Fade out unnecessary code

Co-Authored-By: Nathan Sobo <nathan@zed.dev>

crates/editor/src/display_map/block_map.rs

@@ -819,7 +819,8 @@ impl<'a> Iterator for BlockChunks<'a> {
                 text: unsafe { std::str::from_utf8_unchecked(&NEWLINES[..line_count as usize]) },
                 syntax_highlight_id: None,
                 highlight_style: None,
-                diagnostic: None,
+                diagnostic_severity: None,
+                is_unnecessary: false,
             });
         }
 

crates/editor/src/display_map/fold_map.rs

@@ -1078,7 +1078,8 @@ impl<'a> Iterator for FoldChunks<'a> {
                 text: output_text,
                 syntax_highlight_id: None,
                 highlight_style: None,
-                diagnostic: None,
+                diagnostic_severity: None,
+                is_unnecessary: false,
             });
         }
 

crates/editor/src/element.rs

@@ -665,22 +665,25 @@ impl EditorElement {
                     }
                 }
 
-                if let Some(severity) = chunk.diagnostic {
-                    let diagnostic_style = super::diagnostic_style(severity, true, style);
-                    let diagnostic_highlight = HighlightStyle {
-                        underline: Some(Underline {
-                            color: Some(diagnostic_style.message.text.color),
-                            thickness: 1.0.into(),
-                            squiggly: true,
-                        }),
-                        ..Default::default()
-                    };
+                let mut diagnostic_highlight = HighlightStyle {
+                    ..Default::default()
+                };
 
-                    if let Some(highlight_style) = highlight_style.as_mut() {
-                        highlight_style.highlight(diagnostic_highlight);
-                    } else {
-                        highlight_style = Some(diagnostic_highlight);
-                    }
+                if chunk.is_unnecessary {
+                    diagnostic_highlight.fade_out = Some(style.unnecessary_code_fade);
+                } else if let Some(severity) = chunk.diagnostic_severity {
+                    let diagnostic_style = super::diagnostic_style(severity, true, style);
+                    diagnostic_highlight.underline = Some(Underline {
+                        color: Some(diagnostic_style.message.text.color),
+                        thickness: 1.0.into(),
+                        squiggly: true,
+                    });
+                }
+
+                if let Some(highlight_style) = highlight_style.as_mut() {
+                    highlight_style.highlight(diagnostic_highlight);
+                } else {
+                    highlight_style = Some(diagnostic_highlight);
                 }
 
                 (chunk.text, highlight_style)