Typescript: Better error report for equals instead of colon in object literals

[JoshuaKGoldberg]

TypeScript Version: 3.0.0-dev.201xxxxx

Search Terms: object literal cannot find name equals colon

Code

const container = {
    a: "apple",
    b = "banana",
};

Expected behavior:

Use a : please!

Actual behavior:

Cannot find name 'b'.
'=' can only be used in an object literal property inside a destructuring assignment.

Playground Link: http://www.typescriptlang.org/play/#src=const%20container%20%3D%20%7B%0D%0A%20%20%20%20a%3A%20%22apple%22%2C%0D%0A%20%20%20%20b%20%3D%20%22banana%22%2C%0D%0A%7D%3B

Related Issues: #25257

[Kingwl]

maybe provide a quick fix for that?

[DanielRosenwasser]

@Kingwl Maybe, but I think reporting a better error first like

'=' can only be used in an object literal property inside a destructuring assignment. Did you mean to use a ':'?

would be more ideal. Keep in mind that if there is already a :, you really don't want to provide the new error:

let x = { foo: bar = 10 };

[mhegazy]

Related https://github.com/Microsoft/TypeScript/issues/25201

[Kingwl]

after track, i saw this pattern is included in ShorthandPropertyAssignment,
could we extract that and mixin with PropertyAssignment to handle this issue?

[DanielRosenwasser]

New message is

Did you mean to use a ':'? When following property names in an object literal, '=' implies a destructuring assignment.

Open to switching it in the future to

Did you mean to use a ':'? An '=' can only follow a property name when the containing object literal is part of a destructuring pattern.

Thanks @a-tarasyuk!

[a-tarasyuk]

@DanielRosenwasser I could change the message in PR :(. I'll open a new PR for the new message. Is it ok?

[DanielRosenwasser]

I felt bad making you wait any longer to get an already-good change in. 😬

Do you think the new message is even better? What about you @sandersn?

[sandersn]

Ehhhhh, it's slightly simpler but also slightly longer. I wouldn't change it if I were me, but, like, half of that is because the longer wording has a horizontal scroll bar on my browser.

[DanielRosenwasser]

It's up to you @a-tarasyuk, I'd merge it in if you think it's good and send the change.

[a-tarasyuk]

I felt bad making you wait any longer to get an already-good change in.

@DanielRosenwasser Don't worry about that 😄 . I think it is good, I'll change the message.