Front-end: teach the compiler to generate a .c file for $ld$add$os symbols.

When symbols are moved to this module, this module declares them as HIDE
for the OS versions prior to when the move happened. On the other hand, the
original module should declare ADD them for these OS versions. An executable
can choose the right library to link against depending on the deployment target.
This is a walk-around that linker directives cannot specify other install
name per symbol, we should eventually remove this.

Author: nkcsgexi

include/swift/Basic/SupplementaryOutputPaths.h

@@ -149,6 +149,16 @@ struct SupplementaryOutputPaths {
   /// \sa swift::emitSwiftInterface
   std::string ModuleInterfaceOutputPath;
 
+  /// The path to a .c file where we should declare $ld$add symbols for those
+  /// symbols moved to the current module.
+  /// When symbols are moved to this module, this module declares them as HIDE
+  /// for the OS versions prior to when the move happened. On the other hand, the
+  /// original module should ADD them for these OS versions. An executable
+  /// can choose the right library to link against depending on the deployment target.
+  /// This is a walk-around that linker directives cannot specify other install
+  /// name per symbol, we should eventually remove this.
+  std::string LdAddCFilePath;
+
   SupplementaryOutputPaths() = default;
   SupplementaryOutputPaths(const SupplementaryOutputPaths &) = default;
 
@@ -158,7 +168,7 @@ struct SupplementaryOutputPaths {
            ReferenceDependenciesFilePath.empty() &&
            SerializedDiagnosticsPath.empty() && LoadedModuleTracePath.empty() &&
            TBDPath.empty() && ModuleInterfaceOutputPath.empty() &&
-           ModuleSourceInfoOutputPath.empty();
+           ModuleSourceInfoOutputPath.empty() && LdAddCFilePath.empty();
   }
 };
 } // namespace swift

include/swift/Frontend/Frontend.h

@@ -385,6 +385,8 @@ class CompilerInvocation {
   /// fail an assert if not in that mode.
   std::string getModuleInterfaceOutputPathForWholeModule() const;
 
+  std::string getLdAddCFileOutputPathForWholeModule() const;
+
   SerializationOptions
   computeSerializationOptions(const SupplementaryOutputPaths &outs,
                               bool moduleIsPublic);

include/swift/Option/FrontendOptions.td

@@ -640,4 +640,7 @@ def type_info_dump_filter_EQ : Joined<["-"], "type-info-dump-filter=">,
   Flags<[FrontendOption]>,
   HelpText<"One of 'all', 'resilient' or 'fragile'">;
 
+def emit_ldadd_cfile_path
+  : Separate<["-"], "emit-ldadd-cfile-path">, MetaVarName<"<path>">,
+    HelpText<"Generate .c file defining symbols to add back">;
 } // end let Flags = [FrontendOption, NoDriverOption, HelpHidden]

lib/Frontend/ArgsToFrontendOutputsConverter.cpp

@@ -302,11 +302,12 @@ SupplementaryOutputPathsComputer::getSupplementaryOutputPathsFromArguments()
       options::OPT_emit_module_interface_path);
   auto moduleSourceInfoOutput = getSupplementaryFilenamesFromArguments(
       options::OPT_emit_module_source_info_path);
-
+  auto ldAddCFileOutput  = getSupplementaryFilenamesFromArguments(
+      options::OPT_emit_ldadd_cfile_path);
   if (!objCHeaderOutput || !moduleOutput || !moduleDocOutput ||
       !dependenciesFile || !referenceDependenciesFile ||
       !serializedDiagnostics || !fixItsOutput || !loadedModuleTrace || !TBD ||
-      !moduleInterfaceOutput || !moduleSourceInfoOutput) {
+      !moduleInterfaceOutput || !moduleSourceInfoOutput || !ldAddCFileOutput) {
     return None;
   }
   std::vector<SupplementaryOutputPaths> result;
@@ -328,6 +329,7 @@ SupplementaryOutputPathsComputer::getSupplementaryOutputPathsFromArguments()
     sop.TBDPath = (*TBD)[i];
     sop.ModuleInterfaceOutputPath = (*moduleInterfaceOutput)[i];
     sop.ModuleSourceInfoOutputPath = (*moduleSourceInfoOutput)[i];
+    sop.LdAddCFilePath = (*ldAddCFileOutput)[i];
     result.push_back(sop);
   }
   return result;
@@ -446,6 +448,7 @@ SupplementaryOutputPathsComputer::computeOutputPathsForOneInput(
   sop.TBDPath = tbdPath;
   sop.ModuleInterfaceOutputPath = ModuleInterfaceOutputPath;
   sop.ModuleSourceInfoOutputPath = moduleSourceInfoOutputPath;
+  sop.LdAddCFilePath = pathsFromArguments.LdAddCFilePath;
   return sop;
 }
 
@@ -546,7 +549,8 @@ SupplementaryOutputPathsComputer::readSupplementaryOutputFileMap() const {
         options::OPT_emit_loaded_module_trace_path,
         options::OPT_emit_module_interface_path,
         options::OPT_emit_module_source_info_path,
-        options::OPT_emit_tbd_path)) {
+        options::OPT_emit_tbd_path,
+        options::OPT_emit_ldadd_cfile_path)) {
     Diags.diagnose(SourceLoc(),
                    diag::error_cannot_have_supplementary_outputs,
                    A->getSpelling(), "-supplementary-output-file-map");

lib/Frontend/Frontend.cpp

@@ -124,6 +124,14 @@ std::string CompilerInvocation::getTBDPathForWholeModule() const {
       .SupplementaryOutputs.TBDPath;
 }
 
