Merge pull request #26040 from nathawes/r51995648-placeholder-not-working-inside-pound-if-5.1

[5.1][SourceKit] Fix placeholder expansion not working inside #if

Author: Nathan Hawes

test/SourceKit/CodeExpand/code-expand.swift

@@ -195,3 +195,24 @@ singleExprClosureMultiArg(1) {
 // CHECK: withtrail {
 // CHECK-NEXT: <#code#>
 }
+
+func active() {
+  foo(<#T##value: Foo##Foo#>)
+  // CHECK: foo(Foo)
+}
+func activeWithTrailing() {
+  forEach(<#T##() -> ()#>)
+  // 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

tools/SourceKit/lib/SwiftLang/SwiftEditor.cpp

@@ -1409,6 +1409,22 @@ class PlaceholderExpansionScanner {
       }
       return { true, E };
     }
+
+    bool walkToDeclPre(Decl *D) override {
+      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.
+        for (auto Clause: ICD->getClauses()) {
+          for (auto Elem: Clause.Elements) {
+            Elem.walk(*this);
+          }
+        }
+        return false;
+      }
+      return true;
+    }
   };
 
   class ClosureTypeWalker: public ASTWalker {
@@ -1571,6 +1587,8 @@ class PlaceholderExpansionScanner {
         return true;
       }
 
+      bool shouldWalkInactiveConfigRegion() override { return true; }
+
       Expr *findEnclosingCallArg(SourceFile &SF, SourceLoc SL) {
         EnclosingCallAndArg = {nullptr, nullptr};
         OuterExpr = nullptr;