Expose an interface to expose a given settings' metadata info

Summary:
We don't have a way to get the metadata associated with a given setting name
from outside. This is useful to know the expected type associated with a
given setting name.

Reviewed By: alikhtarov

Differential Revision: D7721340

fbshipit-source-id: e9ad07dd03c172f6f2d4bde5164614ca987c4fd8

folly/experimental/settings/Settings.cpp

@@ -63,8 +63,7 @@ bool setFromString(
   return true;
 }
 
-Optional<std::pair<std::string, std::string>> getAsString(
-    StringPiece settingName) {
+Optional<SettingsInfo> getAsString(StringPiece settingName) {
   auto mapPtr = detail::settingsMap().rlock();
   auto it = mapPtr->find(settingName.str());
   if (it == mapPtr->end()) {
@@ -73,6 +72,15 @@ Optional<std::pair<std::string, std::string>> getAsString(
   return it->second->getAsString();
 }
 
+Optional<SettingMetadata> getSettingsMeta(StringPiece settingName) {
+  auto mapPtr = detail::settingsMap().rlock();
+  auto it = mapPtr->find(settingName.str());
+  if (it == mapPtr->end()) {
+    return folly::none;
+  }
+  return it->second->meta();
+}
+
 bool resetToDefault(StringPiece settingName) {
   auto mapPtr = detail::settingsMap().rlock();
   auto it = mapPtr->find(settingName.str());

folly/experimental/settings/Settings.h

@@ -167,10 +167,20 @@ bool setFromString(
     folly::StringPiece reason);
 
 /**
- * @return If the setting exists, the current (to<string>(value),
- *   reason) pair.  Empty Optional otherwise.
+ * Type that encapsulates the current pair of (to<string>(value), reason)
  */
-folly::Optional<std::pair<std::string, std::string>> getAsString(
+using SettingsInfo = std::pair<std::string, std::string>;
+/**
+ * @return If the setting exists, the current setting information.
+ *         Empty Optional otherwise.
+ */
+folly::Optional<SettingsInfo> getAsString(folly::StringPiece settingName);
+
+/**
+ * @return If the setting exists, returns the current settings metadata.
+ *         Empty Optional otherwise.
+ */
+folly::Optional<SettingMetadata> getSettingsMeta(
     folly::StringPiece settingName);
 
 /**

folly/experimental/settings/test/SettingsTest.cpp

@@ -59,6 +59,26 @@ TEST(Settings, basic) {
   EXPECT_EQ(res->first, "200");
   EXPECT_EQ(res->second, "remote_set");
 
+  {
+    auto meta = folly::settings::getSettingsMeta("follytest_public_flag_to_a");
+    EXPECT_TRUE(meta.hasValue());
+    const auto& md = meta.value();
+    EXPECT_EQ(md.project, "follytest");
+    EXPECT_EQ(md.name, "public_flag_to_a");
+    EXPECT_EQ(md.typeStr, "int");
+    EXPECT_EQ(md.typeId, typeid(int));
+  }
+
+  {
+    auto meta = folly::settings::getSettingsMeta("follytest_some_flag");
+    EXPECT_TRUE(meta.hasValue());
+    const auto& md = meta.value();
+    EXPECT_EQ(md.project, "follytest");
+    EXPECT_EQ(md.name, "some_flag");
+    EXPECT_EQ(md.typeStr, "std::string");
+    EXPECT_EQ(md.typeId, typeid(std::string));
+  }
+
   res = folly::settings::getAsString("follytest_nonexisting");
   EXPECT_FALSE(res.hasValue());