feat: support @ file autocomplete in ask editor

src/ui/autocomplete.ts

@@ -0,0 +1,49 @@
+import { accessSync, constants as fsConstants } from "node:fs";
+import { delimiter, join } from "node:path";
+import { CombinedAutocompleteProvider } from "@mariozechner/pi-tui";
+
+const FD_BINARY_NAMES =
+	process.platform === "win32"
+		? ["fd.exe", "fdfind.exe", "fd", "fdfind"]
+		: ["fd", "fdfind"];
+
+/**
+ * pi resolves fd internally for its main editor, but that resolver is not part of
+ * the public extension API. Custom editors therefore need to supply the fd path
+ * themselves when reusing CombinedAutocompleteProvider for `@` file mentions.
+ */
+export function createAskAutocompleteProvider(cwd: string) {
+	return new CombinedAutocompleteProvider(
+		[],
+		cwd,
+		findAutocompleteBinary(FD_BINARY_NAMES)
+	);
+}
+
+function findAutocompleteBinary(binaryNames: readonly string[]): string | null {
+	const pathValue = process.env.PATH;
+	if (!pathValue) {
+		return null;
+	}
+
+	const directories = pathValue.split(delimiter).filter(Boolean);
+	for (const binaryName of binaryNames) {
+		const executablePath = directories
+			.map((directory) => join(directory, binaryName))
+			.find(isExecutableFile);
+		if (executablePath) {
+			return executablePath;
+		}
+	}
+
+	return null;
+}
+
+function isExecutableFile(path: string): boolean {
+	try {
+		accessSync(path, fsConstants.X_OK);
+		return true;
+	} catch {
+		return false;
+	}
+}