1 files changed, 63 insertions, 0 deletions
diff --git a/builtin/difftool.c b/builtin/difftool.c
new file mode 100644
index 0000000000..53870bbaf7
--- /dev/null
+++ b/builtin/difftool.c
@@ -0,0 +1,63 @@
+/*
+ * "git difftool" builtin command
+ *
+ * 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.
+ * The GIT_DIFF* variables are exported for use by git-difftool--helper.
+ *
+ * Any arguments that are unknown to this script are forwarded to 'git diff'.
+ *
+ * Copyright (C) 2016 Johannes Schindelin
+ */
+#include "builtin.h"
+#include "run-command.h"
+#include "exec_cmd.h"
+
+/*
+ * NEEDSWORK: this function can go once the legacy-difftool Perl script is
+ * retired.
+ *
+ * We intentionally avoid reading the config directly here, to avoid messing up
+ * the GIT_* environment variables when we need to fall back to exec()ing the
+ * Perl script.
+ */
+static int use_builtin_difftool(void) {
+	struct child_process cp = CHILD_PROCESS_INIT;
+	struct strbuf out = STRBUF_INIT;
+	int ret;
+
+	argv_array_pushl(&cp.args,
+			 "config", "--bool", "difftool.usebuiltin", NULL);
+	cp.git_cmd = 1;
+	if (capture_command(&cp, &out, 6))
+		return 0;
+	strbuf_trim(&out);
+	ret = !strcmp("true", out.buf);
+	strbuf_release(&out);
+	return ret;
+}
+
+int cmd_difftool(int argc, const char **argv, const char *prefix)
+{
+	/*
+	 * NEEDSWORK: Once the builtin difftool has been tested enough
+	 * and git-legacy-difftool.perl is retired to contrib/, this preamble
+	 * can be removed.
+	 */
+	if (!use_builtin_difftool()) {
+		const char *path = mkpath("%s/git-legacy-difftool",
+					  git_exec_path());
+
+		if (sane_execvp(path, (char **)argv) < 0)
+			die_errno("could not exec %s", path);
+
+		return 0;
+	}
+	prefix = setup_git_directory();
+	trace_repo_setup(prefix);
+	setup_work_tree();
+
+	die("TODO");
+}