Clang-Tidy — Extra Clang Tools 23.0.0git documentation
Extra Clang Tools 23.0.0git documentation
Clang-Tidy
Extra Clang Tools 23.0.0git (In-Progress) Release Notes
::
Contents
::
Clang-Tidy Checks
Clang-Tidy
See also:
List of Clang-Tidy Checks
Query Based Custom Clang-Tidy Checks
Clang-tidy IDE/Editor Integrations
Getting Involved
External Clang-Tidy Examples
clang-tidy
is a clang-based C++ “linter” tool. Its purpose is to
provide an extensible framework for diagnosing and fixing typical programming
errors, like style violations, interface misuse, or bugs that can be deduced
via static analysis.
clang-tidy
is modular and provides a
convenient interface for writing new checks.
Using Clang-Tidy
clang-tidy
is a
LibTooling
-based tool, and it’s easier to work
with if you set up a compile command database for your project (for an example
of how to do this, see
How To Setup Tooling For LLVM
). You can also specify
compilation options on the command line after
--
clang-tidy
test.cpp
--
-Imy_project/include
-DMY_DEFINES
...
If there are too many options or source files to specify on the command line,
you can store them in a parameter file, and use
clang-tidy
with that
parameters file:
clang-tidy
@parameters_file
clang-tidy
has its own checks and can also run Clang Static Analyzer
checks. Each check has a name and the checks to run can be chosen using the
-checks=
option, which specifies a comma-separated list of positive and
negative (prefixed with
) globs. Positive globs add subsets of checks, and
negative globs remove them. For example,
clang-tidy
test.cpp
-checks
-*,clang-analyzer-*,-clang-analyzer-cplusplus*
will disable all default checks (
-*
) and enable all
clang-analyzer-*
checks except for
clang-analyzer-cplusplus*
ones.
The
-list-checks
option lists all the enabled checks. When used without
-checks=
, it shows checks enabled by default. Use
-checks=*
to see all
available checks or with any other value of
-checks=
to see which checks
are enabled by this value.
There are currently the following groups of checks:
Name prefix
Description
abseil-
Checks related to Abseil library.
altera-
Checks related to OpenCL programming for FPGAs.
android-
Checks related to Android.
boost-
Checks related to Boost library.
bugprone-
Checks that target bug-prone code constructs.
cert-
Checks related to CERT Secure Coding Guidelines.
clang-analyzer-
Clang Static Analyzer checks.
concurrency-
Checks related to concurrent programming (including
threads, fibers, coroutines, etc.).
cppcoreguidelines-
Checks related to C++ Core Guidelines.
darwin-
Checks related to Darwin coding conventions.
fuchsia-
Checks related to Fuchsia coding conventions.
google-
Checks related to Google coding conventions.
hicpp-
Checks related to High Integrity C++ Coding Standard.
linuxkernel-
Checks related to the Linux Kernel coding conventions.
llvm-
Checks related to the LLVM coding conventions.
llvmlibc-
Checks related to the LLVM-libc coding standards.
misc-
Checks that we didn’t have a better category for.
modernize-
Checks that advocate usage of modern (currently
“modern” means “C++11”) language constructs.
mpi-
Checks related to MPI (Message Passing Interface).
objc-
Checks related to Objective-C coding conventions.
openmp-
Checks related to OpenMP API.
performance-
Checks that target performance-related issues.
portability-
Checks that target portability-related issues that
don’t relate to any particular coding style.
readability-
Checks that target readability-related issues that
don’t relate to any particular coding style.
zircon-
Checks related to Zircon kernel coding conventions.
Clang diagnostics are treated in a similar way as check diagnostics. Clang
diagnostics are displayed by
clang-tidy
and can be filtered out
using the
-checks=
option. However, the
-checks=
option does not
affect compilation arguments, so it cannot turn on Clang warnings which are
not already turned on in the build configuration. The
-warnings-as-errors=
option upgrades any warnings emitted under the
-checks=
flag to errors (but
it does not enable any checks itself).
Clang diagnostics have check names starting with
clang-diagnostic-
Diagnostics which have a corresponding warning option, are named
clang-diagnostic-
, e.g. Clang warning controlled by
-Wliteral-conversion
will be reported with check name
clang-diagnostic-literal-conversion
Clang compiler errors (such as syntax errors, semantic errors, or other
failures that prevent Clang from compiling the code) are reported with the
check name
clang-diagnostic-error
. These represent fundamental compilation
failures that must be fixed before
clang-tidy
can perform its
analysis. Unlike other diagnostics,
clang-diagnostic-error
cannot be
disabled, as
clang-tidy
requires valid code to function.
