feat: make WMS crs extensible via a nested provider element, not a registry

Replaces the mutable registerCRS() registry (never released beyond this
branch) with a web-components-first design: any custom element, no base
class required, can provide a CRS Leaflet doesn't ship by nesting inside
<leaflet-tile-layer-wms> and firing a bubbling leaflet-crs-changed event
(detail: { crs: CRS | null }, mirroring icon-changed's { icon: null }
pattern for "revert to default"). The plain `crs="EPSG4326"` attribute
stays as a convenience shortcut for the 4 CRSes Leaflet itself ships; a
nested provider takes priority over it when both are present.

This surfaced a real, previously-undiscovered bug in with-props.ts:
recreateLeafletObject() was declared on the public LeafletElement
interface but only ever implemented as a private #recreateLeafletObject()
-- calling it would throw "is not a function" at runtime despite
type-checking cleanly. Fixed by making it public, and it now also
re-dispatches registerWithParent() for attach !== 'none' components,
which it never did before (previously only safe for attach: 'none'
components like icons, since recreate would otherwise rebuild a layer
without ever re-adding it to whatever registered it the first time --
exactly what leaflet-tile-layer-wms needs when a nested provider's crs
arrives after it already constructed itself with the default).

README.md

@@ -286,6 +286,27 @@ All `<leaflet-tile-layer>` attributes above apply (a WMS layer is a tile layer),
 | `uppercase`   | —              | Use uppercase WMS parameter names                                                            |
 | `crs`         | —              | Coordinate reference system by name: `'EPSG3857'`, `'EPSG4326'`, `'EPSG3395'`, or `'Simple'` |
 
+For a CRS Leaflet doesn't ship (a custom projection from a plugin, say), nest a CRS-providing element instead of using the `crs` attribute. It's just a custom element that fires a `leaflet-crs-changed` event on itself, bubbling, carrying the actual `L.CRS` value — no base class required:
+
+```js
+class MyCRSProvider extends HTMLElement {
+  connectedCallback() {
+    this.dispatchEvent(
+      new CustomEvent('leaflet-crs-changed', { bubbles: true, detail: { crs: myPluginCRS } }),
+    );
+  }
+}
+customElements.define('my-crs-provider', MyCRSProvider);
+```
+
+```html
+<leaflet-tile-layer-wms url="..." layers="...">
+  <my-crs-provider></my-crs-provider>
+</leaflet-tile-layer-wms>
+```
+
+A nested provider takes priority over the `crs` attribute when both are present. `crs` is construction-only (Leaflet has no live setter for it), so picking one up — from either source — rebuilds the whole layer; place the provider so it connects before you need the correct projection to take effect, since there's nothing to revert to partway through a request.
+
 ### `<leaflet-marker>`
 
 | Attribute        | Default | Description                   |

src/components/leaflet-tile-layer-wms.ts

@@ -7,6 +7,7 @@ import {
   type LeafletRemoveEventListener,
 } from '../core/with-props.ts';
 import type { TileLayerEvents } from '../core/event-types.ts';
+import type { LeafletCRSChangedEvent } from '../core/register.ts';
 
 // WMS request parameters have no individual setters -- they're merged into the
 // query string through setParams().
@@ -16,8 +17,10 @@ function param<T>(key: keyof WMSParams): (obj: TileLayer.WMS, value: T) => void
   };
 }
 
-// `crs` takes a CRS instance, not a primitive, so it's looked up by name from
-// Leaflet's built-in set rather than decoded like a plain value. Constructor-
+// `crs` takes a CRS instance, not a primitive. The attribute only covers the
+// 4 CRSes Leaflet ships by name -- a CRS Leaflet doesn't ship comes from a
+// nested child announcing itself via leaflet-crs-changed instead (see
+// #onCrsChanged), which takes priority over this when present. Constructor-
 // only, like the rest of tileLayerProps -- Leaflet has no setter for it.
 const NAMED_CRS = {
   EPSG3857: CRS.EPSG3857,
@@ -51,9 +54,35 @@ export class LeafletTileLayerWMS extends WithProps({
   declare addEventListener: LeafletAddEventListener<TileLayerEvents>;
   declare removeEventListener: LeafletRemoveEventListener<TileLayerEvents>;
 
