external/protobuf: Correct depfile generation when there are no outputs

Prevents the compiler from generating a malformed depfile if an input file
did not lead to any meaningful generation. This is an edge case that is
not exercised often.

I discovered `protoc` outputs a malformed depfile if you run it on a
`proto` file that has no associated `output_filenames`. This was found
using the Android Soong `"grpc-java-plugin"` proto generation plugin
that only outputs a gRPC Java source if the input `proto` has a
`service` definition. Reasonably, there could be shared proto files that
get invoked for gRPC generation that are meant as shared types for
`service` files, but do not define one themselves. There is a workaround
to edit `srcs` passed to Soong, but this removes that requirement.

Cherry picked from upstream: https://github.com/protocolbuffers/protobuf/commit/a44fc2b063d7466d48e2aeba05f9c35654140d87

Test: Built using `lunch aosp_arm-eng; m`.
Bug: b/287536219
Change-Id: I623ba695b9d1ef955f73599f65c4b695c70e7630
1 file changed
tree: 92befe4ac0504e525e215d9771a547b164e13c23
  1. .github/
  2. android/
  3. benchmarks/
  4. build_defs/
  5. cmake/
  6. config/
  7. conformance/
  8. csharp/
  9. docs/
  10. editors/
  11. examples/
  12. java/
  13. javamicro/
  14. javanano/
  15. kokoro/
  16. objectivec/
  17. php/
  18. pkg/
  19. protoc-artifacts/
  20. python/
  21. ruby/
  22. src/
  23. third_party/
  24. toolchain/
  25. util/
  26. .bazelignore
  27. .gitignore
  28. .gitmodules.disabled
  29. .readthedocs.yml
  30. Android.bp
  31. appveyor.bat
  32. appveyor.yml
  33. autogen.sh
  34. BUILD.bazel
  35. build.gradle
  36. build_files_updated_unittest.sh
  37. CHANGES.txt
  38. CleanSpec.mk
  39. CMakeLists.txt
  40. configure.ac
  41. CONTRIBUTING.md
  42. CONTRIBUTORS.txt
  43. fix_permissions.sh
  44. generate_changelog.py
  45. generate_descriptor_proto.sh
  46. global.json
  47. LICENSE
  48. Makefile.am
  49. maven_install.json
  50. METADATA
  51. MODULE_LICENSE_BSD
  52. OWNERS
  53. post_process_dist.sh
  54. Protobuf-C++.podspec
  55. protobuf-lite.pc.in
  56. protobuf.bzl
  57. protobuf.pc.in
  58. Protobuf.podspec
  59. protobuf_deps.bzl
  60. protobuf_release.bzl
  61. protobuf_version.bzl
  62. README.android
  63. README.md
  64. SECURITY.md
  65. TEST_MAPPING
  66. tests.sh
  67. update_compatibility_version.py
  68. update_file_lists.sh
  69. update_version.py
  70. vendor_suffix_test.config
  71. vendor_suffix_test.cpp
  72. version.json
  73. WORKSPACE
README.md

Protocol Buffers - Google's data interchange format

Copyright 2008 Google Inc.

https://developers.google.com/protocol-buffers/

Overview

Protocol Buffers (a.k.a., protobuf) are Google's language-neutral, platform-neutral, extensible mechanism for serializing structured data. You can find protobuf's documentation on the Google Developers site.

This README file contains protobuf installation instructions. To install protobuf, you need to install the protocol compiler (used to compile .proto files) and the protobuf runtime for your chosen programming language.

Protocol Compiler Installation

The protocol compiler is written in C++. If you are using C++, please follow the C++ Installation Instructions to install protoc along with the C++ runtime.

For non-C++ users, the simplest way to install the protocol compiler is to download a pre-built binary from our release page:

https://github.com/protocolbuffers/protobuf/releases

In the downloads section of each release, you can find pre-built binaries in zip packages: protoc-$VERSION-$PLATFORM.zip. It contains the protoc binary as well as a set of standard .proto files distributed along with protobuf.

If you are looking for an old version that is not available in the release page, check out the maven repo here:

https://repo1.maven.org/maven2/com/google/protobuf/protoc/

These pre-built binaries are only provided for released versions. If you want to use the github main version at HEAD, or you need to modify protobuf code, or you are using C++, it's recommended to build your own protoc binary from source.

If you would like to build protoc binary from source, see the C++ Installation Instructions.

Protobuf Runtime Installation

Protobuf supports several different programming languages. For each programming language, you can find instructions in the corresponding source directory about how to install protobuf runtime for that specific language:

LanguageSource
C++ (include C++ runtime and protoc)src
Javajava
Pythonpython
Objective-Cobjectivec
C#csharp
Rubyruby
Goprotocolbuffers/protobuf-go
PHPphp
Dartdart-lang/protobuf

Quick Start

The best way to learn how to use protobuf is to follow the tutorials in our developer guide:

https://developers.google.com/protocol-buffers/docs/tutorials

If you want to learn from code examples, take a look at the examples in the examples directory.

Documentation

The complete documentation for Protocol Buffers is available via the web at:

https://developers.google.com/protocol-buffers/