Tidy up diagnostics more (#29629)

- Stop merging same row diagnostics
- (for Rust) show code fragments surrounded by `'s in monospace

Co-authored-by: Serge Radinovich <sergeradinovich@gmail.com>

Closes #29362

Release Notes:

- diagnostics: Diagnostics are no longer merged when they're on the same
line
- rust: Diagnostics now show code snippets in monospace font:

<img width="551" alt="Screenshot 2025-04-29 at 16 13 45"
src="https://github.com/user-attachments/assets/d289be31-717d-404f-a76a-a0cda3e96fbe"
/>

Co-authored-by: Serge Radinovich <sergeradinovich@gmail.com>

crates/diagnostics/src/diagnostic_renderer.rs

@@ -7,7 +7,7 @@ use editor::{
     scroll::Autoscroll,
 };
 use gpui::{AppContext, Entity, Focusable, WeakEntity};
-use language::{BufferId, DiagnosticEntry};
+use language::{BufferId, Diagnostic, DiagnosticEntry};
 use lsp::DiagnosticSeverity;
 use markdown::{Markdown, MarkdownElement};
 use settings::Settings;
@@ -28,7 +28,6 @@ impl DiagnosticRenderer {
         diagnostic_group: Vec<DiagnosticEntry<Point>>,
         buffer_id: BufferId,
         diagnostics_editor: Option<WeakEntity<ProjectDiagnosticsEditor>>,
-        merge_same_row: bool,
         cx: &mut App,
     ) -> Vec<DiagnosticBlock> {
         let Some(primary_ix) = diagnostic_group
@@ -38,30 +37,12 @@ impl DiagnosticRenderer {
             return Vec::new();
         };
         let primary = diagnostic_group[primary_ix].clone();
-        let mut same_row = Vec::new();
-        let mut close = Vec::new();
-        let mut distant = Vec::new();
         let group_id = primary.diagnostic.group_id;
-        for (ix, entry) in diagnostic_group.into_iter().enumerate() {
+        let mut results = vec![];
+        for entry in diagnostic_group.iter() {
             if entry.diagnostic.is_primary {
-                continue;
-            }
-            if entry.range.start.row == primary.range.start.row && merge_same_row {
-                same_row.push(entry)
-            } else if entry.range.start.row.abs_diff(primary.range.start.row) < 5 {
-                close.push(entry)
-            } else {
-                distant.push((ix, entry))
-            }
-        }
-
-        let mut markdown = String::new();
+                let mut markdown = Self::markdown(&entry.diagnostic);
                 let diagnostic = &primary.diagnostic;
-        markdown.push_str(&Markdown::escape(&diagnostic.message));
-        for entry in same_row {
-            markdown.push_str("\n- hint: ");
-            markdown.push_str(&Markdown::escape(&entry.diagnostic.message))
-        }
                 if diagnostic.source.is_some() || diagnostic.code.is_some() {
                     markdown.push_str(" (");
                 }
@@ -86,58 +67,58 @@ impl DiagnosticRenderer {
                     markdown.push(')');
                 }
 
-        for (ix, entry) in &distant {
+                for (ix, entry) in diagnostic_group.iter().enumerate() {
+                    if entry.range.start.row.abs_diff(primary.range.start.row) >= 5 {
                         markdown.push_str("\n- hint: [");
                         markdown.push_str(&Markdown::escape(&entry.diagnostic.message));
                         markdown.push_str(&format!(
                             "](file://#diagnostic-{buffer_id}-{group_id}-{ix})\n",
                         ))
                     }
-
-        let mut results = vec![DiagnosticBlock {
-            initial_range: primary.range,
+                }
+                results.push(DiagnosticBlock {
+                    initial_range: primary.range.clone(),
                     severity: primary.diagnostic.severity,
                     diagnostics_editor: diagnostics_editor.clone(),
                     markdown: cx.new(|cx| Markdown::new(markdown.into(), None, None, cx)),
-        }];
-
-        for entry in close {
-            let markdown = if let Some(source) = entry.diagnostic.source.as_ref() {
-                format!("{}: {}", source, entry.diagnostic.message)
-            } else {
-                entry.diagnostic.message
-            };
-            let markdown = Markdown::escape(&markdown).to_string();
+                });
+            } else if entry.range.start.row.abs_diff(primary.range.start.row) < 5 {
+                let markdown = Self::markdown(&entry.diagnostic);
 