+  // Set by a nested CRS-providing child; overrides the `crs` attribute's
+  // named lookup when present.
+  #childCrs?: CRS;
+
   createLeafletObject(options: WMSOptions): TileLayer.WMS {
-    return new TileLayer.WMS(this.url, options);
+    return new TileLayer.WMS(
+      this.url,
+      this.#childCrs ? { ...options, crs: this.#childCrs } : options,
+    );
+  }
+
+  connectedCallback(): void {
+    super.connectedCallback();
+    this.addEventListener('leaflet-crs-changed', this.#onCrsChanged);
   }
+
+  disconnectedCallback(): void {
+    this.removeEventListener('leaflet-crs-changed', this.#onCrsChanged);
+    super.disconnectedCallback();
+  }
+
+  // A CRS Leaflet doesn't ship comes from any custom element nested here
+  // that fires this event -- no base class required, just this event shape
+  // (see register.ts). `crs` is constructor-only, so picking it up means
+  // rebuilding the whole layer.
+  #onCrsChanged = (e: LeafletCRSChangedEvent) => {
+    this.#childCrs = e.detail.crs ?? undefined;
+    this.recreateLeafletObject();
+  };
 }
 
 customElements.define('leaflet-tile-layer-wms', LeafletTileLayerWMS);

src/core/register.ts

@@ -1,4 +1,4 @@
-import { DivIcon, Icon, Layer } from 'leaflet';
+import { DivIcon, Icon, Layer, type CRS } from 'leaflet';
 
 // Custom event type for the bubbling registration protocol. Carries the
 // Leaflet object and the originating element so the nearest parent can
@@ -21,6 +21,15 @@ export type LeafletLineSyncEvent = CustomEvent<{ element: HTMLElement; latlng: [
 // Fired by <leaflet-line> on disconnect, so a listening parent can drop it.
 export type LeafletLineRemoveEvent = CustomEvent<{ element: HTMLElement }>;
 
+// A CRS is a plain value (methods + a couple of properties, see Leaflet's
+// own `CRS` interface), not a Layer -- it doesn't fit the leaflet-register
+// protocol above. Any custom element nested inside a component that accepts
+// a `crs` (currently just leaflet-tile-layer-wms) can provide one by firing
+// this itself, bubbling, on connect -- no base class required, just this
+// event shape. `crs: null` (e.g. on disconnect) reverts to that component's
+// own default, mirroring icon-changed's `icon: null`.
+export type LeafletCRSChangedEvent = CustomEvent<{ crs: CRS | null }>;
+
 declare global {
   interface HTMLElementEventMap {
     'leaflet-register': LeafletRegisterEvent;
@@ -29,6 +38,7 @@ declare global {
     'icon-changed': LeafletIconChangedEvent;
     'leaflet-line-sync': LeafletLineSyncEvent;
     'leaflet-line-remove': LeafletLineRemoveEvent;
+    'leaflet-crs-changed': LeafletCRSChangedEvent;
   }
 }
 

src/core/with-props.ts

@@ -178,7 +178,7 @@ export function WithProps<TObj extends Class, TProps extends PropTable<TObj>>(
       const prop = byAttribute.get(name);
       if (!prop) return;
       if (options.recreate) {
-        this.#recreateLeafletObject();
+        this.recreateLeafletObject();
         return;
       }
       const obj = this.#obj;
@@ -189,10 +189,14 @@ export function WithProps<TObj extends Class, TProps extends PropTable<TObj>>(
     }
 
     // Throws the current object away and builds a fresh one from the current
-    // attributes, leaving the element's place in the tree untouched.
-    #recreateLeafletObject(): void {
+    // attributes, leaving the element's place in the tree untouched. Also
+    // re-registers the new object with the parent (attach !== 'none') --
+    // registerWithParent only fires once from connectedCallback otherwise,
+    // so without this a recreated layer would never get (re-)added anywhere.
+    recreateLeafletObject(): void {
       this.#destroyObject();
       this.#createObject();
+      if (attach !== 'none' && this.#obj) registerWithParent(this, this.#obj);
       this.leafletObjectCreated();
     }
 

test/components/tile-layers.test.ts

@@ -1,8 +1,22 @@
-import { TileLayer } from 'leaflet';
+import { CRS, TileLayer } from 'leaflet';
 import { describe, expect, it } from 'vitest';
 import '../../src/components/leaflet-tile-layer.ts';
 import '../../src/components/leaflet-tile-layer-wms.ts';
 
