fix: Const propagation on views

include/rpcspec/RpcSpec.hpp

@@ -239,7 +239,7 @@ struct RpcSpec
      * @return An error on the first failing field; empty on success.
      */
     template <typename V>
-        requires(not SomeObjectView<V>) and HasObjectView<V>
+        requires(not SomeObjectView<V>) and HasObjectView<V> and (not std::is_const_v<V>)
     [[nodiscard]] MaybeError
     process(V& value) const
     {

include/rpcspec/RpcSpecView.hpp

@@ -9,6 +9,7 @@
 #include <rpcspec/Types.hpp>
 
 #include <concepts>
+#include <type_traits>
 
 namespace rpc::spec {
 
@@ -136,7 +137,7 @@ class RpcSpecView
      * @return An error on the first failing field; empty on success.
      */
     template <typename V>
-        requires(not SomeObjectView<V>) and HasObjectView<V>
+        requires(not SomeObjectView<V>) and HasObjectView<V> and (not std::is_const_v<V>)
     [[nodiscard]] MaybeError
     process(V& value) const
     {

include/rpcspec/Typed.hpp

@@ -516,7 +516,7 @@ struct TypedSpec
      * @return The populated `InputT` on success, or an error on the first failing field.
      */
     template <typename V>
-        requires(not SomeObjectView<V>) and HasObjectView<V>
+        requires(not SomeObjectView<V>) and HasObjectView<V> and (not std::is_const_v<V>)
     [[nodiscard]] std::expected<InputT, rpc::Status>
     parse(V& value) const
     {

tests/SpecCoreTests.cpp

@@ -1,4 +1,5 @@
 #include <boost/json/parse.hpp>
+#include <boost/json/value.hpp>
 
 #include <gtest/gtest.h>
 #include <rpcspec/Aliases.hpp>
@@ -24,6 +25,9 @@ using namespace rpc::spec;
 
 namespace {
 
+template <typename Spec, typename V>
+concept CanProcess = requires(Spec const& spec, V& value) { spec.process(value); };
+
 TEST(RpcSpecDSL, ValidRequestPasses)
 {
     static constexpr auto kSpec = RpcSpec{
@@ -153,6 +157,16 @@ TEST(RpcSpecDSL, VersionedSpecViaRpcSpecView)
     EXPECT_TRUE(spec(2).process(valid).has_value());
 }
 
+TEST(RpcSpecDSL, ProcessRejectsAConstDocument)
+{
+    static constexpr auto kSpec = RpcSpec{field("account", required, account)};
+
+    static_assert(CanProcess<decltype(kSpec), boost::json::value>);
+    static_assert(not CanProcess<decltype(kSpec), boost::json::value const>);
+    static_assert(CanProcess<RpcSpecView<ObjectView>, boost::json::value>);
+    static_assert(not CanProcess<RpcSpecView<ObjectView>, boost::json::value const>);
+}
+
 TEST(RpcSpecDSL_Override, ExtendingASpecCanOverrideAnExistingField)
 {
     // V1 requires the field to be a bool; V2 overrides the same key to require a string.

tests/SpecDefaultTests.cpp

@@ -1,4 +1,5 @@
 #include <boost/json/parse.hpp>
+#include <boost/json/value.hpp>
 
 #include <gtest/gtest.h>
 #include <rpcspec/Aliases.hpp>
@@ -48,8 +49,17 @@ parse(char const* json)
     return *result;
 }
 
+template <typename V>
+concept CanParse = requires(V& value) { kSpec.parse(value); };
+
 }  // namespace
 
+TEST(RpcSpecDSL_Default, ParseRejectsAConstDocument)
+{
+    static_assert(CanParse<boost::json::value>);
+    static_assert(not CanParse<boost::json::value const>);
+}
+
 TEST(RpcSpecDSL_Default, AbsentFieldReceivesSpecDefault)
 {
     auto const in = parse(R"JSON({})JSON");