Add diagnostics for rethrows in accessor declaration

Author: StevenWong12

Sources/SwiftParser/Declarations.swift

@@ -1710,8 +1710,24 @@ extension Parser {
     } else {
       parameter = nil
     }
-
-    let effectSpecifiers = self.parseDeclEffectSpecifiers()
+    
+    var effectSpecifiers = self.parseDeclEffectSpecifiers()
+    
+    if introducer.kind == .get,
+       let throwSpecifier = effectSpecifiers?.throwsSpecifier,
+       throwSpecifier.tokenText == "rethrows" {
+      
+      let unexpected = RawUnexpectedNodesSyntax([ effectSpecifiers?.unexpectedBetweenAsyncSpecifierAndThrowsSpecifier, RawUnexpectedNodesSyntax([throwSpecifier], arena: self.arena)], arena: self.arena)
+      
+      effectSpecifiers = RawDeclEffectSpecifiersSyntax(
+        effectSpecifiers?.unexpectedBeforeAsyncSpecifier,
+        asyncSpecifier: effectSpecifiers?.asyncSpecifier,
+        unexpected,
+        throwsSpecifier: nil,
+        effectSpecifiers?.unexpectedAfterThrowsSpecifier,
+        arena: self.arena
+      )
+    }
 
     let body = self.parseOptionalCodeBlock()
     return RawAccessorDeclSyntax(

Sources/SwiftParserDiagnostics/ParseDiagnosticsGenerator.swift

@@ -383,6 +383,22 @@ public class ParseDiagnosticsGenerator: SyntaxAnyVisitor {
 
     return .visitChildren
   }
+  
+  
+  public override func visit(_ node: AccessorDeclSyntax) -> SyntaxVisitorContinueKind {
+    if shouldSkip(node) {
+      return .skipChildren
+    }
+    
+    if let unexpectedBetweenAsyncSpecifierAndThrowsSpecifier = node.effectSpecifiers?.unexpectedBetweenAsyncSpecifierAndThrowsSpecifier,
+       unexpectedBetweenAsyncSpecifierAndThrowsSpecifier.tokens(viewMode: .sourceAccurate).contains(where: {$0.tokenKind == .keyword(.rethrows)}) == true {
+         addDiagnostic(
+          unexpectedBetweenAsyncSpecifierAndThrowsSpecifier, .misspelledThrowsInEffectfulProperties,
+          handledNodes: [unexpectedBetweenAsyncSpecifierAndThrowsSpecifier.id])
+    }
+    
+    return .visitChildren
+  }
 
   public override func visit(_ node: AssociatedtypeDeclSyntax) -> SyntaxVisitorContinueKind {
     if shouldSkip(node) {

Sources/SwiftParserDiagnostics/ParserDiagnosticMessages.swift

@@ -173,6 +173,9 @@ extension DiagnosticMessage where Self == StaticParserError {
   public static var misspelledThrows: Self {
     .init("expected throwing specifier; did you mean 'throws'?")
   }
+  public static var misspelledThrowsInEffectfulProperties: Self {
+    .init("only function declarations may be marked 'rethrows'; did you mean 'throws'?")
+  }
   public static var multiLineStringLiteralMustBeginOnNewLine: Self {
     .init("multi-line string literal content must begin on a new line")
   }