The
-fix
flag instructs
clang-tidy
to fix found errors if
supported by corresponding checks.
An overview of all the command-line options:
clang-tidy
--help
USAGE: clang-tidy [options]
OPTIONS:
Generic Options:
--help - Display available options (--help-hidden for more)
--help-list - Display list of available options (--help-list-hidden for more)
--version - Display the version of this program
clang-tidy options:
--allow-no-checks - Allow empty enabled checks. This suppresses
the "no checks enabled" error when disabling
all of the checks.
--checks=
prefix. Globs are processed in order of
appearance in the list. Globs without '-'
prefix add checks with matching names to the
set, globs with the '-' prefix remove checks
with matching names from the set of enabled
checks. This option's value is appended to the
value of the 'Checks' option in .clang-tidy
file, if any.
--config=
-config="{Checks: '*',
CheckOptions: {x: y}}"
When the value is empty, clang-tidy will
attempt to find a file named .clang-tidy for
each source file in its parent directories.
--config-file=
e.g. --config-file=/some/path/myTidyConfigFile
This option internally works exactly the same way as
--config option after reading specified config file.
Use either --config-file or --config, not both.
--dump-config - Dumps configuration in the YAML format to
stdout. This option can be used along with a
file name (and '--' if the file is outside of a
project with configured compilation database).
The configuration used for this file will be
printed.
Use along with -checks=* to include
configuration of all checks.
--enable-check-profile - Enable per-check timing profiles, and print a
report to stderr.
--enable-module-headers-parsing - Enables preprocessor-level module header parsing
for C++20 and above, empowering specific checks
to detect macro definitions within modules. This
feature may cause performance and parsing issues
and is therefore considered experimental.
--exclude-header-filter=
headers to exclude diagnostics from. Diagnostics
from the main file of each translation unit are
always displayed.
Must be used together with --header-filter.
Can be used together with -line-filter.
This option overrides the 'ExcludeHeaderFilterRegex'
option in .clang-tidy file, if any.
--experimental-custom-checks - Enable experimental clang-query based
custom checks.
see https://clang.llvm.org/extra/clang-tidy/QueryBasedCustomChecks.html.
--explain-config - For each enabled check explains, where it is
enabled, i.e. in clang-tidy binary, command
line or a specific configuration file.
--export-fixes=
stored fixes can be applied to the input source
code with clang-apply-replacements.
--extra-arg=
--extra-arg-before=
--fix - Apply suggested fixes. Without -fix-errors
clang-tidy will bail out if any compilation
errors were found.
--fix-errors - Apply suggested fixes even if compilation
errors were found. If compiler errors have
attached fix-its, clang-tidy will apply them as
well.
--fix-notes - If a warning has no fix, but a single fix can
be found through an associated diagnostic note,
apply the fix.
Specifying this flag will implicitly enable the
'--fix' flag.
--format-style=
- 'none' (default) turns off formatting
- 'file' (literally 'file', not a placeholder)
uses .clang-format file in the closest parent
directory
- '{
-format-style='{BasedOnStyle: llvm, IndentWidth: 8}'
- 'llvm', 'google', 'webkit', 'mozilla'
See clang-format documentation for the up-to-date
information about formatting styles and options.
This option overrides the 'FormatStyle` option in
.clang-tidy file, if any.
--header-filter=
headers to output diagnostics from. The default
value is '.*', i.e. diagnostics from all non-system
headers are displayed by default. Diagnostics
from the main file of each translation unit are
always displayed.
Can be used together with -line-filter.
This option overrides the 'HeaderFilterRegex'
option in .clang-tidy file, if any.
--line-filter=
The range is inclusive on both ends. Can be used together
with -header-filter. The format of the list is a JSON
array of objects. For example:
{"name":"file1.cpp","lines":[[1,3],[5,7]]},
{"name":"file2.h"}
This will output diagnostics from 'file1.cpp' only for
the line ranges [1,3] and [5,7], as well as all from the
entire 'file2.h'.
--list-checks - List all enabled checks and exit. Use with
-checks=* to list all available checks.
--load=
-p
--quiet - Run clang-tidy in quiet mode. This suppresses
printing statistics about ignored warnings and
warnings treated as errors if the respective
options are specified.
