Improve semicolon detection experience for new files

[mjbvz]

TypeScript Version: 3.6.0-dev.20190810

Search Terms:

• semicolon
• format
• auto import

Repo

For a very simple project:

tsconfig.json

{
    "compilerOptions": {
        "module": "commonjs",
        "target": "es2016",
        "jsx": "preserve"
    },
    "exclude": [
        "node_modules",
    ]
}

constants.ts

export const a = 1
export const b = 1
export const c = 1
export const d = 1
export const e = 1
export const f = 1

main.ts

console.log(a)

1. Trigger auto import quick fix in main.ts on a

Expected behavior:
Since constants.js does not use semicolons, the import should not have a semi colon

Actual behavior:
The added import has a semi colon

I believe this is because the current semicolon detection logic (#31801) requires some number of examples in the current file to learn from. For new files, this means we always default to using semicolons even if the rest of the project is semicolonless

I can understand why we do this, but as a user I found it frustrating that TS would still insert semicolons until I added a certain number of imports (or other statements that are also used by the detection code). I don't know if looking at the rest of your project code is feasible or not for semicolon detection but we should discuss if we can improve the experience for new files

/cc @andrewbranch

Related Issues:

• autoimport should care about semicolons #19882

[mjbvz]

The better solution may be to add an explicit preference for semicolons, similar to one we already have for quotes. Trying to infer if semicolons should be used or not from other files in the project could be messy and prone to errors