add fixAwaitInSyncFunction code fix

[srolel]

Fixes #21034

This is pretty straightforward, replacing function expressions/declarations, method declarations and arrow functions with corresponding ones with the async modifier.

There are 2 issues that I need some help with:

1. Replacing the entire node seems to omit the line break at the end of the replaced node. So that this:

class Foo {
    bar() {
        await Promise.resolve();
    }
}

Becomes:

class Foo {
    async bar() {
        await Promise.resolve();
    }}

This happens both in the unit tests, and in manual e2e testing with vscode.

2. codeFixAwaitInSyncFunction7, the test case of an for-await-of loop, fails -

  tests/cases/fourslash/codeFixAwaitInSyncFunction7.ts
         fourslash test codeFixAwaitInSyncFunction7.ts runs correctly:
     Error: Debug Failure. False expression: Token end is child end
      at processChildNode (src\services\formatting\formatting.ts:704:27)
      at src\services\formatting\formatting.ts:629:21
      at visitNode (src\compiler\parser.ts:38:24)
      at Object.forEachChild (src\compiler\parser.ts:285:24)
      at processNode (src\services\formatting\formatting.ts:626:13)
      at processChildNode (src\services\formatting\formatting.ts:712:17)
      at processChildNodes (src\services\formatting\formatting.ts:767:44)
      at src\services\formatting\formatting.ts:632:21
      at visitNodes (src\compiler\parser.ts:44:24)
      at Object.forEachChild (src\compiler\parser.ts:253:24)
      at processNode (src\services\formatting\formatting.ts:626:13)
      at processChildNode (src\services\formatting\formatting.ts:712:17)
      at src\services\formatting\formatting.ts:629:21
      at visitNode (src\compiler\parser.ts:38:24)
      at Object.forEachChild (src\compiler\parser.ts:160:21)
      at processNode (src\services\formatting\formatting.ts:626:13)
      at formatSpanWorker (src\services\formatting\formatting.ts:416:13)
      at src\services\formatting\formatting.ts:346:108
      at Object.getFormattingScanner (src\services\formatting\formattingScanner.ts:41:21)

I tried to debug this for a while, but nothing conclusive. This does not happen when I use the compiled tsserver.js in vscode to test the code fix.

[ghost]

Hi @mosho1, I've created a branch at 1319519 that would just add the keyword to the front of the function instead of replacing the node. That seems to fix the formatting problems since we're only inserting text now.

[srolel]

@andy-ms Thanks, that is a lot better. I picked only the commit with the change, let me know if I should do it differently.

I'm also wondering about those CRs in the tests, I saw them in some tests but not in others. Are they also an outcome of replaceNode or something to do with my editor?

[ghost]

Whoops, I should have removed the comment before pushing.

[ghost]

We could also consider changing an explicit return type T to Promise<T> (if it's not already a promise).

[mhegazy]

nit. Add async modifier to containing function

[mhegazy]

@DanielRosenwasser any better suggestions for the message?

[ghost]

Also check for a .type immediately on either of these, i.e. function(): number { ... } or (): number => { ... }.

[srolel]

After adding this change I refactored getReturnType to not use a switch statement at all since with the added condition the two if statements handle all cases.

[ghost]

if (!entityName || entityName.kind !== SyntaxKind.Identifier || entityName.text !== "Promise")

[ghost]

Use a function getNodes(...): { insertBefore: Node, returnType: Type | undefined } | undefined to avoid repeating this. That would also let you combine the two switch statements from getNodeToInsertBefore and getReturnTypeNode.

[ghost]

(but note @mhegazy's comment about the message)