev/null
-	then
-		: old ones mention --output and new ones just say OPTION...
-		meld_has_output_option=true
-	else
-		meld_has_output_option=false
+		meld_path="$(git config mergetool.meld.path || echo meld)"
+		meld_help_msg=$("$meld_path" --help 2>&1)
+	fi
+}
+
+# Check the features and set flags
+check_meld_for_features () {
+	# Check whether we should use 'meld --output <file>'
+	if test -z "$meld_has_output_option"
+	then
+		meld_has_output_option=$(git config --bool mergetool.meld.hasOutput)
+		case "$meld_has_output_option" in
+		true | false)
+			: use configured value
+			;;
+		*)
+			: empty or invalid configured value, detecting "--output" automatically
+			init_meld_help_msg
+
+			case "$meld_help_msg" in
+			*"--output="* | *'[OPTION...]'*)
+				# All version that has [OPTION...] supports --output
+				meld_has_output_option=true
+				;;
+			*)
+				meld_has_output_option=false
+				;;
+			esac
+			;;
+		esac
+	fi
+	# Check whether we should use 'meld --auto-merge ...'
+	if test -z "$meld_use_auto_merge_option"
+	then
+		meld_use_auto_merge_option=$(
+			git config --bool-or-str mergetool.meld.useAutoMerge
+		)
+		case "$meld_use_auto_merge_option" in
+		true | false)
+			: use well formatted boolean value
+			;;
+		auto)
+			# testing the "--auto-merge" option only if config is "auto"
+			init_meld_help_msg
+
+			case "$meld_help_msg" in
+			*"--auto-merge"* | *'[OPTION...]'*)
+				meld_use_auto_merge_option=true
+				;;
+			*)
+				meld_use_auto_merge_option=false
+				;;
+			esac
+			;;
+		"")
+			meld_use_auto_merge_option=false
+			;;
+		*)
+			die "unknown mergetool.meld.useAutoMerge: $meld_use_auto_merge_option"
+			;;
+		esac
 	fi
 }

third_party/git/mergetools/vimdiff

@@ -5,7 +5,7 @@ diff_cmd () {
 
 merge_cmd () {
 	case "$1" in
-	gvimdiff|vimdiff)
+	*vimdiff)
 		if $base_present
 		then
 			"$merge_tool_path" -f -d -c '4wincmd w | wincmd J' \
@@ -15,11 +15,11 @@ merge_cmd () {
 				"$LOCAL" "$MERGED" "$REMOTE"
 		fi
 		;;
-	gvimdiff2|vimdiff2)
+	*vimdiff2)
 		"$merge_tool_path" -f -d -c 'wincmd l' \
 			"$LOCAL" "$MERGED" "$REMOTE"
 		;;
-	gvimdiff3|vimdiff3)
+	*vimdiff3)
 		if $base_present
 		then
 			"$merge_tool_path" -f -d -c 'hid | hid | hid' \
@@ -34,10 +34,13 @@ merge_cmd () {
 
 translate_merge_tool_path() {
 	case "$1" in
-	gvimdiff|gvimdiff2|gvimdiff3)
+	nvimdiff*)
+		echo nvim
+		;;
+	gvimdiff*)
 		echo gvim
 		;;
-	vimdiff|vimdiff2|vimdiff3)
+	vimdiff*)
 		echo vim
 		;;
 	esac
@@ -46,3 +49,11 @@ translate_merge_tool_path() {
 exit_code_trustable () {
 	true
 }
+
+list_tool_variants () {
+	for prefix in '' g n; do
+		for suffix in '' 2 3; do
+			echo "${prefix}vimdiff${suffix}"
+		done
+	done
+}

third_party/git/mergetools/vimdiff2

@@ -1 +0,0 @@
-. "$MERGE_TOOLS_DIR/vimdiff"

third_party/git/mergetools/vimdiff3

@@ -1 +0,0 @@
-. "$MERGE_TOOLS_DIR/vimdiff"