contrib/difftool: use a separate config namespace for difftool commands

Some users have different mergetool and difftool settings, so teach
difftool to read config vars from the difftool.* namespace.  This allows
having distinct configurations for the diff and merge scenarios.

We don't want to force existing users to set new values for no reason
so difftool falls back to existing mergetool config variables when the
difftool equivalents are not defined.

Signed-off-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

3 files changed, 32 insertions, 23 deletions

diff --git a/contrib/difftool/git-difftool b/contrib/difftool/git-difftool
index 0cda3d2eea..0deda3a0e4 100755
--- a/contrib/difftool/git-difftool
+++ b/contrib/difftool/git-difftool
@@ -4,7 +4,7 @@
 # This is a wrapper around the GIT_EXTERNAL_DIFF-compatible
 # git-difftool-helper script.  This script exports
 # GIT_EXTERNAL_DIFF and GIT_PAGER for use by git, and
-# GIT_DIFFTOOL_NO_PROMPT and GIT_MERGE_TOOL for use by git-difftool-helper.
+# GIT_DIFFTOOL_NO_PROMPT and GIT_DIFF_TOOL for use by git-difftool-helper.
 # Any arguments that are unknown to this script are forwarded to 'git diff'.
 
 use strict;
@@ -49,12 +49,12 @@ sub generate_command
 		}
 		if ($arg eq '-t' or $arg eq '--tool') {
 			usage() if $#ARGV <= $idx;
-			$ENV{GIT_MERGE_TOOL} = $ARGV[$idx + 1];
+			$ENV{GIT_DIFF_TOOL} = $ARGV[$idx + 1];
 			$skip_next = 1;
 			next;
 		}
 		if ($arg =~ /^--tool=/) {
-			$ENV{GIT_MERGE_TOOL} = substr($arg, 7);
+			$ENV{GIT_DIFF_TOOL} = substr($arg, 7);
 			next;
 		}
 		if ($arg eq '--no-prompt') {
diff --git a/contrib/difftool/git-difftool-helper b/contrib/difftool/git-difftool-helper
index db3af6a833..9c0a13452a 100755
--- a/contrib/difftool/git-difftool-helper
+++ b/contrib/difftool/git-difftool-helper
@@ -128,8 +128,10 @@ launch_merge_tool () {
 	cleanup_temp_files
 }
 
-# Verifies that mergetool.<tool>.cmd exists
+# Verifies that (difftool|mergetool).<tool>.cmd exists
 valid_custom_tool() {
+	merge_tool_cmd="$(git config difftool.$1.cmd)"
+	test -z "$merge_tool_cmd" &&
 	merge_tool_cmd="$(git config mergetool.$1.cmd)"
 	test -n "$merge_tool_cmd"
 }
@@ -150,8 +152,11 @@ valid_tool() {
 }
 
 # Sets up the merge_tool_path variable.
-# This handles the mergetool.<tool>.path configuration.
+# This handles the difftool.<tool>.path configuration.
+# This also falls back to mergetool defaults.
 init_merge_tool_path() {
+	merge_tool_path=$(git config difftool."$1".path)
+	test -z "$merge_tool_path" &&
 	merge_tool_path=$(git config mergetool."$1".path)
 	if test -z "$merge_tool_path"; then
 		case "$1" in
@@ -165,15 +170,19 @@ init_merge_tool_path() {
 	fi
 }
 
-# Allow the GIT_MERGE_TOOL variable to provide a default value
+# Allow GIT_DIFF_TOOL and GIT_MERGE_TOOL to provide default values
 test -n "$GIT_MERGE_TOOL" && merge_tool="$GIT_MERGE_TOOL"
+test -n "$GIT_DIFF_TOOL" && merge_tool="$GIT_DIFF_TOOL"
 
-# If not merge tool was specified then use the merge.tool
+# If merge tool was not specified then use the diff.tool
 # configuration variable.  If that's invalid then reset merge_tool.
+# Fallback to merge.tool.
 if test -z "$merge_tool"; then
+	merge_tool=$(git config diff.tool)
+	test -z "$merge_tool" &&
 	merge_tool=$(git config merge.tool)
 	if test -n "$merge_tool" && ! valid_tool "$merge_tool"; then
-		echo >&2 "git config option merge.tool set to unknown tool: $merge_tool"
+		echo >&2 "git config option diff.tool set to unknown tool: $merge_tool"
 		echo >&2 "Resetting to default..."
 		unset merge_tool
 	fi
diff --git a/contrib/difftool/git-difftool.txt b/contrib/difftool/git-difftool.txt
index 6e2610cda6..2b7bc03ec3 100644
--- a/contrib/difftool/git-difftool.txt
+++ b/contrib/difftool/git-difftool.txt
@@ -32,23 +32,23 @@ OPTIONS
 	vimdiff, gvimdiff, ecmerge, and opendiff
 +
 If a merge resolution program is not specified, 'git-difftool'
-will use the configuration variable `merge.tool`.  If the
-configuration variable `merge.tool` is not set, 'git difftool'
+will use the configuration variable `diff.tool`.  If the
+configuration variable `diff.tool` is not set, 'git-difftool'
 will pick a suitable default.
 +
 You can explicitly provide a full path to the tool by setting the
-configuration variable `mergetool.<tool>.path`. For example, you
+configuration variable `difftool.<tool>.path`. For example, you
 can configure the absolute path to kdiff3 by setting
-`mergetool.kdiff3.path`. Otherwise, 'git-difftool' assumes the
+`difftool.kdiff3.path`. Otherwise, 'git-difftool' assumes the
 tool is available in PATH.
 +
 Instead of running one of the known merge tool programs,
 'git-difftool' can be customized to run an alternative program
 by specifying the command line to invoke in a configuration
-variable `mergetool.<tool>.cmd`.
+variable `difftool.<tool>.cmd`.
 +
 When 'git-difftool' is invoked with this tool (either through the
-`-t` or `--tool` option or the `merge.tool` configuration variable)
+`-t` or `--tool` option or the `diff.tool` configuration variable)
 the configured command line will be invoked with the following
 variables available: `$LOCAL` is set to the name of the temporary
 file containing the contents of the diff pre-image and `$REMOTE`
@@ -61,24 +61,24 @@ with custom merge tool commands and has the same value as `$LOCAL`.
 
 CONFIG VARIABLES
 ----------------
-merge.tool::
-	The default merge tool to use.
-+
-See the `--tool=<tool>` option above for more details.
+'git-difftool' falls back to 'git-mergetool' config variables when the
+difftool equivalents have not been defined.
 
-merge.keepBackup::
-	The original, unedited file content can be saved to a file with
-	a `.orig` extension.  Defaults to `true` (i.e. keep the backup files).
+diff.tool::
+	The default merge tool to use.
 
-mergetool.<tool>.path::
+difftool.<tool>.path::
 	Override the path for the given tool.  This is useful in case
 	your tool is not in the PATH.
 
-mergetool.<tool>.cmd::
+difftool.<tool>.cmd::
 	Specify the command to invoke the specified merge tool.
 +
 See the `--tool=<tool>` option above for more details.
 
+merge.keepBackup::
+	The original, unedited file content can be saved to a file with
+	a `.orig` extension.  Defaults to `true` (i.e. keep the backup files).
 
 SEE ALSO
 --------