The CMake module is used by default but isn't compatible with
recent protobuf version.

Try to first look for a protobuf config then fallback to legacy
cmake module.
Signed-off-by: Clément Péron <peron.clem@gmail.com>

protobuf_c_message_unpack(): Fix memory corruption by initializing unknown_fields pointer

The canonical doman is no longer dot-io, though both work.

Makefile.am: Distribute missing Config.cmake.in

CMakeLists.txt: Remove double hyphens

A memory corruption in protobuf_c_message_free_unpacked happens at the
following line:

        if (message->unknown_fields != NULL)
                do_free(allocator, message->unknown_fields);

The do_free will free ->unknown_fields. This is may be wrong, because
protobuf_c_message_unpack uses malloc as the default allocator, allocates
rv with malloc. At the end, however, ->unknown_fields is only initialized
if there are some. That means if there are no such fields ->unknown_fields
is an uninitialized pointer.

The patch initializes the pointer to NULL to ensure the check before free
is performed on initialized memory in case there is no unknown_field.

This fixes https://github.com/protobuf-c/protobuf-c/issues/690Signed-off-by: Stephan Mueller <smueller@chronox.de>

Closes: https://github.com/protobuf-c/protobuf-c/issues/698

Otherwise cmake won't reconize the command.

With double hyphens:
```
$ cmake -E env TESTENV=value -- env | grep TESTENV
cmake -E env: unknown option '--'
```

Without double hyphens:
```
$ cmake -E env TESTENV=value env | grep TESTENV
TESTENV=value
```

[edmonds: Adjust commit message.]

Fixing MSVC build for Msbuild and Makefile generators

Signed-off-by: Guybrush <miguel.barro@live.com>

Signed-off-by: Guybrush <miguel.barro@live.com>

Led to some fixes in the CMake too.
Signed-off-by: Guybrush <miguel.barro@live.com>

Signed-off-by: MiguelBarro <miguelbarro@eprosima.com>

Signed-off-by: MiguelBarro <miguelbarro@eprosima.com>

Silence some compiler diagnostics

This file uses declarations after statements and fixing it would make
the code less readable, so silence this particular diagnostic in this
particular file.

This diagnostic isn't particularly useful since it fires on generated
.pb-c.h files.

Remove protobuf 2.x support

Since we now require protobuf >= 3.0.0, we don't have to support older
protobuf versions that don't recognize the `syntax` syntax, so we can
put `syntax = "proto2";` on these proto files to silence the protoc
compiler's diagnostic "No syntax specified for the proto file".

Now that we require protobuf >= 3.0.0, we are always building with
proto3 syntax support.

Note that the test-generated-code3 test keeps `-DPROTO3` which is
separate from the HAVE_PROTO3 identifier. This test is building built
from the same source file as test-generated-code but the source file
supports proto2 and proto3 syntax depending on how it's compiled.

Since we require protobuf >= 3.0.0 now, the proto3 syntax is always
supported.

Miscellaneous fixes

Since this case immediately returns, the `rv` variable is not used.

See https://github.com/protobuf-c/protobuf-c/issues/517.

`*pstr != NULL` was already checked here.

See https://github.com/protobuf-c/protobuf-c/issues/517.

Apparently in some cases the protobuf compiler is unable to find its own
files, and this fix has been reported to work.

See https://github.com/protobuf-c/protobuf-c/issues/491.

Signed-off-by: Daniel Egger <daniel@eggers-club.de>

[edmonds: From https://github.com/protobuf-c/protobuf-c/pull/523.]

[edmonds: Adjust find string from "0 |" to "0 | ", test against `== 0`
rather than `!= std::string::npos` so that the find/erase calls are
anchored to the same portion of the string.]

This commit updates a few tests where we aren't using the correct C
signature for main() or are not using any of its parameters (in the
case of t/version/version.c.)

This commit fixes the following compiler diagnostics:

    ../protoc-c/c_helpers.cc: In function ‘void google::protobuf::compiler::c::PrintComment(google::protobuf::io::Printer*, std::__cxx11::string)’:
    ../protoc-c/c_helpers.cc:221:25: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::vector<std::__cxx11::basic_string<char> >::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
           for (int i = 0; i < comment_lines.size(); i++)
                           ~~^~~~~~~~~~~~~~~~~~~~~~
    ../protoc-c/c_helpers.cc: In function ‘std::set<std::__cxx11::basic_string<char> > google::protobuf::compiler::c::MakeKeywordsMap()’:
    ../protoc-c/c_helpers.cc:273:21: warning: comparison of integer expressions of different signedness: ‘int’ and ‘long unsigned int’ [-Wsign-compare]
       for (int i = 0; i < GOOGLE_ARRAYSIZE(kKeywordList); i++) {
                         ^

Support for new Google protobuf 22.x, 23.x releases

There are some recent reports of strange build failures that might have
been fixed by compiling in C++17 mode, so it might be a good idea to use
C++17 in general, and not just when building against very recent
protobuf versions.

Since it looks like we've lost protobuf < 3.0.0 support, configure.ac
can be simplified a bit if we just use C++17 by default.