--removed-arg=
line sent to the compiler. Please note that
removing arguments might change the semantic
of the analyzed code, possibly leading to
compiler errors, false positives or
false negatives. This option is applied
before --extra-arg and --extra-arg-before
--store-check-profile=
format to stderr. When this option is passed,
these per-TU profiles are instead stored as JSON.
--system-headers - Display the errors from system headers.
This option overrides the 'SystemHeaders' option
in .clang-tidy file, if any.
--use-color - Use colors in diagnostics. If not set, colors
will be used if the terminal connected to
standard output supports colors.
This option overrides the 'UseColor' option in
.clang-tidy file, if any.
--verify-config - Check the config files to ensure each check and
option is recognized without running any checks.
--vfsoverlay=
over the real file system.
--warnings-as-errors=
'-checks'.
This option's value is appended to the value of
the 'WarningsAsErrors' option in .clang-tidy
file, if any.
-p
For example, it can be a CMake build directory in which a file named
compile_commands.json exists (use -DCMAKE_EXPORT_COMPILE_COMMANDS=ON
CMake option to get this output). When no build path is specified,
a search for compile_commands.json will be attempted through all
parent paths of the first input file . See:
example of setting up Clang Tooling on a source tree.
looked up in the compile command database. If the path of a file is
absolute, it needs to point into CMake's source tree. If the path is
relative, the current working directory needs to be in the CMake
source tree and the file must be in a subdirectory of the current
working directory. "./" prefixes in the relative files will be
automatically removed, but the rest of a relative path must be a
suffix of a path in the compile command database.
Parameters files:
A large number of options or source files can be passed as parameter files
by use '@parameter-file' in the command line.
Configuration files:
clang-tidy attempts to read configuration for each source file from a
.clang-tidy file located in the closest parent directory of the source
file. The .clang-tidy file is specified in YAML format. If any configuration
options have a corresponding command-line option, command-line option takes
precedence.
The following configuration options may be used in a .clang-tidy file:
CheckOptions - List of key-value pairs defining check-specific
options. Example:
CheckOptions:
some-check.SomeOption: 'some value'
Checks - Same as '--checks'. Additionally, the list of
globs can be specified as a list instead of a
string.
CustomChecks - Array of user defined checks based on
Clang-Query syntax.
ExcludeHeaderFilterRegex - Same as '--exclude-header-filter'.
ExtraArgs - Same as '--extra-arg'.
ExtraArgsBefore - Same as '--extra-arg-before'.
FormatStyle - Same as '--format-style'.
HeaderFileExtensions - File extensions to consider to determine if a
given diagnostic is located in a header file.
HeaderFilterRegex - Same as '--header-filter'.
ImplementationFileExtensions - File extensions to consider to determine if a
given diagnostic is located in an
implementation file.
InheritParentConfig - If this option is true in a config file, the
configuration file in the parent directory
(if any exists) will be taken and the current
config file will be applied on top of the
parent one.
RemovedArgs - Same as '--removed-arg'.
SystemHeaders - Same as '--system-headers'.
UseColor - Same as '--use-color'.
User - Specifies the name or e-mail of the user
running clang-tidy. This option is used, for
example, to place the correct user name in
TODO() comments in the relevant check.
WarningsAsErrors - Same as '--warnings-as-errors'.
The effective configuration can be inspected using --dump-config:
clang-tidy
--dump-config
---
Checks: '-*,some-check'
WarningsAsErrors: ''
HeaderFileExtensions: ['', 'h','hh','hpp','hxx']
ImplementationFileExtensions: ['c','cc','cpp','cxx']
HeaderFilterRegex: '.*'
FormatStyle: none
InheritParentConfig: true
User: user
CheckOptions:
some-check.SomeOption: 'some value'
...
Running Clang-Tidy on CUDA Files
clang-tidy
supports analyzing CUDA source files. To ensure correct
header resolution, it is important to specify the CUDA toolkit path using
--cuda-path
. For more details on how Clang handles CUDA, see
Compiling CUDA with Clang
If you are using a GCC + NVCC build setup, the compiler command database will
contain NVCC-specific flags that
clang-tidy
does not understand.
