tools/aapt2/link/ReferenceLinker.cpp - platform/frameworks/base - Git at Google

 /*
  * Copyright (C) 2015 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #include "link/ReferenceLinker.h"

 #include "android-base/logging.h"
 #include "android-base/stringprintf.h"
 #include "androidfw/ResourceTypes.h"

 #include "Diagnostics.h"
 #include "ResourceTable.h"
 #include "ResourceUtils.h"
 #include "ResourceValues.h"
 #include "ValueVisitor.h"
 #include "link/Linkers.h"
 #include "process/IResourceTableConsumer.h"
 #include "process/SymbolTable.h"
 #include "trace/TraceBuffer.h"
 #include "util/Util.h"
 #include "xml/XmlUtil.h"

 using ::aapt::ResourceUtils::StringBuilder;
 using ::android::StringPiece;
 using ::android::base::StringPrintf;

 namespace aapt {

 namespace {

 // The ReferenceLinkerVisitor will follow all references and make sure they point
 // to resources that actually exist, either in the local resource table, or as external
 // symbols. Once the target resource has been found, the ID of the resource will be assigned
 // to the reference object.
 //
 // NOTE: All of the entries in the ResourceTable must be assigned IDs.
 class ReferenceLinkerVisitor : public DescendingValueVisitor {
  public:
   using DescendingValueVisitor::Visit;

   ReferenceLinkerVisitor(const CallSite& callsite, IAaptContext* context, SymbolTable* symbols,
                          StringPool* string_pool, xml::IPackageDeclStack* decl)
       : callsite_(callsite),
         context_(context),
         symbols_(symbols),
         package_decls_(decl),
         string_pool_(string_pool) {}

   void Visit(Reference* ref) override {
     if (!ReferenceLinker::LinkReference(callsite_, ref, context_, symbols_, package_decls_)) {
       error_ = true;
     }
   }

   // We visit the Style specially because during this phase, values of attributes are
   // all RawString values. Now that we are expected to resolve all symbols, we can
   // lookup the attributes to find out which types are allowed for the attributes' values.
   void Visit(Style* style) override {
     if (style->parent) {
       Visit(&style->parent.value());
     }

     for (Style::Entry& entry : style->entries) {
       std::string err_str;

       // Transform the attribute reference so that it is using the fully qualified package
       // name. This will also mark the reference as being able to see private resources if
       // there was a '*' in the reference or if the package came from the private namespace.
       Reference transformed_reference = entry.key;
       ResolvePackage(package_decls_, &transformed_reference);

       // Find the attribute in the symbol table and check if it is visible from this callsite.
       const SymbolTable::Symbol* symbol = ReferenceLinker::ResolveAttributeCheckVisibility(
           transformed_reference, callsite_, context_, symbols_, &err_str);
       if (symbol) {
         // Assign our style key the correct ID. The ID may not exist.
         entry.key.id = symbol->id;

         // Try to convert the value to a more specific, typed value based on the attribute it is
         // set to.
         entry.value = ParseValueWithAttribute(std::move(entry.value), symbol->attribute.get());

         // Link/resolve the final value (mostly if it's a reference).
         entry.value->Accept(this);

         // Now verify that the type of this item is compatible with the
         // attribute it is defined for. We pass `nullptr` as the DiagMessage so that this
         // check is fast and we avoid creating a DiagMessage when the match is successful.
         if (!symbol->attribute->Matches(*entry.value, nullptr)) {
           // The actual type of this item is incompatible with the attribute.
           DiagMessage msg(entry.key.GetSource());

           // Call the matches method again, this time with a DiagMessage so we fill in the actual
           // error message.
           symbol->attribute->Matches(*entry.value, &msg);
           context_->GetDiagnostics()->Error(msg);
           error_ = true;
         }

       } else {
         DiagMessage msg(entry.key.GetSource());
         msg << "style attribute '";
         ReferenceLinker::WriteResourceName(entry.key, callsite_, package_decls_, &msg);
         msg << "' " << err_str;
         context_->GetDiagnostics()->Error(msg);
         error_ = true;
       }
     }
   }

   bool HasError() {
     return error_;
   }

  private:
   DISALLOW_COPY_AND_ASSIGN(ReferenceLinkerVisitor);

