Add do expressions proposal plugin

[pascalduez]

Proposal (stage 1)

https://github.com/tc39/proposal-do-expressions
https://github.com/tc39/proposals#stage-1

ESLint (support through a plugin)

Update our ESLint config, use eslint-plugin-babel.

-  "plugins": ["flowtype", "jest"],
+  "plugins": ["babel", "flowtype",  "jest"],

+    "no-unused-expressions": "off",

+    "babel/no-unused-expressions": "error",

Flow (no support yet)

facebook/flow#560
facebook/flow#6417

TypeScript (no support yet)

microsoft/TypeScript#13156

Prettier

Seems okay

Conclusion

Might still be a bit early?

See also

https://github.com/tc39/proposal-pattern-matching

[ziir]

Ah, too bad Flow will raise unexpected token errors on this.

I would love do-expressions and pattern-matching but I guess we need to wait and see if either of those get further in the standardization process / get supported by Flow ?