Previously ‘RdrName’s were sorted by simple comparison of their names.
However, in ASCII not all “operator-like” symbols go after alpha-numeric
characters. This resulted in this sort of output:
import Linear.Vector ((*^), Additive (..), (^*))
The new ordering scheme allows us to separate operators and other names:
import Linear.Vector (Additive (..), (*^), (^*))
This resolves a class of idempotence issues when the equality sign happens
to be inserted between an element and its comment that follows on the same
line. I had to special-case equality sign for this, because all alternative
approaches (changing comment association logic or trying to find a more
general rule) did not work or fixed this issue yet made other things worse.
There is nothing special about the equality sign per se, but it (always?)
starts definitions which have their own ‘Located’ wrappers and it is those
spans interfere with the logic of comment association (they are detected as
AST elements between the “host” element and its comment) on subsequent
passes. This results in non-idempotent formatting.
The solution is OKish in that it fixes 99% of problems that one will
encounter in practice, but I see how an input can be crafted to show that
there is still an issue with idempotence.
Ormolu can be turned on and off via the special comments:
{- ORMOLU_DISABLE -}
and
{- ORMOLU_ENABLE -}
This allows us to disable formatting selectively for code between these
markers or disable it for the entire file. To achieve the latter, just put
{- ORMOLU_DISABLE -} at the very top. Note that the source code should still
be parseable even without the “excluded” part. Because of that the magic
comments cannot be placed arbitrary, but should rather enclose independent
top-level definitions.