+std::string
+CompilerInvocation::getLdAddCFileOutputPathForWholeModule() const {
+  assert(getFrontendOptions().InputsAndOutputs.isWholeModule() &&
+         "LdAdd cfile only makes sense when the whole module can be seen");
+  return getPrimarySpecificPathsForAtMostOnePrimary()
+    .SupplementaryOutputs.LdAddCFilePath;
+}
+
 std::string
 CompilerInvocation::getModuleInterfaceOutputPathForWholeModule() const {
   assert(getFrontendOptions().InputsAndOutputs.isWholeModule() &&

lib/FrontendTool/FrontendTool.cpp

@@ -1047,6 +1047,59 @@ static bool writeTBDIfNeeded(CompilerInvocation &Invocation,
   return writeTBD(Instance.getMainModule(), TBDPath, tbdOpts);
 }
 
+static std::string changeToLdAdd(StringRef ldHide) {
+  SmallString<64> SymbolBuffer;
+  llvm::raw_svector_ostream OS(SymbolBuffer);
+  auto Parts = ldHide.split("$hide$");
+  assert(!Parts.first.empty());
+  assert(!Parts.second.empty());
+  OS << Parts.first << "$add$" << Parts.second;
+  return OS.str().str();
+}
+
+static bool writeLdAddCFileIfNeeded(CompilerInvocation &Invocation,
+                                    CompilerInstance &Instance) {
+  auto frontendOpts = Invocation.getFrontendOptions();
+  if (!frontendOpts.InputsAndOutputs.isWholeModule())
+    return false;
+  auto Path = Invocation.getLdAddCFileOutputPathForWholeModule();
+  if (Path.empty())
+    return false;
+  if (!frontendOpts.InputsAndOutputs.isWholeModule()) {
+    Instance.getDiags().diagnose(SourceLoc(),
+                                 diag::tbd_only_supported_in_whole_module);
+    return true;
+  }
+  auto tbdOpts = Invocation.getTBDGenOptions();
+  tbdOpts.LinkerDirectivesOnly = true;
+  llvm::StringSet<> ldSymbols;
+  auto *module = Instance.getMainModule();
+  enumeratePublicSymbols(module, ldSymbols, tbdOpts);
+  std::error_code EC;
+  llvm::raw_fd_ostream OS(Path, EC, llvm::sys::fs::F_None);
+  if (EC) {
+    module->getASTContext().Diags.diagnose(SourceLoc(),
+                                           diag::error_opening_output,
+                                           Path, EC.message());
+    return true;
+  }
+  OS << "// Automatically generated C source file from the Swift compiler \n"
+     << "// to add removed symbols back to the high-level framework for deployment\n"
+     << "// targets prior to the OS version when these symbols were moved to\n"
+     << "// a low-level framework " << module->getName().str() << ".\n\n";
+  unsigned Idx = 0;
+  for (auto &S: ldSymbols) {
+    SmallString<32> NameBuffer;
+    llvm::raw_svector_ostream NameOS(NameBuffer);
+    NameOS << "ldAdd_" << Idx;
+    OS << "extern const char " << NameOS.str() << " __asm(\"" <<
+      changeToLdAdd(S.getKey()) << "\");\n";
+    OS << "const char " << NameOS.str() << " = 0;\n";
+    ++ Idx;
+  }
+  return false;
+}
+
 static bool performCompileStepsPostSILGen(
     CompilerInstance &Instance, CompilerInvocation &Invocation,
     std::unique_ptr<SILModule> SM, bool astGuaranteedToCorrespondToSIL,
@@ -1172,6 +1225,9 @@ static bool emitAnyWholeModulePostTypeCheckSupplementaryOutputs(
   {
     hadAnyError |= writeTBDIfNeeded(Invocation, Instance);
   }
+  {
+    hadAnyError |= writeLdAddCFileIfNeeded(Invocation, Instance);
+  }
 
   return hadAnyError;
 }

test/TBD/linker-directives.swift

@@ -15,3 +15,9 @@ public func toast() {}
 
 // CHECK-HAS-NOT-NOT: $ld$hide$os10.15$_$s10ToasterKit5toastyyF
 // CHECK-HAS-NOT-NOT: $ld$hide$os10.7$_$s10ToasterKit5toastyyF
+
+// RUN: %target-swift-frontend -typecheck %s -emit-tbd -emit-tbd-path %t/linker_directives.tbd -emit-ldadd-cfile-path %t/ldAdd.c -module-name AppKit
+// RUN: %FileCheck %s --check-prefix CHECK-C-SYMBOL < %t/ldAdd.c
+
+// CHECK-C-SYMBOL: $ld$add$os10.14$_$s10ToasterKit5toastyyF
+// CHECK-C-SYMBOL: $ld$add$os10.8$_$s10ToasterKit5toastyyF