   // Transform a RawString value into a more specific, appropriate value, based on the
   // Attribute. If a non RawString value is passed in, this is an identity transform.
   std::unique_ptr<Item> ParseValueWithAttribute(std::unique_ptr<Item> value,
                                                 const Attribute* attr) {
     if (RawString* raw_string = ValueCast<RawString>(value.get())) {
       std::unique_ptr<Item> transformed =
           ResourceUtils::TryParseItemForAttribute(*raw_string->value, attr);

       // If we could not parse as any specific type, try a basic STRING.
       if (!transformed && (attr->type_mask & android::ResTable_map::TYPE_STRING)) {
         StringBuilder string_builder;
         string_builder.AppendText(*raw_string->value);
         if (string_builder) {
           transformed =
               util::make_unique<String>(string_pool_->MakeRef(string_builder.to_string()));
         }
       }

       if (transformed) {
         return transformed;
       }
     }
     return value;
   }

   const CallSite& callsite_;
   IAaptContext* context_;
   SymbolTable* symbols_;
   xml::IPackageDeclStack* package_decls_;
   StringPool* string_pool_;
   bool error_ = false;
 };

 class EmptyDeclStack : public xml::IPackageDeclStack {
  public:
   EmptyDeclStack() = default;

   Maybe<xml::ExtractedPackage> TransformPackageAlias(const StringPiece& alias) const override {
     if (alias.empty()) {
       return xml::ExtractedPackage{{}, true /*private*/};
     }
     return {};
   }

  private:
   DISALLOW_COPY_AND_ASSIGN(EmptyDeclStack);
 };

 // The symbol is visible if it is public, or if the reference to it is requesting private access
 // or if the callsite comes from the same package.
 bool IsSymbolVisible(const SymbolTable::Symbol& symbol, const Reference& ref,
                      const CallSite& callsite) {
   if (symbol.is_public || ref.private_reference) {
     return true;
   }

   if (ref.name) {
     const ResourceName& name = ref.name.value();
     if (name.package.empty()) {
       // If the symbol was found, and the package is empty, that means it was found in the local
       // scope, which is always visible (private local).
       return true;
     }

     // The symbol is visible if the reference is local to the same package it is defined in.
     return callsite.package == name.package;
   }

   if (ref.id && symbol.id) {
     return ref.id.value().package_id() == symbol.id.value().package_id();
   }
   return false;
 }

 }  // namespace

 const SymbolTable::Symbol* ReferenceLinker::ResolveSymbol(const Reference& reference,
                                                           const CallSite& callsite,
                                                           IAaptContext* context,
                                                           SymbolTable* symbols) {
   if (reference.name) {
     const ResourceName& name = reference.name.value();
     if (name.package.empty()) {
       // Use the callsite's package name if no package name was defined.
       const SymbolTable::Symbol* symbol = symbols->FindByName(
           ResourceName(callsite.package, name.type, name.entry));
       if (symbol) {
         return symbol;
       }

       // If the callsite package is the same as the current compilation package,
       // check the feature split dependencies as well. Feature split resources
       // can be referenced without a namespace, just like the base package.
       // TODO: modify the package name of included splits instead of having the
       // symbol table look up the resource in in every package. b/136105066
       if (callsite.package == context->GetCompilationPackage()) {
         const auto& split_name_dependencies = context->GetSplitNameDependencies();
         for (const std::string& split_name : split_name_dependencies) {
           std::string split_package =
               StringPrintf("%s.%s", callsite.package.c_str(), split_name.c_str());
           symbol = symbols->FindByName(ResourceName(split_package, name.type, name.entry));
           if (symbol) {
             return symbol;
           }
         }
       }
       return nullptr;
     }
     return symbols->FindByName(name);
   } else if (reference.id) {
     return symbols->FindById(reference.id.value());
   } else {
     return nullptr;
   }
 }

