Produce more useful diagnostics for bogus specifier before arrow and leftbrace

Sources/SwiftParser/Declarations.swift

@@ -1375,7 +1375,8 @@ extension Parser {
     var effectSpecifiers = self.parseDeclEffectSpecifiers()
 
     let output: RawReturnClauseSyntax?
-    if self.at(.arrow) {
+
+    if self.at(.arrow) || self.canRecoverTo(TokenSpec(.arrow, allowAtStartOfLine: false)) != nil {
       output = self.parseFunctionReturnClause(effectSpecifiers: &effectSpecifiers, allowNamedOpaqueResultType: true)
     } else {
       output = nil

Sources/SwiftParser/Recovery.swift

@@ -70,9 +70,10 @@ extension Parser.Lookahead {
     let initialTokensConsumed = self.tokensConsumed
 
     let recoveryPrecedence = min(spec1.recoveryPrecedence, spec2.recoveryPrecedence, spec3.recoveryPrecedence)
+    let shouldSkipOverNewlines = recoveryPrecedence.shouldSkipOverNewlines && spec1.allowAtStartOfLine && spec2.allowAtStartOfLine && spec3.allowAtStartOfLine
 
     while !self.at(.eof) {
-      if !recoveryPrecedence.shouldSkipOverNewlines, self.currentToken.isAtStartOfLine {
+      if !shouldSkipOverNewlines, self.currentToken.isAtStartOfLine {
         break
       }
       let matchedSpec: TokenSpec?

Sources/SwiftParser/TopLevel.swift

@@ -98,7 +98,7 @@ extension Parser {
   /// This function is used when parsing places where function bodies are
   /// optional - like the function requirements in protocol declarations.
   mutating func parseOptionalCodeBlock(allowInitDecl: Bool = true) -> RawCodeBlockSyntax? {
-    guard self.at(.leftBrace) else {
+    guard self.at(.leftBrace) || self.canRecoverTo(TokenSpec(.leftBrace, allowAtStartOfLine: false)) != nil else {
       return nil
     }
     return self.parseCodeBlock(allowInitDecl: allowInitDecl)

Sources/SwiftSyntax/generated/Keyword.swift

@@ -735,7 +735,7 @@ public enum Keyword: UInt8, Hashable {
     }
   }
 
-  /// Whether the token kind is switched from being an identifier to being an identifier to a keyword in the lexer.
+  /// Whether the token kind is switched from being an identifier to a keyword in the lexer.
   /// This is true for keywords that used to be considered non-contextual.
   public var isLexerClassified: Bool {
     switch self {

Tests/SwiftParserTest/translated/EffectfulPropertiesTests.swift

@@ -231,7 +231,7 @@ final class EffectfulPropertiesTests: XCTestCase {
       }
       """,
       diagnostics: [
-        DiagnosticSpec(message: "unexpected code 'bogus {}' in variable")
+        DiagnosticSpec(message: "unexpected code 'bogus' in accessor")
       ]
     )
   }
@@ -257,7 +257,7 @@ final class EffectfulPropertiesTests: XCTestCase {
       }
       """,
       diagnostics: [
-        DiagnosticSpec(message: "unexpected code '-> Int { 0 }' in variable")
+        DiagnosticSpec(message: "unexpected code '-> Int' in accessor")
       ]
     )
   }

