Allow LSP adapters to decide, which diagnostics to underline (#31450)

Closes
https://github.com/zed-industries/zed/pull/31355#issuecomment-2910439798

<img width="1728" alt="image"
src="https://github.com/user-attachments/assets/2eaa8e9b-00bc-4e99-ac09-fceb2d932e41"
/>


Release Notes:

- N/A

crates/language/src/buffer.rs

@@ -231,6 +231,8 @@ pub struct Diagnostic {
     pub is_unnecessary: bool,
     /// Data from language server that produced this diagnostic. Passed back to the LS when we request code actions for this diagnostic.
     pub data: Option<Value>,
+    /// Whether to underline the corresponding text range in the editor.
+    pub underline: bool,
 }
 
 /// An operation used to synchronize this buffer with its other replicas.
@@ -462,6 +464,7 @@ pub struct BufferChunks<'a> {
     information_depth: usize,
     hint_depth: usize,
     unnecessary_depth: usize,
+    underline: bool,
     highlights: Option<BufferChunkHighlights<'a>>,
 }
 
@@ -482,6 +485,8 @@ pub struct Chunk<'a> {
     pub is_unnecessary: bool,
     /// Whether this chunk of text was originally a tab character.
     pub is_tab: bool,
+    /// Whether to underline the corresponding text range in the editor.
+    pub underline: bool,
 }
 
 /// A set of edits to a given version of a buffer, computed asynchronously.
@@ -496,6 +501,7 @@ pub struct Diff {
 pub(crate) struct DiagnosticEndpoint {
     offset: usize,
     is_start: bool,
+    underline: bool,
     severity: DiagnosticSeverity,
     is_unnecessary: bool,
 }
@@ -4388,6 +4394,7 @@ impl<'a> BufferChunks<'a> {
             information_depth: 0,
             hint_depth: 0,
             unnecessary_depth: 0,
+            underline: true,
             highlights,
         };
         this.initialize_diagnostic_endpoints();
@@ -4448,12 +4455,14 @@ impl<'a> BufferChunks<'a> {
                         is_start: true,
                         severity: entry.diagnostic.severity,
                         is_unnecessary: entry.diagnostic.is_unnecessary,
+                        underline: entry.diagnostic.underline,
                     });
                     diagnostic_endpoints.push(DiagnosticEndpoint {
                         offset: entry.range.end,
                         is_start: false,
                         severity: entry.diagnostic.severity,
                         is_unnecessary: entry.diagnostic.is_unnecessary,
+                        underline: entry.diagnostic.underline,
                     });
                 }
                 diagnostic_endpoints
@@ -4559,6 +4568,7 @@ impl<'a> Iterator for BufferChunks<'a> {
                 if endpoint.offset <= self.range.start {
                     self.update_diagnostic_depths(endpoint);
                     diagnostic_endpoints.next();
+                    self.underline = endpoint.underline;
                 } else {
                     next_diagnostic_endpoint = endpoint.offset;
                     break;
@@ -4590,6 +4600,7 @@ impl<'a> Iterator for BufferChunks<'a> {
             Some(Chunk {
                 text: slice,
                 syntax_highlight_id: highlight_id,
+                underline: self.underline,
                 diagnostic_severity: self.current_diagnostic_severity(),
                 is_unnecessary: self.current_code_is_unnecessary(),
                 ..Chunk::default()
@@ -4632,6 +4643,7 @@ impl Default for Diagnostic {
             is_primary: false,
             is_disk_based: false,
             is_unnecessary: false,
+            underline: true,
             data: None,
         }
     }

crates/language/src/language.rs

@@ -245,6 +245,10 @@ impl CachedLspAdapter {
         self.adapter.retain_old_diagnostic(previous_diagnostic, cx)
     }
 
+    pub fn underline_diagnostic(&self, diagnostic: &lsp::Diagnostic) -> bool {
+        self.adapter.underline_diagnostic(diagnostic)
+    }
+
     pub fn diagnostic_message_to_markdown(&self, message: &str) -> Option<String> {
         self.adapter.diagnostic_message_to_markdown(message)
     }
@@ -470,6 +474,16 @@ pub trait LspAdapter: 'static + Send + Sync {
         false
     }
 
+    /// Whether to underline a given diagnostic or not, when rendering in the editor.
+    ///
+    /// https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#diagnosticTag
+    /// states that
+    /// > Clients are allowed to render diagnostics with this tag faded out instead of having an error squiggle.
+    /// for the unnecessary diagnostics, so do not underline them.
+    fn underline_diagnostic(&self, _diagnostic: &lsp::Diagnostic) -> bool {
+        true
+    }
+
     /// Post-processes completions provided by the language server.
     async fn process_completions(&self, _: &mut [lsp::CompletionItem]) {}
 

crates/language/src/proto.rs

@@ -213,6 +213,7 @@ pub fn serialize_diagnostics<'a>(
             } as i32,
             group_id: entry.diagnostic.group_id as u64,
             is_primary: entry.diagnostic.is_primary,
+            underline: entry.diagnostic.underline,
             code: entry.diagnostic.code.as_ref().map(|s| s.to_string()),
             code_description: entry
                 .diagnostic
@@ -429,6 +430,7 @@ pub fn deserialize_diagnostics(
                     is_primary: diagnostic.is_primary,
                     is_disk_based: diagnostic.is_disk_based,
                     is_unnecessary: diagnostic.is_unnecessary,
+                    underline: diagnostic.underline,
                     data,
                 },
             })