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- Code of Conduct
- Filing an Issue
- Looking to Start Contributing to
bindgen
? - Building
- Testing
- Code Overview
- Pull Requests and Code Reviews
- Generating Graphviz Dot Files
- Debug Logging
- Using
creduce
to Minimize Test Cases
We abide by the Rust Code of Conduct and ask that you do as well.
Think you've found a bug? File an issue! To help us understand and reproduce the issue, provide us with:
- A (preferably reduced) C/C++ header file that reproduces the issue
- The
bindgen
flags used to reproduce the issue with the header file - The expected
bindgen
output - The actual
bindgen
output - The debugging logs generated when running
bindgen
on this testcase
- Issues labeled "easy"
- Issues labeled "less easy"
- Issues labeled "help wanted"
- Still can't find something to work on? Drop a comment here
To build the bindgen
library and the bindgen
executable:
$ cargo build
If you installed multiple versions of llvm, it may not be able to locate the latest version of libclang. In that case, you may want to either uninstall other versions of llvm, or specify the path of the desired libclang explicitly:
$ export LIBCLANG_PATH=path/to/clang-9.0/lib
Additionally, you may want to build and test with the testing_only_docs
feature to ensure that you aren't forgetting to document types and functions. CI
will catch it if you forget, but the turn around will be a lot slower ;)
$ cargo build --features testing_only_docs
Input C/C++ test headers reside in the tests/headers
directory. Expected
output Rust bindings live in tests/expectations/tests
. For example,
tests/headers/my_header.h
's expected generated Rust bindings would be
tests/expectations/tests/my_header.rs
.
There are also some integration tests in the ./bindgen-integration
crate, which uses bindgen
to
generate bindings to some C++ code, and then uses the bindings, asserting that
values are what we expect them to be, both on the Rust and C++ side.
The generated and expected bindings are run through rustfmt
before they are
compared. Make sure you have rustfmt
up to date:
$ rustup update nightly
$ rustup component add rustfmt --toolchain nightly
Note: running cargo test
from the root directory of bindgen
's repository does not
automatically test the generated bindings or run the integration tests.
These steps must be performed manually when needed.
To regenerate bindings from the corpus of test headers in tests/headers
and
compare them against the expected bindings in tests/expectations/tests
, run:
$ cargo test
As long as you aren't making any changes to bindgen
's output, running this
should be sufficient to test your local modifications.
You may set the BINDGEN_OVERWRITE_EXPECTED
environment variable to overwrite
the expected bindings with bindgen
's current output:
$ BINDGEN_OVERWRITE_EXPECTED=1 cargo test
If you set the BINDGEN_TESTS_DIFFTOOL environment variable, cargo test
will
execute $BINDGEN_TESTS_DIFFTOOL /path/of/expected/output /path/of/actual/output
when the expected output differs from the actual output. You can use this to
hand check differences by setting it to e.g. "meld" (assuming you have meld
installed).
If you're not changing command line arguments, you may want to set
BINDGEN_DISABLE_ROUNDTRIP_TEST
to avoid a lot of tests for round-tripping of
those.
If your local changes are introducing expected modifications in the
tests/expectations/tests/*
bindings files, then you should test that the
generated bindings files still compile, and that their struct layout tests still
pass. Also, run the integration tests (see below).
You can do this with these commands:
$ cd tests/expectations
$ cargo test
Sometimes its useful to work with one test header from start (generating
bindings for it) to finish (compiling the bindings and running their layout
tests). This can be done with the tests/test-one.sh
script. It supports fuzzy
searching for test headers. For example, to test
tests/headers/what_is_going_on.hpp
, execute this command:
$ ./tests/test-one.sh going
Note that test-one.sh
does not recompile bindgen
, so if you change the code,
you'll need to rebuild it before running the script again.
To add a new test header to the suite, simply put it in the tests/headers
directory. Next, run bindgen
to generate the initial expected output Rust
bindings. Put those in tests/expectations/tests
.
If your new test requires certain flags to be passed to bindgen
, you can
specify them at the top of the test header, with a comment like this:
new_test_header.hpp
:
// bindgen-flags: --enable-cxx-namespaces -- -std=c++14
Then verify the new Rust bindings compile and pass their layout tests:
$ cd tests/expectations
$ cargo test new_test_header
If a test generates different bindings across different libclang
versions (for
example, because we take advantage of better/newer APIs when possible), then you
can add multiple test expectations, one for each supported libclang
version. Instead of having a single tests/expectations/tests/my_test.rs
file,
add each of:
tests/expectations/tests/libclang-9/my_test.rs
tests/expectations/tests/libclang-5/my_test.rs
If you need to update the test expectations for a test file that generates
different bindings for different libclang
versions, you don't need to have
many version of libclang
installed locally. Just make a work-in-progress pull
request, and then when Travis CI fails, it will log a diff of the
expectations. Use the diff to patch the appropriate expectation file locally and
then update your pull request.
