WARNING: master is the development branch. Please use the v1.10 branch.
clazy is a compiler plugin which allows clang to understand Qt semantics. You get more than 50 Qt related compiler warnings, ranging from unneeded memory allocations to misusage of API, including fix-its for automatic refactoring.
Table of contents
- Source Code
- Pre-built binaries
- Build Instructions
- Setting up your project to build with clazy
- List of checks
- Selecting which checks to enable
- clazy-standalone and JSON database support
- Enabling Fixits
- Qt4 compatibility mode
- Reducing warning noise
- Reporting bugs and wishes
- Contributing patches
You can get clazy from:
Clazy has been tested on Linux, macOS and Windows/MSVC. Other platforms are not supported but we'll gladly accept patches.
Pre-built clazy binaries for MSVC and Linux AppImage are produced by KDAB, you can get them from https://downloads.kdab.com/clazy/.
- OpenSUSE tumbleweed:
zypper install cmake git-core llvm llvm-devel llvm-clang llvm-clang-devel
apt install g++ cmake clang llvm-dev git-core libclang-dev
pacman -S make llvm clang python2 cmake git gcc
- Fedora: be sure to remove the llvm-static package and only install the one with dynamic libraries
- Other distros: Check llvm/clang build docs.
Build and install clang
clang and LLVM >= 8.0 are required.
If your distro provides clang then you can skip this step.
$ git clone https://github.com/llvm-mirror/llvm.git <some_directory> $ cd <some_directory>/tools/ && git clone https://github.com/llvm-mirror/clang.git $ cd <some_directory>/projects && git clone https://github.com/llvm-mirror/compiler-rt.git $ mkdir <some_directory>/build && cd <some_directory>/build $ cmake -DCMAKE_INSTALL_PREFIX=<prefix> -DLLVM_TARGETS_TO_BUILD=X86 -DCMAKE_BUILD_TYPE=Release -G Ninja .. $ cmake --build . $ cmake --build . --target install
$ cd clazy/ $ cmake -DCMAKE_INSTALL_PREFIX=<prefix> -DCMAKE_BUILD_TYPE=Release -G Ninja $ cmake --build . $ cmake --build . --target install
See troubleshooting section if you have problems.
Build and install clang
These instructions assume your terminal is suitable for development. Ninja (or equivalent), git, cmake, and cl (msvc2019) should be in your PATH.
clang and LLVM >= 9.0 are required.
Be sure to pass -DLLVM_EXPORT_SYMBOLS_FOR_PLUGINS=ON to CMake when building LLVM, otherwise clazy won't work.
> git clone https://github.com/llvm/llvm-project.git -b llvmorg-11.0.0 <some_directory> > mkdir build # Important that this is outside of the source directory > cd build > cmake -DCMAKE_INSTALL_PREFIX=c:\my_install_folder\llvm\ -DLLVM_EXPORT_SYMBOLS_FOR_PLUGINS=ON -DLLVM_INCLUDE_EXAMPLES=OFF -DLLVM_TARGETS_TO_BUILD="X86" -DLLVM_ENABLE_PROJECTS="clang;clang-tools-extra" -DCMAKE_BUILD_TYPE=Release -G "Ninja" ../<some_directory>/llvm > cmake --build . > cmake --build . --target install > Add c:\my_install_folder\llvm\bin\ to PATH
Also be sure to copy the generated
C:\path\to\llvm-build\lib\clang.lib to your installation folder somewhere. It contains the exported symbols of clang.exe, which the plugins need. Unfortunately LLVM doesn't install it. You can put it anywhere, just save it so you can delete the build directory.
Be sure to point CLANG_LIBRARY_IMPORT to clang.lib. It's probably inside your LLVM build dir since it doesn't get installed.
