Add missing diagnostic for missing brace or if after else

Sources/SwiftParserDiagnostics/ParseDiagnosticsGenerator.swift

@@ -764,6 +764,10 @@ public class ParseDiagnosticsGenerator: SyntaxAnyVisitor {
       addDiagnostic(node.conditions, MissingConditionInStatement(node: node), handledNodes: [node.conditions.id])
     }
 
+    if let leftBrace = node.elseBody?.as(CodeBlockSyntax.self)?.leftBrace, leftBrace.presence == .missing {
+      addDiagnostic(leftBrace, .expectedLeftBraceOrIfAfterElse, handledNodes: [leftBrace.id])
+    }
+
     return .visitChildren
   }
 

Sources/SwiftParserDiagnostics/ParserDiagnosticMessages.swift

@@ -128,6 +128,9 @@ extension DiagnosticMessage where Self == StaticParserError {
   public static var expectedExpressionAfterTry: Self {
     .init("expected expression after 'try'")
   }
+  public static var expectedLeftBraceOrIfAfterElse: Self {
+    .init("expected '{' or 'if' after 'else'")
+  }
   public static var expectedSequenceExpressionInForEachLoop: Self {
     .init("expected Sequence expression for for-each loop")
   }

Tests/SwiftParserTest/translated/RecoveryTests.swift

@@ -2202,8 +2202,7 @@ final class RecoveryTests: XCTestCase {
       }2️⃣
       """,
       diagnostics: [
-        // TODO: Old parser expected error on line 2: expected '{' or 'if' after 'else'
-        DiagnosticSpec(locationMarker: "1️⃣", message: "expected '{' in 'if' statement"),
+        DiagnosticSpec(locationMarker: "1️⃣", message: "expected '{' or 'if' after 'else'"),
         DiagnosticSpec(locationMarker: "2️⃣", message: "expected '}' to end function"),
       ]
     )