Replace Maybe with std::optional

With c++17, std::optional provides the functionality that Maybe
provided.

Bug: 183215655
Test: aapt2_tests
Change-Id: I62bb9c2fa4985dc5217a6ed153df92b85ad9a034
diff --git a/tools/aapt2/java/JavaClassGenerator.cpp b/tools/aapt2/java/JavaClassGenerator.cpp
index de6524d..3b3c6e1 100644
--- a/tools/aapt2/java/JavaClassGenerator.cpp
+++ b/tools/aapt2/java/JavaClassGenerator.cpp
@@ -204,7 +204,7 @@
 }
 
 // Whether or not to skip writing this symbol.
-bool JavaClassGenerator::SkipSymbol(const Maybe<SymbolTable::Symbol>& symbol) {
+bool JavaClassGenerator::SkipSymbol(const std::optional<SymbolTable::Symbol>& symbol) {
   return !symbol || (options_.types == JavaClassGeneratorOptions::SymbolTypes::kPublic &&
                      !symbol.value().is_public);
 }
@@ -212,12 +212,12 @@
 struct StyleableAttr {
   const Reference* attr_ref = nullptr;
   std::string field_name;
-  Maybe<SymbolTable::Symbol> symbol;
+  std::optional<SymbolTable::Symbol> symbol;
 };
 
 static bool operator<(const StyleableAttr& lhs, const StyleableAttr& rhs) {
-  const ResourceId lhs_id = lhs.attr_ref->id.value_or_default(ResourceId(0));
-  const ResourceId rhs_id = rhs.attr_ref->id.value_or_default(ResourceId(0));
+  const ResourceId lhs_id = lhs.attr_ref->id.value_or(ResourceId(0));
+  const ResourceId rhs_id = rhs.attr_ref->id.value_or(ResourceId(0));
   if (lhs_id == rhs_id) {
     return lhs.attr_ref->name.value() < rhs.attr_ref->name.value();
   }
@@ -362,7 +362,7 @@
       array_def->AddElement(field_name);
       r_txt_contents = field_name.ref;
     } else {
-      const ResourceId attr_id = attr.attr_ref->id.value_or_default(ResourceId(0));
+      const ResourceId attr_id = attr.attr_ref->id.value_or(ResourceId(0));
       array_def->AddElement(attr_id);
       r_txt_contents = to_string(attr_id);
     }
@@ -504,9 +504,9 @@
   }
 }
 
-Maybe<std::string> JavaClassGenerator::UnmangleResource(const StringPiece& package_name,
-                                                        const StringPiece& package_name_to_generate,
-                                                        const ResourceEntry& entry) {
+std::optional<std::string> JavaClassGenerator::UnmangleResource(
+    const StringPiece& package_name, const StringPiece& package_name_to_generate,
+    const ResourceEntry& entry) {
   if (SkipSymbol(entry.visibility.level)) {
     return {};
   }
@@ -535,7 +535,7 @@
                                      MethodDefinition* out_rewrite_method_def,
                                      Printer* r_txt_printer) {
   for (const auto& entry : type.entries) {
-    const Maybe<std::string> unmangled_name =
+    const std::optional<std::string> unmangled_name =
         UnmangleResource(package.name, package_name_to_generate, *entry);
     if (!unmangled_name) {
       continue;
diff --git a/tools/aapt2/java/JavaClassGenerator.h b/tools/aapt2/java/JavaClassGenerator.h
index d9d1b39..b45a2f1 100644
--- a/tools/aapt2/java/JavaClassGenerator.h
+++ b/tools/aapt2/java/JavaClassGenerator.h
@@ -46,7 +46,7 @@
 
   // If set, generates code to rewrite the package ID of resources.
   // Implies use_final == true. Default is unset.
-  Maybe<OnResourcesLoadedCallbackOptions> rewrite_callback_options;
+  std::optional<OnResourcesLoadedCallbackOptions> rewrite_callback_options;
 
   enum class SymbolTypes {
     kAll,
@@ -83,13 +83,13 @@
 
  private:
   bool SkipSymbol(Visibility::Level state);
-  bool SkipSymbol(const Maybe<SymbolTable::Symbol>& symbol);
+  bool SkipSymbol(const std::optional<SymbolTable::Symbol>& symbol);
 
