Refactor to use extension trait pattern for DiagnosticSeverity

Move `to_lsp_severity()` from a free function to an extension trait method
following the existing convention in the codebase. This places the LSP type
conversion logic in `ext.rs` alongside other similar extension traits.

Author: claude

crates/djls-ide/src/diagnostics.rs

@@ -7,20 +7,9 @@ use djls_templates::TemplateError;
 use djls_templates::TemplateErrorAccumulator;
 use tower_lsp_server::lsp_types;
 
+use crate::ext::DiagnosticSeverityExt;
 use crate::ext::SpanExt;
 
-/// Convert `DiagnosticSeverity` to LSP diagnostic severity.
-/// Returns None for Off (diagnostic should not be shown).
-fn to_lsp_severity(severity: DiagnosticSeverity) -> Option<lsp_types::DiagnosticSeverity> {
-    match severity {
-        DiagnosticSeverity::Off => None,
-        DiagnosticSeverity::Error => Some(lsp_types::DiagnosticSeverity::ERROR),
-        DiagnosticSeverity::Warning => Some(lsp_types::DiagnosticSeverity::WARNING),
-        DiagnosticSeverity::Info => Some(lsp_types::DiagnosticSeverity::INFORMATION),
-        DiagnosticSeverity::Hint => Some(lsp_types::DiagnosticSeverity::HINT),
-    }
-}
-
 trait DiagnosticError: std::fmt::Display {
     fn span(&self) -> Option<(u32, u32)>;
     fn diagnostic_code(&self) -> &'static str;
@@ -139,7 +128,7 @@ pub fn collect_diagnostics(
             let severity = config.get_severity(code);
 
             // Skip if diagnostic is disabled (severity = off)
-            if let Some(lsp_severity) = to_lsp_severity(severity) {
+            if let Some(lsp_severity) = severity.to_lsp_severity() {
                 diagnostic.severity = Some(lsp_severity);
                 diagnostics.push(diagnostic);
             }
@@ -160,7 +149,7 @@ pub fn collect_diagnostics(
                 let severity = config.get_severity(code);
 
                 // Skip if diagnostic is disabled (severity = off)
-                if let Some(lsp_severity) = to_lsp_severity(severity) {
+                if let Some(lsp_severity) = severity.to_lsp_severity() {
                     diagnostic.severity = Some(lsp_severity);
                     diagnostics.push(diagnostic);
                 }
@@ -180,21 +169,21 @@ mod tests {
 
     #[test]
     fn test_to_lsp_severity() {
-        assert_eq!(to_lsp_severity(DiagnosticSeverity::Off), None);
+        assert_eq!(DiagnosticSeverity::Off.to_lsp_severity(), None);
         assert_eq!(
-            to_lsp_severity(DiagnosticSeverity::Error),
+            DiagnosticSeverity::Error.to_lsp_severity(),
             Some(lsp_types::DiagnosticSeverity::ERROR)
         );
         assert_eq!(
-            to_lsp_severity(DiagnosticSeverity::Warning),
+            DiagnosticSeverity::Warning.to_lsp_severity(),
             Some(lsp_types::DiagnosticSeverity::WARNING)
         );
         assert_eq!(
-            to_lsp_severity(DiagnosticSeverity::Info),
+            DiagnosticSeverity::Info.to_lsp_severity(),
             Some(lsp_types::DiagnosticSeverity::INFORMATION)
         );
         assert_eq!(
-            to_lsp_severity(DiagnosticSeverity::Hint),
+            DiagnosticSeverity::Hint.to_lsp_severity(),
             Some(lsp_types::DiagnosticSeverity::HINT)
         );
     }

crates/djls-ide/src/ext.rs

@@ -1,5 +1,6 @@
 use camino::Utf8Path;
 use camino::Utf8PathBuf;
+use djls_conf::DiagnosticSeverity;
 use djls_source::LineIndex;
 use djls_source::Offset;
 use djls_source::Span;
@@ -44,3 +45,19 @@ impl Utf8PathExt for Utf8PathBuf {
         lsp_types::Uri::from_file_path(self.as_std_path())
     }
 }
+
+pub(crate) trait DiagnosticSeverityExt {
+    fn to_lsp_severity(self) -> Option<lsp_types::DiagnosticSeverity>;
+}
+
+impl DiagnosticSeverityExt for DiagnosticSeverity {
+    fn to_lsp_severity(self) -> Option<lsp_types::DiagnosticSeverity> {
+        match self {
+            DiagnosticSeverity::Off => None,
+            DiagnosticSeverity::Error => Some(lsp_types::DiagnosticSeverity::ERROR),
+            DiagnosticSeverity::Warning => Some(lsp_types::DiagnosticSeverity::WARNING),
+            DiagnosticSeverity::Info => Some(lsp_types::DiagnosticSeverity::INFORMATION),
+            DiagnosticSeverity::Hint => Some(lsp_types::DiagnosticSeverity::HINT),
+        }
+    }
+}