> cd clazy\ > cmake -DCMAKE_INSTALL_PREFIX=c:\my_install_folder\llvm\ -DCLANG_LIBRARY_IMPORT=C:\path\to\llvm-build\lib\clang.lib -DCMAKE_BUILD_TYPE=Release -G "Ninja" > cmake --build . > cmake --build . --target install
macOS with MacPorts
$ sudo port install llvm-11 clang-11 cmake ninja coreutils $ sudo ln -sf /opt/local/bin/llvm-config-mp-11 /opt/local/bin/llvm-config $ sudo port select --set clang mp-clang-11
$ export CXX=clang++ $ cmake -G Ninja $ cmake --build . $ cmake --build . --target install
macOS with Homebrew
The recommended way is to build clazy yourself, but alternatively you can try user recipes, such as:
$ brew install kde-mac/kde/clazy
for stable branch, or for master:
$ brew install kde-mac/kde/clazy --HEAD
As these are not verified or tested by the clazy developers please don't report bugs to us.
For building yourself, read on. You'll have to install clang and build clazy from source.
$ brew install --with-clang llvm
$ export CXX=clang++ $ export LLVM_ROOT=/usr/local/opt/llvm $ cmake -G Ninja $ cmake --build . $ cmake --build . --target install
Setting up your project to build with clazy
clazy is mentioned, replace with
clazy-cl.bat if you're on Windows, or replace with
Clazy-x86_64.AppImage if you're using AppImage. Note: If you prefer running clazy over a JSON compilation database instead of using it as a plugin, jump to clazy-standalone.
You should now have the clazy command available to you, in
<prefix>/bin/. Compile your programs with it instead of clang++/g++.
Note that this command is just a convenience wrapper which calls:
clang++ -Xclang -load -Xclang ClazyPlugin.so -Xclang -add-plugin -Xclang clazy
If you have multiple versions of clang installed (say clang++-10 and clang++-11) you can choose which one to use by setting the CLANGXX environment variable, like so:
export CLANGXX=clang++-11; clazy
To build a CMake project use:
cmake . -DCMAKE_CXX_COMPILER=clazy and rebuild.
To make it the compiler for qmake projects, just run qmake like:
qmake -spec linux-clang QMAKE_CXX="clazy"
On Windows with MSVC it's simply:
Alternatively, if you want to use clang directly, without the wrapper:
qmake -spec linux-clang QMAKE_CXXFLAGS="-Xclang -load -Xclang ClazyPlugin.so -Xclang -add-plugin -Xclang clazy"
On Windows it's similar, just inspect the contents of
It's recommended that you disable pre-compiled headers and don't use ccache.
You're all set, clazy will now run some checks on your project, but not all of them. Read on if you want to enable/disable which checks are run.
List of checks
There are many checks and they are divided in levels:
- level0: Very stable checks, 99.99% safe, mostly no false-positives, very desirable
- level1: The default level. Very similar to level 0, slightly more false-positives but very few.
- level2: Also very few false-positives, but contains noisy checks which not everyone agree should be default.
- manual: Checks here need to be enabled explicitly, as they don't belong to any level. They can be very stable or very unstable.
clazy runs all checks from level1 by default.
Checks from Manual Level:
- qt-keywords (fix-qt-keywords)
- qt4-qstring-from-array (fix-qt4-qstring-from-array)
- qt6-deprecated-api-fixes (fix-qt6-deprecated-api-fixes)
- qt6-fwd-fixes (fix-qt6-fwd-fixes)
- qt6-header-fixes (fix-qt6-header-fixes)
- qt6-qhash-signature (fix-qt6-qhash-signature)
- qt6-qlatin1stringchar-to-u (fix-qt6-qlatin1stringchar-to-u)
Checks from Level 0:
- qdatetime-utc (fix-qdatetime-utc)
- qgetenv (fix-qgetenv)
- qstring-ref (fix-missing-qstringref)
Checks from Level 1:
- auto-unexpected-qstringbuilder (fix-auto-unexpected-qstringbuilder)
- range-loop-detach (fix-range-loop-add-qasconst)
- range-loop-reference (fix-range-loop-add-ref)
Checks from Level 2:
- function-args-by-ref (fix-function-args-by-ref)
- missing-qobject-macro (fix-missing-qobject-macro)
- old-style-connect (fix-old-style-connect)
- qstring-allocations (fix-qlatin1string-allocations,fix-fromLatin1_fromUtf8-allocations,fix-fromCharPtrAllocations)
Selecting which checks to enable
You may want to choose which checks to enable before starting to compile. If you don't specify anything then all checks from level0 and level1 will run. To specify a list of checks to run, or to choose a level, you can use the
CLAZY_CHECKS env variable or pass arguments to the compiler. You can disable checks by prefixing with
no-, in case you don't want all checks from a given level.