 const SymbolTable::Symbol* ReferenceLinker::ResolveSymbolCheckVisibility(const Reference& reference,
                                                                          const CallSite& callsite,
                                                                          IAaptContext* context,
                                                                          SymbolTable* symbols,
                                                                          std::string* out_error) {
   const SymbolTable::Symbol* symbol = ResolveSymbol(reference, callsite, context, symbols);
   if (!symbol) {
     if (out_error) *out_error = "not found";
     return nullptr;
   }

   if (!IsSymbolVisible(*symbol, reference, callsite)) {
     if (out_error) *out_error = "is private";
     return nullptr;
   }
   return symbol;
 }

 const SymbolTable::Symbol* ReferenceLinker::ResolveAttributeCheckVisibility(
     const Reference& reference, const CallSite& callsite, IAaptContext* context,
     SymbolTable* symbols, std::string* out_error) {
   const SymbolTable::Symbol* symbol =
       ResolveSymbolCheckVisibility(reference, callsite, context, symbols, out_error);
   if (!symbol) {
     return nullptr;
   }

   if (!symbol->attribute) {
     if (out_error) *out_error = "is not an attribute";
     return nullptr;
   }
   return symbol;
 }

 Maybe<xml::AaptAttribute> ReferenceLinker::CompileXmlAttribute(const Reference& reference,
                                                                const CallSite& callsite,
                                                                IAaptContext* context,
                                                                SymbolTable* symbols,
                                                                std::string* out_error) {
   const SymbolTable::Symbol* symbol =
       ResolveAttributeCheckVisibility(reference, callsite, context, symbols, out_error);
   if (!symbol) {
     return {};
   }

   if (!symbol->attribute) {
     if (out_error) *out_error = "is not an attribute";
     return {};
   }
   return xml::AaptAttribute(*symbol->attribute, symbol->id);
 }

 void ReferenceLinker::WriteResourceName(const Reference& ref, const CallSite& callsite,
                                         const xml::IPackageDeclStack* decls, DiagMessage* out_msg) {
   CHECK(out_msg != nullptr);
   if (!ref.name) {
     *out_msg << ref.id.value();
     return;
   }

   *out_msg << ref.name.value();

   Reference fully_qualified = ref;
   xml::ResolvePackage(decls, &fully_qualified);

   ResourceName& full_name = fully_qualified.name.value();
   if (full_name.package.empty()) {
     full_name.package = callsite.package;
   }

   if (full_name != ref.name.value()) {
     *out_msg << " (aka " << full_name << ")";
   }
 }

 void ReferenceLinker::WriteAttributeName(const Reference& ref, const CallSite& callsite,
                                          const xml::IPackageDeclStack* decls,
                                          DiagMessage* out_msg) {
   CHECK(out_msg != nullptr);
   if (!ref.name) {
     *out_msg << ref.id.value();
     return;
   }

   const ResourceName& ref_name = ref.name.value();
   CHECK_EQ(ref_name.type, ResourceType::kAttr);

   if (!ref_name.package.empty()) {
     *out_msg << ref_name.package << ":";
   }
   *out_msg << ref_name.entry;

   Reference fully_qualified = ref;
   xml::ResolvePackage(decls, &fully_qualified);

   ResourceName& full_name = fully_qualified.name.value();
   if (full_name.package.empty()) {
     full_name.package = callsite.package;
   }

   if (full_name != ref.name.value()) {
     *out_msg << " (aka " << full_name.package << ":" << full_name.entry << ")";
   }
 }

 bool ReferenceLinker::LinkReference(const CallSite& callsite, Reference* reference,
                                     IAaptContext* context, SymbolTable* symbols,
                                     const xml::IPackageDeclStack* decls) {
   CHECK(reference != nullptr);
   if (!reference->name && !reference->id) {
     // This is @null.
     return true;
   }

   Reference transformed_reference = *reference;
   xml::ResolvePackage(decls, &transformed_reference);

   std::string err_str;
   const SymbolTable::Symbol* s =
       ResolveSymbolCheckVisibility(transformed_reference, callsite, context, symbols, &err_str);
   if (s) {
     // The ID may not exist. This is fine because of the possibility of building
     // against libraries without assigned IDs.
     // Ex: Linking against own resources when building a static library.
     reference->id = s->id;
     reference->is_dynamic = s->is_dynamic;
     return true;
   }

