Merge branch 'nd/export-worktree' into maint

Running an aliased command from a subdirectory when the .git thing
in the working tree is a gitfile pointing elsewhere did not work.

* nd/export-worktree:
  setup: set env $GIT_WORK_TREE when work tree is set, like $GIT_DIR

environment.c

@@ -231,6 +231,8 @@ void set_git_work_tree(const char *new_work_tree)
 	}
 	git_work_tree_initialized = 1;
 	work_tree = xstrdup(real_path(new_work_tree));
+	if (setenv(GIT_WORK_TREE_ENVIRONMENT, work_tree, 1))
+		die("could not set GIT_WORK_TREE to '%s'", work_tree);
 }
 
 const char *get_git_work_tree(void)

t/t0002-gitfile.sh

@@ -99,4 +99,21 @@ test_expect_success 'check rev-list' '
 	test "$SHA" = "$(git rev-list HEAD)"
 '
 
+test_expect_success 'setup_git_dir twice in subdir' '
+	git init sgd &&
+	(
+		cd sgd &&
+		git config alias.lsfi ls-files &&
+		mv .git .realgit &&
+		echo "gitdir: .realgit" >.git &&
+		mkdir subdir &&
+		cd subdir &&
+		>foo &&
+		git add foo &&
+		git lsfi >actual &&
+		echo foo >expected &&
+		test_cmp expected actual
+	)
+'
+
 test_done