Usually, bindgen
's test runner can infer which version of libclang
you
have. If for some reason it can't, you can force a specific libclang
version
to check the bindings against with a cargo feature:
$ cargo test --features testing_only_libclang_$VERSION
Where $VERSION
is one of:
4
3_9
3_8
depending on which version of libclang
you have installed.
The ./bindgen-integration
crate uses bindgen
to
generate bindings to some C++ code, and then uses the bindings, asserting that
values are what we expect them to be, both on the Rust and C++ side.
To run the integration tests, issue the following:
$ cd bindgen-integration
$ cargo test
We <3 finding hidden bugs and the people who help us find them! One way to help
uncover hidden bugs is by running csmith
to generate random headers to test
bindgen
against.
See ./csmith-fuzzing/README.md for details.
The tests/quickchecking
crate generates property tests for bindgen
.
From the crate's directory you can run the tests with cargo run
. For details
on additional configuration including how to preserve / inspect the generated
property tests, see
./tests/quickchecking/README.md.
bindgen
takes C and C++ header files as input and generates corresponding Rust
#[repr(C)]
type definitions and extern
foreign function declarations.
First, we use libclang
to parse the input headers. See src/clang.rs
for our
Rust-y wrappers over the raw C libclang
API that the clang-sys
crate
exposes. We walk over libclang
's AST and construct our own internal
representation (IR). The ir
module and submodules (src/ir/*
) contain the IR
type definitions and libclang
AST into IR parsing code.
The umbrella IR type is the Item
. It contains various nested enum
s that let
us drill down and get more specific about the kind of construct that we're
looking at. Here is a summary of the IR types and their relationships:
Item
contains:- An
ItemId
to uniquely identify it. - An
ItemKind
, which is one of:- A
Module
, which is originally a C++ namespace and becomes a Rust module. It contains the set ofItemId
s ofItem
s that are defined within it. - A
Type
, which contains:- A
Layout
, describing the type's size and alignment. - A
TypeKind
, which is one of:- Some integer type.
- Some float type.
- A
Pointer
to another type. - A function pointer type, with
ItemId
s of its parameter types and return type. - An
Alias
to another type (typedef
orusing X = ...
). - A fixed size
Array
ofn
elements of another type. - A
Comp
compound type, which is either astruct
,class
, orunion
. This is potentially a template definition. - A
TemplateInstantiation
referencing some template definition and a set of template argument types. - Etc...
- A
- A
Function
, which contains:- An ABI
- A mangled name
- a
FunctionKind
, which describes whether this function is a plain function, method, static method, constructor, destructor, etc. - The
ItemId
of its function pointer type.
- A
Var
representing a static variable or#define
constant, which contains:- Its type's
ItemId
- Optionally, a mangled name
- Optionally, a value
- Its type's
- A
- An optional
clang::SourceLocation
that holds the first source code location where theItem
was encountered.
- An
The IR forms a graph of interconnected and inter-referencing types and
functions. The ir::traversal
module provides IR graph traversal
infrastructure: edge kind definitions (base member vs field type vs function
parameter, etc...), the Trace
trait to enumerate an IR thing's outgoing edges,
various traversal types.
After constructing the IR, we run a series of analyses on it. These analyses do
everything from allocate logical bitfields into physical units, compute for
which types we can #[derive(Debug)]
, to determining which implicit template
parameters a given type uses. The analyses are defined in
src/ir/analysis/*
. They are implemented as fixed-point algorithms, using the
ir::analysis::MonotoneFramework
trait.
The final phase is generating Rust source text from the analyzed IR, and it is
defined in src/codegen/*
. We use the quote
crate, which provides the quote! { ... }
macro for quasi-quoting Rust forms.
Ensure that each commit stands alone, and passes tests. This enables better git bisect
ing when needed. If your commits do not stand on their own, then rebase
them on top of the latest master and squash them into a single commit.
All pull requests undergo code review before merging. To request review, comment
r? @github_username_of_reviewer
. They we will respond with r+
to approve the
pull request, or may leave feedback and request changes to the pull request. Any
changes should be squashed into the original commit.