Example via env variable
export CLAZY_CHECKS="unneeded-cast,qmap-with-pointer-key,virtual-call-ctor" # Enables only these 3 checks export CLAZY_CHECKS="level0,no-qenums" # Enables all checks from level0, except for qenums export CLAZY_CHECKS="level0,detaching-temporary" # Enables all from level0 and also detaching-temporary
Example via compiler argument
clazy -Xclang -plugin-arg-clazy -Xclang level0,detaching-temporary Don't forget to re-run cmake/qmake/etc if you altered the c++ flags to specify flags.
clazy-standalone and JSON database support
clazy-standalone binary allows you to run clazy over a compilation database JSON file, in the same way you would use
clang-tidy or other clang tooling. This way you don't need to build your application, only the static analysis is performed.
Note: If you're using the AppImage, use
Clazy-x86_64.AppImage --standalone instead of
clazy-standalone supports the same env variables as the clazy plugin. You can also specify a list of checks via the
Running on one cpp file:
clazy-standalone -checks=install-event-filter,qmap-with-pointer-key,level0 -p compile_commands.json my.file.cpp
Running on all cpp files:
find . -name "*cpp" | xargs clazy-standalone -checks=level2 -p default/compile_commands.json
See https://clang.llvm.org/docs/JSONCompilationDatabase.html for how to generate the compile_commands.json file. Basically it's generated by passing
-DCMAKE_EXPORT_COMPILE_COMMANDS to CMake, or using Bear to intercept compiler commands, or, if you're using
qbs generate --generator clangdb
Note: Be sure the clazy-standalone binary is located in the same folder as the clang binary, otherwise it will have trouble finding builtin headers, like stddef.h. Alternatively, you can symlink to the folder containing the builtin headers:
(Assuming clazy was built with
$ touch foo.c && clang++ '-###' -c foo.c 2>&1 | tr ' ' '\n' | grep -A1 resource # Make sure this clang here is not Apple clang. Use for example clang++-mp-8.0 if on macOS and haven't run `port select` yet. "-resource-dir" "/opt/local/libexec/llvm-8.0/lib/clang/8.0.1" # The interesting part is /opt/local/libexec/llvm-8.0 $ ln -sf /opt/local/libexec/llvm-8.0/lib/clang/ /myprefix/lib/clang $ mkdir /myprefix/include/ $ ln -sf /opt/local/libexec/llvm-8.0/include/c++/ /myprefix/include/c++ # Required on macOS
If that doesn't work, run
clang -v and check what's the InstalledDir. Move clazy-standalone to that folder.
clang-tidy support will be added after https://bugs.llvm.org//show_bug.cgi?id=32739 is fixed.
Some checks support fixits, in which clazy will help re-write your source files whenever it can fix something. Simply pass
-Xclang -plugin-arg-clazy -Xclang export-fixes to clang, or
clazy-standalone. Alternatively, set the
CLAZY_EXPORT_FIXES env variable (works only with the plugin, not with standalone). Then run
clang-apply-replacements <folder_with_yaml_files>, which will modify your code.
When using fixits, prefer to run only a single check each time, so they don't conflict with each other modifying the same source lines.
WARNING: Backup your code and make sure all changes done by clazy are correct.
clang: symbol lookup error:
/usr/lib/x86_64-linux-gnu/ClazyPlugin.so: undefined symbol: _ZNK5clang15DeclarationName11getAsStringEv. This is due to mixing ABIs. Your clang/llvm was compiled with the new gcc c++ ABI but you compiled the clazy plugin with clang (which uses the old ABI).
The solution is to build the clazy plugin with gcc or use a distro which hasn't migrated to gcc5 ABI yet, such as archlinux.
[Fedora] cmake can't find LLVM ? Try building llvm/clang yourself (There are reports that /usr/share/llvm/cmake/LLVM-Config.cmake is buggy).
