Regression: Intersection of array and tuple not assignable to tuple #38348
Description
TypeScript Version: Nightly
Search Terms: tuple intersection array
Expected behavior:
Expected code to compile. It does compile with tsc 3.8, but does not compile with tsc 3.9 (Nightly).
Actual behavior:
In the code below, the following error is reported:
const x: [number, ...number[]]
Type 'number[] & [number, ...number[]]' is not assignable to type '[number, ...number[]]'.(2322)Code
const y: number[] & [number, ...number[]] = [1];
const x: [number, ...number[]] = y;Discussion
Presumably, this is related to the breaking change in 3.9 around handling of tuple types more strictly. I believe the code is correct however and should compile, because the array type number[] is a strict supertype of the tuple type [number, ...number[]] (surely?) - perhaps the special case unifying tuple types with matching element types to an array type hasn't been implemented?
Discovered by @JasonGore and @NWilson (MSFT).
Output
"use strict";
const y = [1];
const x = y;Compiler Options
{
"compilerOptions": {
"noImplicitAny": true,
"strictNullChecks": true,
"strictFunctionTypes": true,
"strictPropertyInitialization": true,
"strictBindCallApply": true,
"noImplicitThis": true,
"noImplicitReturns": true,
"useDefineForClassFields": false,
"alwaysStrict": true,
"allowUnreachableCode": false,
"allowUnusedLabels": false,
"downlevelIteration": false,
"noEmitHelpers": false,
"noLib": false,
"noStrictGenericChecks": false,
"noUnusedLocals": false,
"noUnusedParameters": false,
"esModuleInterop": true,
"preserveConstEnums": false,
"removeComments": false,
"skipLibCheck": false,
"checkJs": false,
"allowJs": false,
"declaration": true,
"experimentalDecorators": false,
"emitDecoratorMetadata": false,
"target": "ES2017",
"module": "ESNext"
}
}Playground Link: Provided