HLCPP object pretty printing
Prequisites
This tutorial builds on the Compiling FIDL tutorial. For the full set of FIDL tutorials, refer to the overview.
Overview
This tutorial walks through how to add debug printing to HLCPP types, using the
fostr
tool.
If you want to write the code yourself, delete the following directories:
rm -r examples/fidl/hlcpp/fostr farnet/public/lib/fostr/fidl
This tutorial contains the following steps:
- Define a
fostr_fidl
target for a FIDL library. This will allow debug printing for types in the library by defining anoperator<<
for each type. - Use the
fostr_fidl
target. - Write examples with the formatter code.
Define fostr_fidl target
Create a directory for the BUILD file inside
//garnet/public/lib/fostr/fidl
:mkdir -p garnet/public/lib/fostr/fidl/fuchsia.examples
Create the BUILD file:
touch garnet/public/lib/fostr/fidl/fuchsia.examples/BUILD.gn
Add the following definition to the build file:
{%includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="garnet/public/lib/fostr/fidl/fuchsia.examples/BUILD.gn" %}
This defines a fostr
target for the fuchsia.examples
library. Any
dependencies to the library needs to be specified in the build file as well,
which doesn’t apply to this tutorial as it has no dependencies. For more complex
examples, refer to the existing definitions in the fostr fidl
directory.
Add a dependency on the fostr_fidl target
The target library that the tutorial uses is a simple host test, which is
located in examples/fidl/hlcpp/fostr
. Notice that the BUILD file for the test
includes the fostr_fidl
target as a dependency:
{%includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/fidl/hlcpp/fostr/BUILD.gn" region_tag="bin" highlight="7" %}
The included library automatically overloads the <<
operator. The path
is based on the name of the FIDL library it is generated for:
{%includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/fidl/hlcpp/fostr/main.cc" region_tag="includes" %}
Write examples using the formatter code
Write some placeholder tests to show off the output:
{%includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="examples/fidl/hlcpp/fostr/main.cc" region_tag="tests" %}
Run the example
To run the example:
Configure the GN build to include the example:
fx set core.x64 --with //examples/fidl/hlcpp/fostr
Run the test:
fx test -vo fostr-example-test