fix: generate valid sample URIs for custom route placeholders

[jalexiscv]

Description

Fixes #9804 - Route Filters are shown as <unknown> when custom placeholders are used.

Problem

When using addPlaceholder() to define custom route placeholders (e.g., (:code)), the php spark routes command shows <unknown> for filters on those routes. This happens because SampleURIGenerator only had predefined sample values for built-in placeholders (any, segment, num, alpha, alphanum, hash).

When an unknown placeholder is encountered, it fell back to ::unknown:: which does not match the actual regex pattern. This caused FilterFinder to throw PageNotFoundException when trying to route the sample URI, resulting in <unknown> filter display.

Solution

Added generateSample() method to SampleURIGenerator that creates valid sample strings from regex patterns:

• Character classes [a-z] → uses the first valid character
• Quantifiers {n}, +, *, ? → repeats accordingly
• Dot . → uses a
• Escaped characters \d → uses the escaped char

This handles common regex patterns like [A-Z]{3}[0-9]+, [a-f0-9]{8}, etc.

Changes

One file: system/Commands/Utilities/Routes/SampleURIGenerator.php

• Replace ::unknown:: fallback with generateSample($regex)
• Add generateSample() private method

Testing

• Custom placeholder [A-Z]{3}[0-9]+ → generates AAA0 ✓
• Built-in :num → continues using predefined 123 ✓
• Built-in :any → continues using predefined 123/abc ✓
• Plain route → unchanged ✓

Ref: #9804
Closes #9804

[mergeable]

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[neznaika0]

You have not added tests for different regex variants. The user can set any complex expression. I doubt that this will be solved by the selection method.

It is preferable to specify the exact placeholders when adding them. This will be a PR feature for v4.8

[jalexiscv]

Thanks for the review @neznaika0! I've updated the PR based on your feedback:

1. Removed generateSample() regex parser — it was unreliable for arbitrary patterns as you pointed out.
2. Added sample parameter to addPlaceholder() — users can now specify exact samples:

   $routes->addPlaceholder("code", "[A-Z]{3}[0-9]+", "ABC123");

3. Fallback priority: user-provided sample → built-in sample → placeholder name

This is a much cleaner approach. Let me know if you have any other concerns.

[neznaika0]

It looks better.There are some shortcomings, but let's wait for the answers from the participants.
Most likely, you will need to change the branch to 4.8, add tests, update the guide and examples.
It may be worth considering default fillers.

[paulbalandan]

Please add some tests and a changelog entry. This should also target 4.8.