Always specify a valid constant for Symbol kind

[cbisnett]

Motivation

Ruby-lsp defines the method kind_for_entry which maps entry types from RubyIndexer to SymbolKind constants as defined in the LSP specification. Zed expects the JSONRPC results to strictly match the protocol specificaion and when they don't it will reject the whole response. Because kind_for_entry did not map every RubyIndexer entry type to a SymbolKind constant, often results would be sent back to the client where the value of kind was null. Since the LSP protocol specification defines SchemaKind as an integer enum, this means the results don't strictly match the specification and the end result was that in almost all cases I was getting no results for project symbols even though I could see the results in the Zed LSP message traces.

Implementation

This PR adds a default SymbolKind value of NULL for unknown RubyIndexer entry classes, which will allow results to always match the protocol specification. Ideally every RubyIndexer entry class is mapped to a SymbolKind enum value, but I don't have enough experience with the LSP specification or the Ruby-lsp project to ensure all of these cases are handled. I did find that there was one entry class, RubyIndexer::Entry::GlobalVariable, that seemed like it would correctly map to the VARIABLE SymbolKind value and I added that here.

I also encountered RubyIndexer::Entry::UnresolvedMethodAlias, but was unsure of which SymbolKind value that would map to. Because this class is not defined in kind_of_entry, it will get the default SymbolKind of NULL. In Zed this is handled as a valid value, but the result is discarded and not displayed in the Project Symbols dialog. I have not tested how other IDEs handle the NULL enum value, but it does conform to the specification, so it should be valid.

Automated Tests

I didn't spend enough time with the codebase to understand how to add tests. If there is a basic example that I can modify to get coverage and ensure no regressions for this and someone can point me to it, I will gladly add a test.

Manual Tests

I verified these changes worked using the Zed LSP debug logs and was able to see the expected symbols in the Project Symbols dialog.

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[cbisnett]

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[vinistock]

Thanks for the PR and the detailed explanation. Are you positive that the Null kind means "no symbol" and not nil? My original understanding of that kind is that it literally meant a null occurrence and not a missing kind.

Also, we should add the correct kinds for the index entries that are missing, so that they are displayed correctly.

What do you think about adding a unit test that will verify if all entry types have a kind? Basically, have the test index the LSP's codebase itself and then request the symbol kind for each entry, asserting that it isn't nil.

That would make it easier to ensure that we don't forget to handle all entry types.