objective-c: Add `objc_class_prefix` generation option.

objectivec/README.md

@@ -133,8 +133,8 @@ This options allow you to provide a custom prefix for all the symbols generated
 from a proto file (classes (from message), enums, the Root for extension
 support).
 
-If not set, the generation option `use_package_as_prefix` (documented below)
-controls what is used instead. Since Objective C uses a global namespace for all
+If not set, the generation options `default_objc_class_prefix` and `use_package_as_prefix`
+(documented below) control what is used instead. Since Objective C uses a global namespace for all
 of its classes, there can be collisions. `use_package_as_prefix=yes` should
 avoid collisions since proto package are used to scope/name things in other
 languages, but this option can be used to get shorter names instead. Convention
@@ -182,6 +182,12 @@ supported keys are:
     having to add the runtime directory to the header search path since the
     generate `#import` will be more complete.
 
+  * `default_objc_class_prefix`: The default ObjC prefix value to use when 
+    generating sources. The generator will use this if the `objc_class_prefix`
+    file option is not set. This option can be useful if multiple iOS apps
+    consume the same proto file but wish to use a different prefix for their
+    generated sources.
+
   * `use_package_as_prefix` and `proto_package_prefix_exceptions_path`: The
     `value` for `use_package_as_prefix` can be `yes` or `no`, and indicates
     if a prefix should be derived from the proto package for all the symbols

src/google/protobuf/compiler/objectivec/objectivec_generator.cc

@@ -190,10 +190,20 @@ bool ObjectiveCGenerator::GenerateAll(
       // header search path since the generate #import will be more complete.
       generation_options.runtime_import_prefix =
           StripSuffixString(options[i].second, "/");
+    } else if (options[i].first == "default_objc_class_prefix") {
+      // The default objc class prefix to use if specified by the command line 
+      // invocation. The file option is always honored first if one is present.
+      std::string value = options[i].second;
+      if (value.empty()) {
+        *error = "error: default_objc_class_prefix cannot be empty.";
+        return false;
+      }
+      SetDefaultObjcClassPrefix(value);
     } else if (options[i].first == "use_package_as_prefix") {
       // Controls how the symbols should be prefixed to avoid symbols
-      // collisions. The objc_class_prefix file option is always honored, this
-      // is just what to do if that isn't set. The available options are:
+      // collisions. The objc_class_prefix file option is always honored first
+      // followed by the default_objc_class_prefix generator option. This is is just 
+      // what to do if either of these options are not set. The available options are:
       //   "no": Not prefixed (the existing mode).
       //   "yes": Make a prefix out of the proto package.
       bool value = false;

src/google/protobuf/compiler/objectivec/objectivec_helpers.cc

@@ -99,6 +99,9 @@ class PrefixModeStorage {
  public:
   PrefixModeStorage();
 
+  const std::string default_objc_class_prefix() const { return default_objc_class_prefix_; }
+  void set_default_objc_class_prefix(const std::string& default_objc_class_prefix) { default_objc_class_prefix_ = default_objc_class_prefix; }
+
   bool use_package_name() const { return use_package_name_; }
   void set_use_package_name(bool on_or_off) { use_package_name_ = on_or_off; }
 
@@ -116,13 +119,14 @@ class PrefixModeStorage {
 
  private:
   bool use_package_name_;
+  std::string default_objc_class_prefix_;
   std::string exception_path_;
   std::string forced_prefix_;
   std::unordered_set<std::string> exceptions_;
 };
 
 PrefixModeStorage::PrefixModeStorage() {
-  // Even thought there are generation options, have an env back door since some
+  // Even though there are generation options, have an env back door since some
   // of these helpers could be used in other plugins.
 
   use_package_name_ = BoolFromEnvVar("GPB_OBJC_USE_PACKAGE_AS_PREFIX", false);
@@ -169,6 +173,10 @@ PrefixModeStorage g_prefix_mode;
 
 }  // namespace
 
+void SetDefaultObjcClassPrefix(const std::string& default_objc_class_prefix) {
+  g_prefix_mode.set_default_objc_class_prefix(default_objc_class_prefix);
+}
+
 bool UseProtoPackageAsDefaultPrefix() {
   return g_prefix_mode.use_package_name();
 }
@@ -526,11 +534,16 @@ std::string BaseFileName(const FileDescriptor* file) {
 }
 
 std::string FileClassPrefix(const FileDescriptor* file) {
-  // Always honor the file option.
+  // Always honor the file option first.
   if (file->options().has_objc_class_prefix()) {
     return file->options().objc_class_prefix();
   }
 
+  // If a default prefix is passed through objc_opt then accept it.
+  if (!g_prefix_mode.default_objc_class_prefix().empty()) {
+    return g_prefix_mode.default_objc_class_prefix();
+  }
+
   // If package prefix isn't enabled, done.
   if (!g_prefix_mode.use_package_name()) {
     return "";

src/google/protobuf/compiler/objectivec/objectivec_helpers.h

@@ -47,6 +47,9 @@ namespace protobuf {
 namespace compiler {
 namespace objectivec {
 
+// Set the default objc class prefix that should be used. This method is used only
+// when default_objc_class_prefix is passed through objc_opt.
+void PROTOC_EXPORT SetDefaultObjcClassPrefix(const std::string& objc_class_prefix);
 // Get/Set if the proto package should be used to make the default prefix for
 // symbols. This will then impact most of the type naming apis below. It is done
 // as a global to not break any other generator reusing the methods since they
@@ -68,6 +71,7 @@ struct Options {
   std::string generate_for_named_framework;
   std::string named_framework_to_proto_path_mappings_path;
   std::string runtime_import_prefix;
+  std::string default_objc_class_prefix;
   bool prefixes_must_be_registered;
   bool require_prefixes;
 };