From b5b764c93403a68ebac783a45e12073a54df57ad Mon Sep 17 00:00:00 2001
From: Rintaro Ishizaki <rishizaki@apple.com>
Date: Fri, 21 Mar 2025 14:23:49 -0700
Subject: [PATCH] [Parser] Always enable `abiAttribute` feature

`ABIAttributeArgumentsSyntax` is still under
`@_spi(ExperimentalLanguageFeatures)`.
Not parsing the interior of `@abi` attribute causes catastrophic breakage
to the tree. Having "unknown" syntax kind in the tree is better than
dealing with structually broken trees.
---
 .../SyntaxSupport/ExperimentalFeatures.swift  | 11 +++
 .../ExperimentalFeaturesFile.swift            | 13 +++
 Sources/SwiftParser/Parser.swift              |  2 +-
 .../generated/ExperimentalFeatures.swift      |  5 ++
 Tests/SwiftParserTest/AttributeTests.swift    | 81 +++++++------------
 5 files changed, 57 insertions(+), 55 deletions(-)

diff --git a/CodeGeneration/Sources/SyntaxSupport/ExperimentalFeatures.swift b/CodeGeneration/Sources/SyntaxSupport/ExperimentalFeatures.swift
index affe9c1b03f..7994dc25c47 100644
--- a/CodeGeneration/Sources/SyntaxSupport/ExperimentalFeatures.swift
+++ b/CodeGeneration/Sources/SyntaxSupport/ExperimentalFeatures.swift
@@ -81,6 +81,17 @@ public enum ExperimentalFeature: String, CaseIterable {
     }
   }
 
+  public var isAlwaysEnabledInParser: Bool {
+    switch self {
+    case .abiAttribute:
+      // `@abi` attributes should be always parsed because not parsing its interior
+      // breaks the tree catastrophically.
+      return true
+    default:
+      return false
+    }
+  }
+
   /// The token that represents the experimental feature case name.
   public var token: TokenSyntax {
     .identifier(rawValue)
diff --git a/CodeGeneration/Sources/generate-swift-syntax/templates/swiftparser/ExperimentalFeaturesFile.swift b/CodeGeneration/Sources/generate-swift-syntax/templates/swiftparser/ExperimentalFeaturesFile.swift
index 0879e1a3a41..3bdd853655e 100644
--- a/CodeGeneration/Sources/generate-swift-syntax/templates/swiftparser/ExperimentalFeaturesFile.swift
+++ b/CodeGeneration/Sources/generate-swift-syntax/templates/swiftparser/ExperimentalFeaturesFile.swift
@@ -40,6 +40,19 @@ let experimentalFeaturesFile = SourceFileSyntax(leadingTrivia: copyrightHeader)
       )
     }
 
+    try! VariableDeclSyntax(
+      """
+      /// Set of features always enabled.
+      static var alwaysEnabledFeatures: Self
+      """
+    ) {
+      ArrayExprSyntax {
+        for feature in ExperimentalFeature.allCases where feature.isAlwaysEnabledInParser {
+          ArrayElementSyntax(expression: ExprSyntax(".\(feature.token)"))
+        }
+      }
+    }
+
     try! InitializerDeclSyntax(
       """
       /// Creates a new value representing the experimental feature with the
diff --git a/Sources/SwiftParser/Parser.swift b/Sources/SwiftParser/Parser.swift
index 6d6e8b37cb3..48863fbca89 100644
--- a/Sources/SwiftParser/Parser.swift
+++ b/Sources/SwiftParser/Parser.swift
@@ -237,7 +237,7 @@ public struct Parser {
 
     self.maximumNestingLevel = maximumNestingLevel ?? Self.defaultMaximumNestingLevel
     self.swiftVersion = swiftVersion ?? Self.defaultSwiftVersion
-    self.experimentalFeatures = experimentalFeatures
+    self.experimentalFeatures = experimentalFeatures.union(.alwaysEnabledFeatures)
     self.lookaheadTrackerOwner = LookaheadTrackerOwner()
 
     self.lexemes = Lexer.tokenize(input, lookaheadTracker: lookaheadTrackerOwner.lookaheadTracker)
diff --git a/Sources/SwiftParser/generated/ExperimentalFeatures.swift b/Sources/SwiftParser/generated/ExperimentalFeatures.swift
index e31d3628ee3..15d758cbbfc 100644
--- a/Sources/SwiftParser/generated/ExperimentalFeatures.swift
+++ b/Sources/SwiftParser/generated/ExperimentalFeatures.swift
@@ -58,6 +58,11 @@ extension Parser.ExperimentalFeatures {
   /// Whether to enable the parsing of sugar type for InlineArray.
   public static let inlineArrayTypeSugar = Self (rawValue: 1 << 10)
 
+  /// Set of features always enabled.
+  static var alwaysEnabledFeatures: Self {
+    [.abiAttribute]
+  }
+
   /// Creates a new value representing the experimental feature with the
   /// given name, or returns nil if the name is not recognized.
   public init?(name: String) {
diff --git a/Tests/SwiftParserTest/AttributeTests.swift b/Tests/SwiftParserTest/AttributeTests.swift
index 6415986681d..5d82301c61e 100644
--- a/Tests/SwiftParserTest/AttributeTests.swift
+++ b/Tests/SwiftParserTest/AttributeTests.swift
@@ -960,23 +960,20 @@ final class AttributeTests: ParserTestCase {
           parameterClause: FunctionParameterClauseSyntax {},
           returnClause: ReturnClauseSyntax(type: TypeSyntax("Int"))
         )
-      ) {},
-      experimentalFeatures: [.abiAttribute]
+      ) {}
     )
 
