Fix parsing bug when a postfix expression is followed by an empty #if clause

Author: ahoppen

Sources/SwiftParser/Attributes.swift

@@ -32,7 +32,7 @@ extension Parser {
   mutating func parseAttribute() -> RawAttributeListSyntax.Element {
     if self.at(.poundIfKeyword) {
       return .ifConfigDecl(
-        self.parsePoundIfDirective { parser -> RawAttributeListSyntax.Element in
+        self.parsePoundIfDirective { (parser, _) -> RawAttributeListSyntax.Element in
           return parser.parseAttribute()
         } syntax: { parser, attributes in
           return .attributes(RawAttributeListSyntax(elements: attributes, arena: parser.arena))

Sources/SwiftParser/Declarations.swift

@@ -165,7 +165,7 @@ extension Parser {
   public mutating func parseDeclaration(inMemberDeclList: Bool = false) -> RawDeclSyntax {
     switch self.at(anyIn: PoundDeclarationStart.self) {
     case (.poundIfKeyword, _)?:
-      let directive = self.parsePoundIfDirective { parser in
+      let directive = self.parsePoundIfDirective { (parser, _) in
         let parsedDecl = parser.parseDeclaration()
         let semicolon = parser.consume(if: .semicolon)
         return RawMemberDeclListItemSyntax(

Sources/SwiftParser/Directives.swift

@@ -66,7 +66,7 @@ extension Parser {
   ///             into a syntax collection.
   @_spi(RawSyntax)
   public mutating func parsePoundIfDirective<Element: RawSyntaxNodeProtocol>(
-    _ parseElement: (inout Parser) -> Element?,
+    _ parseElement: (_ parser: inout Parser, _ isFirstElement: Bool) -> Element?,
     addSemicolonIfNeeded: (_ lastElement: Element, _ newItemAtStartOfLine: Bool, _ parser: inout Parser) -> Element? = { _, _, _ in nil },
     syntax: (inout Parser, [Element]) -> RawIfConfigClauseSyntax.Elements?
   ) -> RawIfConfigDeclSyntax {
@@ -83,7 +83,7 @@ extension Parser {
     do {
       var firstIteration = true
       var loopProgress = LoopProgressCondition()
-      while let poundIfHandle = self.canRecoverTo(any: firstIteration ? [.poundIfKeyword] : [.poundIfKeyword, .poundElseifKeyword, .poundElseKeyword]),
+      while let poundIfHandle = self.canRecoverTo(any: firstIteration ? [.poundIfKeyword] : [.poundElseifKeyword, .poundElseKeyword]),
         loopProgress.evaluate(self.currentToken)
       {
         let (unexpectedBeforePoundIf, poundIf) = self.eat(poundIfHandle)
@@ -104,7 +104,7 @@ extension Parser {
           var elementsProgress = LoopProgressCondition()
           while !self.at(any: [.eof, .poundElseKeyword, .poundElseifKeyword, .poundEndifKeyword]) && elementsProgress.evaluate(currentToken) {
             let newItemAtStartOfLine = self.currentToken.isAtStartOfLine
-            guard let element = parseElement(&self), !element.isEmpty else {
+            guard let element = parseElement(&self, elements.isEmpty), !element.isEmpty else {
               break
             }
             if let lastElement = elements.last, let fixedUpLastItem = addSemicolonIfNeeded(lastElement, newItemAtStartOfLine, &self) {

Sources/SwiftParser/Expressions.swift

@@ -624,7 +624,10 @@ extension Parser {
   ) -> RawExprSyntax {
     assert(self.at(.poundIfKeyword))
 
-    let config = self.parsePoundIfDirective { parser -> RawExprSyntax? in
+    let config = self.parsePoundIfDirective { (parser, isFirstElement) -> RawExprSyntax? in
+      if !isFirstElement {
+        return nil
+      }
       let head: RawExprSyntax
       if parser.at(any: [.period, .prefixPeriod]) {
         head = parser.parseDottedExpressionSuffix(nil)

Sources/SwiftParser/Statements.swift

@@ -752,7 +752,7 @@ extension Parser {
         elements.append(
           .ifConfigDecl(
             self.parsePoundIfDirective(
-              { $0.parseSwitchCases(allowStandaloneStmtRecovery: allowStandaloneStmtRecovery) },
+              { (parser, _) in parser.parseSwitchCases(allowStandaloneStmtRecovery: allowStandaloneStmtRecovery) },
               syntax: { parser, cases in
                 guard cases.count == 1, let firstCase = cases.first else {
                   assert(cases.isEmpty)

Sources/SwiftParser/TopLevel.swift

@@ -201,8 +201,8 @@ extension Parser {
   /// wrapping declaration instead of being consumed by lookeahead.
   private mutating func parseItem(isAtTopLevel: Bool = false, allowInitDecl: Bool = true) -> RawCodeBlockItemSyntax.Item {
     if self.at(.poundIfKeyword) {
-      let directive = self.parsePoundIfDirective {
-        $0.parseCodeBlockItem()
+      let directive = self.parsePoundIfDirective { (parser, _) in
+        parser.parseCodeBlockItem()
       } addSemicolonIfNeeded: { lastElement, newItemAtStartOfLine, parser in
         if lastElement.semicolon == nil && !newItemAtStartOfLine {
           return RawCodeBlockItemSyntax(

Tests/SwiftParserTest/DirectiveTests.swift

@@ -69,6 +69,22 @@ final class DirectiveTests: XCTestCase {
     )
   }
 
+  func testPostfixIfConfigExpressionContainsPoundIf() {
+    AssertParse(
+      """
+      b
+      #if true
+      .a
+      1️⃣#if true
+      #endif
+      #endif
+      """,
+      diagnostics: [
+        DiagnosticSpec(message: "unexpected code in conditional compilation block")
+      ]
+    )
+  }
+
   func testSourceLocation() {
     AssertParse(
       """