Fix extra newline in fullscreen mode (#769)

Author: yukukotani

src/ink.tsx

@@ -238,7 +238,7 @@ export default class Ink {
 
 		if (this.lastOutputHeight >= this.options.stdout.rows) {
 			this.options.stdout.write(
-				ansiEscapes.clearTerminal + this.fullStaticOutput + output + '\n',
+				ansiEscapes.clearTerminal + this.fullStaticOutput + output,
 			);
 			this.lastOutput = output;
 			this.lastOutputHeight = outputHeight;

test/fixtures/fullscreen-no-extra-newline.tsx

@@ -0,0 +1,35 @@
+import process from 'node:process';
+import React, {useEffect} from 'react';
+import {Box, Text, render, useApp} from '../../src/index.js';
+
+function Fullscreen() {
+	const {exit} = useApp();
+
+	useEffect(() => {
+		// Exit after first render to check the output
+		const timer = setTimeout(() => {
+			exit();
+		}, 100);
+
+		return () => {
+			clearTimeout(timer);
+		};
+	}, [exit]);
+
+	// Force the root to occupy exactly terminal rows
+	const rows = Number(process.argv[2]) || 5;
+
+	return (
+		<Box height={rows} flexDirection="column">
+			<Box flexGrow={1}>
+				<Text>Full-screen: top</Text>
+			</Box>
+			<Text>Bottom line (should be usable)</Text>
+		</Box>
+	);
+}
+
+// Set terminal size from argument
+process.stdout.rows = Number(process.argv[2]) || 5;
+
+render(<Fullscreen />);

test/render.tsx

@@ -144,6 +144,32 @@ test.serial('erase screen where state changes in small viewport', async t => {
 	}
 });
 
+test.serial(
+	'fullscreen mode should not add extra newline at the bottom',
+	async t => {
+		const ps = term('fullscreen-no-extra-newline', ['5']);
+		await ps.waitForExit();
+
+		t.true(ps.output.includes('Bottom line'));
+
+		const lastFrame = ps.output.split(ansiEscapes.clearTerminal).at(-1) ?? '';
+
+		// Check that the bottom line is at the end without extra newlines
+		// In a 5-line terminal:
+		// Line 1: Fullscreen: top
+		// Lines 2-4: empty (from flexGrow)
+		// Line 5: Bottom line (should be usable)
+		const lines = lastFrame.split('\n');
+
+		t.is(lines.length, 5, 'Should have exactly 5 lines for 5-row terminal');
+
+		t.true(
+			lines[4]?.includes('Bottom line') ?? false,
+			'Bottom line should be on line 5',
+		);
+	},
+);
+
 test.serial('clear output', async t => {
 	const ps = term('clear');
 	await ps.waitForExit();