   DiagMessage error_msg(reference->GetSource());
   error_msg << "resource ";
   WriteResourceName(*reference, callsite, decls, &error_msg);
   error_msg << " " << err_str;
   context->GetDiagnostics()->Error(error_msg);
   return false;
 }

 bool ReferenceLinker::Consume(IAaptContext* context, ResourceTable* table) {
   TRACE_NAME("ReferenceLinker::Consume");
   EmptyDeclStack decl_stack;
   bool error = false;
   for (auto& package : table->packages) {
     // Since we're linking, each package must have a name.
     CHECK(!package->name.empty()) << "all packages being linked must have a name";

     for (auto& type : package->types) {
       for (auto& entry : type->entries) {
         // First, unmangle the name if necessary.
         ResourceName name(package->name, type->type, entry->name);
         NameMangler::Unmangle(&name.entry, &name.package);

         // Symbol state information may be lost if there is no value for the resource.
         if (entry->visibility.level != Visibility::Level::kUndefined && entry->values.empty()) {
           context->GetDiagnostics()->Error(DiagMessage(entry->visibility.source)
                                                << "no definition for declared symbol '" << name
                                                << "'");
           error = true;
         }

         // Ensure that definitions for values declared as overlayable exist
         if (entry->overlayable_item && entry->values.empty()) {
           context->GetDiagnostics()->Error(DiagMessage(entry->overlayable_item.value().source)
                                            << "no definition for overlayable symbol '"
                                            << name << "'");
           error = true;
         }

         // The context of this resource is the package in which it is defined.
         const CallSite callsite{name.package};
         ReferenceLinkerVisitor visitor(callsite, context, context->GetExternalSymbols(),
                                        &table->string_pool, &decl_stack);

         for (auto& config_value : entry->values) {
           config_value->value->Accept(&visitor);
         }

         if (visitor.HasError()) {
           error = true;
         }
       }
     }
   }
   return !error;
 }

 }  // namespace aapt
	/*
	* Copyright (C) 2015 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#include "link/ReferenceLinker.h"

	#include "android-base/logging.h"
	#include "android-base/stringprintf.h"
	#include "androidfw/ResourceTypes.h"

	#include "Diagnostics.h"
	#include "ResourceTable.h"
	#include "ResourceUtils.h"
	#include "ResourceValues.h"
	#include "ValueVisitor.h"
	#include "link/Linkers.h"
	#include "process/IResourceTableConsumer.h"
	#include "process/SymbolTable.h"
	#include "trace/TraceBuffer.h"
	#include "util/Util.h"
	#include "xml/XmlUtil.h"

	using ::aapt::ResourceUtils::StringBuilder;
	using ::android::StringPiece;
	using ::android::base::StringPrintf;

	namespace aapt {

	namespace {

	// The ReferenceLinkerVisitor will follow all references and make sure they point
	// to resources that actually exist, either in the local resource table, or as external
	// symbols. Once the target resource has been found, the ID of the resource will be assigned
	// to the reference object.
	//
	// NOTE: All of the entries in the ResourceTable must be assigned IDs.
	class ReferenceLinkerVisitor : public DescendingValueVisitor {
	public:
	using DescendingValueVisitor::Visit;

	ReferenceLinkerVisitor(const CallSite& callsite, IAaptContext* context, SymbolTable* symbols,
	StringPool* string_pool, xml::IPackageDeclStack* decl)
	: callsite_(callsite),
	context_(context),
	symbols_(symbols),
	package_decls_(decl),
	string_pool_(string_pool) {}

	void Visit(Reference* ref) override {
	if (!ReferenceLinker::LinkReference(callsite_, ref, context_, symbols_, package_decls_)) {
	error_ = true;
	}
	}

