Merge branch 'jk/diff-result-code-cleanup'

"git diff --no-such-option" and other corner cases around the exit
status of the "diff" command has been corrected.

* jk/diff-result-code-cleanup:
  diff: drop useless "status" parameter from diff_result_code()
  diff: drop useless return values in git-diff helpers
  diff: drop useless return from run_diff_{files,index} functions
  diff: die when failing to read index in git-diff builtin
  diff: show usage for unknown builtin_diff_files() options
  diff-files: avoid negative exit value
  diff: spell DIFF_INDEX_CACHED out when calling run_diff_index()

wt-status.c

@@ -675,7 +675,7 @@ static void wt_status_collect_changes_index(struct wt_status *s)
 	rev.diffopt.flags.recursive = 1;
 
 	copy_pathspec(&rev.prune_data, &s->pathspec);
-	run_diff_index(&rev, 1);
+	run_diff_index(&rev, DIFF_INDEX_CACHED);
 	release_revisions(&rev);
 }
 
@@ -1156,7 +1156,7 @@ static void wt_longstatus_print_verbose(struct wt_status *s)
 		rev.diffopt.a_prefix = "c/";
 		rev.diffopt.b_prefix = "i/";
 	} /* else use prefix as per user config */
-	run_diff_index(&rev, 1);
+	run_diff_index(&rev, DIFF_INDEX_CACHED);
 	if (s->verbose > 1 &&
 	    wt_status_check_worktree_changes(s, &dirty_submodules)) {
 		status_printf_ln(s, c,
@@ -2580,8 +2580,8 @@ int has_unstaged_changes(struct repository *r, int ignore_submodules)
 	}
 	rev_info.diffopt.flags.quick = 1;
 	diff_setup_done(&rev_info.diffopt);
-	result = run_diff_files(&rev_info, 0);
-	result = diff_result_code(&rev_info.diffopt, result);
+	run_diff_files(&rev_info, 0);
+	result = diff_result_code(&rev_info.diffopt);
 	release_revisions(&rev_info);
 	return result;
 }
@@ -2614,8 +2614,8 @@ int has_uncommitted_changes(struct repository *r,
 	}
 
 	diff_setup_done(&rev_info.diffopt);
-	result = run_diff_index(&rev_info, 1);
-	result = diff_result_code(&rev_info.diffopt, result);
+	run_diff_index(&rev_info, DIFF_INDEX_CACHED);
+	result = diff_result_code(&rev_info.diffopt);
 	release_revisions(&rev_info);
 	return result;
 }