Allow unknown namespaced attributes to be emitted in their original case

src/compiler/compile/render_dom/wrappers/Element/Attribute.ts

@@ -8,6 +8,7 @@ import Expression from '../../../nodes/shared/Expression';
 import Text from '../../../nodes/Text';
 import handle_select_value_binding from './handle_select_value_binding';
 import { Identifier, Node } from 'estree';
+import { namespaces, valid_namespaces } from '../../../../utils/namespaces';
 
 export class BaseAttributeWrapper {
 	node: Attribute;
@@ -66,16 +67,32 @@ export default class AttributeWrapper extends BaseAttributeWrapper {
 			}
 		}
 		
+		const namespace = this.parent.node.namespace;
+		// some processing only applies to html namespace (and not MathML, SVG, or Svelte Native etc)
+		if (namespace && namespace != 'html' && namespace != namespaces.html) {
+			// attributes outside of the html namespaced may be case sensitive
+			// namespaces for which we don't have case corrections, are left in their original case (required for svelte-native)
+			this.name = (valid_namespaces.indexOf(namespace) >= 0) ? fix_attribute_casing(this.node.name) : this.node.name;
+			this.is_indirectly_bound_value = false;
+			this.metadata = null;
+			this.property_name = null;
+			this.is_select_value_attribute = false;
+			this.is_input_value = false;
+		} else {
 			this.name = fix_attribute_casing(this.node.name);
 			this.metadata = this.get_metadata();
 			this.is_indirectly_bound_value = is_indirectly_bound_value(this);
 			this.property_name = this.is_indirectly_bound_value
 				? '__value'
 				: this.metadata && this.metadata.property_name;
-		this.is_src = this.name === 'src'; // TODO retire this exception in favour of https://github.com/sveltejs/svelte/issues/3750
+
 			this.is_select_value_attribute = this.name === 'value' && this.parent.node.name === 'select';
 			this.is_input_value = this.name === 'value' && this.parent.node.name === 'input';
+		}
+
+		this.is_src = this.name === 'src'; // TODO retire this exception in favour of https://github.com/sveltejs/svelte/issues/3750
 		this.should_cache = should_cache(this);
+
 	}
 
 	render(block: Block) {

test/runtime/samples/attribute-casing-unknown-namespace/_config.js

@@ -0,0 +1,18 @@
+// Test support for unknown namespaces preserving attribute case (eg svelte-native).
+
+export default {
+	html: `
+		<page xmlns="tns" horizontalAlignment="center">
+			<button textWrap="true" text="button">
+		</page>
+	`,
+	options: {
+		hydrate: false, // Hydrations currently doesn't work, the case sensitivity is only handled for svg elements.
+	},
+
+	test({ assert, target }) {
+		const attr = sel => target.querySelector(sel).attributes[0].name;
+		assert.equal(attr('page'), "horizontalAlignment");
+		assert.equal(attr('button'), "textWrap")
+	}
+};

test/runtime/samples/attribute-casing-unknown-namespace/main.svelte

@@ -0,0 +1,3 @@
+<page horizontalAlignment="center" xmlns="tns">
+	<button textWrap="true" text="button">
+</page>