	// We visit the Style specially because during this phase, values of attributes are
	// all RawString values. Now that we are expected to resolve all symbols, we can
	// lookup the attributes to find out which types are allowed for the attributes' values.
	void Visit(Style* style) override {
	if (style->parent) {
	Visit(&style->parent.value());
	}

	for (Style::Entry& entry : style->entries) {
	std::string err_str;

	// Transform the attribute reference so that it is using the fully qualified package
	// name. This will also mark the reference as being able to see private resources if
	// there was a '*' in the reference or if the package came from the private namespace.
	Reference transformed_reference = entry.key;
	ResolvePackage(package_decls_, &transformed_reference);

	// Find the attribute in the symbol table and check if it is visible from this callsite.
	const SymbolTable::Symbol* symbol = ReferenceLinker::ResolveAttributeCheckVisibility(
	transformed_reference, callsite_, context_, symbols_, &err_str);
	if (symbol) {
	// Assign our style key the correct ID. The ID may not exist.
	entry.key.id = symbol->id;

	// Try to convert the value to a more specific, typed value based on the attribute it is
	// set to.
	entry.value = ParseValueWithAttribute(std::move(entry.value), symbol->attribute.get());

	// Link/resolve the final value (mostly if it's a reference).
	entry.value->Accept(this);

	// Now verify that the type of this item is compatible with the
	// attribute it is defined for. We pass `nullptr` as the DiagMessage so that this
	// check is fast and we avoid creating a DiagMessage when the match is successful.
	if (!symbol->attribute->Matches(*entry.value, nullptr)) {
	// The actual type of this item is incompatible with the attribute.
	DiagMessage msg(entry.key.GetSource());

	// Call the matches method again, this time with a DiagMessage so we fill in the actual
	// error message.
	symbol->attribute->Matches(*entry.value, &msg);
	context_->GetDiagnostics()->Error(msg);
	error_ = true;
	}

	} else {
	DiagMessage msg(entry.key.GetSource());
	msg << "style attribute '";
	ReferenceLinker::WriteResourceName(entry.key, callsite_, package_decls_, &msg);
	msg << "' " << err_str;
	context_->GetDiagnostics()->Error(msg);
	error_ = true;
	}
	}
	}

	bool HasError() {
	return error_;
	}

	private:
	DISALLOW_COPY_AND_ASSIGN(ReferenceLinkerVisitor);

	// Transform a RawString value into a more specific, appropriate value, based on the
	// Attribute. If a non RawString value is passed in, this is an identity transform.
	std::unique_ptr<Item> ParseValueWithAttribute(std::unique_ptr<Item> value,
	const Attribute* attr) {
	if (RawString* raw_string = ValueCast<RawString>(value.get())) {
	std::unique_ptr<Item> transformed =
	ResourceUtils::TryParseItemForAttribute(*raw_string->value, attr);

	// If we could not parse as any specific type, try a basic STRING.
	if (!transformed && (attr->type_mask & android::ResTable_map::TYPE_STRING)) {
	StringBuilder string_builder;
	string_builder.AppendText(*raw_string->value);
	if (string_builder) {
	transformed =
	util::make_unique<String>(string_pool_->MakeRef(string_builder.to_string()));
	}
	}

	if (transformed) {
	return transformed;
	}
	}
	return value;
	}

	const CallSite& callsite_;
	IAaptContext* context_;
	SymbolTable* symbols_;
	xml::IPackageDeclStack* package_decls_;
	StringPool* string_pool_;
	bool error_ = false;
	};

	class EmptyDeclStack : public xml::IPackageDeclStack {
	public:
	EmptyDeclStack() = default;

	Maybe<xml::ExtractedPackage> TransformPackageAlias(const StringPiece& alias) const override {
	if (alias.empty()) {
	return xml::ExtractedPackage{{}, true /private/};
	}
	return {};
	}

	private:
	DISALLOW_COPY_AND_ASSIGN(EmptyDeclStack);
	};

