Ignore inactive IfConfigDecls in SourceKit's syntax model

Clients that need syntactic information should use SourceKit-LSP or
swift-syntax.

Author: DougGregor

CHANGELOG.md

@@ -5,6 +5,22 @@
 
 ## Swift (next)
 
+* Syntactic SourceKit queries no longer attempt to provide information
+  within the inactive `#if` regions. For example, given:
+
+  ```swift
+  #if DEBUG
+  extension MyType: CustomDebugStringConvertible {
+    var debugDescription: String { ... }
+  }
+  #endif
+  ```
+
+  If `DEBUG` is not set, SourceKit results will not involve the
+  inactive code. Clients should use either SourceKit-LSP or
+  swift-syntax for syntactic queries that are independent of the
+  specific build configuration.
+
 * [SE-0442][]:
   TaskGroups can now be created without explicitly specifying their child task's result types:
 

lib/IDE/SyntaxModel.cpp

@@ -416,7 +416,6 @@ class ModelASTWalker : public ASTWalker {
 private:
   static bool findUrlStartingLoc(StringRef Text, unsigned &Start,
                                  std::regex& Regex);
-  bool annotateIfConfigConditionIdentifiers(Expr *Cond);
   bool handleAttrs(const ParsedDeclAttributes &Attrs);
   bool handleAttrs(ArrayRef<TypeOrCustomAttr> Attrs);
 
@@ -1003,24 +1002,8 @@ ASTWalker::PreWalkAction ModelASTWalker::walkToDeclPre(Decl *D) {
     }
     pushStructureNode(SN, VD);
 
-  } else if (auto *ConfigD = dyn_cast<IfConfigDecl>(D)) {
-    for (auto &Clause : ConfigD->getClauses()) {
-      if (Clause.Cond && !annotateIfConfigConditionIdentifiers(Clause.Cond))
-        return Action::SkipNode();
-
-      InactiveClauseRAII inactiveClauseRAII(inInactiveClause, !Clause.isActive);
-      for (auto &Element : Clause.Elements) {
-        if (auto *E = Element.dyn_cast<Expr*>()) {
-          E->walk(*this);
-        } else if (auto *S = Element.dyn_cast<Stmt*>()) {
-          S->walk(*this);
-        } else {
-          Element.get<Decl*>()->walk(*this);
-        }
-        NodesVisitedBefore.insert(Element);
-      }
-    }
-
+  } else if (isa<IfConfigDecl>(D)) {
+    // Note: nothing to do.
   } else if (auto *EnumCaseD = dyn_cast<EnumCaseDecl>(D)) {
     SyntaxStructureNode SN;
     setDecl(SN, D);
@@ -1172,17 +1155,6 @@ class IdRefWalker : public ASTWalker {
 };
 } // end anonymous namespace
 
-bool ModelASTWalker::annotateIfConfigConditionIdentifiers(Expr *Cond) {
-  if (!Cond)
-    return true;
-  auto passNode = [&](CharSourceRange R) {
-    return passNonTokenNode({ SyntaxNodeKind::BuildConfigId, R });
-  };
-
-  IdRefWalker<decltype(passNode)> Walker(passNode);
-  return Cond->walk(Walker);
-}
-
 bool ModelASTWalker::handleSpecialDeclAttribute(const DeclAttribute *D,
                                                 ArrayRef<Token> Toks) {
   if (!D)