fix: show at most one decoration per line

[Skn0tt]

Follow-up to #590.

Instead of capping the number of decorations per file, we now show at most one decoration per line. This still places a good upper limit so we don't overwhelm VS Code rendering with too many decorations. But it also prevents the confusing UI of decorations abruptly cutting off.

Screen.Recording.2025-01-17.at.10.32.07.mov

[pavelfeldman]

A test would be nice!

[pavelfeldman]

drive-by I would pre-compute the editor's uri instead of doing it 1000 times. Maybe even store decorations by line from the get go.

[Skn0tt]

A test would be nice!

the previous PR already added a good test:

playwright-vscode/tests/decorations.spec.ts

Lines 90 to 111 in a95208d

	test('should limit highlights', async ({ activate }) => {
	const { vscode, testController } = await activate({
	'playwright.config.js': `module.exports = { testDir: 'tests' }`,
	'tests/test.spec.ts': `
	import { test, expect } from '@playwright/test';
	test('pass', async () => {
	for (let i = 0; i < 2000; i++) {
	expect(i).toBe(i);
	}
	});
	`,
	});
	await vscode.openEditors('**/test.spec.ts');
	await new Promise(f => testController.onDidChangeTestItem(f));
	await testController.run();
	const decorationsLog = vscode.window.activeTextEditor.renderDecorations(' ');
	const lastState = decorationsLog.substring(decorationsLog.lastIndexOf('------'));
	expect(lastState.split('\n').length).toBeLessThan(2000);
	});