Contributing to FIDL

Overview

The FIDL toolchain is composed of roughly three parts:

1. Front-end, a.k.a. fidlc
   • Parses and validates .fidl files
   • Calculates size, alignment, and offset of various structures
   • Produces a JSON IR (Intermediate Representation)
2. Back-end
   • Works off the IR (except the C back-end)
   • Produces target language specific code, which ties into the libraries for that language
3. Runtime Libraries
   • Implement encoding/decoding/validation of messages
   • Method dispatching mechanics

Code Location

The front-end lives at //zircon/tools/fidl/, with tests in //zircon/system/utest/fidl/.

The back-end and runtime library locations are based on the target:

Target	Back-end	Runtime Libraries
C	//zircon/tools/fidl/lib/c_generator.cc	//zircon/system/ulib/fidl/
C++	//garnet/go/src/fidl/compiler/backend/cpp/	//zircon/system/ulib/fidl/ & //garnet/public/lib/fidl/cpp/
Go	//garnet/go/src/fidl/compiler/backend/golang/	//third_party/go/src/syscall/zx/fidl/
Rust	//garnet/go/src/fidl/compiler/backend/rust/	//garnet/public/lib/fidl/rust/fidl/
Dart	//topaz/bin/fidlgen_dart/	//topaz//public/dart/fidl/ //topaz/bin/fidl_bindings_test/
JavaScipt	chromium:build/fuchsia/fidlgen_fs	chromium:build/fuchsia/fidlgen_js/runtime

Other Tools

TBD: linter, formatter, gidl, difl, regen scripts, etc.

C++ Style Guide

We follow the Fuchsia C++ Style Guide, with additional rules to further remove ambiguity around the application or interpretation of guidelines.

Constructors

Always place the initializer list on a line below the constructor.

// Don't do this.
SomeClass::SomeClass() : field_(1), another_field_(2) {}

// Correct.
SomeClass::SomeClass()
    : field_(1), another_field_(2) {}

Comments

Comments must respect 80 columns line size limit, unlike code which can extend to 100 lines size limit.

Lambda captures

• If a lambda escapes the current scope, capture all variables explicitly.
• If the lambda is local (does not escape the current scope), prefer using a default capture by reference (“[&]”).

Seeing [&] is a strong signal that the lambda exists within the current scope only, and can be used to distinguish local from non-local lambdas.

// Correct.
std::set<const flat::Library*, LibraryComparator> dependencies;
auto add_dependency = [&](const flat::Library* dep_library) {
  if (!dep_library->HasAttribute("Internal")) {
    dependencies.insert(dep_library);
  }
};

General Setup

Fuchsia Setup

Read the Fuchsia Getting Started guide first.

fx set

fx set core.x64 --with //bundles:tests --with //topaz/packages/tests:all --with //sdk:modular_testing

or, to ensure there's no breakage with lots of bindings etc.:

fx set terminal.x64 --with //bundles:kitchen_sink --with //vendor/google/bundles:buildbot

symbolizer

To symbolize backtraces, you'll need a symbolizer in scope:

export ASAN_SYMBOLIZER_PATH="$FUCHSIA_DIR/prebuilt/third_party/clang/$HOST_PLATFORM/bin/llvm-symbolizer"

Compiling, and Running Tests

We provide mostly one-liners to run tests for the various parts. When in doubt, refer to the “Test:” comment in the git commit message; we do our best to describe the commands used to validate our work there.

fidlc

# optional; builds fidlc for the host with ASan <https://github.com/google/sanitizers/wiki/AddressSanitizer>
fx set core.x64 --variant=host_asan

# build fidlc
fx build zircon/tools

fidlc tests

fidlc tests are at:

• //zircon/system/utest/fidl-compiler/.
• //zircon/system/utest/fidl/.
• //zircon/system/utest/fidl-coding/tables/.

