merge(3p/git): Merge git subtree at v2.29.2 r/1890

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

8 files changed, 90 insertions, 25 deletions

diff --git a/third_party/git/mergetools/bc b/third_party/git/mergetools/bc
index 3a69e60faa9c..a89086ee720f 100644
--- a/third_party/git/mergetools/bc
+++ b/third_party/git/mergetools/bc
@@ -21,3 +21,8 @@ translate_merge_tool_path() {
 		echo bcompare
 	fi
 }
+
+list_tool_variants () {
+	echo bc
+	echo bc3
+}
diff --git a/third_party/git/mergetools/bc3 b/third_party/git/mergetools/bc3
deleted file mode 100644
index 5d8dd4818488..000000000000
--- a/third_party/git/mergetools/bc3
+++ /dev/null
@@ -1 +0,0 @@
-. "$MERGE_TOOLS_DIR/bc"
diff --git a/third_party/git/mergetools/gvimdiff3 b/third_party/git/mergetools/gvimdiff3
deleted file mode 100644
index 04a5bb0ea848..000000000000
--- a/third_party/git/mergetools/gvimdiff3
+++ /dev/null
@@ -1 +0,0 @@
-. "$MERGE_TOOLS_DIR/vimdiff"
diff --git a/third_party/git/mergetools/meld b/third_party/git/mergetools/meld
index 7a08470f8836..aab4ebb9355a 100644
--- a/third_party/git/mergetools/meld
+++ b/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}"
+# Get meld help message
+init_meld_help_msg () {
+	if test -z "$meld_help_msg"
+	then
+		meld_path="$(git config mergetool.meld.path || echo meld)"
+		meld_help_msg=$("$meld_path" --help 2>&1)
+	fi
+}
 
-	if meld_has_output_option=$(git config --bool mergetool.meld.hasOutput)
+# Check the features and set flags
+check_meld_for_features () {
+	# Check whether we should use 'meld --output <file>'
+	if test -z "$meld_has_output_option"
 	then
-		: use configured value
-	elif "$meld_path" --help 2>&1 |
-		grep -e '--output=' -e '\[OPTION\.\.\.\]' >/dev/null
+		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
-		: old ones mention --output and new ones just say OPTION...
-		meld_has_output_option=true
-	else
-		meld_has_output_option=false
+		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
 }
diff --git a/third_party/git/mergetools/gvimdiff2 b/third_party/git/mergetools/nvimdiff
index 04a5bb0ea848..04a5bb0ea848 100644
--- a/third_party/git/mergetools/gvimdiff2
+++ b/third_party/git/mergetools/nvimdiff
diff --git a/third_party/git/mergetools/vimdiff b/third_party/git/mergetools/vimdiff
index 10d86f3e1930..abc8ce4ec44e 100644
--- a/third_party/git/mergetools/vimdiff
+++ b/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${suffix}"
+		done
+	done
+}
diff --git a/third_party/git/mergetools/vimdiff2 b/third_party/git/mergetools/vimdiff2
deleted file mode 100644
index 04a5bb0ea848..000000000000
--- a/third_party/git/mergetools/vimdiff2
+++ /dev/null
@@ -1 +0,0 @@
-. "$MERGE_TOOLS_DIR/vimdiff"
diff --git a/third_party/git/mergetools/vimdiff3 b/third_party/git/mergetools/vimdiff3
deleted file mode 100644
index 04a5bb0ea848..000000000000
--- a/third_party/git/mergetools/vimdiff3
+++ /dev/null
@@ -1 +0,0 @@
-. "$MERGE_TOOLS_DIR/vimdiff"