Re: Rewrite cat-file.c : need help to find a bug

From: Jeff King <peff@peff.net>
Date: Dec 29, 2017, 13:22 UTC
Message-ID: <20171229132237.GA12561@sigill.intra.peff.net>
In-Reply-To: <CAL21BmnycG4=Wm_e1S85QVPfs3vV_Q=TAjTAG-sv+f2mK6wbBQ@mail.gmail.com>

On Fri, Dec 29, 2017 at 01:05:50PM +0300, Оля Тележная wrote:

Show 12 quoted lines

> Hi everyone,
> I am trying to reuse formatting logic from ref-filter in cat-file
> command. Now cat-file uses its own formatting code.
> I am trying to achieve that step-by-step, now I want to invoke
> populate_value function, and I have a bug somewhere.
> My code is here.
> https://github.com/telezhnaya/git/commits/catfile
> All commits that starts from "cat-file: " are successfully passing all tests.
> So for now my last commit fails, and I am tired of searching for the
> error. Actually, I just copied some values to another variable and
> move some code to other place. All "intelligent" work will go further,
> but now I need to fix current situation.

The problem is that "cat_file_info" is NULL when you get to populate_value(), so the moved code doesn't trigger.

That variable is usually pulled from format->cat_file_data during verify_ref_format(). But it triggers only when there's an actual format atom to parse, and in this particular test the format is empty! But cat-file is somewhat special here, in that even without any atoms it needs to make sure the object exists.

So the patch below makes the test pass, though I think in the long run all of this cat_file_info stuff would just get folded into regular atoms, and you'd want cat-file to pass a special flag to ask ref-filter to make sure the object exists.

-Peff

---

diff --git a/ref-filter.c b/ref-filter.c
index 62ca83807f..3acea4d2ef 100644
--- a/ref-filter.c
+++ b/ref-filter.c
@@ -742,6 +742,10 @@ int verify_ref_format(struct ref_format *format)
 {
 	const char *cp, *sp;
 
+	/* do this unconditionally, even if we have no atoms! */
+	if (format->cat_file_data)
+		cat_file_info = format->cat_file_data;
+
 	format->need_color_reset_at_eol = 0;
 	for (cp = format->format; *cp && (sp = find_next(cp)); ) {
 		const char *color, *ep = strchr(sp, ')');
@@ -753,7 +757,6 @@ int verify_ref_format(struct ref_format *format)
 
 		if (format->cat_file_data)
 		{
-			cat_file_info = format->cat_file_data;
 			at = parse_ref_filter_atom(format, valid_cat_file_atoms,
 						   ARRAY_SIZE(valid_cat_file_atoms), sp + 2, ep);
 		} else