Support TypeScript 2.4

[azz]

Main changes to syntax are dynamic imports and string enums. Both should probably "just work" by upgrading the "typescript" package.

https://blogs.msdn.microsoft.com/typescript/2017/06/12/announcing-typescript-2-4-rc/

[soda0289]

The biggest issue we encounter is when they change the produced AST. I just tested out 2.4 and all our tests pass. Should be a painless upgrade.

[vjeux]

I also ran prettier tests on 2.4 and they all pass.

[vjeux]

Looks like there's no way to disable this warning though :(

typescript-eslint-parser/parser.js

Lines 20 to 33 in b7220fd

	if (!isRunningSupportedTypeScriptVersion) {
	const border = "=============";
	const versionWarning = [
	border,
	"WARNING: You are currently running a version of TypeScript which is not officially supported by typescript-eslint-parser.",
	"You may find that it works just fine, or you may not.",
	`SUPPORTED TYPESCRIPT VERSIONS: ${SUPPORTED_TYPESCRIPT_VERSIONS}`,
	`YOUR TYPESCRIPT VERSION: ${ACTIVE_TYPESCRIPT_VERSION}`,
	"Please only submit bug reports when using the officially supported version.",
	border
	];
	console.warn(versionWarning.join("\n\n")); // eslint-disable-line no-console
	}

I'd love if you could make a new commit with 2.4 support :)

[soda0289]

I'm not sure if we should change it to typescript 2.4 because then the warning will show when users run typescript 2.3.

We could disable the warning with an option or environment variable. We probably should not be using console.warn anyway and should allow for a logger to be overridden, since this is not a command line tool.

@JamesHenry What do you think should be done in this case?

[vjeux]

What about having a range of versions you support?

[vjeux]

A way to disable it without changing the code would be great though

[azz]

Semver ~2.3.2 || ~2.4?

[JamesHenry]

It does seem a little strange to me to change to explicitly supporting a Release Candidate of an upcoming version... Supporting multiple stable versions would be a different question, and perhaps one we should look into.

@azz @vjeux Even if prettier decides to jump straight into the RC before it is stable, I don't think we need to change things here.

Would you be happy with us exposing a way to suppress the warning as a way to solve this particular issue?