added generation of c++ enum serializer functions.

Added flag cpp-enum-serializers to enable serializing enums in c++;
When this flag is turned on - serialize function declaration will be generated in enum's header and
c++ function definition will be generated to similar cpp file.

Author: ctin

src/source/CppGenerator.scala

@@ -63,10 +63,16 @@ class CppGenerator(spec: Spec) extends Generator(spec) {
       refs.hpp.add("#include <functional>") // needed for std::hash
     }
 
+    val stringExpr = MExpr(MString, Seq.empty[MExpr])
+    refs.find(stringExpr, false)
+
     val flagsType = "unsigned"
     val enumType = "int"
     val underlyingType = if(e.flags) flagsType else enumType
 
+    val stringRetType = marshal.typename(stringExpr)
+    val toStringFunctionName = idCpp.method(s"${self}_to_string")
+
     writeHppFile(ident, origin, refs.hpp, refs.hppFwds, w => {
       w.w(s"enum class $self : $underlyingType").bracedSemi {
         writeEnumOptionNone(w, e, idCpp.enum)
@@ -92,6 +98,9 @@ class CppGenerator(spec: Spec) extends Generator(spec) {
           w.wl(s"return static_cast<$self>(~static_cast<$flagsType>(x));")
         }
       }
+      if(spec.cppEnumSerializers) {
+        w.wl.wl(s"$stringRetType $toStringFunctionName(${withCppNs(self)} arg);")
+      }
     },
     w => {
       // std::hash specialization has to go *outside* of the wrapNs
@@ -110,6 +119,21 @@ class CppGenerator(spec: Spec) extends Generator(spec) {
         )
       }
     })
+    if(spec.cppEnumSerializers) {
+      writeCppFile(ident, origin, refs.cpp, 
+        w => {
+          w.w(s"$stringRetType $toStringFunctionName(${withCppNs(self)} arg)").braced {
+            w.w("switch(arg)").braced {
+              for (o <- normalEnumOptions(e)) {
+                val enumItem = withCppNs(s"$self::${idCpp.enum(o.ident.name)}")
+                w.wl(s"case $enumItem: return ${q(enumItem)};")
+              }
+              val convertValToString = (if (spec.cppUseWideStrings) "std::to_wstring" else "std::to_string") + s"(static_cast<${underlyingType}>(arg))"
+              w.wl(s"default: return $stringRetType(${q(s"$toStringFunctionName: not supported enum value: ")}) + $convertValToString;")
+            }
+          }
+      })
+    }
   }
 
   def shouldConstexpr(c: Const) = {

src/source/Main.scala

@@ -59,6 +59,7 @@ object Main {
     var cppHeaderOutFolderOptional: Option[File] = None
     var cppExt: String = "cpp"
     var cppHeaderExt: String = "hpp"
+    var cppEnumSerializers = false
     var javaIdentStyle = IdentStyle.javaDefault
     var cppIdentStyle = IdentStyle.cppDefault
     var cppTypeEnumIdentStyle: IdentConverter = null
@@ -136,6 +137,7 @@ object Main {
         .text("The filename extension for C++ files (default: \"cpp\").")
       opt[String]("hpp-ext").valueName("<ext>").foreach(cppHeaderExt = _)
         .text("The filename extension for C++ header files (default: \"hpp\").")
+      opt[Boolean]("cpp-enum-serializers").valueName("<true/false>").foreach(x => cppEnumSerializers = x)
       opt[String]("cpp-optional-template").valueName("<template>").foreach(x => cppOptionalTemplate = x)
         .text("The template to use for optional values (default: \"std::optional\")")
       opt[String]("cpp-optional-header").valueName("<header>").foreach(x => cppOptionalHeader = x)
@@ -339,6 +341,7 @@ object Main {
       jniBaseLibIncludePrefix,
       cppExt,
       cppHeaderExt,
+      cppEnumSerializers,
       objcOutFolder,
       objcppOutFolder,
       objcIdentStyle,

src/source/generator.scala

@@ -64,6 +64,7 @@ package object generatorTools {
                    jniBaseLibIncludePrefix: String,
                    cppExt: String,
                    cppHeaderExt: String,
+                   cppEnumSerializers: Boolean,
                    objcOutFolder: Option[File],
                    objcppOutFolder: Option[File],
                    objcIdentStyle: ObjcIdentStyle,

test-suite/Makefile

@@ -6,7 +6,7 @@ djinni:
 	./run_djinni.sh
 
 objc: djinni
-	cd objc; xcodebuild -sdk iphonesimulator -project DjinniObjcTest.xcodeproj -scheme DjinniObjcTest test -destination 'platform=iOS Simulator,name=iPhone 7,OS=latest'
+	cd objc; xcodebuild -sdk iphonesimulator -project DjinniObjcTest.xcodeproj -scheme DjinniObjcTest test -destination 'platform=iOS Simulator,name=iPhone 8,OS=latest'
 
 clean_objc:
 	cd objc && xcodebuild -sdk iphonesimulator -project DjinniObjcTest.xcodeproj -scheme DjinniObjcTest clean

test-suite/run_djinni.sh

@@ -110,6 +110,7 @@ fi
     --cpp-optional-template "std::experimental::optional" \
     --cpp-optional-header "\"../../handwritten-src/cpp/optional.hpp\"" \
     --cpp-extended-record-include-prefix "../../handwritten-src/cpp/" \
+    --cpp-enum-serializers true \
     \
     --jni-out "$temp_out_relative/jni" \
     --ident-jni-class NativeFooBar \