Adds support for multiple language servers per language.

Language Servers are now configured in a separate table in `languages.toml`:

```toml
[langauge-server.mylang-lsp]
command = "mylang-lsp"
args = ["--stdio"]
config = { provideFormatter = true }

[language-server.efm-lsp-prettier]
command = "efm-langserver"

[language-server.efm-lsp-prettier.config]
documentFormatting = true
languages = { typescript = [ { formatCommand ="prettier --stdin-filepath ${INPUT}", formatStdin = true } ] }
```

The language server for a language is configured like this (`typescript-language-server` is configured by default):

```toml
[[language]]
name = "typescript"
language-servers = [ { name = "efm-lsp-prettier", only-features = [ "format" ] }, "typescript-language-server" ]
```

or equivalent:

```toml
[[language]]
name = "typescript"
language-servers = [ { name = "typescript-language-server", except-features = [ "format" ] }, "efm-lsp-prettier" ]
```

Each requested LSP feature is priorized in the order of the `language-servers` array.
For example the first `goto-definition` supported language server (in this case `typescript-language-server`) will be taken for the relevant LSP request (command `goto_definition`).

If no `except-features` or `only-features` is given all features for the language server are enabled, as long as the language server supports these. If it doesn't the next language server which supports the feature is tried.

The list of supported features are:

- `format`
- `goto-definition`
- `goto-declaration`
- `goto-type-definition`
- `goto-reference`
- `goto-implementation`
- `signature-help`
- `hover`
- `document-highlight`
- `completion`
- `code-action`
- `workspace-command`
- `document-symbols`
- `workspace-symbols`
- `diagnostics`
- `rename-symbol`
- `inlay-hints`

Another side-effect/difference that comes with this PR, is that only one language server instance is started if different languages use the same language server.

1 files changed, 9 insertions, 12 deletions

diff --git a/helix-term/src/ui/mod.rs b/helix-term/src/ui/mod.rs
index 3e9a14b0..118836c0 100644
--- a/helix-term/src/ui/mod.rs
+++ b/helix-term/src/ui/mod.rs
@@ -17,7 +17,7 @@ mod text;
 use crate::compositor::{Component, Compositor};
 use crate::filter_picker_entry;
 use crate::job::{self, Callback};
-pub use completion::Completion;
+pub use completion::{Completion, CompletionItem};
 pub use editor::EditorView;
 pub use markdown::Markdown;
 pub use menu::Menu;
@@ -238,6 +238,7 @@ pub mod completers {
     use crate::ui::prompt::Completion;
     use fuzzy_matcher::skim::SkimMatcherV2 as Matcher;
     use fuzzy_matcher::FuzzyMatcher;
+    use helix_core::syntax::LanguageServerFeature;
     use helix_view::document::SCRATCH_BUFFER_NAME;
     use helix_view::theme;
     use helix_view::{editor::Config, Editor};
@@ -393,17 +394,13 @@ pub mod completers {
     pub fn lsp_workspace_command(editor: &Editor, input: &str) -> Vec<Completion> {
         let matcher = Matcher::default();
 
-        let (_, doc) = current_ref!(editor);
-
-        let language_server = match doc.language_server() {
-            Some(language_server) => language_server,
-            None => {
-                return vec![];
-            }
-        };
-
-        let options = match &language_server.capabilities().execute_command_provider {
-            Some(options) => options,
+        let language_servers =
+            doc!(editor).language_servers_with_feature(LanguageServerFeature::WorkspaceCommand);
+        let options = match language_servers
+            .into_iter()
+            .find_map(|ls| ls.capabilities().execute_command_provider.as_ref())
+        {
+            Some(id_options) => id_options,
             None => {
                 return vec![];
             }