feat(editor): select line on CodeMirror line number gutter click

src/cm/lineNumberSelection.ts

@@ -0,0 +1,115 @@
+import { EditorSelection } from "@codemirror/state";
+import type { BlockInfo, EditorView } from "@codemirror/view";
+
+type LineInfo = Pick<BlockInfo, "from" | "to"> | null | undefined;
+
+type LineNumberClickEvent = Pick<
+	MouseEvent,
+	| "button"
+	| "shiftKey"
+	| "altKey"
+	| "ctrlKey"
+	| "metaKey"
+	| "preventDefault"
+	| "defaultPrevented"
+>;
+
+function toDocumentOffset(
+	value: number | null | undefined,
+	fallback = 0,
+): number {
+	const resolved = value != null ? Number(value) : fallback;
+	return Number.isFinite(resolved) ? resolved : fallback;
+}
+
+/**
+ * Resolve the selection range for a clicked document line.
+ * Includes the trailing line break when one exists to mirror Ace's
+ * full-line selection behavior.
+ */
+export function getLineSelectionRange(
+	state: EditorView["state"],
+	line: LineInfo,
+): { from: number; to: number } | null {
+	if (!line) return null;
+	const from = Math.max(0, toDocumentOffset(line.from));
+	const to = Math.max(from, toDocumentOffset(line.to, from));
+	return {
+		from,
+		to: Math.min(to + 1, state.doc.length),
+	};
+}
+
+function getCurrentSelectionLineRange(state: EditorView["state"]): {
+	from: number;
+	to: number;
+} {
+	const selection = state.selection.main;
+	const startLine = state.doc.lineAt(selection.from);
+	const endPos = selection.empty
+		? selection.head
+		: Math.max(selection.to - 1, selection.from);
+	const endLine = state.doc.lineAt(endPos);
+	const startRange = getLineSelectionRange(state, startLine);
+	const endRange = getLineSelectionRange(state, endLine);
+
+	return {
+		from: startRange?.from ?? selection.from,
+		to: endRange?.to ?? selection.to,
+	};
+}
+
+function createLineSelection(range: {
+	from: number;
+	to: number;
+}): EditorSelection {
+	return EditorSelection.single(range.to, range.from);
+}
+
+function createExtendedLineSelection(
+	state: EditorView["state"],
+	clickedRange: { from: number; to: number },
+): EditorSelection {
+	const currentRange = getCurrentSelectionLineRange(state);
+	const from = Math.min(currentRange.from, clickedRange.from);
+	const to = Math.max(currentRange.to, clickedRange.to);
+
+	if (clickedRange.from <= currentRange.from) {
+		return EditorSelection.single(to, from);
+	}
+
+	return EditorSelection.single(from, to);
+}
+
+/**
+ * Select the clicked line from the line-number gutter.
+ * Shift-click extends the current selection by whole lines.
+ * Other modified or non-primary clicks are ignored so they don't interfere
+ * with context menus or alternate selection gestures.
+ */
+export function handleLineNumberClick(
+	view: EditorView | null | undefined,
+	line: LineInfo,
+	event: LineNumberClickEvent | null | undefined,
+): boolean {
+	if (!view || !event || event.defaultPrevented) return false;
+	if ((event.button ?? 0) !== 0) return false;
+	if (event.altKey || event.ctrlKey || event.metaKey) {
+		return false;
+	}
+
+	const range = getLineSelectionRange(view.state, line);
+	if (!range) return false;
+
+	event.preventDefault();
+	view.dispatch({
+		selection: event.shiftKey
+			? createExtendedLineSelection(view.state, range)
+			: createLineSelection(range),
+		userEvent: event.shiftKey ? "select.extend.pointer" : "select.pointer",
+	});
+	view.focus();
+	return true;
+}
+
+export default handleLineNumberClick;

src/lib/editorManager.js

@@ -31,6 +31,7 @@ import {
 	registerExternalCommand,
 	removeExternalCommand,
 } from "cm/commandRegistry";
+import { handleLineNumberClick } from "cm/lineNumberSelection";
 import lspApi from "cm/lsp/api";
 import lspClientManager from "cm/lsp/clientManager";
 import {
@@ -289,6 +290,13 @@ async function EditorManager($header, $body) {
 	function makeLineNumberExtension() {
 		const { linenumbers = true, relativeLineNumbers = false } =
 			appSettings?.value || {};
+		const lineNumberConfig = {
+			domEventHandlers: {
+				click(view, line, event) {
+					return handleLineNumberClick(view, line, event);
+				},
+			},
+		};
 		if (!linenumbers)
 			return EditorView.theme({
 				".cm-gutter": {
@@ -299,9 +307,13 @@ async function EditorManager($header, $body) {
 				},
 			});
 		if (!relativeLineNumbers)
-			return Prec.highest([lineNumbers(), highlightActiveLineGutter()]);
+			return Prec.highest([
+				lineNumbers(lineNumberConfig),
+				highlightActiveLineGutter(),
+			]);
 		return Prec.highest([
 			lineNumbers({
+				...lineNumberConfig,
 				formatNumber: (lineNo, state) => {
 					try {
 						const cur = state.doc.lineAt(state.selection.main.head).number;