Contents
- Clang-Tidy
- Using clang-tidy
- Suppressing Undesired Diagnostics
See also:
- The list of clang-tidy checks
- Clang-tidy IDE/Editor Integrations
- Getting Involved
clang-tidy is a clang-based C++ “linter” tool. Its purpose is toprovide an extensible framework for diagnosing and fixing typical programmingerrors, like style violations, interface misuse, or bugs that can be deduced viastatic analysis. clang-tidy is modular and provides a convenientinterface for writing new checks.
Using clang-tidy¶
clang-tidy is a LibTooling-based tool, and it’s easier to workwith if you set up a compile command database for your project (for an exampleof how to do this, see How To Setup Tooling For LLVM). You can also specifycompilation options on the command line after --:
$ clang-tidy test.cpp -- -Imy_project/include -DMY_DEFINES ...clang-tidy has its own checks and can also run Clang Static Analyzerchecks. 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 andnegative (prefixed with -) globs. Positive globs add subsets of checks, andnegative 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 allavailable checks or with any other value of -checks= to see which checks areenabled 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 (includingthreads, 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’trelate to any particular coding style. |
readability- | Checks that target readability-related issues that don’trelate to any particular coding style. |
zircon- | Checks related to Zircon kernel coding conventions. |
Clang diagnostics are treated in a similar way as check diagnostics. Clangdiagnostics are displayed by clang-tidy and can be filtered out usingthe -checks= option. However, the -checks= option does not affectcompilation arguments, so it cannot turn on Clang warnings which are notalready turned on in the build configuration. The -warnings-as-errors=option upgrades any warnings emitted under the -checks= flag to errors (butit does not enable any checks itself).
Clang diagnostics have check names starting with clang-diagnostic-.Diagnostics which have a corresponding warning option, are namedclang-diagnostic-<warning-option>, e.g. Clang warning controlled by-Wliteral-conversion will be reported with check nameclang-diagnostic-literal-conversion.
The -fix flag instructs clang-tidy to fix found errors ifsupported by corresponding checks.
An overview of all the command-line options:
$ clang-tidy --helpUSAGE: clang-tidy [options] <source0> [... <sourceN>]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 programclang-tidy options: --checks=<string> - Comma-separated list of globs with optional '-' 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=<string> - Specifies a configuration in YAML/JSON format: -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=<string> - Specify the path of .clang-tidy or custom 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. --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=<filename> - YAML file to store suggested fixes in. The stored fixes can be applied to the input source code with clang-apply-replacements. --extra-arg=<string> - Additional argument to append to the compiler command line --extra-arg-before=<string> - Additional argument to prepend to the compiler command line --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=<string> - Style for formatting code around applied fixes: - 'none' (default) turns off formatting - 'file' (literally 'file', not a placeholder) uses .clang-format file in the closest parent directory - '{ <json> }' specifies options inline, e.g. -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=<string> - Regular expression matching the names of the headers to output diagnostics from. 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=<string> - List of files with line ranges to filter the warnings. Can be used together with -header-filter. The format of the list is a JSON array of objects: [ {"name":"file1.cpp","lines":[[1,3],[5,7]]}, {"name":"file2.h"} ] --list-checks - List all enabled checks and exit. Use with -checks=* to list all available checks. --load=<pluginfilename> - Load the specified plugin -p <string> - Build path --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. --store-check-profile=<prefix> - By default reports are printed in tabulated 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. --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. --vfsoverlay=<filename> - Overlay the virtual filesystem described by file over the real file system. --warnings-as-errors=<string> - Upgrades warnings to errors. Same format as '-checks'. This option's value is appended to the value of the 'WarningsAsErrors' option in .clang-tidy file, if any.-p <build-path> is used to read a compile command database. 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: https://clang.llvm.org/docs/HowToSetupToolingForLLVM.html for an example of setting up Clang Tooling on a source tree.<source0> ... specify the paths of source files. These paths are 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.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'. ExtraArgs - Same as '--extra-args'. ExtraArgsBefore - Same as '--extra-args-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-regex'. 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. 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' ...
Suppressing Undesired Diagnostics¶
clang-tidy diagnostics are intended to call out code that does notadhere 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 besilenced by re-initializing the variable after it has been moved out,bugprone-string-integer-assignment can be suppressed byexplicitly casting the integer to char,readability-implicit-bool-conversion can also be suppressed byusing explicit casts, etc.
If a specific suppression mechanism is not available for a certain warning, orits use is not desired for some reason, clang-tidy has a genericmechanism to suppress diagnostics using NOLINT, NOLINTNEXTLINE, andNOLINTBEGIN … NOLINTEND comments.
The NOLINT comment instructs clang-tidy to ignore warnings on thesame line (it doesn’t apply to a function, a block of code or any otherlanguage construct; it applies to the line of code it is on). If introducing thecomment on the same line would change the formatting in an undesired way, theNOLINTNEXTLINE comment allows suppressing clang-tidy warnings on the nextline. The NOLINTBEGIN and NOLINTEND comments allow suppressingclang-tidy warnings on multiple lines (affecting all lines between the twocomments).
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 globsare 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 <some valid reason> // 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-argslint-args: ( check-name-list )check-name-list: check-name check-name-list , check-namelint-command: NOLINT NOLINTNEXTLINE NOLINTBEGIN NOLINTEND
Note that whitespaces betweenNOLINT/NOLINTNEXTLINE/NOLINTBEGIN/NOLINTEND and the openingparenthesis are not allowed (in this case the comment will be treated just asNOLINT/NOLINTNEXTLINE/NOLINTBEGIN/NOLINTEND), whereas in thecheck names list (inside the parentheses), whitespaces can be used and will beignored.
All NOLINTBEGIN comments must be paired by an equal number of NOLINTENDcomments. Moreover, a pair of comments must have matching arguments – forexample, NOLINTBEGIN(check-name) can be paired withNOLINTEND(check-name) but not with NOLINTEND (zero arguments).clang-tidy will generate a clang-tidy-nolint error diagnostic ifany NOLINTBEGIN/NOLINTEND comment violates these requirements.