[PATCH v2 2/5] mergetool: use get_merge_tool_guessed function

[Denton Liu <liu.denton@gmail.com>]

In git-mergetool, the logic for getting which merge tool to use is
duplicated in git-mergetool--lib, except for the fact that it needs to
know whether the tool was guessed or not.

Write `get_merge_tool_guessed` to return whether or not the tool was
guessed in addition to the actual tool and make git-mergetool call this
function instead of duplicating the logic. Also, let
`$GIT_MERGETOOL_GUI` be set to determine whether or not the guitool will
be selected.

Make `get_merge_tool` use this function internally so that code
duplication is reduced.

Signed-off-by: Denton Liu <liu.denton@gmail.com>
---

After thinking about it for a while, I realised that if it was easy to
find one (albeit old) public project using our code, there should be
many others who we don't know about that will also be using our code.

Let's save them the trouble and just introduce a new function instead of
changing the behaviour of the old one.

---
 Documentation/git-mergetool--lib.txt |  9 ++++++++-
 git-mergetool--lib.sh                | 12 +++++++++---
 git-mergetool.sh                     | 11 +++--------
 3 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/Documentation/git-mergetool--lib.txt b/Documentation/git-mergetool--lib.txt
index 055550b2bc..343268d885 100644
--- a/Documentation/git-mergetool--lib.txt
+++ b/Documentation/git-mergetool--lib.txt
@@ -27,8 +27,15 @@ to define the operation mode for the functions listed below.
 
 FUNCTIONS
 ---------
+get_merge_tool_guessed::
+	returns '$is_guessed:$merge_tool'. '$is_guessed' is 'true' if
+	the tool was guessed, else 'false'. '$merge_tool' is the merge
+	tool to use. '$GIT_MERGETOOL_GUI' may be set to 'true' to search
+	for the appropriate guitool.
+
 get_merge_tool::
-	returns a merge tool.
+	returns a merge tool. '$GIT_MERGETOOL_GUI' may be set to 'true'
+	to search for the appropriate guitool.
 
 get_merge_tool_cmd::
 	returns the custom command for a merge tool.
diff --git a/git-mergetool--lib.sh b/git-mergetool--lib.sh
index 83bf52494c..5eedb1a08a 100644
--- a/git-mergetool--lib.sh
+++ b/git-mergetool--lib.sh
@@ -402,15 +402,21 @@ get_merge_tool_path () {
 	echo "$merge_tool_path"
 }
 
-get_merge_tool () {
+get_merge_tool_guessed () {
+	is_guessed=false
 	# Check if a merge tool has been configured
-	merge_tool=$(get_configured_merge_tool)
+	merge_tool=$(get_configured_merge_tool $GIT_MERGETOOL_GUI)
 	# Try to guess an appropriate merge tool if no tool has been set.
 	if test -z "$merge_tool"
 	then
 		merge_tool=$(guess_merge_tool) || exit
+		is_guessed=true
 	fi
-	echo "$merge_tool"
+	echo "$is_guessed:$merge_tool"
+}
+
+get_merge_tool () {
+	get_merge_tool_guessed | sed -e 's/^[a-z]*://'
 }
 
 mergetool_find_win32_cmd () {
diff --git a/git-mergetool.sh b/git-mergetool.sh
index 01b9ad59b2..63e4da1b2f 100755
--- a/git-mergetool.sh
+++ b/git-mergetool.sh
@@ -449,14 +449,9 @@ main () {
 
 	if test -z "$merge_tool"
 	then
-		# Check if a merge tool has been configured
-		merge_tool=$(get_configured_merge_tool $gui_tool)
-		# Try to guess an appropriate merge tool if no tool has been set.
-		if test -z "$merge_tool"
-		then
-			merge_tool=$(guess_merge_tool) || exit
-			guessed_merge_tool=true
-		fi
+		IFS=':' read guessed_merge_tool merge_tool <<-EOF
+		$(GIT_MERGETOOL_GUI=$gui_tool get_merge_tool_guessed)
+		EOF
 	fi
 	merge_keep_backup="$(git config --bool mergetool.keepBackup || echo true)"
 	merge_keep_temporaries="$(git config --bool mergetool.keepTemporaries || echo false)"
-- 
2.21.0.1000.g11cd861522