Revert "Allow return types on initializers"

This reverts commit 595b97b.

Author: meg-gupta

Diff for: Sources/SwiftParser/Declarations.swift

@@ -995,7 +995,7 @@ extension Parser {
     }
 
     // Parse the signature.
-    let signature = self.parseFunctionSignature()
+    let signature = self.parseFunctionSignature(allowOutput: false)
 
     let whereClause: RawGenericWhereClauseSyntax?
     if self.at(.keyword(.where)) {
@@ -1159,7 +1159,7 @@ extension Parser {
     )
   }
 
-  mutating func parseFunctionSignature() -> RawFunctionSignatureSyntax {
+  mutating func parseFunctionSignature(allowOutput: Bool = true) -> RawFunctionSignatureSyntax {
     let parameterClause = self.parseParameterClause(RawFunctionParameterClauseSyntax.self) { parser in
       parser.parseFunctionParameter()
     }
@@ -1179,10 +1179,19 @@ extension Parser {
       returnClause = nil
     }
 
+    var unexpectedAfterReturnClause: RawUnexpectedNodesSyntax?
+    if !allowOutput,
+      let unexpectedOutput = returnClause
+    {
+      returnClause = nil
+      unexpectedAfterReturnClause = RawUnexpectedNodesSyntax([unexpectedOutput], arena: self.arena)
+    }
+
     return RawFunctionSignatureSyntax(
       parameterClause: parameterClause,
       effectSpecifiers: effectSpecifiers,
       returnClause: returnClause,
+      unexpectedAfterReturnClause,
       arena: self.arena
     )
   }

Diff for: Sources/SwiftParserDiagnostics/ParseDiagnosticsGenerator.swift

@@ -1273,6 +1273,14 @@ public class ParseDiagnosticsGenerator: SyntaxAnyVisitor {
       )
     }
 
+    if let unexpectedOutput = node.signature.unexpectedAfterReturnClause {
+      addDiagnostic(
+        unexpectedOutput,
+        .initializerCannotHaveResultType,
+        handledNodes: [unexpectedOutput.id]
+      )
+    }
+
     return .visitChildren
   }
 

Diff for: Sources/SwiftParserDiagnostics/ParserDiagnosticMessages.swift

@@ -176,6 +176,9 @@ extension DiagnosticMessage where Self == StaticParserError {
   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'")
   }

Diff for: Tests/SwiftParserTest/translated/InitDeinitTests.swift

@@ -104,7 +104,10 @@ final class InitDeinitTests: ParserTestCase {
       struct FooStructConstructorD {
         init() 1️⃣-> FooStructConstructorD { }
       }
-      """
+      """,
+      diagnostics: [
+        DiagnosticSpec(message: "initializers cannot have a result type")
+      ]
     )
   }
 
@@ -422,7 +425,10 @@ final class InitDeinitTests: ParserTestCase {
     assertParse(
       """
       init(_ foo: T) 1️⃣-> Int where T: Comparable {}
-      """
+      """,
+      diagnostics: [
+        DiagnosticSpec(message: "initializers cannot have a result type")
+      ]
     )
   }