[Fedora] CommandLine Error:
Option 'opt-bisect-limit' registered more than once!Remove the llvm-static package and use the dynamically linked libraries instead. Alternatively, if you want to use llvm-static, see next item.
Option 'foo' registered more than once!Means you're building against a static version of LLVM (*.a files instead of *.so). Try passing to cmake -DLINK_CLAZY_TO_LLVM=OFF when building clazy, this was tested successfully against a static LLVM 7.0, and might work with other versions.
Some checks are mysteriously not producing warnings or not applying fixits ? Check if you have ccache interfering and turn it off.
fatal error: 'stddef.h' file not found, while using
clazy-standaloneBe sure the clazy-standalone binary is located in the same folder as the clang binary.
Be sure to disable pch.
macOS: Be sure you're not using Apple Clang
macOS: System Integrity Protection blocks the use of DYLD_LIBRARY_PATH. With SIP enabled you need to pass the full path to ClazyPlugin.dylib, otherwise you'll get
image not founderror.
Windows: fatal error LNK1112: module machine type ‘X86’ conflicts with target machine type ‘x64’ If you're building in 32-bit, open clazy-cl.bat and insert a -m32 argument. Should read: %~dp0\clang\clang.exe –driver-mode=cl -m32 (...)
Qt4 compatibility mode
When running on codebases that must still compile with Qt4, you can pass
--qt4compat (a convenience option equivalent to passing
-Xclang -plugin-arg-clazy -Xclang qt4-compat) to disable checks that only make sense with Qt5.
For example, to build a CMake project with Qt4 compatibility use:
CXX="clazy --qt4compat"; cmake . and rebuild.
Reducing warning noise
If you think you found a false-positive, file a bug report. But do make sure to test first without icecc/distcc enabled.
If you want to suppress warnings from headers of Qt or 3rd party code, include them with
-isystem instead of
-I (gcc/clang only). For MSVC use
/external, which is available since VS 15.6.
Alternatively you can set the CLAZY_HEADER_FILTER env variable to a regexp matching the path where you want warnings, for example
You can also exclude paths using a regexp by setting CLAZY_IGNORE_DIRS, for example
You can also suppress individual warnings by file or by line by inserting comments:
To disable clazy in a specific source file, insert this comment, anywhere in the file:
To disable specific checks in a source file, insert a comment such as
To disable specific checks in specific source lines, insert a comment in the same line as the warning:
(...) // clazy:exclude=check1,check2
Don't include the
clazy- prefix. If, for example, you want to disable qstring-allocations you would write:
// clazy:exclude=qstring-allocations not
Reporting bugs and wishes
- bug tracker: https://bugs.kde.org/enter_bug.cgi?product=clazy
- IRC: #kde-clazy (irc.libera.chat)
When reporting a bug please include a minimal compilable testcase. No matter how simple it is, it saves me time from deciphering a bug report. Time spent doing triaging is time not spent writing fixes.
A minimal testcase is also something I can copy to the test suite.
Make sure you can reproduce with clazy (outside of QtCreator), otherwise it can be a QtCreator bug instead, which you can report at https://bugreports.qt.io/.
- Sérgio Martins
with contributions from:
- Allen Winter
- Kevin Funk
- Mathias Hasselmann
- Laurent Montel
- Albert Astals Cid
- Aurélien Gâteau
- Hannah von Reth
- Volker Krause
- Christian Ehrlicher
- Christian Gagneraud
- Nikolai Kosjar
- Jesper K. Pedersen
- Lucie Gerard
- Christian Schärf
- Waqar Ahmed
qt6-* porting checks written by Lucie Gerard [email protected]
and thanks to:
- Klarälvdalens Datakonsult AB (http://www.kdab.com), for letting me work on clazy as a research project
New features go to master and bug fixes go to the 1.10 branch. The prefered way to contributing is by using KDE's GitLab instance, see https://community.kde.org/Infrastructure/GitLab.
If you rather just create a pull request in https://github.com/KDE/clazy for a drive-by change, it's also fine, but beware that the maintainer might forget to check on github and the KDE bot will close the PR. In that case just send a reminder to the maintainer (smartins at kde.org).