# build & run fidlc tests
fx build zircon/system/utest:host
$FUCHSIA_DIR/out/default.zircon/host-x64-linux-clang/obj/system/utest/fidl-compiler/fidl-compiler-test.debug

# build & run fidl-coding-tables tests
# --with-base puts all zircon tests under /boot with the bringup.x64 target, or /system when using the core.x64 target
fx set bringup.x64 --with-base //garnet/packages/tests:zircon   # optionally append "--variant asan"
fx build
fx run -k -c zircon.autorun.boot=/boot/bin/runtests+-t+fidl-coding-tables-test

To regenerate the FIDL definitions used in unit testing, run:

fx build zircon/tools
$FUCHSIA_DIR/out/default.zircon/tools/fidlc \
  --tables $FUCHSIA_DIR/zircon/system/utest/fidl/fidl/extra_messages.cc \
  --files $FUCHSIA_DIR/zircon/system/utest/fidl/fidl/extra_messages.test.fidl

fidlgen (LLCPP, HLCPP, Rust, Go)

Build:

fx build garnet/go/src/fidl

Run:

$FUCHSIA_DIR/out/default/host_x64/fidlgen

Some example tests you can run:

fx run-host-tests fidlgen_cpp_test
fx run-host-tests fidlgen_cpp_ir_test
fx run-host-tests fidlgen_golang_ir_test

To regenerate the goldens:

fx exec garnet/go/src/fidl/compiler/backend/typestest/regen.sh

fidlgen_dart

Some example tests you can run:

fx run-host-tests fidlgen_dart_backend_ir_test

To regenerate the goldens:

fx exec topaz/bin/fidlgen_dart/regen.sh

C runtime

fx set bringup.x64 --with-base //garnet/packages/tests:zircon
fx build
fx run -k -c zircon.autorun.boot=/boot/bin/runtests+-t+fidl-test

When the test completes, you're running in the QEMU emulator. To exit, use Ctrl-A x.

C++ runtime

You first need to have Fuchsia running in an emulator. Here are the steps:

Tab 1> fx build && fx serve-updates

Tab 2> fx run -kN

Tab 3> fx run-test fidl_tests

Go runtime

You first need to have Fuchsia running in an emulator. Here are the steps:

Tab 1> fx build && fx serve-updates

Tab 2> fx run -kN

Tab 3> fx run-test go_fidl_tests

As with normal Go tests, you can pass various flags to control execution, filter test cases, run benchmarks, etc. For instance:

Tab 3> fx run-test go_fidl_tests -- -test.v -test.run 'TestAllSuccessCases/.*xunion.*'

Rust runtime

You first need to have Fuchsia running in an emulator. Here are the steps:

Tab 1> fx build && fx serve-updates

Tab 2> fx run -kN

Tab 3> fx run-test rust_fidl_tests

Dart runtime

The Dart FIDL bindings tests are in //topaz/bin/fidl_bindings_test/.

You first need to have Fuchsia running in an emulator. Here are the steps:

Tab 1> fx build && fx serve-updates

Tab 2> fx run -kN

Tab 3> fx run-test fidl_bindings_test

Compatibility Test

The language bindings compatibility test is located in //topaz/bin/fidl_compatibility_test, and is launched from a shell script.

To build this test, use:

fx build topaz/bin/fidl_compatibility_test/dart:fidl_compatibility_test_server_dart

To run this test, you first need to have a Fuchsia instance running in an emulator:

fx run -N

Then, copy the script to the device, and run it:

fx cp `find topaz -name run_fidl_compatibility_test_topaz.sh` /tmp/
fx shell /tmp/run_fidl_compatibility_test_topaz.sh

All Tests

Name	Test Command	Directories Covered
gidl parser	fx run-host-tests gidl_parser_test	tools/fidl/gidl/parser
fidlgen hlcpp	fx run-host-tests fidlgen_cpp_test	garnet/go/src/fidl/compiler/backend/cpp
fidlgen hlcpp ir	fx run-host-tests fidlgen_cpp_ir_test	garnet/go/src/fidl/compiler/backend/cpp/ir
fidlgen llcpp	fx run-host-tests fidlgen_llcpp_test	garnet/go/src/fidl/compiler/llcpp_backend
fidlgen overnet	fx run-host-tests fidlgen_cpp_overnet_internal_test	garnet/go/src/fidl/compiler/backend/cpp_overnet_internal
fidlgen golang	fx run-host-tests fidlgen_golang_test	garnet/go/src/fidl/compiler/backend/golang
fidlgen golang ir	fx run-host-tests fidlgen_golang_ir_test	garnet/go/src/fidl/compiler/backend/golang/ir
fidlgen rust	fx run-host-tests fidlgen_rust_test	garnet/go/src/fidl/compiler/backend/rust
fidlgen rust ir	fx run-host-tests fidlgen_rust_ir_test	garnet/go/src/fidl/compiler/backend/rust/ir
fidlgen syzkaller	fx run-host-tests fidlgen_syzkaller_test	garnet/go/src/fidl/compiler/backend/syzkaller
fidlgen syzkaller ir	fx run-host-tests fidlgen_syzkaller_ir_test	garnet/go/src/fidl/compiler/backend/syzkaller/ir
fidlgen type definitions	fx run-host-tests fidlgen_types_test	garnet/go/src/fidl/compiler/backend/types
c++ bindings tests	fx run-test fidl_tests	sdk/lib/fidl
go bindings tests	fx run-test go_fidl_tests	third_party/go/syscall/zx/fidl third_party/go/syscall/zx/fidl/fidl_test
dart bindings tests	fx run-test fidl_bindings_test	topaz/public/dart/fidl
rust bindings	fx run-test rust_fidl_tests

