Update Yams dependency to "from: 4.0.0"

[e28eta]

Manually building toolbox-18.3.5 on macOS logs the following compiler warnings:

Working copy of https://github.com/jpsim/Yams.git resolved at 2.0.0
/Users/daniel/Downloads/toolbox-18.3.5/.build/checkouts/Yams/Sources/Yams/Emitter.swift:338:32: warning: initialization of 'UnsafeMutablePointer<yaml_version_directive_t>' (aka 'UnsafeMutablePointer<yaml_version_directive_s>') results in a dangling pointer
            versionDirective = UnsafeMutablePointer(&versionDirectiveValue)
                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Users/daniel/Downloads/toolbox-18.3.5/.build/checkouts/Yams/Sources/Yams/Emitter.swift:338:53: note: implicit argument conversion from 'yaml_version_directive_t' (aka 'yaml_version_directive_s') to 'UnsafeMutablePointer<yaml_version_directive_t>' (aka 'UnsafeMutablePointer<yaml_version_directive_s>') produces a pointer valid only for the duration of the call to 'init(_:)'
            versionDirective = UnsafeMutablePointer(&versionDirectiveValue)
                                                    ^~~~~~~~~~~~~~~~~~~~~~
/Users/daniel/Downloads/toolbox-18.3.5/.build/checkouts/Yams/Sources/Yams/Emitter.swift:338:53: note: use 'withUnsafeMutablePointer' in order to explicitly convert argument to pointer valid for a defined scope
            versionDirective = UnsafeMutablePointer(&versionDirectiveValue)

This issue was solved in Yams v3.0, almost 2 years ago. Looking through the version history, there are other bug fixes, which may/may not have any impact on vapor.

Given that vapor's documentation says Swift 5.2+ is required, and Yams v4 only requires 5.1+ (but Yams v5 requires 5.4+), this feels like a good dependency update to make.

I wasn't able to do a great job testing this, but I think it's working correctly.

• It compiles and runs for me.
• vapor new works with the default template.
• I only found one other template that uses a manifest.yml when searching for vapor + template topics (per recommendation in older versions of the docs). That template also works.

This seems to be the only usage of Yams in the toolbox, that I could find.

toolbox/Sources/VaporToolbox/New/New.swift

Lines 32 to 45 in 5ffe48f

	let gitUrl = signature.templateURL ?? "https://github.com/vapor/template"
	let cwd = FileManager.default.currentDirectoryPath
	let workTree = signature.outputDirectory?.asDirectoryURL.path ?? cwd.appendingPathComponents(name)
	let templateTree = workTree.deletingLastPathComponents().appendingPathComponents(".vapor-template")
	context.console.info("Cloning template...")
	try? FileManager.default.removeItem(atPath: templateTree)
	let gitBranch = signature.templateBranch ?? "main"
	_ = try Process.git.clone(repo: gitUrl, toFolder: templateTree, branch: gitBranch)
	if FileManager.default.fileExists(atPath: templateTree.appendingPathComponents("manifest.yml")) {
	try FileManager.default.createDirectory(atPath: workTree, withIntermediateDirectories: false, attributes: nil)
	let yaml = try String(contentsOf: templateTree.appendingPathComponents("manifest.yml").asFileURL, encoding: .utf8)
	let manifest = try YAMLDecoder().decode(TemplateManifest.self, from: yaml)

[0xTim]

Thanks for fixing this!