In this case, you should use the
RemovedArgs
configuration option (or
--removed-arg
command-line option) to remove these flags, and
ExtraArgs
(or
--extra-arg
) to provide the
--cuda-path
For example, to remove the NVCC-specific
-gencode
flag and provide the
CUDA path:
clang-tidy
source.cu
--removed-arg
"-gencode"
--removed-arg
"arch=.."
--extra-arg
"--cuda-path=/path/to/cuda"
By default,
clang-tidy
will analyze both host and device code.
To restrict the analysis to a specific side and specifically choose device
compilation flags, use the
--extra-arg
flag to pass the arguments.
For example, to perform device analysis only, use
the
--cuda-device-only
flag:
clang-tidy
source.cu
--extra-arg
"--cuda-device-only"
--extra-arg
"--cuda-path=/path/to/cuda"
Clang-Tidy Automation
clang-tidy
can analyze multiple source files by specifying them on
the command line. For larger projects, automation scripts provide additional
functionality like parallel execution and integration with version control
systems.
Running Clang-Tidy in Parallel
clang-tidy
can process multiple files sequentially, but for projects
with many source files, the
run-clang-tidy.py
script provides
parallel execution to significantly reduce analysis time. This script is
included with clang-tidy and runs
clang-tidy
over all files in a
compilation database or a specified path concurrently.
The script requires a compilation database (
compile_commands.json
) which
can be generated by build systems like CMake (using
-DCMAKE_EXPORT_COMPILE_COMMANDS=ON
) or by tools like
Bear
The script supports most of the same options as
clang-tidy
itself,
including
-checks=
-fix
-header-filter=
, and configuration
options. Run
run-clang-tidy.py
--help
for a complete list of available
options.
Example invocations:
Run
clang-tidy
on
all
files
in
the
compilation
database
in
parallel
run-clang-tidy.py
-p
build/
Run
with
specific
checks
and
apply
fixes
run-clang-tidy.py
-p
build/
-fix
-checks
-*,readability-*
Run
on
specific
files/directories
with
header
filtering
run-clang-tidy.py
-p
build/
-header-filter
src/
src/
Run
with
parallel
execution
uses
all
CPU
cores
by
default
run-clang-tidy.py
-p
build/
-j
Running Clang-Tidy on Diff
The
clang-tidy-diff.py
script allows you to run
clang-tidy
on the lines that have been modified in your working
directory or in a specific diff. Importantly,
clang-tidy-diff.py
only reports
diagnostics for changed lines;
clang-tidy
still analyzes the entire
file and filters out unchanged lines after analysis, so this does not improve
performance. This is particularly useful for code reviews and continuous
integration, as it focuses analysis on the changed code rather than the entire
codebase.
The script can work with various diff sources:
Git working directory changes
Output from
git
diff
Output from
svn
diff
Patch files
Example invocations:
Run
clang-tidy
on
all
changes
in
the
working
directory
git
diff
-U0
--no-color
HEAD^
clang-tidy-diff.py
-p1
Run
with
specific
checks
and
apply
fixes
git
diff
-U0
--no-color
HEAD^
clang-tidy-diff.py
-p1
-fix
-checks
-*,readability-*
Run
on
staged
changes
git
diff
-U0
--no-color
--cached
clang-tidy-diff.py
-p1
Run
on
changes
between
two
commits
git
diff
-U0
--no-color
HEAD~2
HEAD
clang-tidy-diff.py
-p1
Run
on
patch
file
clang-tidy-diff.py
-p1
changes.patch
The
-p1
option tells the script to strip one level of path prefix from
the diff, which is typically needed for Git diffs. The script supports most of
the same options as
clang-tidy
itself, including
-checks=
-fix
-header-filter=
, and configuration options.
While
clang-tidy-diff.py
is useful for focusing on recent changes,
relying solely on it may lead to incomplete analysis. Since the script only
reports warnings from the modified lines, it may miss issues that are caused
by the changes but manifest elsewhere in the code. For example, changes that
only add lines to a function may cause it to violate size limits (e.g.,
readability-function-size
), but the
diagnostic will be reported at the function declaration, which may not be in
the diff and thus filtered out. Modifications to header files may also affect
many implementation files, but only warnings in the modified header lines will
be reported.
For comprehensive analysis, especially before merging significant changes,
consider running
clang-tidy
on the entire affected files or the
whole project using
run-clang-tidy.py
Suppressing Undesired Diagnostics
clang-tidy
diagnostics are intended to call out code that does not
adhere to a coding standard, or is otherwise problematic in some way. However,
if the code is known to be correct, it may be useful to silence the warning.
