Using && with spread operator causes "overridden" error if one of the types is "any"

[mastrzyz]

We are having problems with TypeScript 3.9 upgrade for our repositories and the spread operator and "&&" with any types. TypeScript compiler says the value will be always overridden even though an any type isn't 100% always null/undefined.

TypeScript Version: 3.9.5
Search Terms:

• specified more than once, so this usage will be overwritten.
• any type and spread operator

Code

Doesn't work

let isTreeHeader : any = null!;
function foo(){
    return {
        display: "block",
        ...(isTreeHeader && {
          display: "flex",
        })
    }
}
foo()

Works

let isTreeHeader : number = null!;
function foo(){
    return {
        display: "block",
        ...(isTreeHeader && {
          display: "flex",
        })
    }
}
foo()

Expected behavior:

any type can be undefined or can have a non nullable value so we shouldn't get an error with the spread operator

Actual behavior:

'display' is specified more than once, so this usage will be overwritten.ts(2783)

Playground Link:
https://www.typescriptlang.org/play/?ssl=1&ssc=1&pln=2&pc=22#code/DYUwLgBAlgzgKgJxCAEiAhgExAiAuCdAOwE8IBeCIgV2GAEIBuAKADNqiBjMKAeyIitevABQBKAN7MISMNQQCpETLAAOwdCQIAiAEbBenANbaANNIB0VkbETI0WHBABkziEpUx1mna1AAPM2kAXzEQ5mC2YXEgA

Related Issues:

[mastrzyz]

@andrewbranch is there any guidance for this issue in the time currently.

We are on TS 3.8 but would really want to upgrade to TS 3.9 to get the speed and developer improvements.

Is there an acceptable workaround :)

[andrewbranch]

Sure: https://www.typescriptlang.org/play/#code/DYUwLgBAlgzgKgJxCAEiAhgExAgXBdAOwE8IBeCQgV2GAEIBuAKADMrCBjMKAe0IhY8eACgCUEAN5MIMiEjBUE-KbNURMsAA7B0xfACIARsB4cA1voA00tTIB0D4XTqxEyNFhwQAZN8k3bVQ0YbV0DFlAADysAtQBfUVi4pmTBEVEgA

I assume you didn’t mean to close this 😄

[mastrzyz]

Thanks, that will work for us!

Unfortunately after adding that fix to some of our instances we are getting an OOM from the TypeScript compiler.

Will try and get a isolated repro case and file a new issue 👍

[andrewbranch]

@mastrzyz interesting, you get an OOM going from 3.8 to 3.9?

[mastrzyz]

@andrewbranch I get the OOM in TS 3.9 when trying to use the workaround with "!!". The file is rather huge so I have been struggling so far to get an isolated repro.