Fix two diagnostics when building swift-syntax using pre Swift-6 compilers

CodeGeneration/Sources/SyntaxSupport/KeywordSpec.swift

@@ -43,8 +43,17 @@ public struct KeywordSpec {
   ///
   /// This is typically used to mark APIs as SPI when the keyword is part of an experimental language feature.
   public var apiAttributes: AttributeListSyntax {
-    guard isExperimental else { return "" }
-    return AttributeListSyntax("@_spi(ExperimentalLanguageFeatures)").with(\.trailingTrivia, .newline)
+    let attrList = AttributeListSyntax {
+      if isExperimental {
+        let experimentalSPI: AttributeListSyntax = """
+          #if compiler(>=5.8)
+          @_spi(ExperimentalLanguageFeatures)
+          #endif
+          """
+        experimentalSPI.with(\.trailingTrivia, .newline)
+      }
+    }
+    return attrList.with(\.trailingTrivia, attrList.isEmpty ? [] : .newline)
   }
 
   /// Initializes a new `KeywordSpec` instance.

Sources/SwiftParser/generated/Parser+TokenSpecSet.swift

@@ -802,11 +802,15 @@ extension DeclModifierSyntax {
     case `private`
     case `public`
     case reasync
+    #if compiler(>=5.8)
     @_spi(ExperimentalLanguageFeatures)
+    #endif
     case _resultDependsOnSelf
     case required
     case `static`
+    #if compiler(>=5.8)
     @_spi(ExperimentalLanguageFeatures)
+    #endif
     case transferring
     case unowned
     case weak
@@ -2907,11 +2911,17 @@ extension OptionalBindingConditionSyntax {
     case `let`
     case `var`
     case `inout`
+    #if compiler(>=5.8)
     @_spi(ExperimentalLanguageFeatures)
+    #endif
     case _mutating
+    #if compiler(>=5.8)
     @_spi(ExperimentalLanguageFeatures)
+    #endif
     case _borrowing
+    #if compiler(>=5.8)
     @_spi(ExperimentalLanguageFeatures)
+    #endif
     case _consuming
 
     init?(lexeme: Lexer.Lexeme, experimentalFeatures: Parser.ExperimentalFeatures) {
@@ -3332,9 +3342,13 @@ extension SimpleTypeSpecifierSyntax {
     case _const
     case borrowing
     case consuming
+    #if compiler(>=5.8)
     @_spi(ExperimentalLanguageFeatures)
+    #endif
     case transferring
+    #if compiler(>=5.8)
     @_spi(ExperimentalLanguageFeatures)
+    #endif
     case _resultDependsOn
 
     init?(lexeme: Lexer.Lexeme, experimentalFeatures: Parser.ExperimentalFeatures) {
@@ -3879,11 +3893,17 @@ extension ValueBindingPatternSyntax {
     case `let`
     case `var`
     case `inout`
+    #if compiler(>=5.8)
     @_spi(ExperimentalLanguageFeatures)
+    #endif
     case _mutating
+    #if compiler(>=5.8)
     @_spi(ExperimentalLanguageFeatures)
+    #endif
     case _borrowing
+    #if compiler(>=5.8)
     @_spi(ExperimentalLanguageFeatures)
+    #endif
     case _consuming
 
     init?(lexeme: Lexer.Lexeme, experimentalFeatures: Parser.ExperimentalFeatures) {
@@ -3970,11 +3990,17 @@ extension VariableDeclSyntax {
     case `let`
     case `var`
     case `inout`
+    #if compiler(>=5.8)
     @_spi(ExperimentalLanguageFeatures)
+    #endif
     case _mutating
+    #if compiler(>=5.8)
     @_spi(ExperimentalLanguageFeatures)
+    #endif
     case _borrowing
+    #if compiler(>=5.8)
     @_spi(ExperimentalLanguageFeatures)
+    #endif
     case _consuming
 
     init?(lexeme: Lexer.Lexeme, experimentalFeatures: Parser.ExperimentalFeatures) {

Sources/SwiftSyntax/Syntax.swift

@@ -16,7 +16,11 @@
 public struct Syntax: SyntaxProtocol, SyntaxHashable {
   /// We need a heap indirection to store a syntax node's parent. We could use an indirect enum here but explicitly
   /// modelling it using a class allows us to re-use these heap-allocated objects in `SyntaxVisitor`.
-  final class Info: Sendable {
+  ///
+  /// - Note: `@unchecked Sendable` because `info` is mutable. In Swift 6 and above the variable can be declared as
+  ///   `nonisolated(unsafe)` but that attribute doesn't exist in previous Swift versions and a checked Sendable
+  ///   conformance generates a warning.
+  final class Info: @unchecked Sendable {
     // For root node.
     struct Root: Sendable {
       private var arena: RetainedSyntaxArena

Sources/SwiftSyntax/generated/Keyword.swift

@@ -20,14 +20,18 @@ public enum Keyword: UInt8, Hashable, Sendable {
   case _alignment
   case _backDeploy
   case _borrow
+  #if compiler(>=5.8)
   @_spi(ExperimentalLanguageFeatures)
+  #endif
   case _borrowing
   case _BridgeObject
   case _cdecl
   case _Class
   case _compilerInitialized
   case _const
+  #if compiler(>=5.8)
   @_spi(ExperimentalLanguageFeatures)
+  #endif
   case _consuming
   case _documentation
   case _dynamicReplacement
@@ -39,7 +43,9 @@ public enum Keyword: UInt8, Hashable, Sendable {
   case _local
   case _modify
   case _move
+  #if compiler(>=5.8)
   @_spi(ExperimentalLanguageFeatures)
+  #endif
   case _mutating
   case _NativeClass
   case _NativeRefCountedObject
@@ -104,7 +110,9 @@ public enum Keyword: UInt8, Hashable, Sendable {
   case `default`
   case `defer`
   case `deinit`
+  #if compiler(>=5.8)
   @_spi(ExperimentalLanguageFeatures)
+  #endif
   case dependsOn
   case deprecated
   case derivative
@@ -187,17 +195,23 @@ public enum Keyword: UInt8, Hashable, Sendable {
   case renamed
   case `repeat`
   case required
+  #if compiler(>=5.8)
   @_spi(ExperimentalLanguageFeatures)
+  #endif
   case _resultDependsOn
+  #if compiler(>=5.8)
   @_spi(ExperimentalLanguageFeatures)
+  #endif
   case _resultDependsOnSelf
   case `rethrows`
   case retroactive
   case `return`
   case reverse
   case right
   case safe
+  #if compiler(>=5.8)
   @_spi(ExperimentalLanguageFeatures)
+  #endif
   case scoped
   case `self`
   case `Self`
@@ -217,7 +231,9 @@ public enum Keyword: UInt8, Hashable, Sendable {
   case then
   case `throw`
   case `throws`
+  #if compiler(>=5.8)
   @_spi(ExperimentalLanguageFeatures)
+  #endif
   case transferring
   case transpose
   case `true`