[PATCH 4/5] difftool: make --gui, --tool and --extcmd exclusive

[Denton Liu]

In git-difftool, these options specify which tool to ultimately run. As
a result, they are logically conflicting. Explicitly disallow these
options from being used together.

Signed-off-by: Denton Liu <liu.den...@gmail.com>
---
 builtin/difftool.c  | 11 ++++++++++-
 t/t7800-difftool.sh |  8 ++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/builtin/difftool.c b/builtin/difftool.c
index a3ea60ea71..5ad39c9172 100644
--- a/builtin/difftool.c
+++ b/builtin/difftool.c
@@ -690,7 +690,7 @@ static int run_file_diff(int prompt, const char *prefix,
 int cmd_difftool(int argc, const char **argv, const char *prefix)
 {
        int use_gui_tool = 0, dir_diff = 0, prompt = -1, symlinks = 0,
-           tool_help = 0;
+           tool_help = 0, count = 0;
        static char *difftool_cmd = NULL, *extcmd = NULL;
        struct option builtin_difftool_options[] = {
                OPT_BOOL('g', "gui", &use_gui_tool,
@@ -731,6 +731,15 @@ int cmd_difftool(int argc, const char **argv, const char 
*prefix)
        setenv(GIT_DIR_ENVIRONMENT, absolute_path(get_git_dir()), 1);
        setenv(GIT_WORK_TREE_ENVIRONMENT, absolute_path(get_git_work_tree()), 
1);
 
+       if (use_gui_tool)
+               count++;
+       if (difftool_cmd)
+               count++;
+       if (extcmd)
+               count++;
+       if (count > 1)
+               die(_("--gui, --tool and --extcmd are exclusive"));
+
        if (use_gui_tool && diff_gui_tool && *diff_gui_tool)
                setenv("GIT_DIFF_TOOL", diff_gui_tool, 1);
        else if (difftool_cmd) {
diff --git a/t/t7800-difftool.sh b/t/t7800-difftool.sh
index bb9a7f4ff9..107f31213d 100755
--- a/t/t7800-difftool.sh
+++ b/t/t7800-difftool.sh
@@ -705,4 +705,12 @@ test_expect_success SYMLINKS 'difftool --dir-diff handles 
modified symlinks' '
        test_cmp expect actual
 '
 
+test_expect_success 'difftool --gui, --tool and --extcmd are exclusive' '
+       difftool_test_setup &&
+       test_must_fail git difftool --gui --tool=test-tool &&
+       test_must_fail git difftool --gui --extcmd=cat &&
+       test_must_fail git difftool --tool=test-tool --extcmd=cat &&
+       test_must_fail git difftool --gui --tool=test-tool --extcmd=cat
+'
+
 test_done
-- 
2.21.0.967.gf85e14fd49