refactor: yarn constraint determination

[rarkins]

Changes

Refactors and adds a test for yarn constraint determination.

Context

Preparing for #27656

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

[rarkins]

Apparently we fall back to Yarn 2 right now:

renovate/lib/modules/manager/npm/extract/yarn.ts

Lines 102 to 116 in 66db519

	export function getYarnVersionFromLock(lockfile: LockFile): string {
	const { lockfileVersion, isYarn1 } = lockfile;
	if (isYarn1) {
	return '^1.22.18';
	}
	if (lockfileVersion && lockfileVersion >= 8) {
	// https://github.com/yarnpkg/berry/commit/9bcd27ae34aee77a567dd104947407532fa179b3
	return '^3.0.0';
	} else if (lockfileVersion && lockfileVersion >= 6) {
	// https://github.com/yarnpkg/berry/commit/f753790380cbda5b55d028ea84b199445129f9ba
	return '^2.2.0';
	}
	return '^2.0.0';
	}

[rarkins]

Apparently we default to Yarn v2 due to this:

renovate/lib/modules/manager/npm/extract/yarn.ts

Lines 102 to 116 in 66db519

	export function getYarnVersionFromLock(lockfile: LockFile): string {
	const { lockfileVersion, isYarn1 } = lockfile;
	if (isYarn1) {
	return '^1.22.18';
	}
	if (lockfileVersion && lockfileVersion >= 8) {
	// https://github.com/yarnpkg/berry/commit/9bcd27ae34aee77a567dd104947407532fa179b3
	return '^3.0.0';
	} else if (lockfileVersion && lockfileVersion >= 6) {
	// https://github.com/yarnpkg/berry/commit/f753790380cbda5b55d028ea84b199445129f9ba
	return '^2.2.0';
	}
	return '^2.0.0';
	}

[rarkins]

These lines are unreachable due to

renovate/lib/modules/manager/npm/extract/yarn.ts

Lines 102 to 116 in 66db519

	export function getYarnVersionFromLock(lockfile: LockFile): string {
	const { lockfileVersion, isYarn1 } = lockfile;
	if (isYarn1) {
	return '^1.22.18';
	}
	if (lockfileVersion && lockfileVersion >= 8) {
	// https://github.com/yarnpkg/berry/commit/9bcd27ae34aee77a567dd104947407532fa179b3
	return '^3.0.0';
	} else if (lockfileVersion && lockfileVersion >= 6) {
	// https://github.com/yarnpkg/berry/commit/f753790380cbda5b55d028ea84b199445129f9ba
	return '^2.2.0';
	}
	return '^2.0.0';
	}

[viceice]

so simply return lock constraint?

[viceice]

didn't we agree to use this first?

[viceice]

so simply return lock constraint?

[viceice]

we should latest yarn if no constraints can be found.