In C# files nothing gets semantic highlighting — class fields and other
identifiers are colored by tree-sitter only, so a private field looks
the same as a plain local variable.
The reason: Roslyn (the C# language server) doesn't declare
`semanticTokensProvider` statically in its `initialize` response. It
registers it **dynamically** (`client/registerCapability`), and only
when the client advertises
`textDocument.semanticTokens.dynamicRegistration = true`. Zed advertised
`false` and didn't handle such a registration, so Roslyn never offered
semantic tokens at all. (rust-analyzer/gopls are unaffected — they
declare the capability statically.)
This is the first of two PRs. This one makes Roslyn actually **send**
semantic tokens. The companion PR (#60027) maps Roslyn's C#-specific
token types to theme styles — without it the tokens arrive but most are
dropped, since their types aren't in Zed's default rules.
## Solution
- Advertise `textDocument.semanticTokens.dynamicRegistration = true`.
- Handle the `textDocument/semanticTokens` registration and
unregistration so the capability is stored, following the existing arms
for `documentLink`, diagnostics, etc.
## Testing
- Added a test that dynamically registers and unregisters
`textDocument/semanticTokens` and checks the stored capability appears
and is cleared.
- Verified manually against Roslyn on a C# project: Zed now sends
`textDocument/semanticTokens/full` and gets tokens back; before this
change there was no semantic-token traffic at all.
## Self-Review Checklist:
- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable
---
Release Notes:
- Support dynamic registration of the `textDocument/semanticTokens`
capability.
---------
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
