Done, but do not merge yet: Async/Await syntax. #600

operand-expr += `await` unary-expr

operand-expr += `async` es6-arrow-expression

Existing code using async/await as identifiers in e.g. record field names will keep working.

…d as async arrow function

Reasoning: In JavaScript `await` is a keyword *only* inside async functions. ```javascript let await = 1 // OK ✅ async function wait() { let await = 1 // NOT OK ❌ } ``` The plot twist is that the newer browsers (chrome or node) support top-level await. (By implicitly wrapping everything in an async function?) ```javascript let await = 1 // NOT OK, with top level await ❌ ``` This makes me think: * We can replicate JavaScript parser; inside async function expressions, use of `await` as identifier will result into a syntax error - Downside: this feels like a responsibility for another part of the compiler, not the parser? This is already implemented in cristianoc/rescript-compiler-experiments#1, so we would also be doing double work. - Other downside: if we ever allow top-level await, then we just implemented the above for nothing. * Allow `await` as a "non-keyword" everywhere with some "tricks". ```javascript let await = 1 let x = await // Ok, now it gets tricky. Does this start an "await"-expression? = await fetch(url) // could be this = await() // could be this = await await() // or even this = await // or we might just be assigning the identifier `await` to `x` ``` Seems like we can infer the following rules for an `await expression`: - space after `await` - next token is on the same line as `await` - next token indicates the start of a unary expression But this "breaks down" in the case of ```javascript let x = await - 1 // could be a binary expression: "identifier" MINUS "1" // could also be an await expression with a unary expression: `await` `(-1)` ``` These whitespace sensitive rules kinda feel super arbitrary. Which makes me think that introducing `await` as a keyword is an ok compromise.

See #600 (comment)

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Done, but do not merge yet: Async/Await syntax. #600

Done, but do not merge yet: Async/Await syntax. #600

Commits on Jul 18, 2022