Unsure who to ask for review? Ask any of:
@emilio
@fitzgen
More resources:
We can generate Graphviz dot files from
our internal representation of a C/C++ input header, and then you can create a
PNG or PDF from it with Graphviz's dot
program. This is very useful when
debugging bindgen!
First, make sure you have Graphviz and dot
installed:
$ brew install graphviz # OS X
$ sudo dnf install graphviz # Fedora
$ # Etc...
Then, use the --emit-ir-graphviz
flag to generate a dot
file from our IR:
$ cargo run -- example.hpp --emit-ir-graphviz output.dot
Finally, convert the dot
file to an image:
$ dot -Tpng output.dot -o output.png
The final result will look something like this:
To help debug what bindgen
is doing, you can define the environment variable
RUST_LOG=bindgen
to get a bunch of debugging log spew.
$ RUST_LOG=bindgen ./target/debug/bindgen [flags...] ~/path/to/some/header.h
This logging can also be used when debugging failing tests:
$ RUST_LOG=bindgen cargo test
If you find a test case that triggers an unexpected panic in bindgen
, causes
bindgen
to emit bindings that won't compile, define structs with the wrong
size/alignment, or results in any other kind of incorrectness, then using
creduce
can help reduce the test case to a minimal one that still exhibits
that same bad behavior.
Reduced test cases are SUPER helpful when filing bug reports!
Often, you can install creduce
from your OS's package manager:
$ sudo apt install creduce
$ brew install creduce
$ # Etc...
Otherwise, follow these instructions for building and/or installing creduce
.
Running creduce
requires two things:
-
Your isolated test case, and
-
A script to act as a predicate script describing whether the behavior you're trying to isolate occurred.
With those two things in hand, running creduce
looks like this:
$ creduce ./predicate.sh ./isolated-test-case.h
If you're using bindgen
as a command line tool, pass
--dump-preprocessed-input
flag.
If you're using bindgen
as a Rust library, invoke the
bindgen::Builder::dump_preprocessed_input
method where you call
bindgen::Builder::generate
.
Afterwards, there should be a __bindgen.i
or __bindgen.ii
file containing
the combined and preprocessed input headers, which is usable as an isolated,
standalone test case.
Writing a predicate.sh
script for a bindgen
test case is straightforward. We
already have a general purpose predicate script that you can use, you just have
to wrap and configure it.
#!/usr/bin/env bash
# Exit the script with a nonzero exit code if:
# * any individual command finishes with a nonzero exit code, or
# * we access any undefined variable.
set -eu
# Invoke the general purpose predicate script that comes in the
# `bindgen` repository.
#
# You'll need to replace `--whatever-flags` with things that are specific to the
# incorrectness you're trying to pin down. See below for details.
path/to/rust-bindgen/csmith-fuzzing/predicate.py \
--whatever-flags \
./isolated-test-case.h
When hunting down a particular panic emanating from inside bindgen
, you can
invoke predicate.py
like this:
path/to/rust-bindgen/csmith-fuzzing/predicate.py \
--expect-bindgen-fail \
--bindgen-grep "thread main panicked at '<insert panic message here>'" \
./isolated-test-case.h
Alternatively, when hunting down a bad #[derive(Eq)]
that is causing rustc
to fail to compile bindgen
's emitted bindings, you can invoke predicate.py
like this:
path/to/rust-bindgen/csmith-fuzzing/predicate.py \
--bindings-grep NameOfTheStructThatIsErroneouslyDerivingEq \
--expect-compile-fail \
--rustc-grep 'error[E0277]: the trait bound `f64: std::cmp::Eq` is not satisfied' \
./isolated-test-case.h
Or, when minimizing a failing layout test in the compiled bindings, you can
invoke predicate.py
like this:
path/to/rust-bindgen/csmith-fuzzing/predicate.py \
--bindings-grep MyStruct \
--expect-layout-tests-fail \
--layout-tests-grep "thread 'bindgen_test_layout_MyStruct' panicked" \
./isolated-test-case.h
For details on all the flags that you can pass to predicate.py
, run:
$ path/to/rust-bindgen/csmith-fuzzing/predicate.py --help
And you can always write your own, arbitrary predicate script if you prefer.
(Although, maybe we should add extra functionality to predicate.py
-- file an
issue if you think so!)
creduce
is really helpful and can cut hundreds of thousands of lines of test
case down to 5 lines.
Happy bug hunting and test case reducing!