Enable @typescript-eslint/explicit-function-return-type in /src (#9788)

* Enable `@typescript-eslint/explicit-member-accessibility` on /src

* Prettier

* Enable `@typescript-eslint/explicit-function-return-type` in /src

* Fix types

* tsc strict fixes

* Delint

* Fix test

* Fix bad merge

src/components/views/emojipicker/Category.tsx

@@ -49,7 +49,7 @@ interface IProps {
 }
 
 class Category extends React.PureComponent<IProps> {
-    private renderEmojiRow = (rowIndex: number) => {
+    private renderEmojiRow = (rowIndex: number): JSX.Element => {
         const { onClick, onMouseEnter, onMouseLeave, selectedEmojis, emojis } = this.props;
         const emojisForRow = emojis.slice(rowIndex * 8, (rowIndex + 1) * 8);
         return (
@@ -69,7 +69,7 @@ class Category extends React.PureComponent<IProps> {
         );
     };
 
-    public render() {
+    public render(): JSX.Element {
         const { emojis, name, heightBefore, viewportHeight, scrollTop } = this.props;
         if (!emojis || emojis.length === 0) {
             return null;

src/components/views/emojipicker/Emoji.tsx

@@ -30,7 +30,7 @@ interface IProps {
 }
 
 class Emoji extends React.PureComponent<IProps> {
-    public render() {
+    public render(): JSX.Element {
         const { onClick, onMouseEnter, onMouseLeave, emoji, selectedEmojis } = this.props;
         const isSelected = selectedEmojis && selectedEmojis.has(emoji.unicode);
         return (

src/components/views/emojipicker/EmojiPicker.tsx

@@ -141,7 +141,7 @@ class EmojiPicker extends React.Component<IProps, IState> {
         ];
     }
 
-    private onScroll = () => {
+    private onScroll = (): void => {
         const body = this.scrollRef.current?.containerRef.current;
         this.setState({
             scrollTop: body.scrollTop,
@@ -150,7 +150,7 @@ class EmojiPicker extends React.Component<IProps, IState> {
         this.updateVisibility();
     };
 
-    private updateVisibility = () => {
+    private updateVisibility = (): void => {
         const body = this.scrollRef.current?.containerRef.current;
         const rect = body.getBoundingClientRect();
         for (const cat of this.categories) {
@@ -177,13 +177,13 @@ class EmojiPicker extends React.Component<IProps, IState> {
         }
     };
 
-    private scrollToCategory = (category: string) => {
+    private scrollToCategory = (category: string): void => {
         this.scrollRef.current?.containerRef.current
             ?.querySelector(`[data-category-id="${category}"]`)
             .scrollIntoView();
     };
 
-    private onChangeFilter = (filter: string) => {
+    private onChangeFilter = (filter: string): void => {
         const lcFilter = filter.toLowerCase().trim(); // filter is case insensitive
         for (const cat of this.categories) {
             let emojis;
@@ -216,7 +216,7 @@ class EmojiPicker extends React.Component<IProps, IState> {
         );
     };
 
-    private onEnterFilter = () => {
+    private onEnterFilter = (): void => {
         const btn =
             this.scrollRef.current?.containerRef.current?.querySelector<HTMLButtonElement>(".mx_EmojiPicker_item");
         if (btn) {
@@ -224,32 +224,32 @@ class EmojiPicker extends React.Component<IProps, IState> {
         }
     };
 
-    private onHoverEmoji = (emoji: IEmoji) => {
+    private onHoverEmoji = (emoji: IEmoji): void => {
         this.setState({
             previewEmoji: emoji,
         });
     };
 
-    private onHoverEmojiEnd = (emoji: IEmoji) => {
+    private onHoverEmojiEnd = (emoji: IEmoji): void => {
         this.setState({
             previewEmoji: null,
         });
     };
 
-    private onClickEmoji = (emoji: IEmoji) => {
+    private onClickEmoji = (emoji: IEmoji): void => {
         if (this.props.onChoose(emoji.unicode) !== false) {
             recent.add(emoji.unicode);
         }
     };
 
-    private static categoryHeightForEmojiCount(count: number) {
+    private static categoryHeightForEmojiCount(count: number): number {
         if (count === 0) {
             return 0;
         }
         return CATEGORY_HEADER_HEIGHT + Math.ceil(count / EMOJIS_PER_ROW) * EMOJI_HEIGHT;
     }
 
-    public render() {
+    public render(): JSX.Element {
         let heightBefore = 0;
         return (
             <div className="mx_EmojiPicker" data-testid="mx_EmojiPicker">

src/components/views/emojipicker/Header.tsx

@@ -29,7 +29,7 @@ interface IProps {
 }
 
 class Header extends React.PureComponent<IProps> {
-    private findNearestEnabled(index: number, delta: number) {
+    private findNearestEnabled(index: number, delta: number): number {
         index += this.props.categories.length;
         const cats = [...this.props.categories, ...this.props.categories, ...this.props.categories];
 
@@ -39,12 +39,12 @@ class Header extends React.PureComponent<IProps> {
         }
     }
 