                 results.push(DiagnosticBlock {
-                initial_range: entry.range,
+                    initial_range: entry.range.clone(),
                     severity: entry.diagnostic.severity,
                     diagnostics_editor: diagnostics_editor.clone(),
                     markdown: cx.new(|cx| Markdown::new(markdown.into(), None, None, cx)),
                 });
-        }
-
-        for (_, entry) in distant {
-            let markdown = if let Some(source) = entry.diagnostic.source.as_ref() {
-                format!("{}: {}", source, entry.diagnostic.message)
             } else {
-                entry.diagnostic.message
-            };
-            let mut markdown = Markdown::escape(&markdown).to_string();
+                let mut markdown = Self::markdown(&entry.diagnostic);
                 markdown.push_str(&format!(
                     " ([back](file://#diagnostic-{buffer_id}-{group_id}-{primary_ix}))"
                 ));
 
                 results.push(DiagnosticBlock {
-                initial_range: entry.range,
+                    initial_range: entry.range.clone(),
                     severity: entry.diagnostic.severity,
                     diagnostics_editor: diagnostics_editor.clone(),
                     markdown: cx.new(|cx| Markdown::new(markdown.into(), None, None, cx)),
                 });
             }
+        }
 
         results
     }
+
+    fn markdown(diagnostic: &Diagnostic) -> String {
+        let mut markdown = String::new();
+
+        if let Some(md) = &diagnostic.markdown {
+            markdown.push_str(md);
+        } else {
+            markdown.push_str(&Markdown::escape(&diagnostic.message));
+        };
+        markdown
+    }
 }
 
 impl editor::DiagnosticRenderer for DiagnosticRenderer {
@@ -149,7 +130,7 @@ impl editor::DiagnosticRenderer for DiagnosticRenderer {
         editor: WeakEntity<Editor>,
         cx: &mut App,
     ) -> Vec<BlockProperties<Anchor>> {
-        let blocks = Self::diagnostic_blocks_for_group(diagnostic_group, buffer_id, None, true, cx);
+        let blocks = Self::diagnostic_blocks_for_group(diagnostic_group, buffer_id, None, cx);
         blocks
             .into_iter()
             .map(|block| {
@@ -176,8 +157,7 @@ impl editor::DiagnosticRenderer for DiagnosticRenderer {
         buffer_id: BufferId,
         cx: &mut App,
     ) -> Option<Entity<Markdown>> {
-        let blocks =
-            Self::diagnostic_blocks_for_group(diagnostic_group, buffer_id, None, false, cx);
+        let blocks = Self::diagnostic_blocks_for_group(diagnostic_group, buffer_id, None, cx);
         blocks.into_iter().find_map(|block| {
             if block.initial_range == range {
                 Some(block.markdown)
@@ -211,7 +191,7 @@ impl DiagnosticBlock {
         let cx = &bcx.app;
         let status_colors = bcx.app.theme().status();
 
-        let max_width = bcx.em_width * 100.;
+        let max_width = bcx.em_width * 120.;
 
         let (background_color, border_color) = match self.severity {
             DiagnosticSeverity::ERROR => (status_colors.error_background, status_colors.error),

crates/diagnostics/src/diagnostics.rs

@@ -416,7 +416,6 @@ impl ProjectDiagnosticsEditor {
                         group,
                         buffer_snapshot.remote_id(),
                         Some(this.clone()),
-                        true,
                         cx,
                     )
                 })?;

crates/editor/src/hover_popover.rs

@@ -633,7 +633,7 @@ pub fn hover_markdown_style(window: &Window, cx: &App) -> MarkdownStyle {
         base_text_style,
         code_block: StyleRefinement::default().my(rems(1.)).font_buffer(cx),
         inline_code: TextStyleRefinement {
-            background_color: Some(cx.theme().colors().background),
+            background_color: Some(cx.theme().colors().editor_background.opacity(0.5)),
             font_family: Some(buffer_font_family),
             font_fallbacks: buffer_font_fallbacks,
             ..Default::default()

crates/language/src/buffer.rs

@@ -213,6 +213,8 @@ pub struct Diagnostic {
     pub severity: DiagnosticSeverity,
     /// The human-readable message associated with this diagnostic.
     pub message: String,
+    /// The human-readable message (in markdown format)
+    pub markdown: Option<String>,
     /// An id that identifies the group to which this diagnostic belongs.
     ///
     /// When a language server produces a diagnostic with
@@ -4616,6 +4618,7 @@ impl Default for Diagnostic {
             code_description: None,
             severity: DiagnosticSeverity::ERROR,
             message: Default::default(),
+            markdown: None,
             group_id: 0,
             is_primary: false,
             is_disk_based: false,

crates/language/src/language.rs

@@ -239,6 +239,10 @@ impl CachedLspAdapter {
             .process_diagnostics(params, server_id, existing_diagnostics)
     }
 