   // Returns the unmangled resource entry name if the unmangled package is the same as
   // package_name_to_generate. Returns nothing if the resource should be skipped.
-  Maybe<std::string> UnmangleResource(const android::StringPiece& package_name,
-                                      const android::StringPiece& package_name_to_generate,
-                                      const ResourceEntry& entry);
+  std::optional<std::string> UnmangleResource(const android::StringPiece& package_name,
+                                              const android::StringPiece& package_name_to_generate,
+                                              const ResourceEntry& entry);
 
   bool ProcessType(const android::StringPiece& package_name_to_generate,
                    const ResourceTablePackage& package, const ResourceTableType& type,
diff --git a/tools/aapt2/java/ManifestClassGenerator.cpp b/tools/aapt2/java/ManifestClassGenerator.cpp
index 09ea03b..a0db41b 100644
--- a/tools/aapt2/java/ManifestClassGenerator.cpp
+++ b/tools/aapt2/java/ManifestClassGenerator.cpp
@@ -19,19 +19,17 @@
 #include <algorithm>
 
 #include "Source.h"
-#include "java/AnnotationProcessor.h"
 #include "java/ClassDefinition.h"
 #include "java/JavaClassGenerator.h"
 #include "text/Unicode.h"
-#include "util/Maybe.h"
 #include "xml/XmlDom.h"
 
 using ::aapt::text::IsJavaIdentifier;
 
 namespace aapt {
 
-static Maybe<std::string> ExtractJavaIdentifier(IDiagnostics* diag, const Source& source,
-                                                const std::string& value) {
+static std::optional<std::string> ExtractJavaIdentifier(IDiagnostics* diag, const Source& source,
+                                                        const std::string& value) {
   std::string result = value;
   size_t pos = value.rfind('.');
   if (pos != std::string::npos) {
@@ -63,7 +61,7 @@
     return false;
   }
 
-  Maybe<std::string> result =
+  std::optional<std::string> result =
       ExtractJavaIdentifier(diag, source.WithLine(el->line_number), attr->value);
   if (!result) {
     return false;
diff --git a/tools/aapt2/java/ProguardRules.cpp b/tools/aapt2/java/ProguardRules.cpp
index d9a4caa..b939f35 100644
--- a/tools/aapt2/java/ProguardRules.cpp
+++ b/tools/aapt2/java/ProguardRules.cpp
@@ -48,7 +48,7 @@
 
   void Visit(xml::Element* node) override {
     if (!node->namespace_uri.empty()) {
-      Maybe<xml::ExtractedPackage> maybe_package =
+      std::optional<xml::ExtractedPackage> maybe_package =
           xml::ExtractPackageFromNamespace(node->namespace_uri);
       if (maybe_package) {
         // This is a custom view, let's figure out the class name from this.
@@ -270,14 +270,16 @@
         get_name = true;
         xml::Attribute* attr = node->FindAttribute(xml::kSchemaAndroid, "backupAgent");
         if (attr) {
-          Maybe<std::string> result = util::GetFullyQualifiedClassName(package_, attr->value);
+          std::optional<std::string> result =
+              util::GetFullyQualifiedClassName(package_, attr->value);
           if (result) {
             AddClass(node->line_number, result.value(), "");
           }
         }
         attr = node->FindAttribute(xml::kSchemaAndroid, "appComponentFactory");
         if (attr) {
-          Maybe<std::string> result = util::GetFullyQualifiedClassName(package_, attr->value);
+          std::optional<std::string> result =
+              util::GetFullyQualifiedClassName(package_, attr->value);
           if (result) {
             AddClass(node->line_number, result.value(), "");
           }
@@ -285,7 +287,8 @@
 
         attr = node->FindAttribute(xml::kSchemaAndroid, "zygotePreloadName");
         if (attr) {
-          Maybe<std::string> result = util::GetFullyQualifiedClassName(package_, attr->value);
+          std::optional<std::string> result =
+              util::GetFullyQualifiedClassName(package_, attr->value);
           if (result) {
             AddClass(node->line_number, result.value(), "");
           }
@@ -317,7 +320,8 @@
         get_name = attr != nullptr;
 
         if (get_name) {
-          Maybe<std::string> result = util::GetFullyQualifiedClassName(package_, attr->value);
+          std::optional<std::string> result =
+              util::GetFullyQualifiedClassName(package_, attr->value);
           if (result) {
             AddClass(node->line_number, result.value(), "");
           }