[Toybox] patch and fuzz

[enh]

(sorry, been ooo.)

On Sun, Jun 28, 2020 at 11:21 PM Rob Landley <rob at landley.net> wrote:

> On 6/26/20 2:35 PM, enh via Toybox wrote:
> > toybox patch fails to apply the patch
> >
> https://android.googlesource.com/platform/external/snakeyaml/+/refs/heads/master/src/patches/android/Representer.patch
>
> That's html, I clicked the ".txt" link at the bottom and it downloaded a
> block
> of
> "Zy95YW1sL3NuYWtleWFtbC9yZXByZXNlbnRlci9SZXByZXNlbnRlci5qYXZhCkBAIC0xNSw3"
> which I don't recognize the encoding of?
>
>   $ file Representer.txt
>   Representer.txt: ASCII text, with very long lines, with no line
> terminators
>
> The debian file command is editorializing, but not helpful.
>
> > to the file
> https://android.googlesource.com/platform/external/snakeyaml/+/refs/heads/master/src/main/java/org/yaml/snakeyaml/representer/Representer.java
> .
>
> Could you send me the two files?
>

attached.

note that when you're finding gittiles unhelpful (which, let's face it, it
usually is), you can just chop the first part off the URL and `git clone`.
so here, for example, `git clone
https://android.googlesource.com/platform/external/snakeyaml/` will check
out this single git project, which isn't very large.


> > the worst part is that it _thinks_ it succeeds :-(
> >
> > the interesting bit happens when we come to apply this hunk:
> >
> > @@ -15,7 +15,6 @@
> > */
> >  package org.yaml.snakeyaml.representer;
> >
> > -import java.beans.IntrospectionException;
> >  import java.util.ArrayList;
> >  import java.util.Arrays;
> >  import java.util.Iterator;
> >
> > here:
> >
> > package org.yaml.snakeyaml.representer;
> >
> > import java.beans.IntrospectionException;
> > import java.util.ArrayList;
> > import java.util.Arrays;
> > import java.util.Collections;
> > import java.util.Iterator;
> > import java.util.List;
> >
> > the eagle-eyed human will notice that there's an extra "Collections"
> > in the actual file that isn't in the patch, because the patch was
> > actually against an older version of the source.
>
> Didn't commit 333a10f9ef59 fix this back in February? (It was supposed
> to...)
>
> > the bug is that toybox drops that new line in its output.
> >
> > it reads it:
> >
> > MAYBE:
> > IN: import java.beans.IntrospectionException;
> > MAYBE: -import java.beans.IntrospectionException;
> > IN: import java.util.ArrayList;
> > MAYBE:  import java.util.ArrayList;
> > IN: import java.util.Arrays;
> > MAYBE:  import java.util.Arrays;
> > IN: import java.util.Collections;
> > FUZZED: 21  import java.util.Iterator;
> >
> > but then it does a `goto fuzzed` and explicitly drops that line it
> > just read. which is clearly wrong here, but the code comment
> > explicitly calls out this behavior:
> >
> >     // If match failed, flush first line of buffered data and
> >     // recheck buffered data for a new match until we find one or run
> >     // out of buffer.
>
> That's leading data. The idea was if you're matching
>
> @@
>   abc
> - def
>   ghi
>
> And the data says:
>
>  abc
>  abc
>  def
>  ghi
>
> It shouldn't see the first abc, read in the second abc and go "nope,
> that's not
> def" and then discard _both_ before checking again. (It has to advance
> _one_
> line and try again, thus checking at every possible offset, including
> rechecking
> the data it's already buffered  because it thought it might be a later
> part of
> the hunk under consideration. The actual _start_ of the hunk might be in
> that
> mismatched later part it's already read in.)
>
> > so i'm not quite sure i understand the intended logic here. when would
> > you ever want to drop an input line that doesn't have a '-' or '+'
> > line in the hunk?
>
> Can you send me the test files? (I can try to put together a test from what
> you've sent me, but I'd rather have the real one.)
>
> Thanks,
>
> Rob
>
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