[AST Printer] Avoid synthesizing decls when printing for diagnostics.

(cherry picked from commit 5e8ed8d)

Author: DougGregor

include/swift/AST/PrintOptions.h

@@ -304,6 +304,11 @@ struct PrintOptions {
   /// such as _silgen_name, transparent, etc.
   bool PrintUserInaccessibleAttrs = true;
 
+  /// Whether to limit ourselves to printing only the "current" set of members
+  /// in a nominal type or extension, which is semantically unstable but can
+  /// prevent printing from doing "extra" work.
+  bool PrintCurrentMembersOnly = false;
+
   /// List of attribute kinds that should not be printed.
   std::vector<AnyAttrKind> ExcludeAttrList = {DAK_Transparent, DAK_Effects,
                                               DAK_FixedLayout,
@@ -517,6 +522,7 @@ struct PrintOptions {
     result.ShouldQualifyNestedDeclarations =
         QualifyNestedDeclarations::TypesOnly;
     result.PrintDocumentationComments = false;
+    result.PrintCurrentMembersOnly = true;
     return result;
   }
 
@@ -538,6 +544,7 @@ struct PrintOptions {
     result.SkipUnderscoredKeywords = true;
     result.EnumRawValues = EnumRawValueMode::PrintObjCOnly;
     result.MapCrossImportOverlaysToDeclaringModule = true;
+    result.PrintCurrentMembersOnly = false;
     return result;
   }
 

lib/AST/ASTPrinter.cpp

@@ -2050,24 +2050,29 @@ void PrintAST::printMembersOfDecl(Decl *D, bool needComma,
                                   bool openBracket,
                                   bool closeBracket) {
   llvm::SmallVector<Decl *, 3> Members;
-  auto AddDeclFunc = [&](ArrayRef<Decl *> Range) {
-    for (auto RD : Range)
-      Members.push_back(RD);
+  auto AddMembers = [&](IterableDeclContext *idc) {
+    if (Options.PrintCurrentMembersOnly) {
+      for (auto RD : idc->getMembers())
+        Members.push_back(RD);
+    } else {
+      for (auto RD : idc->getAllMembers())
+        Members.push_back(RD);
+    }
   };
 
   if (auto Ext = dyn_cast<ExtensionDecl>(D)) {
-    AddDeclFunc(Ext->getAllMembers());
+    AddMembers(Ext);
   } else if (auto NTD = dyn_cast<NominalTypeDecl>(D)) {
-    AddDeclFunc(NTD->getAllMembers());
+    AddMembers(NTD);
     for (auto Ext : NTD->getExtensions()) {
       if (Options.printExtensionContentAsMembers(Ext))
-        AddDeclFunc(Ext->getAllMembers());
+        AddMembers(Ext);
     }
     if (Options.PrintExtensionFromConformingProtocols) {
       for (auto Conf : NTD->getAllConformances()) {
         for (auto Ext : Conf->getProtocol()->getExtensions()) {
           if (Options.printExtensionContentAsMembers(Ext))
-            AddDeclFunc(Ext->getAllMembers());
+            AddMembers(Ext);
         }
       }
     }