no_leading_underscores_for_library_prefixes

The library prefix '{0}' starts with an underscore.

The analyzer produces this diagnostic when the name of a prefix declared on an import starts with an underscore.

Library prefixes are inherently not visible outside the declaring library, so a leading underscore indicating private adds no value.

The following code produces this diagnostic because the prefix _core starts with an underscore:

import 'dart:core' as _core;

Remove the underscore:

import 'dart:core' as core;