Tests/SwiftParserTest/translated/InvalidTests.swift

@@ -205,7 +205,8 @@ final class InvalidTests: XCTestCase {
         DiagnosticSpec(locationMarker: "2️⃣", message: "expected ')' in function type"),
         DiagnosticSpec(locationMarker: "3️⃣", message: "expected return type in function type"),
         DiagnosticSpec(locationMarker: "3️⃣", message: "expected ')' to end parameter clause"),
-        DiagnosticSpec(locationMarker: "4️⃣", message: "extraneous code ') {}' at top level"),
+        DiagnosticSpec(locationMarker: "3️⃣", message: "unexpected code '<T>()' in function signature"),
+        DiagnosticSpec(locationMarker: "4️⃣", message: "unexpected code ')' in function"),
       ]
     )
   }
@@ -484,6 +485,7 @@ final class InvalidTests: XCTestCase {
       diagnostics: [
         DiagnosticSpec(locationMarker: "1️⃣", message: "expected '(' to start parameter clause"),
         DiagnosticSpec(locationMarker: "2️⃣", message: "expected ')' to end parameter clause"),
+        DiagnosticSpec(locationMarker: "2️⃣", message: "unexpected code '()' in function"),
       ]
     )
   }
@@ -497,6 +499,7 @@ final class InvalidTests: XCTestCase {
       diagnostics: [
         DiagnosticSpec(locationMarker: "1️⃣", message: "expected '(' to start parameter clause"),
         DiagnosticSpec(locationMarker: "2️⃣", message: "expected ')' to end parameter clause"),
+        DiagnosticSpec(locationMarker: "2️⃣", message: "unexpected code '(x: T)' in function"),
       ]
     )
   }

Tests/SwiftParserTest/translated/RecoveryTests.swift

@@ -1206,13 +1206,14 @@ final class RecoveryTests: XCTestCase {
         func bar() -> Int3️⃣] {
           return [0]
         }
-      }
+      4️⃣}
       """,
       diagnostics: [
         DiagnosticSpec(locationMarker: "1️⃣", message: "expected '}' to end struct"),
         DiagnosticSpec(locationMarker: "2️⃣", message: "expected ']' to end array"),
         // TODO: Old parser expected error on line 5: unexpected ']' in type; did you mean to write an array type?, Fix-It replacements: 17 - 17 = '['
-        DiagnosticSpec(locationMarker: "3️⃣", message: "extraneous code at top level"),
+        DiagnosticSpec(locationMarker: "3️⃣", message: "unexpected code ']' in function"),
+        DiagnosticSpec(locationMarker: "4️⃣", message: "extraneous brace at top level"),
       ]
     )
   }
@@ -1247,7 +1248,7 @@ final class RecoveryTests: XCTestCase {
       """,
       diagnostics: [
         // TODO: Old parser expected error on line 2: array types are now written with the brackets around the element type, Fix-It replacements: 17 - 17 = '[', 20 - 21 = ''
-        DiagnosticSpec(message: "unexpected code in struct")
+        DiagnosticSpec(message: "unexpected code '[0]' in function")
       ]
     )
   }
@@ -1263,7 +1264,7 @@ final class RecoveryTests: XCTestCase {
       """,
       diagnostics: [
         // TODO: Old parser expected error on line 2: array types are now written with the brackets around the element type, Fix-It replacements: 17 - 17 = '[', 20 - 21 = ''
-        DiagnosticSpec(message: "unexpected code in struct")
+        DiagnosticSpec(message: "unexpected code '[0_1]' in function")
       ]
     )
   }
@@ -1279,7 +1280,7 @@ final class RecoveryTests: XCTestCase {
       """,
       diagnostics: [
         // TODO: Old parser expected error on line 2: array types are now written with the brackets around the element type, Fix-It replacements: 17 - 17 = '[', 20 - 21 = ''
-        DiagnosticSpec(message: "unexpected code in struct")
+        DiagnosticSpec(message: "unexpected code '[0b1]' in function")
       ]
     )
   }
@@ -2205,4 +2206,20 @@ final class RecoveryTests: XCTestCase {
     )
   }
 
+  func testRecovery182() {
+    AssertParse(
+      "func foo() 1️⃣bogus {}",
+      diagnostics: [
+        DiagnosticSpec(message: "unexpected code 'bogus' in function")
+      ]
+    )
+
+    AssertParse(
+      "func foo() 1️⃣bogus -> Int {}",
+      diagnostics: [
+        DiagnosticSpec(message: "unexpected code 'bogus' in function signature")
+      ]
+    )
+  }
+
 }