[Server] Fix to make Symfony Finder component optional

[bigdevlarry]

Motivation and Context

The changes make the Symfony Finder component optional, as referenced in issue #263

How Has This Been Tested?

Yes

Breaking Changes

Not a breaking change

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

[soyuka]

Can you also add a change to https://github.com/modelcontextprotocol/php-sdk/blob/main/src/Server/Builder.php#L526 ? Avoid calling the createDiscoverer when Finder isn't accessible + log? This makes php-sdk not dependent from the Finder.

[bigdevlarry]

@soyuka, this means the discoverer will never be called if there's no finder, and we won't be able to raise the exception to prompt the installation of the finder itself. By your suggestion, adding a null check silences the error in the logs, and the program continues as expected. Is this the ideal behaviour, or should we halt the program with the exception as we have it, so users go back to install? Let me know what you think as well @chr-hertel

[soyuka]

Mhh from this PR I thought you wanted to move the Finder to a dev-requirement making this a soft dependency. From my point of view if that's the case the code should work after installing with composer and I'd have thought that it'd make sense to skip classes dependent from the Finder.

If we don't want to move this requirement, then I'm not sure I understand how this code path is going to happen as its required in our dependencies.

[chr-hertel]

Mhh from this PR I thought you wanted to move the Finder to a dev-requirement making this a soft dependency.
yes

and yes, the code should work unless you want to use the built-in discoverer.

if a user calls setDiscovery we can expect the intend is clear - calling setDiscovery, not calling setDiscoverer with an custom implementation, but not installing the symfony/finder should raise a warning or exception from my point of view.

We should add this as BC break to changelog tho, since users would need to install symfony/finder now themselves.

[chr-hertel]

@soyuka this is now what you've been thinking, right?