     assertParse(
       """
       @abi(associatedtype AssocTy)
       associatedtype AssocTy
-      """,
-      experimentalFeatures: [.abiAttribute]
+      """
     )
     assertParse(
       """
       @abi(deinit)
       deinit {}
-      """,
-      experimentalFeatures: [.abiAttribute]
+      """
     )
     assertParse(
       """
@@ -984,50 +981,43 @@ final class AttributeTests: ParserTestCase {
         @abi(case someCase)
         case someCase
       }
-      """,
-      experimentalFeatures: [.abiAttribute]
+      """
     )
     assertParse(
       """
       @abi(func fn())
       func fn()
-      """,
-      experimentalFeatures: [.abiAttribute]
+      """
     )
     assertParse(
       """
       @abi(init())
       init() {}
-      """,
-      experimentalFeatures: [.abiAttribute]
+      """
     )
     assertParse(
       """
       @abi(subscript(i: Int) -> Element)
       subscript(i: Int) -> Element {}
-      """,
-      experimentalFeatures: [.abiAttribute]
+      """
     )
     assertParse(
       """
       @abi(typealias Typealias = @escaping () -> Void)
       typealias Typealias = () -> Void
-      """,
-      experimentalFeatures: [.abiAttribute]
+      """
     )
     assertParse(
       """
       @abi(let c1, c2)
       let c1, c2
-      """,
-      experimentalFeatures: [.abiAttribute]
+      """
     )
     assertParse(
       """
       @abi(var v1, v2)
       var v1, v2
-      """,
-      experimentalFeatures: [.abiAttribute]
+      """
     )
 
     assertParse(
@@ -1042,8 +1032,7 @@ final class AttributeTests: ParserTestCase {
       ),
       diagnostics: [
         DiagnosticSpec(locationMarker: "1️⃣", message: "editor placeholder in source file")
-      ],
-      experimentalFeatures: [.abiAttribute]
+      ]
     )
 
     assertParse(
@@ -1067,8 +1056,7 @@ final class AttributeTests: ParserTestCase {
       ),
       diagnostics: [
         DiagnosticSpec(locationMarker: "1️⃣", message: "import is not permitted as ABI-providing declaration")
-      ],
-      experimentalFeatures: [.abiAttribute]
+      ]
     )
 
     //
@@ -1079,15 +1067,13 @@ final class AttributeTests: ParserTestCase {
       """
       @abi(associatedtype AssocTy = T)
       associatedtype AssocTy
-      """,
-      experimentalFeatures: [.abiAttribute]
+      """
     )
     assertParse(
       """
       @abi(deinit {})
       deinit {}
-      """,
-      experimentalFeatures: [.abiAttribute]
+      """
     )
     assertParse(
       """
@@ -1095,50 +1081,43 @@ final class AttributeTests: ParserTestCase {
         @abi(case someCase = 42)
         case someCase
       }
-      """,
-      experimentalFeatures: [.abiAttribute]
+      """
     )
     assertParse(
       """
       @abi(func fn() {})
       func fn()
-      """,
-      experimentalFeatures: [.abiAttribute]
+      """
     )
     assertParse(
       """
       @abi(init() {})
       init() {}
-      """,
-      experimentalFeatures: [.abiAttribute]
+      """
     )
     assertParse(
       """
       @abi(subscript(i: Int) -> Element { get {} set {} })
       subscript(i: Int) -> Element {}
-      """,
-      experimentalFeatures: [.abiAttribute]
+      """
     )
     assertParse(
       """
       @abi(let c1 = 1, c2 = 2)
       let c1, c2
-      """,
-      experimentalFeatures: [.abiAttribute]
+      """
     )
     assertParse(
       """
       @abi(var v1 = 1, v2 = 2)
       var v1, v2
-      """,
-      experimentalFeatures: [.abiAttribute]
+      """
     )
     assertParse(
       """
       @abi(var v3 { get {} set {} })
       var v3
-      """,
-      experimentalFeatures: [.abiAttribute]
+      """
     )
 
     //
@@ -1160,8 +1139,7 @@ final class AttributeTests: ParserTestCase {
       fixedSource: """
         @abi(var <#pattern#>)
         var v1
-        """,
-      experimentalFeatures: [.abiAttribute]
+        """
     )
     assertParse(
       """
@@ -1184,8 +1162,7 @@ final class AttributeTests: ParserTestCase {
       fixedSource: """
         @abi(var v2)
         var v2
-        """,
-      experimentalFeatures: [.abiAttribute]
+        """
     )
     assertParse(
       """
@@ -1203,8 +1180,7 @@ final class AttributeTests: ParserTestCase {
       fixedSource: """
         @abi(<#declaration#>)
         func fn2() {}
-        """,
-      experimentalFeatures: [.abiAttribute]
+        """
     )
     assertParse(
       """
@@ -1221,8 +1197,7 @@ final class AttributeTests: ParserTestCase {
       fixedSource: """
         @abi(<#declaration#>)
         func fn3() {}
-        """,
-      experimentalFeatures: [.abiAttribute]
+        """
     )
     assertParse(
       """
@@ -1244,8 +1219,7 @@ final class AttributeTests: ParserTestCase {
       fixedSource: """
         @abi(<#declaration#>) func fn4_abi())
         func fn4() {}
-        """,
-      experimentalFeatures: [.abiAttribute]
+        """
     )
 
     // `#if` is banned inside an `@abi` attribute.
@@ -1278,8 +1252,7 @@ final class AttributeTests: ParserTestCase {
           func _fn<E: Error>() throws(E)
         )
         func fn<E: Error>() throws(E) {}
-        """,
-      experimentalFeatures: [.abiAttribute]
+        """
     )
   }