YAML: long property names/keys get prefixed with question mark `?`, and colon `:` gets wrapped onto the next line

Prettier 1.15.3 Playground link

--parser yaml

Input:

very_long_name_in_fact_it_is_longer_than_80_characters_123123123123123123123123123:
  foo: "bar"

Output:

? very_long_name_in_fact_it_is_longer_than_80_characters_123123123123123123123123123
: foo: "bar"

Expected behavior:

Doesn’t wrap the : to the second line, i.e. leaves the whole thing intact.

very_long_name_in_fact_it_is_longer_than_80_characters_123123123123123123123123123:
  foo: "bar"

This issue looks simple to fix, where would I look for the related code if I wanted to make a PR?

[pdavies]

I hit this bug and have fixed it - see PR just above. For anyone interested, there’s some real black magic going on which made this pretty hard to figure out, but which feels commensurate to the wolf in sheep’s clothing that is the YAML grammar.

The intention of the code was to:

• look at whether the key should break
• if it does, use explicit mapping syntax. The bug was that if a key is long enough that it wants to break, it will trigger this, whether or not it actually can break onto multiple lines
• if not, use implicit (ie normal) syntax

This is all pretty edge case stuff - many people will never know that yaml mapping keys can be multiline entities like arrays or multiline strings!

The extra dose of confusion comes from the pointless-looking call to conditionalGroup. It turns out that conditionalGroup has the undocumented behaviour of forcing the printer into MODE_FLAT, which the yaml formatter extensively relies on to prevent various breaks from occurring. Sensible-looking attempts to rewrite the code can very easily result in tons of line breaks appearing out of nowhere!

[deltaidea]

@nasht00 One lazy workaround that I’ve used for this is setting max line length to 999 for Yaml files. Fixes the issue immediately but doesn’t look great if you have long lists with commas - they might get inlined.