The following requires: fx set bringup.x64 --with-base //garnet/packages/tests:zircon

Name	Test Command	Directories Covered
fidlc host test	$FUCHSIA_DIR/out/default.zircon/host-x64-linux-clang/obj/system/utest/fidl-compiler/fidl-compiler-test.debug	zircon/system/host/fidl
fidl coding tables test	fx run -k -c zircon.autorun.boot=/boot/bin/runtests+-t+fidl-coding-tables-test	zircon/system/host/fidl
fidl c runtime test	fx run -k -c zircon.autorun.boot=/boot/bin/runtests+-t+fidl-test	zircon/system/ulib/fidl
fidl c-llcpp interop test	fx run -k -c zircon.autorun.boot=/boot/bin/runtests+-t+fidl-llcpp-interop-test	zircon/system/ulib/fidl

All Regen Commands

Name	Regen Commands	Input	Output
fidlgen goldens	fx exec $FUCHSIA_DIR/garnet/go/src/fidl/compiler/backend/typestest/regen.sh	garnet/go/src/fidl/compiler/backend/goldens	garnet/go/src/fidl/compiler/backend/goldens
dart fidlgen goldens	fx exec $FUCHSIA_DIR/topaz/bin/fidlgen_dart/regen.sh	garnet/go/src/fidl/compiler/backend/goldens	topaz/bin/fidlgen_dart/goldens
gidl conformance test generation	fx exec $FUCHSIA_DIR/tools/fidl/gidl-conformance-suite/regen.sh	tools/fidl/gidl-conformance-suite	third_party/go/src/syscall/zx/fidl/conformance/impl.go third_party/go/src/syscall/zx/fidl/fidl_test/conformance_test.go sdk/lib/fidl/cpp/conformance_test.cc topaz/bin/fidl_bindings_test/test/test/conformance_test_types.dart topaz/bin/fidl_bindings_test/test/test/conformance_test.dart
dangerous identifiers	garnet/tests/fidl-dangerous-identifiers/generate.py	garnet/tests/fidl-dangerous-identifiers/dangerous_identifiers.txt	garnet/tests/fidl-dangerous-identifiers/cpp/ garnet/tests/fidl-dangerous-identifiers/fidl/
regen third party go	fx exec $FUCHSIA_DIR/third_party/go/regen-fidl

Workflows

Language evolutions

One common task is to evolve the language, or introduce stricter checks in fidlc. These changes typically follow a three phase approach:

1. Write the new compiler code in fidlc;
2. Use this updated fidlc to compile all layers, including vendor/google, make changes as needed;
3. When all is said and done, the fidlc changes can finally be merged.

All of this assumes that (a) code which wouldn't pass the new checks, or (b) code that has new features, is not introduced concurrently between step 2 and step 3. That typically is the case, however, it is ok to deal with breaking rollers once in a while.

Go fuchsia.io and fuchsia.net

To update all the saved fidlgen files, run the following command, which automatically searches for and generates the necessary go files:

fx exec third_party/go/regen-fidl

FAQs

Why is the C back-end different than all other back-ends?

TBD

Why is fidlc in the zircon repo?

TBD

Why aren't all back-ends in one tool?

We'd actually like all back-ends to be in separate tools!

Down the road, we plan to have a script over all the various tools (fidlc, fidlfmt, the various back-ends) to make all things accessible easily, and manage the chaining of these things. For instance, it should be possible to generate Go bindings in one command such as:

fidl gen --library my_library.fidl --binding go --out-dir go/src/my/library

Or format a library in place with:

fidl fmt --library my_library.fidl -i