[interop] AST printer should only visit one original namespace decl to avoid printing redecls over and over again

Also, lookup namespace members directly without doing a lookup. This helps us print the libc++ module interface in < 1s on M1

Author: hyp

include/swift/AST/ASTPrinter.h

@@ -28,6 +28,10 @@
 // ambiguities with type names, in AliasModuleNames mode.
 #define MODULE_DISAMBIGUATING_PREFIX "Module___"
 
+namespace clang {
+class Decl;
+}
+
 namespace swift {
   class Decl;
   class DeclContext;
@@ -111,6 +115,7 @@ class ASTPrinter {
   unsigned CurrentIndentation = 0;
   unsigned PendingNewlines = 0;
   TypeOrExtensionDecl SynthesizeTarget;
+  llvm::SmallPtrSet<const clang::Decl *, 8> printedClangDecl;
 
   void printTextImpl(StringRef Text);
 
@@ -331,6 +336,12 @@ class ASTPrinter {
     printStructurePre(Kind, D);
   }
 
+  /// Return true when the given redeclared clang decl is being printed for the
+  /// first time.
+  bool shouldPrintRedeclaredClangDecl(const clang::Decl *d) {
+    return printedClangDecl.insert(d).second;
+  }
+
 private:
   virtual void anchor();
 };

lib/AST/ASTPrinter.cpp

@@ -14,8 +14,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "InlinableText.h"
 #include "swift/AST/ASTPrinter.h"
+#include "InlinableText.h"
 #include "swift/AST/ASTContext.h"
 #include "swift/AST/ASTMangler.h"
 #include "swift/AST/ASTVisitor.h"
@@ -61,6 +61,7 @@
 #include "clang/AST/DeclObjC.h"
 #include "clang/Basic/Module.h"
 #include "clang/Basic/SourceManager.h"
+#include "clang/Lex/MacroInfo.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/Support/Compiler.h"
@@ -2323,10 +2324,16 @@ static void addNamespaceMembers(Decl *decl,
       if (!name)
         continue;
 
-      CXXNamespaceMemberLookup lookupRequest({cast<EnumDecl>(decl), name});
-      for (auto found : evaluateOrDefault(ctx.evaluator, lookupRequest, {})) {
-        if (addedMembers.insert(found).second)
-          members.push_back(found);
+      auto allResults = evaluateOrDefault(
+          ctx.evaluator, ClangDirectLookupRequest({decl, redecl, name}), {});
+
+      for (auto found : allResults) {
+        auto clangMember = found.get<clang::NamedDecl *>();
+        if (auto importedDecl =
+                ctx.getClangModuleLoader()->importDeclDirectly(clangMember)) {
+          if (addedMembers.insert(importedDecl).second)
+            members.push_back(importedDecl);
+        }
       }
     }
   }
@@ -3593,6 +3600,13 @@ void PrintAST::visitAssociatedTypeDecl(AssociatedTypeDecl *decl) {
 }
 
 void PrintAST::visitEnumDecl(EnumDecl *decl) {
+  if (const auto *namespaceDecl =
+          dyn_cast_or_null<clang::NamespaceDecl>(decl->getClangDecl())) {
+    // Enum that correponds to the C++ namespace should only be printed once.
+    if (!Printer.shouldPrintRedeclaredClangDecl(
+            namespaceDecl->getOriginalNamespace()))
+      return;
+  }
   printDocumentationComment(decl);
   printAttributes(decl);
   printAccess(decl);

test/Interop/Cxx/stdlib/print-libcxx-module-interface.swift

@@ -0,0 +1,10 @@
+// RUN: %target-swift-ide-test -print-module -module-to-print=std -I %S/Inputs -source-filename=x -enable-experimental-cxx-interop -enable-objc-interop -module-print-submodules | %FileCheck %s
+
+// REQUIRES: OS=macosx
+
+// CHECK: enum std {
+// CHECK-NEXT: enum __1 {
+
+// CHECK: typealias string =
+
+// CHECK-NOT: enum std