Improve diagnostics message for init declaration

Sources/SwiftParser/Declarations.swift

@@ -1059,7 +1059,7 @@ extension Parser {
     }
 
     // Parse the signature.
-    let signature = self.parseFunctionSignature()
+    let signature = self.parseFunctionSignature(allowOutput: false)
 
     let whereClause: RawGenericWhereClauseSyntax?
     if self.at(.keyword(.where)) {
@@ -1389,12 +1389,12 @@ extension Parser {
   }
 
   @_spi(RawSyntax)
-  public mutating func parseFunctionSignature() -> RawFunctionSignatureSyntax {
+  public mutating func parseFunctionSignature(allowOutput: Bool = true) -> RawFunctionSignatureSyntax {
     let input = self.parseParameterClause(for: .functionParameters)
 
     var effectSpecifiers = self.parseDeclEffectSpecifiers()
 
-    let output: RawReturnClauseSyntax?
+    var output: RawReturnClauseSyntax?
 
     /// Only allow recovery to the arrow with exprKeyword precedence so we only
     /// skip over misplaced identifiers and don't e.g. recover to an arrow in a 'where' clause.
@@ -1404,10 +1404,19 @@ extension Parser {
       output = nil
     }
 
+    var unexpectedAfterOutput: RawUnexpectedNodesSyntax?
+    if !allowOutput,
+      let unexpectedOutput = output
+    {
+      output = nil
+      unexpectedAfterOutput = RawUnexpectedNodesSyntax([unexpectedOutput], arena: self.arena)
+    }
+
     return RawFunctionSignatureSyntax(
       input: input,
       effectSpecifiers: effectSpecifiers,
       output: output,
+      unexpectedAfterOutput,
       arena: self.arena
     )
   }

Sources/SwiftParserDiagnostics/ParseDiagnosticsGenerator.swift

@@ -748,6 +748,41 @@ public class ParseDiagnosticsGenerator: SyntaxAnyVisitor {
     return .visitChildren
   }
 
+  public override func visit(_ node: InitializerDeclSyntax) -> SyntaxVisitorContinueKind {
+    if shouldSkip(node) {
+      return .skipChildren
+    }
+
+    if let unexpectedName = node.signature.input.unexpectedBeforeLeftParen,
+      let previous = unexpectedName.previousToken(viewMode: .sourceAccurate)
+    {
+      addDiagnostic(
+        unexpectedName,
+        .initializerCannotHaveName,
+        fixIts: [
+          FixIt(
+            message: RemoveNodesFixIt(unexpectedName),
+            changes: [
+              .makeMissing(unexpectedName),
+              FixIt.Changes(changes: [.replaceTrailingTrivia(token: previous, newTrivia: .zero)]),
+            ]
+          )
+        ],
+        handledNodes: [unexpectedName.id]
+      )
+    }
+
+    if let unexpectedOutput = node.signature.unexpectedAfterOutput {
+      addDiagnostic(
+        unexpectedOutput,
+        .initializerCannotHaveResultType,
+        handledNodes: [unexpectedOutput.id]
+      )
+    }
+
+    return .visitChildren
+  }
+
   public override func visit(_ node: MemberDeclListItemSyntax) -> SyntaxVisitorContinueKind {
     if shouldSkip(node) {
       return .skipChildren

Sources/SwiftParserDiagnostics/ParserDiagnosticMessages.swift

@@ -131,6 +131,12 @@ extension DiagnosticMessage where Self == StaticParserError {
   public static var initializerInPattern: Self {
     .init("unexpected initializer in pattern; did you mean to use '='?")
   }
+  public static var initializerCannotHaveName: Self {
+    .init("initializers cannot have a name")
+  }
+  public static var initializerCannotHaveResultType: Self {
+    .init("initializers cannot have a result type")
+  }
   public static var invalidFlagAfterPrecedenceGroupAssignment: Self {
     .init("expected 'true' or 'false' after 'assignment'")
   }

