[c#] add support for init-only setters on generated classes

Author: enioluwas

compiler/Main.hs

@@ -114,6 +114,8 @@ csCodegen options@Cs {..} = do
             else csTypeMapping
     fieldMapping = if readonly_properties
             then ReadOnlyProperties
+            else if init_only_properties
+                 then InitOnlyProperties
             else if fields
                  then PublicFields
                  else Properties

compiler/Options.hs

@@ -53,6 +53,7 @@ data Options
         , namespace :: [String]
         , collection_interfaces :: Bool
         , readonly_properties :: Bool
+        , init_only_properties :: Bool
         , fields :: Bool
         , jobs :: Maybe Int
         , no_banner :: Bool
@@ -106,9 +107,10 @@ cs :: Options
 cs = Cs
     { collection_interfaces = def &= name "c" &= help "Use interfaces rather than concrete collection types"
     , readonly_properties = def &= name "r" &= help "Generate private property setters"
+    , init_only_properties = def &= name "init-only" &= help "Generate init-only property setters"
     , fields = def &= name "f" &= help "Generate public fields rather than properties"
     , structs_enabled = True &= explicit &= name "structs" &= help "Generate C# types for Bond structs and enums (true by default, use \"--structs=false\" to disable)"
-    , constructor_parameters = def &= explicit &= name "preview-constructor-parameters" &= help "PREVIEW FEATURE: Generate a constructor that takes all the fields as parameters. Typically used with readonly-properties."
+    , constructor_parameters = def &= explicit &= name "preview-constructor-parameters" &= help "PREVIEW FEATURE: Generate a constructor that takes all the fields as parameters. Typically used with readonly-properties or init-only-properties."
     } &=
     name "c#" &=
     help "Generate C# code"

compiler/src/Language/Bond/Codegen/Cs/Types_cs.hs

@@ -31,7 +31,8 @@ data StructMapping =
 data FieldMapping =
     PublicFields |          -- ^ public fields
     Properties |            -- ^ auto-properties
-    ReadOnlyProperties      -- ^ auto-properties with private setter
+    ReadOnlyProperties |    -- ^ auto-properties with private setter
+    InitOnlyProperties      -- ^ auto-properties with init-only setter
     deriving Eq
 
 -- | Options for how constructors should be generated.
@@ -186,6 +187,7 @@ namespace #{csNamespace}
                 PublicFields        -> [lt|#{optional fieldInitializer $ csDefault f};|]
                 Properties          -> [lt| { get; set; }|]
                 ReadOnlyProperties  -> [lt| { get; private set; }|]
+                InitOnlyProperties  -> [lt| { get; init; }|]
             fieldInitializer x = [lt| = #{x}|]
             new = if isBaseField fieldName structBase then "new " else "" :: String
 

compiler/tests/TestMain.hs

@@ -151,6 +151,13 @@ tests = testGroup "Compiler tests"
                 ]
                 "complex_inheritance"
                 "constructor-parameters"
+            , verifyCodegenVariation
+                [ "c#"
+                , "--preview-constructor-parameters"
+                , "--init-only-properties"
+                ]
+                "complex_inheritance"
+                "constructor-parameters"
             , verifyCodegenVariation
                 [ "c#"
                 , "--preview-constructor-parameters"
@@ -180,6 +187,13 @@ tests = testGroup "Compiler tests"
                 ]
                 "empty_struct"
                 "constructor-parameters"
+            , verifyCodegenVariation
+                [ "c#"
+                , "--preview-constructor-parameters"
+                , "--init-only-properties"
+                ]
+                "empty_struct"
+                "constructor-parameters"
             ]
         , testGroup "Java"
             [ verifyJavaCodegen "attributes"

compiler/tests/Tests/Codegen.hs

@@ -93,6 +93,8 @@ verifyFiles options baseName variation =
     verify = verifyFile options baseName
     fieldMapping Cs {..} = if readonly_properties
         then ReadOnlyProperties
+        else if init_only_properties
+             then InitOnlyProperties
         else if fields
              then PublicFields
              else Properties

cs/nuget/bond.csharp.test.csproj

@@ -40,4 +40,9 @@
       <Options>$(BondOptions) --using="DateTime=System.DateTime"</Options>
     </BondCodegen>
   </ItemGroup>
+  <ItemGroup Condition="$(TargetFramework.StartsWith('net5.0')) or $(TargetFramework.StartsWith('net6.0'))">
+      <BondCodegen Update="..\test\core\InitOnly.bond">
+      <Options>$(BondOptions) --init-only-properties</Options>
+    </BondCodegen>
+  </ItemGroup>
 </Project>

cs/test/core/SerializationTests.cs

@@ -83,6 +83,20 @@ public void ReadonlySimpleContainers()
             TestSerialization<Readonly.SimpleContainers>();
         }
 
+#if NET5_0_OR_GREATER
+        [Test]
+        public void InitOnlyBasicTypes()
+        {
+            TestSerialization<InitOnly.BasicTypes>();
+        }
+
+        [Test]
+        public void InitOnlySimpleContainers()
+        {
+            TestSerialization<InitOnly.SimpleContainers>();
+        }
+#endif
+
         [Test]
         public void Nested()
         {

cs/test/coreNS10/CoreNS10.csproj

@@ -37,6 +37,10 @@
       <Options Condition=" '$(Configuration)' != 'Fields' ">$(BondOptions) --readonly-properties</Options>
       <Options Condition=" '$(Configuration)' == 'Fields' ">--readonly-properties --collection-interfaces</Options>
     </BondCodegen>
+    <BondCodegen Update="InitOnly.bond">
+      <Options Condition=" '$(Configuration)' != 'Fields' ">$(BondOptions) --init-only-properties</Options>
+      <Options Condition=" '$(Configuration)' == 'Fields' ">--init-only-properties --collection-interfaces</Options>
+    </BondCodegen>
     <BondCodegen Include="..\core\Containers.bond">
       <Options Condition=" '$(Configuration)' != 'Fields' ">$(BondOptions) --collection-interfaces</Options>
       <Options Condition=" '$(Configuration)' == 'Fields' ">--fields</Options>
@@ -53,6 +57,7 @@
     <Compile Include="$(IntermediateOutputPath)\NamespaceConflict_types.cs" Condition="False" />
     <Compile Include="$(IntermediateOutputPath)\NamespaceConflictBond_types.cs" Condition="False" />
     <Compile Include="$(IntermediateOutputPath)\ReadOnly_types.cs" Condition="False" />
+    <Compile Include="$(IntermediateOutputPath)\InitOnly_types.cs" Condition="False" />
     <Compile Include="$(IntermediateOutputPath)\UnitTest_types.cs" Condition="False" />
     <!-- End Resharper Workaround -->
   </ItemGroup>

doc/src/bond_cs.md

@@ -127,11 +127,16 @@ Schema fields are represented by properties with public getter and private
 setter and initialized to the default values in the default constructor.
 Classes with read-only properties are fully supported by all Bond APIs.
 
+`--init-only-properties`
+
+Schema fields are represented by properties with public getter and
+[C# 9 init-only setter](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/init) and initialized to the default values in the default constructor. Classes with init-only properties are fully supported by all Bond APIs.
+
 `--preview-constructor-parameters`
 
 A constructor is generated with a parameter to initialize each of the schema
 fields. This option is typically used in conjunction with
-`--readonly-properties`.  This functionailty is in preview and may change.
+`--readonly-properties` or `--init-only-properties`.  This functionailty is in preview and may change.
 
 `--collection-interfaces`