Run GitHub actions also on pull requests

The push trigger didn't seem to work for PRs based in outside repos. So
limit the push trigger to master and next and enable a PR trigger.

protobuf-c.c: fix packed repeated bool parsing

protoc-c: add custom options support

protobuf-c: don't use ProtobufCWireType internally

protoc-c: fix shared lib build on windows, migrate from Travis CI to GitHub Actions

From https://developers.google.com/protocol-buffers/docs/proto3#updating:
  int32, uint32, int64, uint64, and bool are all compatible – this means
  you can change a field from one of these types to another without
  breaking forwards- or backwards-compatibility. If a number is parsed
  from the wire which doesn't fit in the corresponding type, you will
  get the same effect as if you had cast the number to that type in C++
  (e.g. if a 64-bit number is read as an int32, it will be truncated to
  32 bits).

Until this fix, protobuf-c did not conform to the rule above when it
came to deserializing non-boolean packed repeated data into a
protobuf_c_boolean array. Fully scan the varint and use parse_boolean to
truncate the resulting value.

Fixes #440

This option allows to override the top-level 'package' setting, or even
remove the package prefix altogether (if set to "").

Fixes #322

FullName* methods are designed to split a full name based on '.' in the
name. name() does not have '.' separators, so call CamelToLower and
CamelToUpper in place of FullNameToLower and FullNameToUpper.

Allows for generic oneof offset lookups based on the name of the oneof,
instead of having to know the field name. All oneof fields should have
the same offset, since they are members of a union.

Fixes #204

Keep default as false to preserve backwards compatibility.

Fixes #239

Allows treating proto strings as ProtobufCBinaryData to work around
limitations such as NULL characters in strings, which are allowed in
protobuf, but not allowed in 'char *' types.

Fixes #203

Fixes #287

Add options controller helper function generation. Preserve existing
behavior of not generating pack/unpack functions for sub-messages if
option is not explicitly set.

Fixes #240
Fixes #442

Allows suppression of .pb-c.{c,h} file generation on a .proto file
basis.

protobuf-c.proto: Use the new option in itself, because the options are
never used by protobuf-c runtime, only by the protoc-gen-c compiler.

t/test-full.proto: import protobuf-c.proto to test that
protobuf-c.pb-c.h dependency does not get included in test-full.pb-c.h.

We are now able to build against Mac and Windows.
But, mainly, see:
https://blog.travis-ci.com/2020-11-02-travis-ci-new-billing
https://docs.travis-ci.com/user/migrate/open-source-on-travis-ci-com/

Matches protobuf default behavior:
https://github.com/protocolbuffers/protobuf/tree/master/cmake#dlls-vs-static-linking

Bump min cmake version to use Protobuf_USE_STATIC_LIBS:
https://cmake.org/cmake/help/latest/module/FindProtobuf.html

MSVC has issues importing protobuf_c_empty_string from the DLL and using
it in initializers, resulting in errors like when linking against
protobuf-c.dll:
  test-proto3.pb-c.c(13): error C2099: initializer is not a constant
  test-proto3.pb-c.c(19): error C2440: 'initializing': cannot convert from 'void *' to 'Foo__Person__PhoneType'

Work around the issue by not exporting protobuf_c_empty string and
defining it as static const char[] in the protobuf-c.h file itself. This
change only applies to _WIN32 shared library builds.

This reverts commit 4c8043d0.

Fixes #458
Signed-off-by: Ilya Lipnitskiy <ilya.lipnitskiy@gmail.com>

protobuf-c parsing code operates on wire type as uint8_t, so keep it
defined as such to avoid confusion and unnecessary compiler warnings.

Avoid "unused function parameter" compiler warning

fix invalid unsigned arithmetic.

Install debug symbols alongside the protobuf-c.lib

A user of the protobuf-c library is confronted with MSVC warnings about missing
PDB if the library happens to be built/configured using the CMAKE_BUILD_TYPE
"Debug" or "RelWithDebInfo". This commit deals away with the warning by
installing the "protobuf-c.pdb" alongside the lib. The .pdb is installed only
if it exists. Configuring "Release" or building under Linux won't produce and
won't install the PDB.

Updated the generator to fully qualify std::string

The protobuf common.h header currently has a "using std::string;"
statement that pulls std::string into the google::protobuf namespace:
https://github.com/protocolbuffers/protobuf/blob/ce66f6047db44df3234bccd6fcf468bccc14a760/src/google/protobuf/stubs/common.h#L195

I plan to delete that line soon. To keep protobuf-c working, this commit
updates the generator to fully qualify std::string.

Travis CI: Test on other platforms

Travis CI now supports testing on arm64, ppc64le and s390x. It would
be nice to test on them.
Signed-off-by: Daniel Axtens <dja@axtens.net>

Bionic contains more recent compilers, which are required to have
the sanitisers work under s390x.

While we're at it, the 'sudo' key is deprecated, so remove it:

https://blog.travis-ci.com/2018-11-19-required-linux-infrastructure-migration

(It used to be used to mark VM vs docker container infrastructure,
but currently all amd64 builds run on VMs and all other archs run
inside LXD containers.)
Signed-off-by: Daniel Axtens <dja@axtens.net>

Pack nested messages inline

protoc-c: Remove leading underscores from structs

protobuf-c.c: Cast %lu args to unsigned long int