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, 5 insertions, 12 deletions

diff --git a/helix-term/src/ui/editor.rs b/helix-term/src/ui/editor.rs
index f0989fa8..43b5d1af 100644
--- a/helix-term/src/ui/editor.rs
+++ b/helix-term/src/ui/editor.rs
@@ -33,7 +33,7 @@ use std::{mem::take, num::NonZeroUsize, path::PathBuf, rc::Rc, sync::Arc};
 
 use tui::{buffer::Buffer as Surface, text::Span};
 
-use super::statusline;
+use super::{completion::CompletionItem, statusline};
 use super::{document::LineDecoration, lsp::SignatureHelp};
 
 pub struct EditorView {
@@ -650,7 +650,7 @@ impl EditorView {
             .primary()
             .cursor(doc.text().slice(..));
 
-        let diagnostics = doc.diagnostics().iter().filter(|diagnostic| {
+        let diagnostics = doc.shown_diagnostics().filter(|diagnostic| {
             diagnostic.range.start <= cursor && diagnostic.range.end >= cursor
         });
 
@@ -953,20 +953,13 @@ impl EditorView {
         &mut self,
         editor: &mut Editor,
         savepoint: Arc<SavePoint>,
-        items: Vec<helix_lsp::lsp::CompletionItem>,
-        offset_encoding: helix_lsp::OffsetEncoding,
+        items: Vec<CompletionItem>,
         start_offset: usize,
         trigger_offset: usize,
         size: Rect,
     ) -> Option<Rect> {
-        let mut completion = Completion::new(
-            editor,
-            savepoint,
-            items,
-            offset_encoding,
-            start_offset,
-            trigger_offset,
-        );
+        let mut completion =
+            Completion::new(editor, savepoint, items, start_offset, trigger_offset);
 
         if completion.is_empty() {
             // skip if we got no completion results