Allow image pasting in plain mode in RTE (#11056)

* get rough funcitonality working

* try to tidy up types

* fix merge error

* fix signature change error

* type wrangling

* use onBeforeInput listener

* add onBeforeInput handler, add logic to onPaste

* fix type error

* bring plain text listeners in line with useInputEventProcessor

* extract common function to util file, move tests

* tidy comment

* tidy comments

* fix typo

* add util tests

* add text paste test

test/components/views/rooms/wysiwyg_composer/components/PlainTextComposer-test.tsx

@@ -290,4 +290,16 @@ describe("PlainTextComposer", () => {
 
         expect(screen.getByTestId("autocomplete-wrapper")).toBeInTheDocument();
     });
+
+    it("Should allow pasting of text values", async () => {
+        customRender();
+
+        const textBox = screen.getByRole("textbox");
+
+        await userEvent.click(textBox);
+        await userEvent.type(textBox, "hello");
+        await userEvent.paste(" world");
+
+        expect(textBox).toHaveTextContent("hello world");
+    });
 });

test/components/views/rooms/wysiwyg_composer/hooks/utils-test.tsx

@@ -16,11 +16,14 @@ limitations under the License.
 import { IEventRelation, MatrixEvent } from "matrix-js-sdk/src/matrix";
 import { waitFor } from "@testing-library/react";
 
-import { handleClipboardEvent } from "../../../../../../src/components/views/rooms/wysiwyg_composer/hooks/useInputEventProcessor";
 import { TimelineRenderingType } from "../../../../../../src/contexts/RoomContext";
 import { mkStubRoom, stubClient } from "../../../../../test-utils";
 import ContentMessages from "../../../../../../src/ContentMessages";
 import { IRoomState } from "../../../../../../src/components/structures/RoomView";
+import {
+    handleClipboardEvent,
+    isEventToHandleAsClipboardEvent,
+} from "../../../../../../src/components/views/rooms/wysiwyg_composer/hooks/utils";
 
 const mockClient = stubClient();
 const mockRoom = mkStubRoom("mock room", "mock room", mockClient);
@@ -285,3 +288,26 @@ describe("handleClipboardEvent", () => {
         expect(output).toBe(true);
     });
 });
+
+describe("isEventToHandleAsClipboardEvent", () => {
+    it("returns true for ClipboardEvent", () => {
+        const input = new ClipboardEvent("clipboard");
+        expect(isEventToHandleAsClipboardEvent(input)).toBe(true);
+    });
+
+    it("returns true for special case input", () => {
+        const input = new InputEvent("insertFromPaste", { inputType: "insertFromPaste" });
+        Object.assign(input, { dataTransfer: "not null" });
+        expect(isEventToHandleAsClipboardEvent(input)).toBe(true);
+    });
+
+    it("returns false for regular InputEvent", () => {
+        const input = new InputEvent("input");
+        expect(isEventToHandleAsClipboardEvent(input)).toBe(false);
+    });
+
+    it("returns false for other input", () => {
+        const input = new KeyboardEvent("keyboard");
+        expect(isEventToHandleAsClipboardEvent(input)).toBe(false);
+    });
+});