Function canonical_geometry_subtype 

pub fn canonical_geometry_subtype(name: &str) -> Option<&'static str>

Normalises a schema-written geometry subtype to its canonical PostGIS casing, or None if it isn’t a recognised subtype.

Matching is case-insensitive on both the base name and the dimensionality suffix, because PostGIS’s own type modifier parser is. Rejecting an unrecognised name is the entire point of making the column declarable: before cratestack#842 a typo’d spatial column was simply not expressible, and the workaround (an undeclared column plus a hand-written migration) pushed the typo to a runtime SQL error.