TypeScript Version: 3.8.0-dev.20191121

Search Terms:

callback overload mismatch

Code

declare function fn(x: string): string;
declare function fn(x: string[]): string;

declare function map<A, R>(fn: (item: A) => R, list: A[]): R[];

const mapped = map(fn, ['1']) // error

Expected behavior:

TypeScript does infer A as string and could choose the right overload fn(x: string), decline the ones that don't fit.

Actual behavior:

Checks the last overload only, so it shows an error.

Playground Link: http://www.typescriptlang.org/play/?ssl=7&ssc=1&pln=1&pc=1#code/CYUwxgNghgTiAEAzArgOzAFwJYHtVNQAoAPALngGcMYtUBzASnKpvoG4AoUSWBFdbHgIlm1WnQDaAXSaUx7Dl3DQ4SNJlz4AtlAAOAHgCCAGngAlAHyFEqcoSwYQW8oYbwAvBfOmIWKi+lZM2lODjA8KngdXV0QYA8ovWtUUwkAcgBGNJkOIA

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