fix: prevent false positive warnings for fetch in Firefox and Safari

[eltigerchino]

fixes #7992

Only Chrome-like browsers have a short stack trace, leading to a correct fetch warning. However, Safari and Firefox both have a stack trace from the beginning of the client-side initialisation, leading to false positive warnings.

The fix is to cut off the stack trace at the point where the load function is invoked/mentioned. This makes the stack traces for Firefox and Safari similar to Chrome.

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[benmccann]

do you think there's some test we could add for this to the cross-browser test suite that runs in webkit?

[eltigerchino]

do you think there's some test we could add for this to the cross-browser test suite that runs in webkit?

You're right! I think we can definitely add one. I'll try to cook up something tonight.

[eltigerchino]

There's already a test in test/client.test.js that I considered moving to cross-platform and adapting to include the false-positive test.

kit/packages/kit/test/apps/basics/test/client.test.js

Lines 231 to 262 in 4315e0b

	if (process.env.DEV) {
	test('using window.fetch causes a warning', async ({ page, baseURL }) => {
	await Promise.all([
	page.goto('/load/window-fetch/incorrect'),
	page.waitForEvent('console', {
	predicate: (message) => {
	return (
	message.text() ===
	`Loading ${baseURL}/load/window-fetch/data.json using \`window.fetch\`. For best results, use the \`fetch\` that is passed to your \`load\` function: https://kit.svelte.dev/docs/load#making-fetch-requests`
	);
	},
	timeout: 3_000
	})
	]);
	expect(await page.textContent('h1')).toBe('42');
	/** @type {string[]} */
	const warnings = [];
	page.on('console', (msg) => {
	if (msg.type() === 'warning') {
	warnings.push(msg.text());
	}
	});
	await page.goto('/load/window-fetch/correct');
	expect(await page.textContent('h1')).toBe('42');
	expect(warnings).not.toContain(
	`Loading ${baseURL}/load/window-fetch/data.json using \`window.fetch\`. For best results, use the \`fetch\` that is passed to your \`load\` function: https://kit.svelte.dev/docs/load#making-fetch-requests`
	);
	});
	}

Ultimately, decided against it but did use it as a reference for the false-positive specific test in test/cross-platform/client.test.js. Still feels a bit weird not co-locating it with the actual window.fetch warning test.

[eltigerchino]

I wasn't sure where to put this test, or how best to describe it. Open to suggestions.

[Rich-Harris]

this seems like as good a place as any 👍