undefined_identifier

Undefined name '{0}'.

The analyzer produces this diagnostic when it encounters an identifier that either isn't defined or isn't visible in the scope in which it's being referenced.

The following code produces this diagnostic because the name rihgt isn't defined:

int min(int left, int right) => left <= rihgt ? left : right;

If the identifier isn't defined, then either define it or replace it with an identifier that is defined. The example above can be corrected by fixing the spelling of the variable:

int min(int left, int right) => left <= right ? left : right;

If the identifier is defined but isn't visible, then you probably need to add an import or re-arrange your code to make the identifier visible.