Only consider the active clauses of IfConfigDecls in placeholder expansion

This is another step toward the removal of IfConfigDecl

Author: DougGregor

test/SourceKit/CodeExpand/code-expand.swift

@@ -147,17 +147,11 @@ braced2(x: {<#T##() -> Void#>}, y: Int)
 // CHECK-NEXT:  }, y: Int)
 
 braced3({
-  #if true
   <#T##() -> Int#>
-  #endif
 })
-// CHECK:      braced3({
-// CHECK-NEXT:   #if true
-// CHECK-NEXT:    {
+// CHECK:      braced3 {
 // CHECK-NEXT:      <#code#>
-// CHECK-NEXT:    }
-// CHECK-NEXT:    #endif
-// CHECK-NEXT:  })
+// CHECK-NEXT:  }
 
 func returnTrailing() -> Int {
   return withtrail(<#T##() -> ()#>)
@@ -260,17 +254,6 @@ func activeWithTrailing() {
   // CHECK: forEach {
   // CHECK-NEXT: <#code#>
 }
-#if false
-func inactive() {
-  foo(<#T##value: Foo##Foo#>)
-  // CHECK: foo(Foo)
-}
-func inactiveWithTrailing() {
-  forEach(<#T##() -> ()#>)
-  // CHECK: forEach {
-  // CHECK-NEXT: <#code#>
-}
-#endif
 
 expandClosureWithInternalParameterNames {
   withtrail(<#T##callback: (Int, Int) -> Bool##(_ a: Int, _ b: Int) -> Bool#>)

tools/SourceKit/lib/SwiftLang/SwiftEditor.cpp

@@ -1608,9 +1608,11 @@ class PlaceholderExpansionScanner {
       if (auto *ICD = dyn_cast<IfConfigDecl>(D)) {
         // The base walker assumes the content of active IfConfigDecl clauses
         // has been injected into the parent context and will be walked there.
-        // This doesn't hold for pre-typechecked ASTs and we need to find
-        // placeholders in inactive clauses anyway, so walk them here.
+        // This doesn't hold for pre-typechecked ASTs, so walk them here.
         for (auto Clause: ICD->getClauses()) {
+          if (!Clause.isActive)
+            continue;
+
           for (auto Elem: Clause.Elements) {
             Elem.walk(*this);
           }
@@ -1798,20 +1800,6 @@ class PlaceholderExpansionScanner {
         return Action::Continue(S);
       }
 
-      PreWalkAction walkToDeclPre(Decl *D) override {
-        if (auto *ICD = dyn_cast<IfConfigDecl>(D)) {
-          for (auto Clause : ICD->getClauses()) {
-            // Active clase elements are visited normally.
-            if (Clause.isActive)
-              continue;
-            for (auto Member : Clause.Elements)
-              Member.walk(*this);
-          }
-          return Action::SkipNode();
-        }
-        return Action::Continue();
-      }
-
       ArgumentList *findEnclosingCallArg(SourceFile &SF, SourceLoc SL) {
         EnclosingCallAndArg = {nullptr, nullptr};
         OuterExpr = nullptr;