[Parser] Stop producing PoundLineExprSyntax nodes.

Instead, have `#line` create the more general
`MacroExpansionExprSyntax` node.

Author: DougGregor

Sources/SwiftParser/Directives.swift

@@ -123,22 +123,6 @@ extension Parser {
 }
 
 extension Parser {
-  /// Parse a #line literal.
-  ///
-  /// Grammar
-  /// =======
-  ///
-  ///     literal-expression → '#line'
-  @_spi(RawSyntax)
-  public mutating func parsePoundLineDirective() -> RawPoundLineExprSyntax {
-    let (unexpectedBeforeToken, token) = self.expect(.poundLineKeyword)
-    return RawPoundLineExprSyntax(
-      unexpectedBeforeToken,
-      poundLine: token,
-      arena: self.arena
-    )
-  }
-
   /// Parse a line control directive.
   ///
   /// Grammar

Sources/SwiftParser/Expressions.swift

@@ -1047,12 +1047,6 @@ extension Parser {
         poundFunction: tok,
         arena: self.arena
       ))
-    case (.poundLineKeyword, let handle)?:
-      let tok = self.eat(handle)
-      return RawExprSyntax(RawPoundLineExprSyntax(
-        poundLine: tok,
-        arena: self.arena
-      ))
     case (.__line__Keyword, let handle)?:
       let tok = self.eat(handle)
       return RawExprSyntax(RawPoundLineExprSyntax(

Sources/SwiftParser/Lexer.swift

@@ -1539,7 +1539,6 @@ extension Lexer.Cursor {
     let kind: RawTokenKind
     switch literal {
     case "keyPath": kind = .poundKeyPathKeyword
-    case "line": kind = .poundLineKeyword
     case "selector": kind = .poundSelectorKeyword
     case "file": kind = .poundFileKeyword
     case "fileID": kind = .poundFileIDKeyword

Sources/SwiftParser/RawTokenKindSubset.swift

@@ -110,7 +110,6 @@ enum CanBeDeclaratinStart: RawTokenKindSubset {
   case operatorKeyword
   case poundErrorKeyword
   case poundIfKeyword
-  case poundLineKeyword
   case poundSourceLocationKeyword
   case poundWarningKeyword
   case precedencegroupKeyword
@@ -142,7 +141,6 @@ enum CanBeDeclaratinStart: RawTokenKindSubset {
     case .operatorKeyword: self = .operatorKeyword
     case .poundErrorKeyword: self = .poundErrorKeyword
     case .poundIfKeyword: self = .poundIfKeyword
-    case .poundLineKeyword where lexeme.isAtStartOfLine: self = .poundLineKeyword
     case .poundSourceLocationKeyword: self = .poundSourceLocationKeyword
     case .poundWarningKeyword: self = .poundWarningKeyword
     case .precedencegroupKeyword: self = .precedencegroupKeyword
@@ -177,7 +175,6 @@ enum CanBeDeclaratinStart: RawTokenKindSubset {
     case .operatorKeyword: return .operatorKeyword
     case .poundErrorKeyword: return .poundErrorKeyword
     case .poundIfKeyword: return .poundIfKeyword
-    case .poundLineKeyword: return .poundLineKeyword
     case .poundSourceLocationKeyword: return .poundSourceLocationKeyword
     case .poundWarningKeyword: return .poundWarningKeyword
     case .precedencegroupKeyword: return .precedencegroupKeyword
@@ -751,7 +748,6 @@ enum PrimaryExpressionStart: RawTokenKindSubset {
   case poundFunctionKeyword
   case poundImageLiteralKeyword
   case poundKeyPathKeyword
-  case poundLineKeyword
   case poundSelectorKeyword
   case prefixPeriod
   case regexLiteral
@@ -791,7 +787,6 @@ enum PrimaryExpressionStart: RawTokenKindSubset {
     case .poundFunctionKeyword: self = .poundFunctionKeyword
     case .poundImageLiteralKeyword: self = .poundImageLiteralKeyword
     case .poundKeyPathKeyword: self = .poundKeyPathKeyword
-    case .poundLineKeyword: self = .poundLineKeyword
     case .poundSelectorKeyword: self = .poundSelectorKeyword
     case .prefixPeriod: self = .prefixPeriod
     case .regexLiteral: self = .regexLiteral
@@ -834,7 +829,6 @@ enum PrimaryExpressionStart: RawTokenKindSubset {
     case .poundFunctionKeyword: return .poundFunctionKeyword
     case .poundImageLiteralKeyword: return .poundImageLiteralKeyword
     case .poundKeyPathKeyword: return .poundKeyPathKeyword
-    case .poundLineKeyword: return .poundLineKeyword
     case .poundSelectorKeyword: return .poundSelectorKeyword
     case .prefixPeriod: return .prefixPeriod
     case .regexLiteral: return .regexLiteral

Sources/SwiftParser/TopLevel.swift

@@ -172,8 +172,6 @@ extension Parser {
         return RawSyntax(RawCodeBlockItemListSyntax(elements: items, arena: parser.arena))
       }
       return RawSyntax(directive)
-    } else if self.at(.poundLineKeyword) {
-      return RawSyntax(self.parsePoundLineDirective())
     } else if self.at(.poundSourceLocationKeyword) {
       return RawSyntax(self.parsePoundSourceLocationDirective())
     } else if self.atStartOfDeclaration() {

Tests/SwiftParserTest/Expressions.swift

@@ -301,7 +301,12 @@ final class ExpressionTests: XCTestCase {
       ]
       """,
       substructure: Syntax(DictionaryElementSyntax.init(
-        keyExpression: ExprSyntax(PoundLineExprSyntax(poundLine: .poundLineKeyword())),
+        keyExpression: ExprSyntax(
+          MacroExpansionExprSyntax(
+            poundToken: .poundToken(), macro: .identifier("line"),
+            leftParen: nil, argumentList: TupleExprElementListSyntax([]),
+            rightParen: nil, trailingClosure: nil,
+            additionalTrailingClosures: nil)),
         colon: .colonToken(),
         valueExpression: ExprSyntax(FunctionCallExprSyntax(
           calledExpression: ExprSyntax(IdentifierExprSyntax(identifier: .identifier("Calendar"), declNameArguments: nil)),