mergetool: new config guiDefault supports auto-toggling gui by DISPLAY

When no merge.tool or diff.tool is configured or manually selected, the
selection of a default tool is sensitive to the DISPLAY variable; in a
GUI session a gui-specific tool will be proposed if found, and
otherwise a terminal-based one. This "GUI-optimizing" behavior is
important because a GUI can make a huge difference to a user's ability
to understand and correctly complete a non-trivial conflicting merge.

Some time ago the merge.guitool and diff.guitool config options were
introduced to enable users to configure both a GUI tool, and a non-GUI
tool (with fallback if no GUI tool configured), in the same environment.

Unfortunately, the --gui argument introduced to support the selection of
the guitool is still explicit. When using configured tools, there is no
equivalent of the no-tool-configured "propose a GUI tool if we are in a GUI
environment" behavior.

As proposed in <xmqqmtb8jsej.fsf@gitster.g>, introduce new configuration
options, difftool.guiDefault and mergetool.guiDefault, supporting a special
value "auto" which causes the corresponding tool or guitool to be selected
depending on the presence of a non-empty DISPLAY value. Also support "true"
to say "default to the guitool (unless --no-gui is passed on the
commandline)", and "false" as the previous default behavior when these new
configuration options are not specified.

Signed-off-by: Tao Klerks <tao@klerks.biz>
Acked-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 52 insertions, 0 deletions

diff --git a/t/t7800-difftool.sh b/t/t7800-difftool.sh
index 24297e26ca..59d3847bf8 100755
--- a/t/t7800-difftool.sh
+++ b/t/t7800-difftool.sh
@@ -155,6 +155,58 @@ test_expect_success 'difftool honors --gui' '
 	test_cmp expect actual
 '
 
+test_expect_success 'difftool with guiDefault auto selects gui tool when there is DISPLAY' '
+	difftool_test_setup &&
+	test_config merge.tool bogus-tool &&
+	test_config diff.tool bogus-tool &&
+	test_config diff.guitool test-tool &&
+	test_config difftool.guiDefault auto &&
+	DISPLAY=SOMETHING && export DISPLAY &&
+
+	echo branch >expect &&
+	git difftool --no-prompt branch >actual &&
+	test_cmp expect actual
+'
+test_expect_success 'difftool with guiDefault auto selects regular tool when no DISPLAY' '
+	difftool_test_setup &&
+	test_config diff.guitool bogus-tool &&
+	test_config diff.tool test-tool &&
+	test_config difftool.guiDefault Auto &&
+	DISPLAY= && export DISPLAY &&
+
+	echo branch >expect &&
+	git difftool --no-prompt branch >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'difftool with guiDefault true selects gui tool' '
+	difftool_test_setup &&
+	test_config diff.tool bogus-tool &&
+	test_config diff.guitool test-tool &&
+	test_config difftool.guiDefault true &&
+
+	DISPLAY= && export DISPLAY &&
+	echo branch >expect &&
+	git difftool --no-prompt branch >actual &&
+	test_cmp expect actual &&
+
+	DISPLAY=Something && export DISPLAY &&
+	echo branch >expect &&
+	git difftool --no-prompt branch >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'difftool --no-gui trumps config guiDefault' '
+	difftool_test_setup &&
+	test_config diff.guitool bogus-tool &&
+	test_config diff.tool test-tool &&
+	test_config difftool.guiDefault true &&
+
+	echo branch >expect &&
+	git difftool --no-prompt --no-gui branch >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'difftool --gui last setting wins' '
 	difftool_test_setup &&
 	: >expect &&