+    pub fn diagnostic_message_to_markdown(&self, message: &str) -> Option<String> {
+        self.adapter.diagnostic_message_to_markdown(message)
+    }
+
     pub async fn process_completions(&self, completion_items: &mut [lsp::CompletionItem]) {
         self.adapter.process_completions(completion_items).await
     }
@@ -460,6 +464,10 @@ pub trait LspAdapter: 'static + Send + Sync {
     /// Post-processes completions provided by the language server.
     async fn process_completions(&self, _: &mut [lsp::CompletionItem]) {}
 
+    fn diagnostic_message_to_markdown(&self, _message: &str) -> Option<String> {
+        None
+    }
+
     async fn labels_for_completions(
         self: Arc<Self>,
         completions: &[lsp::CompletionItem],

crates/language/src/proto.rs

@@ -203,6 +203,7 @@ pub fn serialize_diagnostics<'a>(
             start: Some(serialize_anchor(&entry.range.start)),
             end: Some(serialize_anchor(&entry.range.end)),
             message: entry.diagnostic.message.clone(),
+            markdown: entry.diagnostic.markdown.clone(),
             severity: match entry.diagnostic.severity {
                 DiagnosticSeverity::ERROR => proto::diagnostic::Severity::Error,
                 DiagnosticSeverity::WARNING => proto::diagnostic::Severity::Warning,
@@ -422,6 +423,7 @@ pub fn deserialize_diagnostics(
                         proto::diagnostic::Severity::None => return None,
                     },
                     message: diagnostic.message,
+                    markdown: diagnostic.markdown,
                     group_id: diagnostic.group_id as usize,
                     code: diagnostic.code.map(lsp::NumberOrString::from_string),
                     code_description: diagnostic

crates/languages/src/rust.rs

@@ -283,6 +283,12 @@ impl LspAdapter for RustLspAdapter {
         }
     }
 
+    fn diagnostic_message_to_markdown(&self, message: &str) -> Option<String> {
+        static REGEX: LazyLock<Regex> =
+            LazyLock::new(|| Regex::new(r"(?m)\n *").expect("Failed to create REGEX"));
+        Some(REGEX.replace_all(message, "\n\n").to_string())
+    }
+
     async fn label_for_completion(
         &self,
         completion: &lsp::CompletionItem,

crates/project/src/lsp_store.rs

@@ -8575,6 +8575,8 @@ impl LspStore {
         let mut sources_by_group_id = HashMap::default();
         let mut supporting_diagnostics = HashMap::default();
 
+        let adapter = self.language_server_adapter_for_id(language_server_id);
+
         // Ensure that primary diagnostics are always the most severe
         params.diagnostics.sort_by_key(|item| item.severity);
 
@@ -8622,6 +8624,9 @@ impl LspStore {
                             .as_ref()
                             .map(|d| d.href.clone()),
                         severity: diagnostic.severity.unwrap_or(DiagnosticSeverity::ERROR),
+                        markdown: adapter.as_ref().and_then(|adapter| {
+                            adapter.diagnostic_message_to_markdown(&diagnostic.message)
+                        }),
                         message: diagnostic.message.trim().to_string(),
                         group_id,
                         is_primary: true,
@@ -8644,6 +8649,9 @@ impl LspStore {
                                         .as_ref()
                                         .map(|c| c.href.clone()),
                                     severity: DiagnosticSeverity::INFORMATION,
+                                    markdown: adapter.as_ref().and_then(|adapter| {
+                                        adapter.diagnostic_message_to_markdown(&info.message)
+                                    }),
                                     message: info.message.trim().to_string(),
                                     group_id,
                                     is_primary: false,

crates/proto/proto/buffer.proto

@@ -271,6 +271,7 @@ message Diagnostic {
     }
     optional string data = 12;
     optional string code_description = 13;
+    optional string markdown = 14;
 }
 
 message SearchQuery {