Fix bug when recovering to an accessor introducer

# Conflicts:
#	Sources/SwiftParser/Declarations.swift
#	Tests/SwiftParserTest/StatementTests.swift

Author: ahoppen

Sources/SwiftParser/Declarations.swift

@@ -1520,6 +1520,7 @@ extension Parser {
     var attributes: RawAttributeListSyntax?
     var modifier: RawDeclModifierSyntax?
     var kind: AccessorKind
+    var unexpectedBeforeToken: RawUnexpectedNodesSyntax?
     var token: RawTokenSyntax
   }
 
@@ -1528,7 +1529,7 @@ extension Parser {
     var look = self.lookahead()
     let _ = look.consumeAttributeList()
     let hasModifier = look.consume(ifAny: [], contextualKeywords: ["mutating", "nonmutating", "__consuming"]) != nil
-    guard let (kind, handle) = look.at(anyIn: AccessorKind.self) else {
+    guard let (kind, _) = look.at(anyIn: AccessorKind.self) else {
       return nil
     }
 
@@ -1547,11 +1548,12 @@ extension Parser {
       modifier = nil
     }
 
-    let introducer = self.eat(handle)
+    let (unexpectedBeforeIntroducer, introducer) = self.expect(kind.rawTokenKind)
     return AccessorIntroducer(
       attributes: attrs,
       modifier: modifier,
       kind: kind,
+      unexpectedBeforeToken: unexpectedBeforeIntroducer,
       token: introducer
     )
   }
@@ -1703,6 +1705,7 @@ extension Parser {
           RawAccessorDeclSyntax(
             attributes: introducer.attributes,
             modifier: introducer.modifier,
+            introducer.unexpectedBeforeToken,
             accessorKind: introducer.token,
             parameter: parameter,
             asyncKeyword: asyncKeyword,

Tests/SwiftParserTest/DeclarationTests.swift

@@ -759,7 +759,7 @@ final class DeclarationTests: XCTestCase {
       }
       """,
       diagnostics: [
-        DiagnosticSpec(message: "unexpected code 'bogus rethrows set' in variable")
+        DiagnosticSpec(message: "found an unexpected second identifier in accessor")
       ]
     )
   }

Tests/SwiftParserTest/StatementTests.swift

@@ -603,4 +603,20 @@ final class StatementTests: XCTestCase {
       )
     )
   }
+
+  func testRecoveryInFrontOfAccessorIntroducer() {
+    AssertParse(
+      """
+      subscript(1️⃣{@2️⃣self3️⃣ _modify
+      """,
+      diagnostics: [
+        DiagnosticSpec(locationMarker: "1️⃣", message: "expected type and ')' to end parameter clause"),
+        DiagnosticSpec(locationMarker: "1️⃣", message: "expected '->' and return type in subscript"),
+        DiagnosticSpec(locationMarker: "2️⃣", message: "expected name in attribute"),
+        DiagnosticSpec(locationMarker: "2️⃣", message: "expected identifier in accessor"),
+        DiagnosticSpec(locationMarker: "2️⃣", message: "expected '}' to end subscript"),
+        DiagnosticSpec(locationMarker: "3️⃣", message: "consecutive statements on a line must be separated by ';'"),
+      ]
+    )
+  }
 }

Tests/SwiftParserTest/translated/EffectfulPropertiesTests.swift

@@ -271,7 +271,7 @@ final class EffectfulPropertiesTests: XCTestCase {
       """,
       diagnostics: [
         // TODO: Old parser expected error on line 2: expected '{' to start getter definition
-        DiagnosticSpec(message: "unexpected code 'bogus rethrows {}' in variable")
+        DiagnosticSpec(message: "found an unexpected second identifier in accessor")
       ]
     )
   }
@@ -331,7 +331,7 @@ final class EffectfulPropertiesTests: XCTestCase {
       """,
       diagnostics: [
         // TODO: Old parser expected error on line 2: expected get or set in a protocol property
-        DiagnosticSpec(locationMarker: "1️⃣", message: "unexpected code 'bogus rethrows set' in variable"),
+        DiagnosticSpec(locationMarker: "1️⃣", message: "found an unexpected second identifier in accessor"),
         // TODO: Old parser expected error on line 3: only function declarations may be marked 'rethrows'; did you mean 'throws'?
         // TODO: Old parser expected error on line 3: expected get or set in a protocol property
         DiagnosticSpec(locationMarker: "2️⃣", message: "unexpected code 'bogus set' in variable"),