[Variadic Generics] diagnostics + fixits for parameter pack syntax change: T... -> each T

Sources/SwiftParser/Declarations.swift

@@ -474,13 +474,24 @@ extension Parser {
         let attributes = self.parseAttributeList()
 
         // Parse the 'each' keyword for a type parameter pack 'each T'.
-        let each = self.consume(if: .keyword(.each))
+        var each = self.consume(if: .keyword(.each))
 
         let (unexpectedBetweenEachAndName, name) = self.expectIdentifier()
-        if attributes == nil && unexpectedBetweenEachAndName == nil && name.isMissing && elements.isEmpty {
+        if attributes == nil && each == nil && unexpectedBetweenEachAndName == nil && name.isMissing && elements.isEmpty {
           break
         }
 
+        // Parse the unsupported ellipsis for a type parameter pack 'T...'.
+        let unexpectedBetweenNameAndColon: RawUnexpectedNodesSyntax?
+        if let ellipsis = tryConsumeEllipsisPrefix() {
+          unexpectedBetweenNameAndColon = RawUnexpectedNodesSyntax([ellipsis], arena: self.arena)
+          if each == nil {
+            each = missingToken(.each)
+          }
+        } else {
+          unexpectedBetweenNameAndColon = nil
+        }
+
         // Parse the ':' followed by a type.
         let colon = self.consume(if: .colon)
         let unexpectedBeforeInherited: RawUnexpectedNodesSyntax?
@@ -513,6 +524,7 @@ extension Parser {
             each: each,
             unexpectedBetweenEachAndName,
             name: name,
+            unexpectedBetweenNameAndColon,
             colon: colon,
             unexpectedBeforeInherited,
             inheritedType: inherited,
@@ -937,7 +949,15 @@ extension Parser {
     _ handle: RecoveryConsumptionHandle
   ) -> RawAssociatedtypeDeclSyntax {
     let (unexpectedBeforeAssocKeyword, assocKeyword) = self.eat(handle)
-    let (unexpectedBeforeName, name) = self.expectIdentifier(keywordRecovery: true)
+
+    // Detect an attempt to use a type parameter pack.
+    let eachKeyword = self.consume(if: .keyword(.each))
+
+    var (unexpectedBeforeName, name) = self.expectIdentifier(keywordRecovery: true)
+    if eachKeyword != nil {
+      unexpectedBeforeName = RawUnexpectedNodesSyntax(combining: eachKeyword, unexpectedBeforeName, arena: self.arena)
+    }
+
     if unexpectedBeforeName == nil && name.isMissing {
       return RawAssociatedtypeDeclSyntax(
         attributes: attrs.attributes,
@@ -953,7 +973,7 @@ extension Parser {
       )
     }
 
-    // Detect an attempt to use a type parameter pack.
+    // Detect an attempt to use (early syntax) type parameter pack.
     let ellipsis = tryConsumeEllipsisPrefix()
 
     // Parse optional inheritance clause.

Sources/SwiftParserDiagnostics/ParseDiagnosticsGenerator.swift

@@ -389,6 +389,13 @@ public class ParseDiagnosticsGenerator: SyntaxAnyVisitor {
     if shouldSkip(node) {
       return .skipChildren
     }
+    // Emit a custom diagnostic for an unexpected 'each' before an associatedtype
+    // name.
+    removeToken(
+      node.unexpectedBetweenAssociatedtypeKeywordAndIdentifier,
+      where: { $0.tokenKind == .keyword(.each) },
+      message: { _ in .associatedTypeCannotUsePack }
+    )
     // Emit a custom diagnostic for an unexpected '...' after an associatedtype
     // name.
     removeToken(
@@ -615,6 +622,32 @@ public class ParseDiagnosticsGenerator: SyntaxAnyVisitor {
     if shouldSkip(node) {
       return .skipChildren
     }
+    // Emit a custom diagnostic for an unexpected '...' after the type name.
+    if node.each?.presence == .present {
+      removeToken(
+        node.unexpectedBetweenNameAndColon,
+        where: { $0.tokenKind == .ellipsis },
+        message: { _ in .typeParameterPackEllipsis }
+      )
+    } else if let unexpected = node.unexpectedBetweenNameAndColon,
+      let unexpectedEllipsis = unexpected.onlyToken(where: { $0.tokenKind == .ellipsis }),
+      let each = node.each
+    {
+      addDiagnostic(
+        unexpected,
+        .typeParameterPackEllipsis,
+        fixIts: [
+          FixIt(
+            message: ReplaceTokensFixIt(replaceTokens: [unexpectedEllipsis], replacement: .keyword(.each)),
+            changes: [
+              .makeMissing(unexpected),
+              .makePresent(each, trailingTrivia: .space),
+            ]
+          )
+        ],
+        handledNodes: [unexpected.id, each.id]
+      )
+    }
     if let inheritedTypeName = node.inheritedType?.as(SimpleTypeIdentifierSyntax.self)?.name {
       exchangeTokens(
         unexpected: node.unexpectedBetweenColonAndInheritedType,

