TBDGen: avoid emitting symbols with OBJC_CLASS and OBJC_METACLASS prefixes

rdar://60057489

Author: nkcsgexi

lib/TBDGen/TBDGen.cpp

@@ -56,16 +56,28 @@ using namespace llvm::yaml;
 using StringSet = llvm::StringSet<>;
 using SymbolKind = llvm::MachO::SymbolKind;
 
+static constexpr StringLiteral ObjC2ClassNamePrefix = "_OBJC_CLASS_$_";
+static constexpr StringLiteral ObjC2MetaClassNamePrefix = "_OBJC_METACLASS_$_";
+
 static bool isGlobalOrStaticVar(VarDecl *VD) {
   return VD->isStatic() || VD->getDeclContext()->isModuleScopeContext();
 }
 
+// If a symbol is implied, we don't need to emit it explictly into the tbd file.
+// e.g. When a symbol is in the `objc-classes` section in a tbd file, a additional
+// symbol with `_OBJC_CLASS_$_` is implied.
+static bool isSymbolImplied(StringRef name) {
+  return name.startswith(ObjC2ClassNamePrefix) ||
+    name.startswith(ObjC2MetaClassNamePrefix);
+}
+
 void TBDGenVisitor::addSymbolInternal(StringRef name,
                                       llvm::MachO::SymbolKind kind,
                                       bool isLinkerDirective) {
   if (!isLinkerDirective && Opts.LinkerDirectivesOnly)
     return;
-  Symbols.addSymbol(kind, name, Targets);
+  if (!isSymbolImplied(name))
+    Symbols.addSymbol(kind, name, Targets);
   if (StringSymbols && kind == SymbolKind::GlobalSymbol) {
     auto isNewValue = StringSymbols->insert(name).second;
     (void)isNewValue;

test/TBD/implied_objc_symbols.swift

@@ -0,0 +1,12 @@
+// REQUIRES: VENDOR=apple
+// RUN: %empty-directory(%t)
+
+// RUN: echo "import Foundation" > %t/main.swift
+// RUN: echo "@objc public class ObjCOnly {}" >> %t/main.swift
+// RUN: %target-swift-frontend -emit-ir -o/dev/null -parse-as-library -module-name test -import-objc-header %S/Inputs/objc_class_header.h -validate-tbd-against-ir=missing %t/main.swift -disable-objc-attr-requires-foundation-module -emit-tbd -emit-tbd-path %t/main.tbd
+
+// RUN: %FileCheck %s < %t/main.tbd
+
+// CHECK: __TtC4test8ObjCOnly
+// CHECK-NOT: _OBJC_CLASS_
+// CHECK-NOT: _OBJC_METACLASS_