Use a objc class prefix mappings path generator option instead.

objectivec/README.md

@@ -133,7 +133,7 @@ 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 options `default_objc_class_prefix` and `use_package_as_prefix`
+If not set, the generation options `objc_class_prefix_mappings_path` 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
@@ -182,10 +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
+  * `objc_class_prefix_mappings_path`: The `value` used for this key
+    is a path to a file containing a list of prefixes and proto files.
+    The generator will use this to locate a ObjC class prefix to use when
+    generating sources. The generator will first honor the `objc_class_prefix`
+    file option if it is set. This option can be useful if multiple iOS apps
+    consume a common set of proto files but wish to use a different prefix for
     generated sources.
 
   * `use_package_as_prefix` and `proto_package_prefix_exceptions_path`: The

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

@@ -190,19 +190,21 @@ 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 == "objc_class_prefix_mappings_path") {
+      // Path to use for when loading the objc class prefix mappings to use.
+      // The `objc_class_prefix` option is always honored first if one is present.
+      // 
+      // The format of the file is:
+      //   - An entry is a line of "objc_class_prefix: file.proto, dir/file2.proto".
+      //   - Comments start with "#".
+      //   - A comment can go on a line after a expected package/prefix pair.
+      //     (i.e. - "GPB: descriptor.proto # comment")
+      //
+      SetObjCClassPrefixMappingsPath(options[i].second);
     } 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 first
-      // followed by the default_objc_class_prefix generator option. This is is just 
+      // followed by the objc_class_prefix_mappings_path 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.

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

@@ -99,8 +99,13 @@ 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; }
+  const std::string objc_class_prefix_mappings_path() const { return objc_class_prefix_mappings_path_; }
+  void set_objc_class_prefix_mappings_path(const std::string& path) {
+    objc_class_prefix_mappings_path_ = path;
+    objc_class_prefix_map_.clear();
+  }
+
+  std::string objc_class_prefix(const FileDescriptor* file);
 
   bool use_package_name() const { return use_package_name_; }
   void set_use_package_name(bool on_or_off) { use_package_name_ = on_or_off; }
@@ -119,7 +124,8 @@ class PrefixModeStorage {
 
  private:
   bool use_package_name_;
-  std::string default_objc_class_prefix_;
+  std::map<std::string, std::string> objc_class_prefix_map_;
+  std::string objc_class_prefix_mappings_path_;
   std::string exception_path_;
   std::string forced_prefix_;
   std::unordered_set<std::string> exceptions_;
@@ -144,6 +150,38 @@ PrefixModeStorage::PrefixModeStorage() {
   }
 }
 
+std::string PrefixModeStorage::objc_class_prefix(const FileDescriptor* file) {
+  if (!file) {
+    return "";
+  }
+
+  if (objc_class_prefix_map_.empty() && !objc_class_prefix_mappings_path_.empty()) {
+    std::string error_str;
+    // Re use the same collector as we use for the named framework paths as the file
+    // is expected to be in the same format.
+    ImportWriter::ProtoFrameworkCollector collector(&objc_class_prefix_map_);
+    if (!ParseSimpleFile(objc_class_prefix_mappings_path_, &collector, &error_str)) {
+      if (error_str.empty()) {
+        error_str = std::string("protoc:0: warning: Failed to parse")
+           + std::string(" objc class prefix mappings file: ")
+           + objc_class_prefix_mappings_path_;
+      }
+      std::cerr << error_str << std::endl;
+      std::cerr.flush();
+      objc_class_prefix_map_.clear();
+    }
+  }
+
+  std::map<std::string, std::string>::iterator objc_class_prefix_lookup =
+  objc_class_prefix_map_.find(file->name());
+
+  if (objc_class_prefix_lookup != objc_class_prefix_map_.end()) {
+    return objc_class_prefix_lookup->second;
+  }  
+
+  return "";
+}
+
 bool PrefixModeStorage::is_package_exempted(const std::string& package) {
   if (exceptions_.empty() && !exception_path_.empty()) {
     std::string error_str;
@@ -173,8 +211,12 @@ 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);
+std::string GetObjCClassPrefixMappingsPath() {
+  return g_prefix_mode.objc_class_prefix_mappings_path();
+}
+
+void SetObjCClassPrefixMappingsPath(const std::string& file_path) {
+  g_prefix_mode.set_objc_class_prefix_mappings_path(file_path);
 }
 
 bool UseProtoPackageAsDefaultPrefix() {
@@ -539,9 +581,10 @@ std::string FileClassPrefix(const FileDescriptor* file) {
     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 is specified in an objc class prefix mapping file then use that.
+  std::string objc_class_prefix = g_prefix_mode.objc_class_prefix(file);
+  if (!objc_class_prefix.empty()) {
+    return objc_class_prefix;
   }
 
   // If package prefix isn't enabled, done.

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

@@ -47,9 +47,10 @@ 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);
+// TODO
+std::string PROTOC_EXPORT GetObjCClassPrefixMappingsPath();
+void PROTOC_EXPORT SetObjCClassPrefixMappingsPath(
+    const std::string& file_path);
 // 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
@@ -71,7 +72,7 @@ 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;
+  std::string objc_class_prefix_mappings_path;
   bool prefixes_must_be_registered;
   bool require_prefixes;
 };
@@ -315,7 +316,6 @@ class PROTOC_EXPORT ImportWriter {
                                   const std::string& runtime_import_prefix,
                                   bool default_cpp_symbol = false);
 
- private:
   class ProtoFrameworkCollector : public LineConsumer {
    public:
     ProtoFrameworkCollector(std::map<std::string, std::string>* inout_proto_file_to_framework_name)