[capnproto] Compilation failure with JsonCodec

[Krzysztof Sakrejda]

I'm looking for a suggestion about where to look next for fixing this
issue. With these three lines I get a compilation failure:

capnp::JsonCodec json;
capnp::SegmentArrayMessageReader reader(builder.getSegmentsForOutput());
kj::String json_encoded = json.encode(reader);


The failure is on the third line, I'm failing to see if I did something
wrong or if there are caveats to the JSON
encode function that I'm missing. These are schema I can already write out
to a binary stream successfully and
read back so I think those are ok.

Here's the compiler message:

[ 83%] Building CXX object src/capnstan/CMakeFiles/config_writer.dir/
config_writer.cpp.o
In file included from /home/krzysztof/packages/capnStan/downloads/capnproto-
c++/src/capnp/raw-schema.h:29:0,
from /home/krzysztof/packages/capnStan/capnStan/../
downloads/capnproto-c++/src/capnp/generated-header-support.h:31,
from /home/krzysztof/packages/capnStan/capnStan/src/capnp/
stan-config.capnp.h:7,
from /home/krzysztof/packages/capnStan/capnStan/src/
capnstan/config_switch.hpp:34,
from /home/krzysztof/packages/capnStan/capnStan/src/
capnstan/config_writer.cpp:1:
/home/krzysztof/packages/capnStan/downloads/capnproto-c++/src/capnp/common.h
: In substitution of ‘template<class T> using FromAny = typename capnp::
FromAny_<T>::Type [with T = kj::Decay_<capnp::SegmentArrayMessageReader&>::
Type]’:
/home/krzysztof/packages/capnStan/capnStan/../downloads/capnproto-c++/src/
capnp/compat/json.h:215:33: required from ‘kj::String capnp::JsonCodec::
encode(T&&) [with T = capnp::SegmentArrayMessageReader&]’
/home/krzysztof/packages/capnStan/capnStan/src/capnstan/config_writer.cpp:26
:51: required from here
/home/krzysztof/packages/capnStan/downloads/capnproto-c++/src/capnp/common.h
:290:43: error: invalid use of incomplete type ‘struct capnp::FromAny_<capnp
::SegmentArrayMessageReader, void>’
using FromAny = typename FromAny_<T>::Type;
^
/home/krzysztof/packages/capnStan/downloads/capnproto-c++/src/capnp/common.h
:256:8: note: declaration of ‘struct capnp::FromAny_<capnp::
SegmentArrayMessageReader, void>’
struct FromAny_;
^~~~~~~~

['Kenton Varda' via Cap'n Proto]

Hi Krzystof,

The parameter to encode() should be a specific typed Reader, not a
MessageReader. So, something like:

capnp::JsonCodec json;
kj::String json_encoded = json.encode(builder.getRoot<
MyStructType>().asReader());

-Kenton

On Thu, Mar 1, 2018 at 1:50 PM, Krzysztof Sakrejda <

Post by Krzysztof Sakrejda
I'm looking for a suggestion about where to look next for fixing this
capnp::JsonCodec json;
capnp::SegmentArrayMessageReader reader(builder.getSegmentsForOutput
());
kj::String json_encoded = json.encode(reader);
The failure is on the third line, I'm failing to see if I did something
wrong or if there are caveats to the JSON
encode function that I'm missing. These are schema I can already write
out to a binary stream successfully and
read back so I think those are ok.
[ 83%] Building CXX object src/capnstan/CMakeFiles/config_writer.dir/
config_writer.cpp.o
In file included from /home/krzysztof/packages/capnStan/downloads/
capnproto-c++/src/capnp/raw-schema.h:29:0,
from /home/krzysztof/packages/capnStan/capnStan/../
downloads/capnproto-c++/src/capnp/generated-header-support.h:31,
from /home/krzysztof/packages/capnStan/capnStan/src/capnp
/stan-config.capnp.h:7,
from /home/krzysztof/packages/capnStan/capnStan/src/
capnstan/config_switch.hpp:34,
from /home/krzysztof/packages/capnStan/capnStan/src/
/home/krzysztof/packages/capnStan/downloads/capnproto-c++/src/capnp/common
FromAny_<T>::Type [with T = kj::Decay_<capnp::SegmentArrayMessageReader
/home/krzysztof/packages/capnStan/capnStan/../downloads/capnproto-c++/src/
encode(T&&) [with T = capnp::SegmentArrayMessageReader&]’
26:51: required from here
/home/krzysztof/packages/capnStan/downloads/capnproto-c++/src/capnp/common
.h:290:43: error: invalid use of incomplete type ‘struct capnp::FromAny_<
capnp::SegmentArrayMessageReader, void>’
using FromAny = typename FromAny_<T>::Type;
^
/home/krzysztof/packages/capnStan/downloads/capnproto-c++/src/capnp/common
.h:256:8: note: declaration of ‘struct capnp::FromAny_<capnp::Segment
ArrayMessageReader, void>’
struct FromAny_;
^~~~~~~~
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[Krzysztof Sakrejda]

That makes the "incomplete type" message make a lot of sense, thanks! K

Post by 'Kenton Varda' via Cap'n Proto
Hi Krzystof,
The parameter to encode() should be a specific typed Reader, not a
capnp::JsonCodec json;
kj::String json_encoded =
json.encode(builder.getRoot<MyStructType>().asReader());
-Kenton

Post by Krzysztof Sakrejda
I'm looking for a suggestion about where to look next for fixing this
capnp::JsonCodec json;
capnp::SegmentArrayMessageReader reader(builder.getSegmentsForOutput
());
kj::String json_encoded = json.encode(reader);
The failure is on the third line, I'm failing to see if I did something
wrong or if there are caveats to the JSON
encode function that I'm missing. These are schema I can already write
out to a binary stream successfully and
read back so I think those are ok.
[ 83%] Building CXX object src/capnstan/CMakeFiles/config_writer.dir/
config_writer.cpp.o
In file included from /home/krzysztof/packages/capnStan/downloads/
capnproto-c++/src/capnp/raw-schema.h:29:0,
from /home/krzysztof/packages/capnStan/capnStan/../
downloads/capnproto-c++/src/capnp/generated-header-support.h:31,
from /home/krzysztof/packages/capnStan/capnStan/src/
capnp/stan-config.capnp.h:7,
from /home/krzysztof/packages/capnStan/capnStan/src/
capnstan/config_switch.hpp:34,
from /home/krzysztof/packages/capnStan/capnStan/src/
/home/krzysztof/packages/capnStan/downloads/capnproto-c++/src/capnp/
common.h: In substitution of ‘template<class T> using FromAny = typename
/home/krzysztof/packages/capnStan/capnStan/../downloads/capnproto-c++/src
/capnp/compat/json.h:215:33: required from ‘kj::String capnp::JsonCodec
::encode(T&&) [with T = capnp::SegmentArrayMessageReader&]’
/home/krzysztof/packages/capnStan/capnStan/src/capnstan/config_writer.cpp
:26:51: required from here
/home/krzysztof/packages/capnStan/downloads/capnproto-c++/src/capnp/
FromAny_<capnp::SegmentArrayMessageReader, void>’
using FromAny = typename FromAny_<T>::Type;
^
/home/krzysztof/packages/capnStan/downloads/capnproto-c++/src/capnp/
SegmentArrayMessageReader, void>’
struct FromAny_;
^~~~~~~~
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