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Improve type inference in @turf/helpers' geometry and geometryCollection #2971

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Merged
mfedderly merged 2 commits into from
Dec 16, 2025
+28 −14
Merged

Improve type inference in @turf/helpers' geometry and geometryCollection #2971

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Improve type inference in @turf/helpers' geometry and geometryCollect…
mfedderly Dec 15, 2025
511d943
Remove wayward satisfies use
mfedderly Dec 16, 2025
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42 changes: 28 additions & 14 deletions packages/turf-helpers/index.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -207,30 +207,39 @@ export function feature<
* var geometry = turf.geometry(type, coordinates);
* // => geometry
*/
export function geometry(
type:
export function geometry<
T extends
| "Point"
| "LineString"
| "Polygon"
| "MultiPoint"
| "MultiLineString"
| "MultiPolygon",
>(
type: T,
coordinates: any[],
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@mfedderly mfedderly Dec 15, 2025

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In a simliar fashion, we could narrow this any[] based on T, but that would be a breaking change, we can file it against the 8.0 milestone. I suppose you could also just make the case that we should do this in 7.x, because it is explicitly a bug in the caller if they aren't passing in the correctly shaped coordinates. My only concern with that is some amount of weirdness with number[] vs [number, number] issues, which might crop up depending on how consumers wrote their own types.

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@smallsaucepan smallsaucepan Dec 16, 2025

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The [number, number] thing is going to haunt us forever 😅

_options: Record<string, never> = {}
) {
): {
Point: Point;
LineString: LineString;
Polygon: Polygon;
MultiPoint: MultiPoint;
MultiLineString: MultiLineString;
MultiPolygon: MultiPolygon;
}[T] {
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@mfedderly mfedderly Dec 15, 2025

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I had considered making this a named interface and mapping against that instead (GeometryTypeNameToType), and referencing that instead of as any below, but I opted to not increase the public API for a mapping we only used in a single place.

switch (type) {
case "Point":
return point(coordinates).geometry;
return point(coordinates).geometry as any;
case "LineString":
return lineString(coordinates).geometry;
return lineString(coordinates).geometry as any;
case "Polygon":
return polygon(coordinates).geometry;
return polygon(coordinates).geometry as any;
case "MultiPoint":
return multiPoint(coordinates).geometry;
return multiPoint(coordinates).geometry as any;
case "MultiLineString":
return multiLineString(coordinates).geometry;
return multiLineString(coordinates).geometry as any;
case "MultiPolygon":
return multiPolygon(coordinates).geometry;
return multiPolygon(coordinates).geometry as any;
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@mfedderly mfedderly Dec 15, 2025

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This as any casts are a little unfortunate. The case statements don't actually narrow our understanding of T, and so we need to reaffirm that we know what we're doing here.

microsoft/TypeScript#33014

default:
throw new Error(type + " is invalid");
}
Expand Down Expand Up @@ -598,15 +607,20 @@ export function multiPolygon<P extends GeoJsonProperties = GeoJsonProperties>(
* // => collection
*/
export function geometryCollection<
G extends
| Point
| LineString
| Polygon
| MultiPoint
| MultiLineString
| MultiPolygon,
P extends GeoJsonProperties = GeoJsonProperties,
>(
geometries: Array<
Point | LineString | Polygon | MultiPoint | MultiLineString | MultiPolygon
>,
geometries: Array<G>,
properties?: P,
options: { bbox?: BBox; id?: Id } = {}
): Feature<GeometryCollection, P> {
const geom: GeometryCollection = {
): Feature<GeometryCollection<G>, P> {
const geom: GeometryCollection<G> = {
type: "GeometryCollection",
geometries,
};
Expand Down