Two `ShowCombinator`s and two `HideCombinator`s should have error

[FMorschel]

If you have the following code:

import 'dart:core' show List show int hide String;   // Notice the double `show` but no analyzer error

void foo(List<int> list, String str) {}

Not List, int or String (of course) is correctly analysed showing errors like non_type_as_type_argument.

But if we remove the second show and add a , it works as expected.

I believe we should have an error message about writing down two shows or two hides if they make everything else stop working.

[dart-github-bot]

Summary: The analyzer fails to detect an error when two show combinators are used in a single import statement, leading to unexpected behavior where no types are correctly analyzed. The issue suggests adding an error message to flag this syntax error.

[lrhn]

You never need more than one show or one hide combinator to achieve any hiding-goal.
I'd warn about any time you have more than one.

Here the second show, show int, should definitely warn, since it's showing a name that isn't available to be shown (because it was hidden by the prior show). Similarly hide String is hiding a name that isn't available after either of the first two shows.

[FMorschel]

Somewhat related:

• Warning for multiple equal imports with hide combinator #59907
• Lint for merging equal import/exports with different show combinators #59722