Options to force trailing comma on interfaces declaration

[Strate]

I want to force trailing comma on interface declaration:

interface A {
  prop1: string,
  prop2: string,
  prop3: string,
}

Is there any option to do this?

[jkillian]

The trailing-comma rule only checks array literals, object literals, named import lists, and destructuring constructs right now, so unfortunately there's no way to have object literal types checked, whether in an interface declaration like this or as a declared type somewhere else.

Seems like a reasonable feature request though - I've tagged it as such.

[adidahiya]

aren't fields in an interface supposed to end with a trailing semicolon?

http://www.typescriptlang.org/Handbook#interfaces

[jkillian]

I had thought so also, but the Interface grammar allows for semicolons or commas.

[jkillian]

See #1233 for discussion on this issue. The "ignore-interfaces" option for the semicolon rule will let users make a custom rule for this request if desired.

[schickling]

Since version 4.0 this seems to be always enforced when using multiline: "always". Is there a way to allow to omit trailing commas for interfaces? I imagine the following:

  "rules": {
    "trailing-comma": [
      true,
      {
        "multiline": "always",
        "singleline": "never"
      },
      "ignore-interfaces"
    ]
  }

Unfortunately this change seemed to have broke all of our build once we upgraded to v4.

[schickling]

Maybe @jkillian knows something about this?

[adidahiya]

@schickling the "ignore-interfaces" is supported in the semicolon rule, not the trailing-comma rule (see the linked PR #1233). What exact format are you looking to write interfaces with? I'm a little hesitant to add more options to this rule, especially since TSLint v4 will automatically fix all violations of the trailing-comma rule for you.

[schickling]

This is the way how we write interfaces:

interface Post {
  title: string
  age: number
}

[Zjaaspoer]

We're writing our interfaces the exact same way as @schickling (basically interfaces without semicolons). Right now Tslint is adding trailing commas to the last row like so:

interface Post {
  title: string
  age: number,
}

which is a bit undesirable... :) I'm not sure what the best strategy is to resolve this, but probably the trailing comma's should only be added if the other rows in the interface already have a comma?

[adidahiya]

Yeah that makes sense @Zjaaspoer; filed #1810 for you and @schickling

[Zjaaspoer]

great thanks!

[theodorejb]

We use commas to separate interface properties, and I'd really like an option to enforce this.

[muuvmuuv]

This affects this case as well:

fs.writeFile(
    ContentsJSONFile,
    JSON.stringify(ContentsJSON, null, 2),
    (err) => {
      if (err) {
        throw new Error(err.message)
      }

      console.log(chalk.green(`Wrote \`Contents.json\` file for ${set.name}!`))
    } // <!-- Missing trailing comma (trailing-comma) tslint(1)
  )