Add diagnostic for empty switch cases

Author: kimdv

Sources/SwiftParser/Expressions.swift

@@ -2224,6 +2224,8 @@ extension Parser {
 
     let subject: RawExprSyntax
 
+    // When dosing this if-check, we ensure not passing an missing expression `{ foo }`
+    // as a closure expression.
     if self.at(.leftBrace) {
       subject = RawExprSyntax(RawMissingExprSyntax(arena: self.arena))
     } else {

Sources/SwiftParserDiagnostics/ParseDiagnosticsGenerator.swift

@@ -1034,6 +1034,10 @@ public class ParseDiagnosticsGenerator: SyntaxAnyVisitor {
       addDiagnostic(node.expression, .missingExpressionInSwitchStatement, handledNodes: [node.expression.id])
     }
 
+    if node.cases.isEmpty && !node.leftBrace.isMissingAllTokens && !node.rightBrace.isMissingAllTokens {
+      addDiagnostic(node.cases, .emptySwitchExprBody, handledNodes: [node.cases.id])
+    }
+
     return .visitChildren
   }
 

Sources/SwiftParserDiagnostics/ParserDiagnosticMessages.swift

@@ -122,6 +122,9 @@ extension DiagnosticMessage where Self == StaticParserError {
   public static var editorPlaceholderInSourceFile: Self {
     .init("editor placeholder in source file")
   }
+  public static var emptySwitchExprBody: Self {
+    .init("'switch' statement body must have at least one 'case' or 'default' block")
+  }
   public static var escapedNewlineAtLatlineOfMultiLineStringLiteralNotAllowed: Self {
     .init("escaped newline at the last line of a multi-line string literal is not allowed")
   }

Tests/SwiftParserTest/translated/RecoveryTests.swift

@@ -621,12 +621,12 @@ final class RecoveryTests: XCTestCase {
   func testRecovery46() {
     AssertParse(
       """
-      switch 1️⃣{
+      switch 1️⃣{2️⃣
       }
       """,
       diagnostics: [
-        DiagnosticSpec(message: "expected expression in 'switch' statement")
-        // TODO: Old parser expected error on line 1: 'switch' statement body must have at least one 'case' or 'default' block
+        DiagnosticSpec(locationMarker: "1️⃣", message: "expected expression in 'switch' statement"),
+        DiagnosticSpec(locationMarker: "2️⃣", message: "'switch' statement body must have at least one 'case' or 'default' block"),
       ]
     )
   }
@@ -635,12 +635,12 @@ final class RecoveryTests: XCTestCase {
     AssertParse(
       """
       switch 1️⃣
-      {
+      {2️⃣
       }
       """,
       diagnostics: [
-        DiagnosticSpec(message: "expected expression in 'switch' statement")
-        // TODO: Old parser expected error on line 1: 'switch' statement body must have at least one 'case' or 'default' block
+        DiagnosticSpec(locationMarker: "1️⃣", message: "expected expression in 'switch' statement"),
+        DiagnosticSpec(locationMarker: "2️⃣", message: "'switch' statement body must have at least one 'case' or 'default' block"),
       ]
     )
   }
@@ -667,10 +667,8 @@ final class RecoveryTests: XCTestCase {
       }
       """,
       diagnostics: [
-        DiagnosticSpec(locationMarker: "1️⃣", message: "expected expression in 'switch' statement"),
+        DiagnosticSpec(locationMarker: "1️⃣", message: "expected expression in 'switch' statement")
         // TODO: Old parser expected error on line 2: 'is' keyword required to pattern match against type name, Fix-It replacements: 10 - 10 = 'is '
-        DiagnosticSpec(locationMarker: "2️⃣", message: "'case' can only appear inside a 'switch' statement or 'enum' declaration"),
-        DiagnosticSpec(locationMarker: "3️⃣", message: "'case' can only appear inside a 'switch' statement or 'enum' declaration"),
       ]
     )
   }