optional normalizations (loose matching mode)

[kazcw]

Structural grepping could benefit from optional normalization so that this pattern:

match $_ { Ok($p0) => $p0, Err($p1) => $p1 } }

Would match both of these:

match x { Ok(a) => a, Err(b) => b } }
match x { Err(a) => a, Ok(b) => b } }

The normalization pass in this case would be: when tracing a node that can have a collection of descendants whose order may not be significant, trace all the children, and then sort the traces (arbitrarily, but consistent for the same content). All optional normalizations are lossy; in this case, no attempt will be made to determine whether e.g. a previous guarded match affects a later match so that rearrangement is semantically effectful.

There are other normalizations that would be useful. The API should support enabling individual normalizations, and also define a standard set to enable for "loose matching mode".

[kazcw]

The loose matching flag would be the interface for structural grep. For lints, etc. explicitness and fine-grained loosening would be preferable. An attribute in the patterns seems like the right interface there:

#[comacro(any_order)]
match $_ { Ok($p0) => $p0, Err($p1) => $p1 } }