+// Stands in for a plugin's CRS-providing element: a plain custom element,
+// no base class from this package, that fires leaflet-crs-changed on
+// connect -- exactly the shape a third party would write.
+class TestCRSProvider extends HTMLElement {
+  crs?: CRS;
+
+  connectedCallback(): void {
+    this.dispatchEvent(
+      new CustomEvent('leaflet-crs-changed', { bubbles: true, detail: { crs: this.crs ?? null } }),
+    );
+  }
+}
+customElements.define('test-crs-provider', TestCRSProvider);
+
 describe('leaflet-tile-layer', () => {
   it('creates a TileLayer from the url attribute with tileLayerProps options', () => {
     const el = document.createElement('leaflet-tile-layer');
@@ -45,8 +59,7 @@ describe('leaflet-tile-layer-wms', () => {
     el.remove();
   });
 
-  it('resolves crs by name to the matching Leaflet CRS instance', async () => {
-    const { CRS } = await import('leaflet');
+  it('resolves crs by name to the matching Leaflet CRS instance', () => {
     const el = document.createElement('leaflet-tile-layer-wms');
     el.setAttribute('url', 'https://wms.example/service');
     el.setAttribute('layers', 'basic');
@@ -56,4 +69,44 @@ describe('leaflet-tile-layer-wms', () => {
     expect(el.leafletObject?.options.crs).toBe(CRS.EPSG4326);
     el.remove();
   });
+
+  it('picks up a CRS Leaflet does not ship from a nested provider element', () => {
+    const pluginCrs = { ...CRS.EPSG3857 } as CRS;
+
+    const el = document.createElement('leaflet-tile-layer-wms');
+    el.setAttribute('url', 'https://wms.example/service');
+    el.setAttribute('layers', 'basic');
+    document.body.append(el);
+    // No attribute and no provider yet -- Leaflet's own default (null, falls
+    // back to the map's crs internally) applies, nothing of ours sets it.
+    expect(el.leafletObject?.options.crs).toBeNull();
+
+    const provider = document.createElement('test-crs-provider') as TestCRSProvider;
+    provider.crs = pluginCrs;
+    const objectBeforeRecreate = el.leafletObject;
+    // Connecting fires leaflet-crs-changed, bubbling to el.
+    el.append(provider);
+
+    // crs is construction-only: picking it up means a rebuilt object.
+    expect(el.leafletObject).not.toBe(objectBeforeRecreate);
+    expect(el.leafletObject?.options.crs).toBe(pluginCrs);
+    el.remove();
+  });
+
+  it('a nested provider overrides the crs attribute', () => {
+    const pluginCrs = { ...CRS.EPSG3857 } as CRS;
+
+    const el = document.createElement('leaflet-tile-layer-wms');
+    el.setAttribute('url', 'https://wms.example/service');
+    el.setAttribute('layers', 'basic');
+    el.setAttribute('crs', 'EPSG4326');
+
+    const provider = document.createElement('test-crs-provider') as TestCRSProvider;
+    provider.crs = pluginCrs;
+    el.append(provider);
+    document.body.append(el);
+
+    expect(el.leafletObject?.options.crs).toBe(pluginCrs);
+    el.remove();
+  });
 });

test/core/with-props.test.ts

@@ -254,6 +254,41 @@ describe('WithProps: recreate option', () => {
     expect(created).toHaveBeenCalledTimes(2);
     node.remove();
   });
+
+  it('re-registers the new object with the parent (recreateLeafletObject is a public method)', () => {
+    const props = { radius: num<FakeObj>(5) } as const;
+    class El extends WithProps<FakeObj, typeof props>(props) {
+      createLeafletObject(): FakeObj {
+        return new FakeObj();
+      }
+    }
+    const tag = 'wp-recreate-reregisters';
+    customElements.define(tag, El);
+
+    const parent = document.createElement('div');
+    document.body.append(parent);
+    const registrations: unknown[] = [];
+    parent.addEventListener('leaflet-register', (e: LeafletRegisterEvent) => {
+      registrations.push(e.detail.leafletObject);
+    });
+
+    const node = document.createElement(tag) as HTMLElement & {
+      leafletObject?: FakeObj;
+      recreateLeafletObject(): void;
+    };
+    parent.append(node);
+    expect(registrations).toEqual([node.leafletObject]);
+
+    const first = node.leafletObject;
+    // recreateLeafletObject is declared on the public LeafletElement interface
+    // but, until fixed, only a private implementation existed -- this call
+    // would have thrown "is not a function" at runtime despite type-checking.
+    node.recreateLeafletObject();
+
+    expect(node.leafletObject).not.toBe(first);
+    expect(registrations).toEqual([first, node.leafletObject]);
+    parent.remove();
+  });
 });
 
 describe('WithProps: property accessors', () => {