Re: Syntax errors in YAML blocks

[BPJ <melroch-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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Perhaps it should be pointed out that the body of YAML block scalars must
be indented relative to the line with the `|` or `>`. Not doing so is
indeed a YAML syntax error, so Pandoc does the right thing when not
considering it valid YAML, however unfortunate it is that Pandoc may think
it is something else.

The overview of YAML syntax on Wikipedia is quite good. Perhaps the manual
could link to (some specific version of) it.

https://en.m.wikipedia.org/wiki/YAML#Syntax

Den ons 2 juni 2021 21:21John MacFarlane <jgm-TVLZxgkOlNX2fBVCVOL8/A@public.gmane.org> skrev:

>
> The problem is that basically anything is valid Markdown,
> it's just a matter of how it is interpreted.  It does seem
> to me that in the second case we might want to at least emit
> a warning -- if not downright fail.  It's just so unlikely
> that someone would write a block beginning with `---`
> and ending with `...` and intend it to be something other
> than YAML metadata.  If you'd like, you could submit an
> issue for this.  I'd rather not suggest avoiding complex
> YAML blocks -- sometimes they're fine, if the syntax is
> correct!
>
> William Lupton <wlupton-QSt+ys/nuMyEUIsrzH9SikB+6BGkLq7r@public.gmane.org> writes:
>
> > Thanks. Yes, I guess I realised it had something to do with ambiguous
> > grammars, but I hadn't really considered that my input was a valid table
> > (mea culpa).
> >
> > So I thought aha! I'll change the terminating "---" to "..." (in the hope
> > of an error), but this of course gives the output shown below.
> >
> > I wonder whether there could be a warning in the manual (or maybe there
> is
> > and I've missed it?) and/or perhaps a suggestion that it might be a good
> > idea to avoid complex YAML metadata blocks (in favour of metadata files)?
> > I'd be happy to create an issue and/or a MANUAL.md pull request.
> >
> > % cat bad.md
> > ---
> > history:
> > - number: Release 1.2
> >   changes: |
> >   - TBD
> > ...
> >
> > % pandoc bad.md
> > <hr />
> > <p>history: - number: Release 1.2 changes: | - TBD …</p>
> >
> >
> > On Wed, 2 Jun 2021 at 17:47, John MacFarlane <jgm-TVLZxgkOlNX2fBVCVOL8/A@public.gmane.org> wrote:
> >
> >>
> >> Well, this actually IS a valid "simple table".  So how is
> >> pandoc to know that you intended it as a YAML metadata block?
> >> Pandoc tries first to parse things as YAML blocks, and then as
> >> tables, if either works, the parse succeeds with no error.
> >>
> >> William Lupton <wlupton-QSt+ys/nuMyEUIsrzH9SikB+6BGkLq7r@public.gmane.org> writes:
> >>
> >> > Should I expect syntax errors in YAML blocks to be detected and
> reported?
> >> >
> >> > This has a syntax error in the YAML block:
> >> >
> >> > % cat bad.md
> >> > ---
> >> > history:
> >> > - number: Release 1.2
> >> >   changes: |
> >> >   - TBD
> >> > ---
> >> >
> >> > This fixes it:
> >> >
> >> > % diff bad.md good.md
> >> > 5c5
> >> > <   - TBD
> >> > ---
> >> >>     - TBD
> >> >
> >> > The latest pandoc:
> >> >
> >> > % ~/Downloads/pandoc-2.14.0.1/bin/pandoc -v
> >> > pandoc 2.14.0.1
> >> > ...
> >> >
> >> > Pandoc thinks the bad YAML is a table:
> >> >
> >> > % ~/Downloads/pandoc-2.14.0.1/bin/pandoc bad.md
> >> > <table>
> >> > <tbody>
> >> > <tr class="odd">
> >> > <td>history:</td>
> >> > </tr>
> >> > <tr class="even">
> >> > <td>- number: Release 1.2</td>
> >> > </tr>
> >> > <tr class="odd">
> >> > <td>changes: |</td>
> >> > </tr>
> >> > <tr class="even">
> >> > <td>- TBD</td>
> >> > </tr>
> >> > </tbody>
> >> > </table>
> >> >
> >> > But it's OK with the good YAML:
> >> >
> >> > % ~/Downloads/pandoc-2.14.0.1/bin/pandoc good.md
> >> >
> >> > Parsing the file as YAML reports the error:
> >> >
> >> > % ~/Downloads/pandoc-2.14.0.1/bin/pandoc --metadata-file bad.md
> >> > Error at "bad.md" (line 5, column 0):
> >> > Unexpected ' '
> >> >
> >> > % ~/Downloads/pandoc-2.14.0.1/bin/pandoc --metadata-file good.md
> >> > ^C
> >> >
> >> > --
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> >> > To view this discussion on the web visit
> >>
> https://groups.google.com/d/msgid/pandoc-discuss/CAEe_xxjF3Un2J-xg5UOs7uReZ5cO27TATA%2BfDY%2BAtghAsVhShA%40mail.gmail.com
> >> .
> >>
>
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