Tracing V2: Proto fields reflection.

components/tracing/tools/proto_zero_plugin/proto_zero_generator.cc

Index: components/tracing/tools/proto_zero_plugin/proto_zero_generator.cc
diff --git a/components/tracing/tools/proto_zero_plugin/proto_zero_generator.cc b/components/tracing/tools/proto_zero_plugin/proto_zero_generator.cc
index 713d3cca42fea6c28cb102b900dff6842c26bad2..d79fc8f0305c7b1ae6e985e5dbdde86d3a805a32 100644
--- a/components/tracing/tools/proto_zero_plugin/proto_zero_generator.cc
+++ b/components/tracing/tools/proto_zero_plugin/proto_zero_generator.cc
@@ -101,6 +101,23 @@ class GeneratorJob {
     return name;
   }
 
+  inline std::string Capitalize(const std::string& str) {

[Primiano Tucci (use gerrit), 2016/08/31 09:04:07]

honestly I feel this is just overkill as you use only in one place.

Just easier if online 111 you do:

std::string name = field->camelcase_name();
name[0] = std::toupper(name[0])
name = "k" + name + "FieldNumer" (there should be no need for the explicit
std::string("k"))

+    std::string copy(str);
+    copy.at(0) = toupper(copy.at(0));
+    return copy;
+  }
+
+  inline std::string GetFieldNumberConstant(const FieldDescriptor* field) {
+    std::string name = field->camelcase_name();
+    if (!name.empty()) {
+      name = std::string("k") + Capitalize(name) + "FieldNumber";
+    } else {
+      // Protoc allows fields like 'bool _ = 1'.
+      Abort("Empty field name in camel case notation.");
+    }
+    return name;
+  }
+
   // Small enums can be written faster without involving VarInt encoder.
   inline bool IsTinyEnumField(const FieldDescriptor* field) {
     if (field->type() != FieldDescriptor::TYPE_ENUM)
@@ -229,6 +246,7 @@ class GeneratorJob {
         "#define $guard$\n\n"
         "#include <stddef.h>\n"
         "#include <stdint.h>\n\n"

[Primiano Tucci (use gerrit), 2016/08/31 09:04:07]

I think you need also cctype for std::toupper

+        "#include <string>\n\n"
         "#include \"components/tracing/core/proto_zero_message.h\"\n",
         "greeting", greeting,
         "guard", guard);
@@ -435,6 +453,57 @@ class GeneratorJob {
         "outer_class", outer_class);
   }
 
+  void GenerateReflectionHelpers(const Descriptor* message) {
+    // Field numbers.

[Primiano Tucci (use gerrit), 2016/08/31 09:04:07]

I'd make this more clear:
// Field Numbers (e.g., kXXXFieldNumber = 42)

[kraynov, 2016/08/31 17:43:33]

Acknowledged.

+    if (message->field_count() > 0) {
+      stub_h_->Print("enum : int32_t {\n");

[Primiano Tucci (use gerrit), 2016/08/31 09:04:07]

just realized this, so far we used uint32_t for field numbers.

[kraynov, 2016/08/31 17:43:33]

Acknowledged.

+      stub_h_->Indent();
+
+      for (int i = 0; i < message->field_count(); ++i) {
+        const FieldDescriptor* field = message->field(i);
+        stub_h_->Print(
+            "$name$ = $id$,\n",
+            "name", GetFieldNumberConstant(field),
+            "id", std::to_string(field->number()));
+      }
+      stub_h_->Outdent();
+      stub_h_->Print("};\n");
+    }
+
+    // Fields reflection.
+    stub_h_->Print(
+        "static ::tracing::v2::proto::FieldReflection "
+        "GetFieldReflection(uint32_t field_id);");
+    stub_cc_->Print(
+        "::tracing::v2::proto::FieldReflection "
+        "$class$::GetFieldReflection(uint32_t field_id) {\n",
+        "class", GetCppClassName(message));
+    stub_cc_->Indent();
+    stub_cc_->Print("switch (field_id) {\n");
+    stub_cc_->Indent();
+
+    for (int i = 0; i < message->field_count(); ++i) {
+      const FieldDescriptor* field = message->field(i);
+      stub_cc_->Print(
+          "case $id$:\n"
+          "  return ::tracing::v2::proto::FieldReflection(\"$name$\", "

[Primiano Tucci (use gerrit), 2016/08/31 09:04:07]

Hmm this is going to be slow.
Can we make this just a lookup in a table where you have all the descriptors, so
this returns a FieldDescirptor*.
Something along the lines of http://pastebin.com/WPJWsnJH .
I think that if the table is fully const that should not require any static
initializers, as all the data will end up in the .rodata (or equivalent).
So this can generate just something like:

switch(field_id) {
  case 1:
    return &DescriptorTable[12];
  case 2: 
    return &DescriptorTable[7];
  etc

}

[kraynov, 2016/08/31 17:43:33]

Done.

+          "::tracing::v2::proto::ProtoType::kProtoType$type$,"
+          "$id$, $repeated$);\n",
+          "name", field->name(),
+          "type", Capitalize(FieldDescriptor::TypeName(field->type())),
+          "id", GetFieldNumberConstant(field),
+          "repeated", std::to_string(field->is_repeated()));
+    }
+    stub_cc_->Print(
+        "default:\n"
+        "  return ::tracing::v2::proto::FieldReflection::CreateInvalid();\n");
+
+    stub_cc_->Outdent();
+    stub_cc_->Print("}\n");
+    stub_cc_->Outdent();
+    stub_cc_->Print("}\n\n");
+  }
+
   void GenerateMessageDescriptor(const Descriptor* message) {
     stub_h_->Print(
         "class $name$ : public ::tracing::v2::ProtoZeroMessage {\n"
@@ -442,6 +511,8 @@ class GeneratorJob {
         "name", GetCppClassName(message));
     stub_h_->Indent();
 
+    GenerateReflectionHelpers(message);
+
     // Using statements for nested messages.
     for (int i = 0; i < message->nested_type_count(); ++i) {
       const Descriptor* nested_message = message->nested_type(i);
@@ -475,30 +546,6 @@ class GeneratorJob {
       }
     }
 
-    // Field numbers.
-    if (message->field_count() > 0) {
-      stub_h_->Print("enum : int32_t {\n");
-      stub_h_->Indent();
-
-      for (int i = 0; i < message->field_count(); ++i) {
-        const FieldDescriptor* field = message->field(i);
-        std::string name = field->camelcase_name();
-        if (!name.empty()) {
-          name.at(0) = toupper(name.at(0));
-        } else {
-          // Protoc allows fields like 'bool _ = 1'.
-          Abort("Empty field name in camel case notation.");
-        }
-
-        stub_h_->Print(
-            "k$name$FieldNumber = $id$,\n",
-            "name", name,
-            "id", std::to_string(field->number()));
-      }
-      stub_h_->Outdent();
-      stub_h_->Print("};\n");
-    }
-
     // Field descriptors.
     for (int i = 0; i < message->field_count(); ++i) {
       const FieldDescriptor* field = message->field(i);