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Object literal array type inconsistently inferred when using spread #30761
Description
TypeScript Version: 3.3.3333
Search Terms:
- object literal array type
- object array property does not exist
- spread object literal array
Code
Playground: http://tinyurl.com/y65n9b3o
const array1 = [
{ a: 'a', b: 'b' },
{ a: 'a', c: 'c' },
] // inferred: Partial<{ a, b, c }>[]
array1.map(({ c }) => c); // works ✅
const array2 = [
{ a: 'a', b: 'b' },
{ a: 'a', ...{ c: 'c' } },
]
array2.map(({ c }) => c); // suddenly error? ❌Expected behavior:
I'm not sure if this is a bug but I expect both map calls to type-check identically. If it's not a bug, it's very unintuitive why the spread syntax completely changes how the array type is inferred. The only workaround I have is to explicitly write the full type (which isn't as concise as the example above).
Activity
RyanCavanaugh commentedon Apr 10, 2019
We have "special" logic for unifying object literals in these cases; the spread syntax interferes with that.
If you post a more representative sample where it's not just spreading for the sake of spreading, we may be able to advise more.
ssynix commentedon Apr 10, 2019
Here's almost the same code that reproduces the error.
Is the special logic documented somewhere? It would help avoid surprises and confusion if the logic is more explicitly defined, or if there are ways to control the inference.