Fix C++ code generation for Float32s with integral defaults.

Appending 'f' to an integer literal doesn't make it a float. We have to add '.0' first.

Fixes #119.

c++/src/capnp/compiler/capnpc-c++.c++

@@ -300,7 +300,15 @@ private:
       case schema::Value::UINT16: return kj::strTree(value.getUint16(), "u");
       case schema::Value::UINT32: return kj::strTree(value.getUint32(), "u");
       case schema::Value::UINT64: return kj::strTree(value.getUint64(), "llu");
-      case schema::Value::FLOAT32: return kj::strTree(value.getFloat32(), "f");
+      case schema::Value::FLOAT32: {
+        auto text = kj::str(value.getFloat32());
+        if (text.findFirst('.') == nullptr &&
+            text.findFirst('e') == nullptr &&
+            text.findFirst('E') == nullptr) {
+          text = kj::str(text, ".0");
+        }
+        return kj::strTree(kj::mv(text), "f");
+      }
       case schema::Value::FLOAT64: return kj::strTree(value.getFloat64());
       case schema::Value::ENUM: {
         EnumSchema schema = schemaLoader.get(type.getEnum().getTypeId()).asEnum();

c++/src/capnp/encoding-test.c++

@@ -1704,6 +1704,16 @@ TEST(Encoding, DefaultFloatPlusNan) {
   EXPECT_TRUE(d != d);
 }
 
+TEST(Encoding, WholeFloatDefault) {
+  MallocMessageBuilder message;
+  auto root = message.initRoot<test::TestWholeFloatDefault>();
+
+  EXPECT_EQ(123.0f, root.getField());
+  EXPECT_EQ(123e30f, root.getBigField());
+  EXPECT_EQ(456.0f, test::TestWholeFloatDefault::CONSTANT);
+  EXPECT_EQ(456e30f, test::TestWholeFloatDefault::BIG_CONSTANT);
+}
+
 }  // namespace
 }  // namespace _ (private)
 }  // namespace capnp

c++/src/capnp/test.capnp

@@ -494,6 +494,15 @@ struct TestPrintInlineStructs {
   }
 }
 
+struct TestWholeFloatDefault {
+  # At one point, these failed to compile in C++ because it would produce literals like "123f",
+  # which is not valid; it needs to be "123.0f".
+  field @0 :Float32 = 123;
+  bigField @1 :Float32 = 123e30;
+  const constant :Float32 = 456;
+  const bigConstant :Float32 = 456e30;
+}
+
 struct TestEmptyStruct {}
 
 struct TestConstants {