Async Functions

[rbuckton]

Support for Async Functions, as per the proposal in #1664.

• Adds a node factory and node tree visitor (factory.ts, factory.generated.ts)
• Adds a general code generator and locals builder (generator.ts)
• Adds a node rewriter for destructuring, spread element, and async functions (rewriter.ts)
• Adds support for parsing async functions and the await keyword (scanner.ts, parser.ts)
• Adds type check for await and async function return types
• Adds call to rewriter for async functions during emit (emitter.ts)
• Adds __awaiter and __generator helper functions to emit output (emitter.ts)

[JsonFreeman]

When you say "the type has a construct signature...", you don't really mean the type. You mean the type resulting from resolving the name of that type as a value.

[JsonFreeman]

I understand now. This is very ES6-y. I prefer the model where ambient flags are passed by just doing nothing, and flags are explicitly turned on and off. I know that what you've done here is more to the grammar, but for some reason I find it less intuitive.

[teobugslayer]

Hello @rbuckton,

I've tried to use your branch and found a compiler crash. Using this code:

async function read(): string {
    return "";
}

gives this output:

c:\Work\asyncpoc\node_modules\typescript\bin\tsc.js:10207
                    if (target.flags & 1)
                              ^
TypeError: Cannot read property 'flags' of undefined
    at isRelatedTo (c:\Work\asyncpoc\node_modules\typescript\bin\tsc.js:10207:31)
    at checkTypeRelatedTo (c:\Work\asyncpoc\node_modules\typescript\bin\tsc.js:10183:26)
    at checkTypeAssignableTo (c:\Work\asyncpoc\node_modules\typescript\bin\tsc.js:10167:20)
    at checkReturnStatement (c:\Work\asyncpoc\node_modules\typescript\bin\tsc.js:14272:29)
    at checkSourceElement (c:\Work\asyncpoc\node_modules\typescript\bin\tsc.js:15005:28)
    at Object.forEach (c:\Work\asyncpoc\node_modules\typescript\bin\tsc.js:74:30)
    at checkBlock (c:\Work\asyncpoc\node_modules\typescript\bin\tsc.js:13881:16)
    at checkSourceElement (c:\Work\asyncpoc\node_modules\typescript\bin\tsc.js:14986:28)
    at checkFunctionLikeDeclaration (c:\Work\asyncpoc\node_modules\typescript\bin\tsc.js:13863:13)
    at checkFunctionDeclaration (c:\Work\asyncpoc\node_modules\typescript\bin\tsc.js:13838:17)

I am using node 0.12.2 x64 on Windows 8.1 and the tsconfig.json is:

{
    "compilerOptions": {
        "module": "commonjs",
        "noImplicitAny": true,
        "removeComments": false,
        "preserveConstEnums": true,
        "sourceMap": true,
        "target": "ES6"
    },
    "files": [ "index.ts", "node.d.ts" ]
}

Hope this helps!

[mhegazy]

closing this in favor of: #3078

[tinganho]

@mhegazy does this mean async functions are only supported in ES6? Then why is that?

[rbuckton]

@tinganho Downlevel support for async functions will likely end up in a separate PR. This one is extremely out of date.

[tinganho]

Ok thanks for explanation @rbuckton . I really want this feature in at least ES5 too.

[nippur72]

@teobugslayer perhaps it's related to #3978, with the difference that one is in the master branch.

[coveralls]

Changes Unknown when pulling d57fe72 on prototypeAsync into * on master*.