Add support for diagnostics display funcref for more flexible integration

Author: martskins

doc/LanguageClient.txt

@@ -635,6 +635,51 @@ Highlight group to be used for code lens.
 
 Default: 'Comment'
 
+2.42 g:LanguageClient_diagnosticsDisplayFuncref          *g:LanguageClient_diagnosticsDisplayFuncref*
+
+If set, LanguageClient-neovim will call this function instead of setting the diagnostics signs. This
+is useful to delegate the display of diagnostics to other engines. The function is called with two
+arguments, the first one is the file name of which the diagnostics correspond to, and the seconds one
+is the list of diagnostics for said file. Those diagnostics are as specified in the LSP specification.
+
+For example, if you wanted to use `dense-analysis/ale` to display diagnostics instead of this plugin
+you could use something like this:
+
+```
+function! g:DisplayDiagnostics(filename, diagnostics) abort
+  let s:diagnostics = []
+
+  for d in a:diagnostics
+    let s:severity = 'I'
+    if d.severity == 1
+      let s:severity = 'E'
+    elseif d.severity == 2
+      let s:severity = 'W'
+    endif
+
+    call add(s:diagnostics, {
+      \ "filename": a:filename,
+      \ "text": d.message,
+      \ "lnum": d.range.start.line + 1,
+      \ "end_lnum": d.range.end.line + 1,
+      \ "col": d.range.end.character,
+      \ "end_col": d.range.end.character,
+      \ "type": s:severity,
+      \ })
+  endfor
+
+  call ale#other_source#ShowResults(bufnr('%'), 'LanguageClientNeovim', s:diagnostics)
+endfunction
+
+let g:LanguageClient_diagnosticsDisplayFuncref = 'g:DisplayDiagnostics'
+```
+
+Keep in mind that to complete the integration between `ale` and `LanguageClient-neovim` you need to
+add `LanguageClientNeovim` (or the name of the linter you used in the call to ShowResults) to the list
+of linters to be used in `ale`.
+
+Default: v:null
+
 ==============================================================================
 3. Commands                                           *LanguageClientCommands*
 

src/language_server_protocol.rs

@@ -165,6 +165,7 @@ impl LanguageClient {
 
         #[allow(clippy::type_complexity)]
         let (
+            diagnostics_display_funcref,
             diagnostics_signs_max,
             diagnostics_max_severity,
             diagnostics_ignore_sources,
@@ -180,6 +181,7 @@ impl LanguageClient {
             enable_extensions,
             code_lens_hl_group,
         ): (
+            Option<String>,
             Option<usize>,
             String,
             Vec<String>,
@@ -196,6 +198,7 @@ impl LanguageClient {
             String,
         ) = self.vim()?.eval(
             [
+                "get(g:, 'LanguageClient_diagnosticsDisplayFuncref', v:null)",
                 "get(g:, 'LanguageClient_diagnosticsSignsMax', v:null)",
                 "get(g:, 'LanguageClient_diagnosticsMaxSeverity', 'Hint')",
                 "get(g:, 'LanguageClient_diagnosticsIgnoreSources', [])",
@@ -328,6 +331,8 @@ impl LanguageClient {
             state.preferred_markup_kind = preferred_markup_kind;
             state.enable_extensions = enable_extensions;
             state.code_lens_hl_group = code_lens_hl_group;
+            state.diagnostics_display_funcref = diagnostics_display_funcref;
+
             Ok(())
         })?;
 
@@ -2470,6 +2475,14 @@ impl LanguageClient {
             }
         }
 
+        // if a diagnostics display funcref has been configured then call that function and return
+        if let Some(funcref) = self.get(|state| state.diagnostics_display_funcref.clone())? {
+            self.vim()?
+                .rpcclient
+                .notify(funcref, json!([filename, diagnostics]))?;
+            return Ok(());
+        }
+
         let current_filename: String = self.vim()?.get_filename(&Value::Null)?;
         if filename != current_filename.canonicalize() {
             return Ok(());

src/types.rs

@@ -211,6 +211,7 @@ pub struct State {
     pub hide_virtual_texts_on_insert: bool,
     pub echo_project_root: bool,
     pub enable_extensions: Option<HashMap<String, bool>>,
+    pub diagnostics_display_funcref: Option<String>,
 
     pub server_stderr: Option<String>,
     pub logger: Logger,
@@ -296,6 +297,7 @@ impl State {
             preferred_markup_kind: None,
             enable_extensions: None,
             code_lens_hl_group: "Comment".into(),
+            diagnostics_display_funcref: None,
 
             logger,
         })