	// The symbol is visible if it is public, or if the reference to it is requesting private access
	// or if the callsite comes from the same package.
	bool IsSymbolVisible(const SymbolTable::Symbol& symbol, const Reference& ref,
	const CallSite& callsite) {
	if (symbol.is_public \|\| ref.private_reference) {
	return true;
	}

	if (ref.name) {
	const ResourceName& name = ref.name.value();
	if (name.package.empty()) {
	// If the symbol was found, and the package is empty, that means it was found in the local
	// scope, which is always visible (private local).
	return true;
	}

	// The symbol is visible if the reference is local to the same package it is defined in.
	return callsite.package == name.package;
	}

	if (ref.id && symbol.id) {
	return ref.id.value().package_id() == symbol.id.value().package_id();
	}
	return false;
	}

	} // namespace

	const SymbolTable::Symbol* ReferenceLinker::ResolveSymbol(const Reference& reference,
	const CallSite& callsite,
	IAaptContext* context,
	SymbolTable* symbols) {
	if (reference.name) {
	const ResourceName& name = reference.name.value();
	if (name.package.empty()) {
	// Use the callsite's package name if no package name was defined.
	const SymbolTable::Symbol* symbol = symbols->FindByName(
	ResourceName(callsite.package, name.type, name.entry));
	if (symbol) {
	return symbol;
	}

	// If the callsite package is the same as the current compilation package,
	// check the feature split dependencies as well. Feature split resources
	// can be referenced without a namespace, just like the base package.
	// TODO: modify the package name of included splits instead of having the
	// symbol table look up the resource in in every package. b/136105066
	if (callsite.package == context->GetCompilationPackage()) {
	const auto& split_name_dependencies = context->GetSplitNameDependencies();
	for (const std::string& split_name : split_name_dependencies) {
	std::string split_package =
	StringPrintf("%s.%s", callsite.package.c_str(), split_name.c_str());
	symbol = symbols->FindByName(ResourceName(split_package, name.type, name.entry));
	if (symbol) {
	return symbol;
	}
	}
	}
	return nullptr;
	}
	return symbols->FindByName(name);
	} else if (reference.id) {
	return symbols->FindById(reference.id.value());
	} else {
	return nullptr;
	}
	}

	const SymbolTable::Symbol* ReferenceLinker::ResolveSymbolCheckVisibility(const Reference& reference,
	const CallSite& callsite,
	IAaptContext* context,
	SymbolTable* symbols,
	std::string* out_error) {
	const SymbolTable::Symbol* symbol = ResolveSymbol(reference, callsite, context, symbols);
	if (!symbol) {
	if (out_error) *out_error = "not found";
	return nullptr;
	}

	if (!IsSymbolVisible(*symbol, reference, callsite)) {
	if (out_error) *out_error = "is private";
	return nullptr;
	}
	return symbol;
	}

	const SymbolTable::Symbol* ReferenceLinker::ResolveAttributeCheckVisibility(
	const Reference& reference, const CallSite& callsite, IAaptContext* context,
	SymbolTable* symbols, std::string* out_error) {
	const SymbolTable::Symbol* symbol =
	ResolveSymbolCheckVisibility(reference, callsite, context, symbols, out_error);
	if (!symbol) {
	return nullptr;
	}

	if (!symbol->attribute) {
	if (out_error) *out_error = "is not an attribute";
	return nullptr;
	}
	return symbol;
	}

	Maybe<xml::AaptAttribute> ReferenceLinker::CompileXmlAttribute(const Reference& reference,
	const CallSite& callsite,
	IAaptContext* context,
	SymbolTable* symbols,
	std::string* out_error) {
	const SymbolTable::Symbol* symbol =
	ResolveAttributeCheckVisibility(reference, callsite, context, symbols, out_error);
	if (!symbol) {
	return {};
	}

	if (!symbol->attribute) {
	if (out_error) *out_error = "is not an attribute";
	return {};
	}
	return xml::AaptAttribute(*symbol->attribute, symbol->id);
	}

	void ReferenceLinker::WriteResourceName(const Reference& ref, const CallSite& callsite,
	const xml::IPackageDeclStack* decls, DiagMessage* out_msg) {
	CHECK(out_msg != nullptr);
	if (!ref.name) {
	*out_msg << ref.id.value();
	return;
	}

	*out_msg << ref.name.value();

