Add a test for generic mixins.

Author: bicknellr

test/flavors/custom-element/member-test.ts

@@ -35,7 +35,7 @@ tsTest("Member types can be retrieved", t => {
 	t.truthy(isAssignableToType({ kind: "NUMBER" }, toSimpleType(type, checker)));
 });
 
-tsTest("Property declaration member types are specialized", t => {
+tsTest("Property declaration member types are specialized (classes)", t => {
 	const {
 		results: [result],
 		checker
@@ -70,6 +70,44 @@ tsTest("Property declaration member types are specialized", t => {
 	t.truthy(isAssignableToType(optional({ kind: "BOOLEAN" }), toSimpleType(booleanElementPropType, checker)));
 });
 
+tsTest("Property declaration member types are specialized (mixins)", t => {
+	const {
+		results: [result],
+		checker
+	} = analyzeTextWithCurrentTsModule([
+		{
+			fileName: "main.ts",
+			text: `
+				const SomeMixin = <T, C>(Base: C) => {
+					class Mixin extends Base {
+						prop?: T;
+					}
+					return Mixin;
+				}
+
+				class NumberPropElement extends SomeMixin<number>(HTMLElement) {}
+
+				class BooleanPropElement extends SomeMixin<boolean>(HTMLElement) {}
+
+				declare global {
+					interface HTMLElementTagNameMap {
+						"number-prop-element": NumberPropElement;
+						"boolean-prop-element": BooleanPropElement;
+					}
+				}
+			`
+		}
+	]);
+
+	const numberElementDecl = result.componentDefinitions.find(x => x.tagName === "number-prop-element")!.declaration!;
+	const numberElementPropType = getComponentProp(numberElementDecl.members, "prop")!.type!(numberElementDecl);
+	t.truthy(isAssignableToType(optional({ kind: "NUMBER" }), toSimpleType(numberElementPropType, checker)));
+
+	const booleanElementDecl = result.componentDefinitions.find(x => x.tagName === "boolean-prop-element")!.declaration!;
+	const booleanElementPropType = getComponentProp(booleanElementDecl.members, "prop")!.type!(booleanElementDecl);
+	t.truthy(isAssignableToType(optional({ kind: "BOOLEAN" }), toSimpleType(booleanElementPropType, checker)));
+});
+
 tsTest("Getter member types are specialized", t => {
 	const {
 		results: [result],