fix #9467, Custom validation message in custom prop validator

[znck]

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• It's submitted to the dev branch for v2.x (or to a previous version branch), not the master branch
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• All tests are passing: https://github.com/vuejs/vue/blob/dev/.github/CONTRIBUTING.md#development-setup
• New/updated tests are included

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information: #9467

[posva]

Will close #8726 too

[jacekkarczmarczyk]

What about

const message = result instanceof Error ? result.message : 'custom validator check failed';
warn(`Invalid prop ${name}: ${message}`);

without introducing the interpolation thing?

[MrZyr0]

Hi everyone 👋

I am desperately trying to customize my validator error message.
I've browsed many other issues, it doesn't seem to be possible at the moment and the community is working on it.

How far along is the development for this feature?