Some clang-tidy checks provide a check-specific way to silence the diagnostics,
e.g.
bugprone-use-after-move
can be
silenced by re-initializing the variable after it has been moved out,
bugprone-string-integer-assignment
can be suppressed by
explicitly casting the integer to
char
readability-implicit-bool-conversion
can also be suppressed by
using explicit casts, etc.
If a specific suppression mechanism is not available for a certain warning, or
its use is not desired for some reason,
clang-tidy
has a generic
mechanism to suppress diagnostics using
NOLINT
NOLINTNEXTLINE
, and
NOLINTBEGIN
NOLINTEND
comments.
The
NOLINT
comment instructs
clang-tidy
to ignore warnings on
the
same line
(it doesn’t apply to a function, a block of code or any other
language construct; it applies to the line of code it is on). If introducing
the comment on the same line would change the formatting in an undesired way,
the
NOLINTNEXTLINE
comment allows suppressing clang-tidy warnings on the
next line
. The
NOLINTBEGIN
and
NOLINTEND
comments allow suppressing
clang-tidy warnings on
multiple lines
(affecting all lines between the two
comments).
All comments can be followed by an optional list of check names in parentheses
(see below for the formal syntax). The list of check names supports globbing,
with the same format and semantics as for enabling checks. Note: negative globs
are ignored here, as they would effectively re-activate the warning.
For example:
class
Foo
// Suppress all the diagnostics for the line
Foo
int
param
);
// NOLINT
// Consider explaining the motivation to suppress the warning
Foo
char
param
);
// NOLINT: Allow implicit conversion from `char`, because
// Silence only the specified checks for the line
Foo
double
param
);
// NOLINT(google-explicit-constructor, google-runtime-int)
// Silence all checks from the `google` module
Foo
bool
param
);
// NOLINT(google*)
// Silence all checks ending with `-avoid-c-arrays`
int
array
10
];
// NOLINT(*-avoid-c-arrays)
// Silence only the specified diagnostics for the next line
// NOLINTNEXTLINE(google-explicit-constructor, google-runtime-int)
Foo
bool
param
);
// Silence all checks from the `google` module for the next line
// NOLINTNEXTLINE(google*)
Foo
bool
param
);
// Silence all checks ending with `-avoid-c-arrays` for the next line
// NOLINTNEXTLINE(*-avoid-c-arrays)
int
array
10
];
// Silence only the specified checks for all lines between the BEGIN and END
// NOLINTBEGIN(google-explicit-constructor, google-runtime-int)
Foo
short
param
);
Foo
long
param
);
// NOLINTEND(google-explicit-constructor, google-runtime-int)
// Silence all checks from the `google` module for all lines between the BEGIN and END
// NOLINTBEGIN(google*)
Foo
bool
param
);
// NOLINTEND(google*)
// Silence all checks ending with `-avoid-c-arrays` for all lines between the BEGIN and END
// NOLINTBEGIN(*-avoid-c-arrays)
int
array
10
];
// NOLINTEND(*-avoid-c-arrays)
};
The formal syntax of
NOLINT
NOLINTNEXTLINE
, and
NOLINTBEGIN
NOLINTEND
is the following:
lint-comment:
lint-command
lint-command lint-args
lint-args:
check-name-list
check-name-list:
check-name
check-name-list
check-name
lint-command:
NOLINT
NOLINTNEXTLINE
NOLINTBEGIN
NOLINTEND
Note that whitespaces between
NOLINT
NOLINTNEXTLINE
NOLINTBEGIN
NOLINTEND
and the opening
parenthesis are not allowed (in this case the comment will be treated just as
NOLINT
NOLINTNEXTLINE
NOLINTBEGIN
NOLINTEND
), whereas in the
check names list (inside the parentheses), whitespaces can be used and will be
ignored.
All
NOLINTBEGIN
comments must be paired by an equal number of
NOLINTEND
comments. Moreover, a pair of comments must have matching arguments – for
example,
NOLINTBEGIN(check-name)
can be paired with
NOLINTEND(check-name)
but not with
NOLINTEND
(zero arguments)
clang-tidy
will generate a
clang-tidy-nolint
error diagnostic if
any
NOLINTBEGIN
NOLINTEND
comment violates these requirements.
Extra Clang Tools 23.0.0git (In-Progress) Release Notes
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Clang-Tidy Checks
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