	Reference fully_qualified = ref;
	xml::ResolvePackage(decls, &fully_qualified);

	ResourceName& full_name = fully_qualified.name.value();
	if (full_name.package.empty()) {
	full_name.package = callsite.package;
	}

	if (full_name != ref.name.value()) {
	*out_msg << " (aka " << full_name << ")";
	}
	}

	void ReferenceLinker::WriteAttributeName(const Reference& ref, const CallSite& callsite,
	const xml::IPackageDeclStack* decls,
	DiagMessage* out_msg) {
	CHECK(out_msg != nullptr);
	if (!ref.name) {
	*out_msg << ref.id.value();
	return;
	}

	const ResourceName& ref_name = ref.name.value();
	CHECK_EQ(ref_name.type, ResourceType::kAttr);

	if (!ref_name.package.empty()) {
	*out_msg << ref_name.package << ":";
	}
	*out_msg << ref_name.entry;

	Reference fully_qualified = ref;
	xml::ResolvePackage(decls, &fully_qualified);

	ResourceName& full_name = fully_qualified.name.value();
	if (full_name.package.empty()) {
	full_name.package = callsite.package;
	}

	if (full_name != ref.name.value()) {
	*out_msg << " (aka " << full_name.package << ":" << full_name.entry << ")";
	}
	}

	bool ReferenceLinker::LinkReference(const CallSite& callsite, Reference* reference,
	IAaptContext* context, SymbolTable* symbols,
	const xml::IPackageDeclStack* decls) {
	CHECK(reference != nullptr);
	if (!reference->name && !reference->id) {
	// This is @null.
	return true;
	}

	Reference transformed_reference = *reference;
	xml::ResolvePackage(decls, &transformed_reference);

	std::string err_str;
	const SymbolTable::Symbol* s =
	ResolveSymbolCheckVisibility(transformed_reference, callsite, context, symbols, &err_str);
	if (s) {
	// The ID may not exist. This is fine because of the possibility of building
	// against libraries without assigned IDs.
	// Ex: Linking against own resources when building a static library.
	reference->id = s->id;
	reference->is_dynamic = s->is_dynamic;
	return true;
	}

	DiagMessage error_msg(reference->GetSource());
	error_msg << "resource ";
	WriteResourceName(*reference, callsite, decls, &error_msg);
	error_msg << " " << err_str;
	context->GetDiagnostics()->Error(error_msg);
	return false;
	}

	bool ReferenceLinker::Consume(IAaptContext* context, ResourceTable* table) {
	TRACE_NAME("ReferenceLinker::Consume");
	EmptyDeclStack decl_stack;
	bool error = false;
	for (auto& package : table->packages) {
	// Since we're linking, each package must have a name.
	CHECK(!package->name.empty()) << "all packages being linked must have a name";

	for (auto& type : package->types) {
	for (auto& entry : type->entries) {
	// First, unmangle the name if necessary.
	ResourceName name(package->name, type->type, entry->name);
	NameMangler::Unmangle(&name.entry, &name.package);

	// Symbol state information may be lost if there is no value for the resource.
	if (entry->visibility.level != Visibility::Level::kUndefined && entry->values.empty()) {
	context->GetDiagnostics()->Error(DiagMessage(entry->visibility.source)
	<< "no definition for declared symbol '" << name
	<< "'");
	error = true;
	}

	// Ensure that definitions for values declared as overlayable exist
	if (entry->overlayable_item && entry->values.empty()) {
	context->GetDiagnostics()->Error(DiagMessage(entry->overlayable_item.value().source)
	<< "no definition for overlayable symbol '"
	<< name << "'");
	error = true;
	}

	// The context of this resource is the package in which it is defined.
	const CallSite callsite{name.package};
	ReferenceLinkerVisitor visitor(callsite, context, context->GetExternalSymbols(),
	&table->string_pool, &decl_stack);

	for (auto& config_value : entry->values) {
	config_value->value->Accept(&visitor);
	}

	if (visitor.HasError()) {
	error = true;
	}
	}
	}
	}
	return !error;
	}

	} // namespace aapt