fix(ngShow/ngHide): follow javscript truthy/falsy logic

[lgalfaso]

Make ngShow and ngHide follow javascript truthy/falsy logic and
not the custom toBoolean logic

Closes #5414
Closes #4277

[caitp]

If this does get merged, it is in fact a breaking change, and the commit message needs a BREAKING CHANGE block.

[lgalfaso]

@caitp you are right, amended the patch with a commit message stating that this is a breaking change

[caitp]

Yeah, it's a bit more than that, toBoolean() treats some pretty weird values as falsy ("f", "n", "no") etc. I can't imagine anyone is actually using these, but just in case they are it would be good to show how to migrate so that they can get the same functionality after this patch.

[lgalfaso]

I think that there is no easy way to migrate without exposing the toBoolean function or asking the user to write a function/expression that has this special logic present.

Do you think it would be good to add something like

To migrate, add the special cases to the expression. E.g. from

<div ng-hide="foo">X</div>

to

<div ng-hide="foo || foo == '[]'">X</div>

[caitp]

If you were previously doing ng-show="exp" where $scope.exp = 'no' // (or 'n' or 'f'), then instead write ng-show="exp && exp !== 'no' (or 'n' or 'f'). It's just showing a basic short-term hack to get it working while they refactor the logic

[lgalfaso]

@caitp Thanks!

[tbosch]

Hi,
could you double check which other directives also use the toBoolean logic and change them also with your PR? E.g. ngIf, ...

Thanks!

[lgalfaso]

@tbosch please look at #4005

[lgalfaso]

This issue is going to be handled as part of #4005