Parse IfConfigs in Attribute Lists

Author: CodaFi

Sources/SwiftParser/Attributes.swift

@@ -14,7 +14,7 @@
 
 extension Parser {
   mutating func parseAttributeList() -> RawAttributeListSyntax? {
-    guard self.at(.atSign) else {
+    guard self.at(any: [.atSign, .poundIfKeyword]) else {
       return nil
     }
 
@@ -23,13 +23,21 @@ extension Parser {
     repeat {
       let attribute = self.parseAttribute()
       elements.append(attribute)
-    } while self.at(.atSign) && loopProgress.evaluate(currentToken)
+    } while self.at(any: [.atSign, .poundIfKeyword]) && loopProgress.evaluate(currentToken)
     return RawAttributeListSyntax(elements: elements, arena: self.arena)
   }
 }
 
 extension Parser {
   mutating func parseAttribute() -> RawSyntax {
+    if self.at(.poundIfKeyword) {
+      return RawSyntax(self.parsePoundIfDirective { parser -> RawSyntax in
+        return parser.parseAttribute()
+      } syntax: { parser, attributes in
+        return RawSyntax(RawAttributeListSyntax(elements: attributes, arena: parser.arena))
+      })
+    }
+
     guard let declAttr = DeclarationAttribute(rawValue: self.peek().tokenText) else {
       return RawSyntax(self.parseCustomAttribute())
     }

Sources/SwiftParser/Declarations.swift

@@ -47,6 +47,11 @@ extension TokenConsumer {
       }
     }
 
+    if subparser.at(.poundIfKeyword) {
+      var attrLookahead = subparser.lookahead()
+      return attrLookahead.consumeIfConfigOfAttributes()
+    }
+
     let declStartKeyword: DeclarationStart?
     if allowRecovery {
       declStartKeyword = subparser.canRecoverTo(

Sources/SwiftParser/Lookahead.swift

@@ -197,6 +197,44 @@ extension Parser.Lookahead {
     }
     return true
   }
+
+  mutating func consumeIfConfigOfAttributes() -> Bool {
+    while true {
+      // #if / #else / #elseif
+      self.consumeAnyToken()
+
+      // <expression>
+      self.skipUntilEndOfLine()
+
+      while true {
+        if self.at(.atSign) {
+          _ = self.consumeAttributeList()
+          continue
+        }
+
+        if self.at(.poundIfKeyword) {
+          _ = self.consumeIfConfigOfAttributes()
+          continue
+        }
+
+        break
+      }
+
+      guard self.at(any: [ .poundElseifKeyword, .poundElseKeyword ]) else {
+        break
+      }
+    }
+
+    // If we ran out of tokens, say we consumed the rest.
+    if self.at(.eof) {
+      return true
+    }
+
+    guard self.currentToken.isAtStartOfLine else {
+      return false
+    }
+    return self.consume(if: .poundEndifKeyword) != nil
+  }
 }
 
 // MARK: Lookahead

Tests/SwiftParserTest/Directives.swift

@@ -111,4 +111,42 @@ final class DirectiveTests: XCTestCase {
     )
   }
 
+  func testHasAttribute() {
+    AssertParse(
+      """
+      @frozen
+      #if hasAttribute(foo)
+      @foo
+      #endif
+      public struct S2 { }
+      """)
+
+    AssertParse(
+      """
+      struct Inner {
+        @frozen
+      #if hasAttribute(foo)
+        #if hasAttribute(bar)
+        @foo @bar
+        #endif
+      #endif
+        public struct S2 { }
+
+      #if hasAttribute(foo)
+        @foo
+      #endif
+        @inlinable
+        func f1() { }
+
+      #if hasAttribute(foo)
+        @foo
+      #else
+        @available(*, deprecated, message: "nope")
+        @frozen
+      #endif
+        public struct S3 { }
+      }
+      """)
+  }
+
 }