Index: Accept compiler errors during index-while-building

Force allowing reading from modules with compiler errors during
index-while-building as a way to recover from more deserialization
issues.

Author: xymus

include/swift/AST/ASTContext.h

@@ -380,6 +380,12 @@ class ASTContext final {
   /// files?
   bool IgnoreAdjacentModules = false;
 
+  /// Override to accept reading errors from swiftmodules and being generally
+  /// more tolerant to inconsistencies. This is enabled for
+  /// index-while-building as it runs last and it can afford to read an AST
+  /// with inconsistencies.
+  bool ForceAllowModuleWithCompilerErrors = false;
+
   // Define the set of known identifiers.
 #define IDENTIFIER_WITH_NAME(Name, IdStr) Identifier Id_##Name;
 #include "swift/AST/KnownIdentifiers.def"

lib/Index/Index.cpp

@@ -2156,14 +2156,19 @@ void index::indexSourceFile(SourceFile *SF, IndexDataConsumer &consumer) {
 
 void index::indexModule(ModuleDecl *module, IndexDataConsumer &consumer) {
   PrettyStackTraceDecl trace("indexing module", module);
+  ASTContext &ctx = module->getASTContext();
   assert(module);
+
   auto mName = module->getRealName().str();
-  if (module->getASTContext().blockListConfig.hasBlockListAction(mName,
+  if (ctx.blockListConfig.hasBlockListAction(mName,
       BlockListKeyKind::ModuleName,
       BlockListAction::SkipIndexingModule)) {
     return;
   }
-  IndexSwiftASTWalker walker(consumer, module->getASTContext());
+
+  llvm::SaveAndRestore<bool> S(ctx.ForceAllowModuleWithCompilerErrors, true);
+
+  IndexSwiftASTWalker walker(consumer, ctx);
   walker.visitModule(*module);
   consumer.finish();
 }

lib/Serialization/ModuleFile.cpp

@@ -135,7 +135,8 @@ ModuleFile::ModuleFile(std::shared_ptr<const ModuleFileSharedCore> core)
 }
 
 bool ModuleFile::allowCompilerErrors() const {
-  return getContext().LangOpts.AllowModuleWithCompilerErrors;
+  return getContext().LangOpts.AllowModuleWithCompilerErrors ||
+         getContext().ForceAllowModuleWithCompilerErrors;
 }
 
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