* [xDS Proto] Modernize buildgen scripts
* This PR only covers some buildgen scripts that will be used by xDS
proto
* This PR also improves the debuggability of some scripts
* Merge with master
* Adopt reviewer's advices
* Ran `2to3` on `tools/buildgen` and the `gen_build_yaml.py` files.
* Updated the invocations of python to be explicitly Python 3.
* Changed the loader in `mako_renderer.py` to allow pickle to find the module for pickling `external_version.Version`
* Added a few open-as-binary to placate readers/writers expecting bytes.
* Hand tweaked the templates to remove `iteritems` and fiddle with encodings.
Partially addresses #24359.
All these changes need to go together to make sense
- changes to use new version of upb in bazel
- allowing includes in build target option
- script for generating c code (upb) for protos
- generated code for example protos
- adding changes for non-bazel builds
- change sanity tests to ignore the generated files.
protos
All these changes need to go together to make sense
- changes to use new version of upb in bazel
- allowing includes in build target option
- script for generating c code for protos
- generated code for example build
- adding changes for non-bazel builds
- change sanity tests to ignore the generated files.
- make the directory structure match the package structure
- sanitize the package structure (test --> testing)
- add auto-detection of proto file dependencies