Test active code regions with postfix #if

Author: DougGregor

Sources/SwiftIfConfig/IfConfigRewriter.swift

@@ -287,9 +287,6 @@ class ActiveSyntaxRewriter<Configuration: BuildConfiguration>: SyntaxRewriter {
     return applyBaseToPostfixExpression(base: base, postfix: postfixExpr)
   }
 
-  // FIXME: PostfixIfConfigExprSyntax has a different form that doesn't work
-  // well with the way dropInactive is written. We essentially need to
-  // thread a the "base" into the active clause.
   override func visit(_ node: PostfixIfConfigExprSyntax) -> ExprSyntax {
     let rewrittenNode = dropInactive(outerBase: nil, postfixIfConfig: node)
     if rewrittenNode == ExprSyntax(node) {

Tests/SwiftIfConfigTest/ActiveRegionTests.swift

@@ -51,4 +51,33 @@ public class ActiveRegionTests: XCTestCase {
       ]
     )
   }
+
+  func testActiveRegionsInPostfix() throws {
+    try assertActiveCode(
+      """
+      4️⃣a.b()
+      #if DEBUG
+      0️⃣.c()
+      #elseif ASSERTS
+      1️⃣.d()
+      #if compiler(>=8.0)
+      2️⃣.e()
+      #else
+      3️⃣.f()
+      #endif
+      #endif
+      5️⃣.g()
+      """,
+      configuration: linuxBuildConfig,
+      states: [
+        "0️⃣": .active,
+        "1️⃣": .inactive,
+        "2️⃣": .unparsed,
+        "3️⃣": .inactive,
+        "4️⃣": .active,
+        "5️⃣": .active,
+      ]
+    )
+
+  }
 }