Frontend: add a frontend flag to generate empty ABI descriptors to workaround deserialization issues

ABI descriptors should always be emitted as sidecars for library-evolution-enabled modules.
However, generating these files requires traversing the entire module (like indexing), which may
hit additional deserialization issues. To unblock builds, this patch introduces a flag to skip
the traversing logic so that we emit an empty ABI descriptor file. The empty file serves as
a placeholder so that build system doesn't need to know the details.

include/swift/APIDigester/ModuleAnalyzerNodes.h

@@ -816,7 +816,7 @@ int dumpSDKContent(const CompilerInvocation &InitInvok,
                    const llvm::StringSet<> &ModuleNames,
                    StringRef OutputFile, CheckerOptions Opts);
 
-void dumpModuleContent(ModuleDecl *MD, StringRef OutputFile, bool ABI);
+void dumpModuleContent(ModuleDecl *MD, StringRef OutputFile, bool ABI, bool Empty);
 
 /// Mostly for testing purposes, this function de-serializes the SDK dump in
 /// dumpPath and re-serialize them to OutputPath. If the tool performs correctly,

include/swift/Frontend/FrontendOptions.h

@@ -447,6 +447,11 @@ public:
   /// to encode the actual paths into the .swiftmodule file.
   PathObfuscator serializedPathObfuscator;
 
+  /// Avoid printing actual module content into the ABI descriptor file.
+  /// This should only be used as a workaround when emitting ABI descriptor files
+  /// crashes the compiler.
+  bool emptyABIDescriptor = false;
+
 private:
   static bool canActionEmitDependencies(ActionType);
   static bool canActionEmitReferenceDependencies(ActionType);

include/swift/Option/FrontendOptions.td

@@ -169,6 +169,9 @@ def serialize_debugging_options : Flag<["-"], "serialize-debugging-options">,
 def serialized_path_obfuscate : Separate<["-"], "serialized-path-obfuscate">,
     HelpText<"Remap source paths in debug info">, MetaVarName<"<prefix=replacement>">;
 
+def empty_abi_descriptor : Flag<["-"], "empty-abi-descriptor">,
+  HelpText<"Avoid printing actual module content into ABI descriptor file">;
+
 def no_serialize_debugging_options :
   Flag<["-"], "no-serialize-debugging-options">,
   HelpText<"Never serialize options for debugging (default: only for apps)">;

include/swift/Serialization/SerializationOptions.h

@@ -33,6 +33,7 @@ namespace swift {
     const char *DocOutputPath = nullptr;
     const char *SourceInfoOutputPath = nullptr;
     std::string ABIDescriptorPath;
+    bool emptyABIDescriptor = false;
     llvm::VersionTuple UserModuleVersion;
     std::string SDKName;
 

lib/APIDigester/ModuleAnalyzerNodes.cpp

@@ -2498,7 +2498,7 @@ int swift::ide::api::deserializeSDKDump(StringRef dumpPath, StringRef OutputPath
 }
 
 void swift::ide::api::dumpModuleContent(ModuleDecl *MD, StringRef OutputFile,
-                                        bool ABI) {
+                                        bool ABI, bool Empty) {
   CheckerOptions opts;
   opts.ABI = ABI;
   opts.SwiftOnly = true;
@@ -2509,12 +2509,17 @@ void swift::ide::api::dumpModuleContent(ModuleDecl *MD, StringRef OutputFile,
   opts.Verbose = false;
   SDKContext ctx(opts);
   SwiftDeclCollector collector(ctx);
-  collector.lookupVisibleDecls({MD});
   ConstExtractor extractor(ctx, MD->getASTContext());
-  extractor.extract(MD);
   PayLoad payload;
-  payload.allContsValues = &extractor.getAllConstValues();
+  SWIFT_DEFER {
-  dumpSDKRoot(collector.getSDKRoot(), payload, OutputFile);
+    payload.allContsValues = &extractor.getAllConstValues();
+    dumpSDKRoot(collector.getSDKRoot(), payload, OutputFile);
+  };
+  if (Empty) {
+    return;
+  }
+  collector.lookupVisibleDecls({MD});
+  extractor.extract(MD);
 }
 
 int swift::ide::api::findDeclUsr(StringRef dumpPath, CheckerOptions Opts) {

lib/Frontend/ArgsToFrontendOptionsConverter.cpp

@@ -297,6 +297,7 @@ bool ArgsToFrontendOptionsConverter::convert(
     auto SplitMap = StringRef(A).split('=');
     Opts.serializedPathObfuscator.addMapping(SplitMap.first, SplitMap.second);
   }
+  Opts.emptyABIDescriptor = Args.hasArg(OPT_empty_abi_descriptor);
   return false;
 }
 

lib/Frontend/Frontend.cpp

@@ -158,7 +158,8 @@ SerializationOptions CompilerInvocation::computeSerializationOptions(
       getIRGenOptions().PublicLinkLibraries;
   serializationOpts.SDKName = getLangOptions().SDKName;
   serializationOpts.ABIDescriptorPath = outs.ABIDescriptorOutputPath.c_str();
-  
+  serializationOpts.emptyABIDescriptor = opts.emptyABIDescriptor;
+
   if (!getIRGenOptions().ForceLoadSymbolName.empty())
     serializationOpts.AutolinkForceLoad = true;
 

lib/Serialization/Serialization.cpp

@@ -5802,10 +5802,11 @@ bool Serializer::allowCompilerErrors() const {
 
 static void emitABIDescriptor(ModuleOrSourceFile DC,
                               const SerializationOptions &options) {
+  using namespace swift::ide::api;
   if (!options.ABIDescriptorPath.empty()) {
     if (DC.is<ModuleDecl*>()) {
-      swift::ide::api::dumpModuleContent(DC.get<ModuleDecl*>(),
+      dumpModuleContent(DC.get<ModuleDecl*>(), options.ABIDescriptorPath, true,
-                                         options.ABIDescriptorPath, true);
+                        options.emptyABIDescriptor);
     }
   }
 }

test/api-digester/empty-abi-descriptor.swift

@@ -0,0 +1,6 @@
+// RUN: %empty-directory(%t)
+
+// RUN: %target-swift-frontend -emit-module -o %t/Foo.swiftmodule -emit-abi-descriptor-path %t/abi.json %S/Inputs/ConstExtraction/SimpleReferences.swift -empty-abi-descriptor
+// RUN: %api-digester -deserialize-sdk -input-paths %t/abi.json -o %t/abi.result.json
+// RUN: %api-digester -generate-empty-baseline -o %t/abi-tool.json -avoid-tool-args -abi
+// RUN: diff -u %t/abi-tool.json %t/abi.result.json