Tests/SwiftParserTest/translated/InitDeinitTests.swift

@@ -83,11 +83,11 @@ final class InitDeinitTests: XCTestCase {
     AssertParse(
       """
       struct FooStructConstructorD {
-        init() -> FooStructConstructorD { }
+        init() 1️⃣-> FooStructConstructorD { }
       }
       """,
       diagnostics: [
-        // TODO: Old parser expected error on line 2: initializers cannot have a result type
+        DiagnosticSpec(message: "initializers cannot have a result type")
       ]
     )
   }
@@ -391,6 +391,17 @@ final class InitDeinitTests: XCTestCase {
     )
   }
 
+  func testInitDeinit28() {
+    AssertParse(
+      """
+      init(_ foo: T) 1️⃣-> Int where T: Comparable {} 
+      """,
+      diagnostics: [
+        DiagnosticSpec(message: "initializers cannot have a result type")
+      ]
+    )
+  }
+
   func testDeinitInSwiftinterfaceIsFollowedByFinalFunc() {
     AssertParse(
       """

Tests/SwiftParserTest/translated/RecoveryTests.swift

@@ -1741,7 +1741,7 @@ final class RecoveryTests: XCTestCase {
         DiagnosticSpec(locationMarker: "1️⃣", message: "expected '>' to end generic parameter clause"),
         DiagnosticSpec(locationMarker: "2️⃣", message: "expected type and ')' to end parameter clause"),
         DiagnosticSpec(locationMarker: "3️⃣", message: "unexpected code ')}' before struct"),
-        DiagnosticSpec(locationMarker: "4️⃣", message: "unexpected code 'x' before parameter clause"),
+        DiagnosticSpec(locationMarker: "4️⃣", message: "initializers cannot have a name", fixIts: ["remove 'x'"]),
       ]
     )
   }
@@ -1752,9 +1752,11 @@ final class RecoveryTests: XCTestCase {
       init 1️⃣a(b: Int) {}
       """,
       diagnostics: [
-        // TODO: (good first issue) Old parser expected error on line 3: initializers cannot have a name, Fix-It replacements: 8 - 9 = ''
-        DiagnosticSpec(message: "unexpected code 'a' before parameter clause")
-      ]
+        DiagnosticSpec(message: "initializers cannot have a name", fixIts: ["remove 'a'"])
+      ],
+      fixedSource: """
+        init(b: Int) {}
+        """
     )
   }
 
@@ -1764,9 +1766,11 @@ final class RecoveryTests: XCTestCase {
       init? 1️⃣c(_ d: Int) {}
       """,
       diagnostics: [
-        // TODO: (good first issue) Old parser expected error on line 1: initializers cannot have a name, Fix-It replacements: 9 - 10 = ''
-        DiagnosticSpec(message: "unexpected code 'c' before parameter clause")
-      ]
+        DiagnosticSpec(message: "initializers cannot have a name", fixIts: ["remove 'c'"])
+      ],
+      fixedSource: """
+        init?(_ d: Int) {}
+        """
     )
   }
 
@@ -1776,9 +1780,11 @@ final class RecoveryTests: XCTestCase {
       init 1️⃣e<T>(f: T) {}
       """,
       diagnostics: [
-        // TODO: (good first issue) Old parser expected error on line 1: initializers cannot have a name, Fix-It replacements: 8 - 9 = ''
-        DiagnosticSpec(message: "unexpected code 'e<T>' before parameter clause")
-      ]
+        DiagnosticSpec(message: "initializers cannot have a name", fixIts: ["remove 'e<T>'"])
+      ],
+      fixedSource: """
+        init(f: T) {}
+        """
     )
   }
 
@@ -1788,9 +1794,11 @@ final class RecoveryTests: XCTestCase {
       init? 1️⃣g<T>(_: T) {}
       """,
       diagnostics: [
-        // TODO: (good first issue) Old parser expected error on line 1: initializers cannot have a name, Fix-It replacements: 9 - 10 = ''
-        DiagnosticSpec(message: "unexpected code 'g<T>' before parameter clause")
-      ]
+        DiagnosticSpec(message: "initializers cannot have a name", fixIts: ["remove 'g<T>'"])
+      ],
+      fixedSource: """
+        init?(_: T) {}
+        """
     )
   }