-    private changeCategoryRelative(delta: number) {
+    private changeCategoryRelative(delta: number): void {
         const current = this.props.categories.findIndex((c) => c.visible);
         this.changeCategoryAbsolute(current + delta, delta);
     }
 
-    private changeCategoryAbsolute(index: number, delta = 1) {
+    private changeCategoryAbsolute(index: number, delta = 1): void {
         const category = this.props.categories[this.findNearestEnabled(index, delta)];
         if (category) {
             this.props.onAnchorClick(category.id);
@@ -54,7 +54,7 @@ class Header extends React.PureComponent<IProps> {
 
     // Implements ARIA Tabs with Automatic Activation pattern
     // https://www.w3.org/TR/wai-aria-practices/examples/tabs/tabs-1/tabs.html
-    private onKeyDown = (ev: React.KeyboardEvent) => {
+    private onKeyDown = (ev: React.KeyboardEvent): void => {
         let handled = true;
 
         const action = getKeyBindingsManager().getAccessibilityAction(ev);
@@ -82,7 +82,7 @@ class Header extends React.PureComponent<IProps> {
         }
     };
 
-    public render() {
+    public render(): JSX.Element {
         return (
             <nav
                 className="mx_EmojiPicker_header"

src/components/views/emojipicker/Preview.tsx

@@ -24,7 +24,7 @@ interface IProps {
 }
 
 class Preview extends React.PureComponent<IProps> {
-    public render() {
+    public render(): JSX.Element {
         const {
             unicode,
             label,

src/components/views/emojipicker/QuickReactions.tsx

@@ -47,19 +47,19 @@ class QuickReactions extends React.Component<IProps, IState> {
         };
     }
 
-    private onMouseEnter = (emoji: IEmoji) => {
+    private onMouseEnter = (emoji: IEmoji): void => {
         this.setState({
             hover: emoji,
         });
     };
 
-    private onMouseLeave = () => {
+    private onMouseLeave = (): void => {
         this.setState({
             hover: null,
         });
     };
 
-    public render() {
+    public render(): JSX.Element {
         return (
             <section className="mx_EmojiPicker_footer mx_EmojiPicker_quick mx_EmojiPicker_category">
                 <h2 className="mx_EmojiPicker_quick_header mx_EmojiPicker_category_label">

src/components/views/emojipicker/ReactionPicker.tsx

@@ -50,14 +50,14 @@ class ReactionPicker extends React.Component<IProps, IState> {
         this.addListeners();
     }
 
-    public componentDidUpdate(prevProps) {
+    public componentDidUpdate(prevProps): void {
         if (prevProps.reactions !== this.props.reactions) {
             this.addListeners();
             this.onReactionsChange();
         }
     }
 
-    private addListeners() {
+    private addListeners(): void {
         if (this.props.reactions) {
             this.props.reactions.on(RelationsEvent.Add, this.onReactionsChange);
             this.props.reactions.on(RelationsEvent.Remove, this.onReactionsChange);
@@ -65,7 +65,7 @@ class ReactionPicker extends React.Component<IProps, IState> {
         }
     }
 
-    public componentWillUnmount() {
+    public componentWillUnmount(): void {
         if (this.props.reactions) {
             this.props.reactions.removeListener(RelationsEvent.Add, this.onReactionsChange);
             this.props.reactions.removeListener(RelationsEvent.Remove, this.onReactionsChange);
@@ -86,13 +86,13 @@ class ReactionPicker extends React.Component<IProps, IState> {
         );
     }
 
-    private onReactionsChange = () => {
+    private onReactionsChange = (): void => {
         this.setState({
             selectedEmojis: new Set(Object.keys(this.getReactions())),
         });
     };
 
-    private onChoose = (reaction: string) => {
+    private onChoose = (reaction: string): boolean => {
         this.componentWillUnmount();
         this.props.onFinished();
         const myReactions = this.getReactions();
@@ -130,7 +130,7 @@ class ReactionPicker extends React.Component<IProps, IState> {
         return true;
     };
 
-    public render() {
+    public render(): JSX.Element {
         return (
             <EmojiPicker
                 onChoose={this.onChoose}

src/components/views/emojipicker/Search.tsx

@@ -30,12 +30,12 @@ interface IProps {
 class Search extends React.PureComponent<IProps> {
     private inputRef = React.createRef<HTMLInputElement>();
 
-    public componentDidMount() {
+    public componentDidMount(): void {
         // For some reason, neither the autoFocus nor just calling focus() here worked, so here's a window.setTimeout
         window.setTimeout(() => this.inputRef.current.focus(), 0);
     }
 
-    private onKeyDown = (ev: React.KeyboardEvent) => {
+    private onKeyDown = (ev: React.KeyboardEvent): void => {
         const action = getKeyBindingsManager().getAccessibilityAction(ev);
         switch (action) {
             case KeyBindingAction.Enter:
@@ -46,7 +46,7 @@ class Search extends React.PureComponent<IProps> {
         }
     };
 
-    public render() {
+    public render(): JSX.Element {
         let rightButton;
         if (this.props.query) {
             rightButton = (