Instructions for Developers
We welcome patches and rely on your contributions to make IWYU smarter.
Use GitHub's pull request system to submit change requests to the
It's usually a good idea to run ideas by the IWYU mailing list to get general agreement on directions before you start hacking.
Running the Tests
If fixing a bug in clang, please add a test to the test suite! You can create a file called
whatever.cc (not .cpp), and, if necessary,
whatever-<extension>.h. You may be able to get away without adding any
.h files, and just including
direct.h -- see, for instance,
To run the IWYU tests, run
It runs one test for each
.cc file in the
tests/ directory. (We have additional tests in
more_tests/, but have not yet gotten the testing framework set up for those tests.) The test runner searches for IWYU in the system
PATH by default.
The output can be a bit hard to read, but if a test fails, the reason why will be listed after the
ERROR:root:Test failed for xxx line.
You can select individual tests by listing their filename without extension as arguments
python run_iwyu_tests.py array macro_location
If you don't want to modify your
PATH you can specify which IWYU executable to use for testing
python run_iwyu_tests.py -- ./include-what-you-use
(put any test names before '--' and the IWYU path after.)
fix_includes.py, add a test case to
fix_includes_test.py and run
It's possible to run include-what-you-use in
gdb, to debug that way. Another useful tool -- especially in combination with
gdb -- is to get the verbose include-what-you-use output. See
iwyu_output.h for a description of the verbose levels. Level 7 is very verbose -- it dumps basically the entire AST as it's being traversed, along with IWYU decisions made as it goes -- but very useful for that:
env IWYU_VERBOSE=7 make -k CXX=/path/to/llvm/Debug+Asserts/bin/include-what-you-use 2>&1 > /tmp/iwyu.verbose
A Quick Tour of the Codebase
The codebase is strewn with TODOs of known problems, and also language constructs that aren't adequately tested yet. So there's plenty to do! Here's a brief guide through the codebase:
iwyu.cc: the main file, it includes the logic for deciding when a symbol has been 'used', and whether it's a full use (definition required) or forward-declare use (only a declaration required). It also includes the logic for following uses through template instantiations.
iwyu_driver.cc: responsible for creating and configuring a Clang compiler from command-line arguments.
iwyu_output.cc: the file that translates from 'uses' into IWYU violations. This has the logic for deciding if a use is covered by an existing
#include(or is a built-in). It also, as the name suggests, prints the IWYU output.
iwyu_preprocessor.cc: handles the preprocessor directives, the
#ifdefs, to construct the existing include-tree. This is obviously essential for include-what-you-use analysis. This file also handles the IWYU pragma-comments.
iwyu_include_picker.cc: this finds canonical
#includes, handling private->public mappings (like
vector) and symbols with multiple possible #includes (like
NULL). Additional mappings are maintained in a set of .imp files separately, for easier per-platform/-toolchain customization.
iwyu_cache.cc: holds the cache of instantiated templates (may hold other cached info later). This is data that is expensive to compute and may be used more than once.
iwyu_globals.cc: holds various global variables. We used to think globals were bad, until we saw how much having this file simplified the code...
.cc: utility functions of various types. The most interesting, perhaps, is
iwyu_ast_util.h, which has routines that make it easier to navigate and analyze the clang AST. There are also some STL helpers, string helpers, filesystem helpers, etc.
iwyu_verrs.cc: debug logging for IWYU.
port.h: shim header for various non-portable constructs.
iwyu_getopt.cc: portability shim for GNU
getopt(_long)implementation for Windows.
fix_includes.py: the helper script that edits a file based on the IWYU recommendations.