Failed to parse patch

[weiznich]

I've tried to integrate diffy into diesel_cli as suggested on reddit by @sgrif. While this is conceptually working it fails because diffy expects patches to include a file name header. As far as I understand the code this is caused by those lines

In detail the following patch file from our test suite fails to parse:

@@ -1,12 +1,13 @@
 diesel::table! {
     users1 (id) {
-        id -> Nullable<Integer>,
+        id -> Integer,
     }
 }

 diesel::table! {
-    users2 (id) {
-        id -> Nullable<Integer>,
+    users2 (myid) {
+        #[sql_name = "id"]
+        myid -> Integer,
     }
 }

[bmwill]

Thanks for reporting this. I was expecting there to be some issues with that parsing logic given that there doesn't really seem to be a good specification for the actual format of a unified diff, specifically for the format that is accepted by patch. Most patches/diffs you generally see include the filename headers but as you pointed out it seems that patch is able to handle patches just fine without them (assuming you also provide the file to be patched since it can no longer be inferred from the patch itself).

I'll try and get a fix out soon for this, making the existence of filename headers optional.

[bmwill]

Just for reference, patch does print a warning when using a patch file that is missing a filename header:

$ patch schema schema.patch
missing header for unified diff at line 1 of patch
patching file schema

It also seems to be able to handle parsing filename headers which are in the reverse order ('+++' line before '---' line) as well as when one of them is missing.

[bmwill]

@weiznich One other interesting thing about that test patch is that the hunk header doesn't actually match the hunk lines. The header indicates that this hunk corresponds to a chunk of 12 lines in the old file and 13 lines in the new file yet there's actually only 11 pre-image lines (context and '-' lines) and 12 post-image lines (context and '+' lines). I think this is probably due to missing a trailing empty line based on looking at the expected result.

I'm not exactly sure what the best thing to do for this is though since the header is incorrect but patch seems to not care.

[weiznich]

It's interesting that patch does just work with those "broken" files. Those files are only synthetic test cases for diesel itself, have a look here for a realistically used patch file. That one should just work with diffy as it is. I think it would also be fine to just update our test cases there to something that works with diffy.

[bmwill]

Given that here's what I'm thinking, there's probably some benefit to wanting to parse a patch that's missing the headers so I can go ahead and finish tweaking the parsing logic to handle that (and eventually change the API so that those filenames are wrapped in Option types) and you could slightly tweak that test case so that the hunk header matches the hunk lines (making it @@ -1,11 +1,12 @@ should do it). How does that sound?

[weiznich]

That sounds great 👍 Thanks for your support

[bmwill]

This should be fixed with 39f787f and I'll do another release shortly.