From cab738b8e58d85b2ac60f20e955196c97f5cbc73 Mon Sep 17 00:00:00 2001
From: Rintaro Ishizaki <rishizaki@apple.com>
Date: Fri, 1 Aug 2025 16:57:53 -0700
Subject: [PATCH] [SwiftParser] Handle nested '#if' in attribute list correctly

Parse the following '#if' directive as an attribute list for the func
decl.
  ```
  #if condition
  #if condition
  @attr
  #endif
  #endif
  func foo()
  ```

(cherry picked from commit 191392bd13f71f60e2030675a8948bc4800ba304)
---
 Sources/SwiftParser/Lookahead.swift        |  4 ++-
 Tests/SwiftParserTest/DirectiveTests.swift | 36 ++++++++++++++++++++++
 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/Sources/SwiftParser/Lookahead.swift b/Sources/SwiftParser/Lookahead.swift
index 9aa7afe8c4b..82ff8228b2d 100644
--- a/Sources/SwiftParser/Lookahead.swift
+++ b/Sources/SwiftParser/Lookahead.swift
@@ -254,7 +254,9 @@ extension Parser.Lookahead {
           didSeeAnyAttributes = true
           _ = self.consumeAttributeList()
         case .poundIf:
-          _ = self.consumeIfConfigOfAttributes()
+          if self.consumeIfConfigOfAttributes() {
+            didSeeAnyAttributes = true
+          }
         default:
           break ATTRIBUTE_LOOP
         }
diff --git a/Tests/SwiftParserTest/DirectiveTests.swift b/Tests/SwiftParserTest/DirectiveTests.swift
index d89d1431d1f..a42e72c1059 100644
--- a/Tests/SwiftParserTest/DirectiveTests.swift
+++ b/Tests/SwiftParserTest/DirectiveTests.swift
@@ -157,6 +157,42 @@ final class DirectiveTests: ParserTestCase {
     )
   }
 
+  func testPoundIfNestedStructure() {
+    assertParse(
+      """
+      #if true
+      #if true
+      @frozen
+      #endif
+      #endif
+      public struct S {}
+      """,
+      substructure: AttributeListSyntax([
+        .ifConfigDecl(
+          IfConfigDeclSyntax(clauses: [
+            IfConfigClauseSyntax(
+              poundKeyword: .poundIfToken(),
+              condition: ExprSyntax("true"),
+              elements: .attributes([
+                .ifConfigDecl(
+                  IfConfigDeclSyntax(clauses: [
+                    IfConfigClauseSyntax(
+                      poundKeyword: .poundIfToken(),
+                      condition: ExprSyntax("true"),
+                      elements: .attributes([
+                        .attribute("@frozen")
+                      ])
+                    )
+                  ])
+                )
+              ])
+            )
+          ])
+        )
+      ])
+    )
+  }
+
   func testHasAttribute() {
     assertParse(
       """