Sources/SwiftParserDiagnostics/ParserDiagnosticMessages.swift

@@ -197,6 +197,9 @@ extension DiagnosticMessage where Self == StaticParserError {
   public static var tryOnInitialValueExpression: Self {
     .init("'try' must be placed on the initial value expression")
   }
+  public static var typeParameterPackEllipsis: Self {
+    .init("ellipsis operator cannot be used with a type parameter pack")
+  }
   public static var unexpectedPoundElseSpaceIf: Self {
     .init("unexpected 'if' keyword following '#else' conditional compilation directive; did you mean '#elseif'?")
   }
@@ -504,7 +507,7 @@ public struct MoveTokensInFrontOfFixIt: ParserFixIt {
   /// The token that should be moved
   public let movedTokens: [TokenSyntax]
 
-  /// The token after which 'try' should be moved
+  /// The token before which 'movedTokens' should be moved
   public let inFrontOf: TokenKind
 
   public var message: String {

Tests/SwiftParserTest/VariadicGenericsTests.swift

@@ -74,6 +74,37 @@ final class VariadicGenericsTests: XCTestCase {
     )
   }
 
+  func testTypeParameterPackEllipsis() {
+    AssertParse(
+      """
+      func invalid<T1️⃣...>(_ t: repeat each T) {}
+      """,
+      diagnostics: [
+        DiagnosticSpec(
+          message: "ellipsis operator cannot be used with a type parameter pack",
+          fixIts: ["replace '...' with 'each'"]
+        )
+      ],
+      fixedSource: """
+        func invalid<each T>(_ t: repeat each T) {}
+        """
+    )
+  }
+
+  func testTypeParameterPackEachEllipsis() {
+    AssertParse(
+      """
+      func invalid<each T1️⃣...>(_ t: repeat each T) {}
+      """,
+      diagnostics: [
+        DiagnosticSpec(
+          message: "ellipsis operator cannot be used with a type parameter pack",
+          fixIts: ["remove '...'"]
+        )
+      ]
+    )
+  }
+
   func testPackElementExprSimple() {
     AssertParse(
       """
@@ -293,6 +324,21 @@ final class TypeParameterPackTests: XCTestCase {
     )
   }
   func testParameterPacks4() {
+    AssertParse(
+      """
+      protocol P {
+        associatedtype 1️⃣each T
+      }
+      """,
+      diagnostics: [
+        DiagnosticSpec(
+          message: "associated types cannot be variadic",
+          fixIts: ["remove 'each'"]
+        )
+      ]
+    )
+  }
+  func testParameterPacks4EarlySyntax() {
     AssertParse(
       """
       protocol P {

Tests/SwiftParserTest/translated/RecoveryTests.swift

@@ -1007,6 +1007,19 @@ final class RecoveryTests: XCTestCase {
     )
   }
 
+  func testRecovery87b() {
+    AssertParse(
+      """
+      struct ErrorGenericParameterList1<each1️⃣
+      """,
+      diagnostics: [
+        DiagnosticSpec(message: "expected name in generic parameter"),
+        DiagnosticSpec(message: "expected '>' to end generic parameter clause"),
+        DiagnosticSpec(message: "expected member block in struct"),
+      ]
+    )
+  }
+
   func testRecovery88() {
     AssertParse(
       """