feat: add jsx support

[erquhart]

Adds JSX support.

Notes

• Changed the general test suite to use the esprima dependency rather than 1.0.0-dev
• Upgraded esprima from 3.1.3 to 4.0.1 for improved JSX support in tests
• Esprima upgrade is causing tests to fail for two reasons:
  • Esprima outputs string literals with double quotes in 1.0.0, but switched to single quotes in 1.1.0 (source)
  • Esprima no longer represents the presence of a leading 0 in a decimal, so instead of "0.14" it's ".14", both for value and raw
• Besides the above mentioned issues, tests are passing
• JSX SpreadChild and Fragments are not supported in this PR, as support for them is not quite widespread (esprima supports neither, I'd consider that to be a decent indicator)

Todo

• determine if any cases merit throwing an error
• format output appropriately for compact/non-compact
• precedence/flag usage review by a maintainer for all uses of generateExpression()

Closes #333.

[papandreou]

I'm no JSX expert, I just wanted to get serialization support in assetgraph. Thanks a lot for picking this up!

I tried npm linking escodegen in with this change, and it seems to do the job! 👍

Would be nice to get support for JSXFragment while you're at it. It's not supported by esprima yet, but you can test that with acorn or espree, for example.

[papandreou]

You also need to handle expr.value.type === 'JSXElement' here.

> require('escodegen').generate(require('esprima').parse('(<Foo bar=<Quux/>/>)', {jsx: true}));
'<Foo undefined />;'

And JSXFragment as well, if you go for that: https://github.com/facebook/jsx/blob/master/AST.md#jsx-attributes

[erquhart]

Totally forgot about boolean attributes, good catch 👍

[erquhart]

Haven't forgotten about this, will circle back soon.

[zouxuoz]

@erquhart how I can help you to finish this update?

[erquhart]

Just a matter of when, haven't circled back yet. An old fork (https://github.com/ng-vu/escodegen-jsx) that introduced (incompatible) jsx support had some things that felt necessary, so the plan has been to pull in the more thorough bits from there. If you want to take this across the finish line, by all means please do!

[sag1v]

Is JSX going to be supported or is there any other way to do it?

[smol-honk]

What if we added this https://github.com/wallabyjs/escodegen?