commit f56d15c2f320a6046ae7eab91c2e4fc6cf88f330
author Mitchell Kember <mkember@google.com> Wed May 27 23:03:21 2020 +0000
committer CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org> Wed May 27 23:03:21 2020 +0000
tree 37c1b6ab2cfeaa6e9d8b5d0ed7c7724064c56772
parent 370943b6ecd09869ca7647e9964aa3c24bcf4bfa

[fidlgen_rust] Default implementations for transitional methods

This CL makes fidlgen_rust emit default implementations for
ProxyInterface methods if their corresponding FIDL protocol method is
marked [Transitional]. This makes it possible to add methods in a soft
transition without breaking uses of the ProxyInterface traits.

Context: If you have a FIDL protocol called Foo, the Rust bindings will
have a trait FooProxyInterface and a struct FooProxy implementing the
trait, which clients use to make async requests. Sometimes people will
implement FooProxyInterface for their own types, e.g. for FakeFooProxy
in unit tests. With this change, FakeFooProxy would continue to compile
if you add a transitional method to Foo.

The default implementations call unimplemented!(), which panics. They do
this, rather than e.g. returning a new fidl::Error variant, because
calling one of these methods is always a programmer error, not something
that makes sense to recover from.

In addition, this CL fixes the command for regenerating fidldoc goldens
in contributing_to_fidl.md and fidldoc/README.md:

* It must be invoked as host_x64/fidldoc_bin_test, not fidldoc_bin_test
* Must append -- golden_test, not --golden_test
* The REGENERATE_GOLDENS_FOLDER variable must be set to a particular
  value, not the unspecified value $FOLDER

Test: fx test host_x64/fidlgen_rust_test
Fixed: 52607
Change-Id: Ifa1b10149e583401f20e1eefcda99443f554961b
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/392258
Commit-Queue: Mitchell Kember <mkember@google.com>
Reviewed-by: Pascal Perez <pascallouis@google.com>
Reviewed-by: Felix Zhu <fcz@google.com>
Testability-Review: Felix Zhu <fcz@google.com>