Reasons:
- Performance: HsYAML is around 20 times slower in parsing
large YAML bibliographies (#6084).
- An issue was submitted to HsYAML, but it hasn't gotten
any attention. HsYAML seems borderline unmaintained; it hasn't
had a commit in over a year.
- Unfortunately this goes back on our attempts to free ourselves
from C dependencies (#4535). But I don't see a better alternative
until a better pure Haskell parser is available.
Closes#6084.
Notes:
- We've removed the FromYAML instances for all types that had
them, since this is a HsYAML-specific typeclass [API change].
(The yaml package just uses From/ToJSON.)
- Unlike HsYAML (in the configuration we were using), yaml
parses 'Y', 'N', 'Yes', 'No', 'On', 'Off' as boolean values.
Users may need to quote these when they are meant to be
interpreted as strings. Similarly, 'null' is parsed as
a YAML null value (and will be treated as an empty string
by pandoc rather than the string 'null'). Quoting it will
force it to be interpreted as a string.
- Some tests had to be adjusted accordingly.
- Pandoc now behaves better when the YAML metadata contains
escaping errors: instead of just falling back on treating
the section as a table, it raises a YAML parsing error.
Update tests.
Reason: it turns out that the native output generated by
pretty-simple isn't always readable by the native reader.
According to https://github.com/cdepillabout/pretty-simple/issues/99
it is not a design goal of the library that the rendered values
be readable using 'read'. This makes it unsuitable for our
purposes.
pretty-show is a bit slower and it uses 4-space indents
(non-configurable), but it doesn't have this serious drawback.
Previously we used our own homespun formatting. But this
produces over-long lines that aren't ideal for diffs in tests.
Easier to use something off-the-shelf and standard.
Closes#7580.
Performance is slower by about a factor of 10, but this isn't
really a problem because native isn't suitable as a serialization
format. (For serialization you should use json, because the reader
is so much faster than native.)
